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The utilization of I-125 seeds as a substitute for Ir-192 seeds in temporary interstitial implants: An overview and a description of the william beaumont hospital technique
Inf. J. Radiation OncologyEMT/.Phys., Vol. 15, pp. 1027-1033 Printed in the U.S.A. All rights reserved.
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??Technical Innovations and Notes
THE UTILIZATION OF I-125 SEEDS AS A SUBSTITUTE FOR h-192 SEEDS IN TEMPORARY INTERSTITIAL IMPLANTS: AN OVERVIEW AND A DESCRIPTION OF THE WILLIAM BEAUMONT HOSPITAL TECHNIQUE DANIEL H. CLARKE, M.D., GREGORY K. EDMUNDSON, R.T.(T), ALVARO MARTINEZ, RICHARD C. MATTER, M.D. AND CATHY WARMELINK, M.S.
M.D.,
Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI In August of 1986, the Department of Radiation Oncology at William Beaumont Hospital (WBH) initiated the routine use of high activity I-125 seeds as a substitute for B-192 seeds in temporary implants where the afterloading plastic tube technique was used. Through March 6,1987,42 temporary I-125 implants were performed as a boost for curative therapy (38 breasts, 2 sarcomas, 2 tongues). Thus far, we have observed no differences in acute toxicity. Sources ranging from 2 to 5 mCi were utilized. The advantages of I-125 are as follows: (a) Easy to shield; (b) Radiation safety; (c) Decreased exposure to sensitive organs in close proximity to the implanted site; (d) Dosimetric advantages both intrinsic and extrinsic; and (e) Any private room can be used for these patients allowing a central brachytherapy ward to be established. While the advantages were obvious, we anticipated potential disadvantages and shortcomings and these will be discussed in detail. Furthermore because of significant differences in tube and ribbon construction, the I-125 afterloading plastic tube technique has important differences from that technique used with Ir-192. These modifications must be fully understood to maintain the integrity of the I125 seed-ribbon afterloading tube assembly. A detailed description of the technique will be emphasized. Iodine 125 seeds, Interstitial temporary implants, Brachytherapy, Radiation safety.
and this further increased the number of implants performed.4.14.1%23These changes resulted in higher radiation exposure for hospital employees.22 Because of the large number of brachytherapy cases currently being performed in the Radiation Oncology Department at WBH, we have implemented the routine use of I-125 seeds as a substitute for Ir-192 seeds where the afterloading plastic tube technique is used. While radiation safety was the overriding factor for making this change, there were other significant advantages which will be described below. The I-125 implant technique will be described.
INTRODUCTION
In the U.S., during the mid to late 1970’s, there was a renewed interest in brachytherapy when it became apparent that the high energy linear accelerator was not an ample substitute for implant therapy. With an increasing awareness of the importance of radiation safety, afterloading techniques (Cs- 137 for intracavitary and Ir- 192 for interstitial implants) became routine to decrease radiation exposure. Further refinements included the introduction of remote afterloaders for both intracavitaryE, 18.25 and interstitial implants.’ 7 As complex interstitial techniques evolved, such as those used in head and neck tumors9’20’26and gynecologic templates’5.2’,24 and as the indications for brachytherapy expanded, as in soft tissue sarcomas’2 and thoracic tumors, ’’both the number of interstitial implants as well as the implanted volumes increased dramatically. In the late 1970’s and early 1980’s breast conservation therapy, in lieu of mastectomy, became widely accepted,
METHODS
AND
MATERIALS
Between August 1986 and March 6, 1987,42 temporary I-125 implants were performed. All patients were undergoing curative therapy. The implant served as a boost either prior to or after external beam radiation
Presented at the 9th Annual Mid-Winter Meeting of the American Endocurietherapy Society, San Juan, Puerto Rico, December 1986. Reprint requests to: Daniel H. Clarke, M.D., 3601 W. 13 Mile Road, Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48072.
Acknowledgement-We would like to thank Glenda Noble, C.P.S. for her secretarial assistance in the preparation of this manuscript and the Radiation Oncology Residents for helping in the care of these patients. We would also like to thank Pat Banks for her outstanding artistic work. Accepted for publication 2 1 April 1988. 1027
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therapy (38 breasts, 2 sarcomas, 1 base of tongue, 1 oral tongue). Our breast implant technique uses a generous target volume around the tumor bed. All patients have had a 2, 3, or 4 plane implant to a full breast quadrant or an equivalent thereof, which provides a substantial margin around the operative bed. I6 The minimal tumor dose rate line is that isodose line, calculated in a plane perpendicular to the ribbons at the center of the implant, which continuously encompasses the target volume without significant irregularities. Most breast implants had lo12 ribbons (5-6/plane). The activity ranged from 200 mCi to 900 mCi (mean 400 mCi).27 Initial concerns Increasedplastic tube diameter. Figure 1 illustrates the differences between an I-l 25 and an Ir- 192 afterloading plastic tube. It is evident that the outer diameter of the I125 plastic tube is slightly greater than that of the iridium afterloading tube. However, the I-125 seed ribbon has a significantly greater diameter than does the iridium seed ribbon (Fig. 2). Therefore, unlike afterloading an Ir- 192 implant, there is a very snug fit between the I-125 seed ribbon and the I- 125 plastic tube. We had several concerns regarding the I- 125 plastic tubes: (a) We felt that the larger tube diameter might result in clinically significant soft tissue injury, particularly in head and neck implants; (b) Since many of our patients undergo breast implants under local anesthesia, we were concerned about the possibility of increased patient discomfort during implantation necessitating general anesthesia; (c) If the plastic tube was stretched at the time of the implant, there could be difficulties afterloading the sources because of the snug tube-ribbon fit. To avoid this potential problem the afterloading catheters were designed with an inner support tube.* (Fig. 1) Cost. Cost has been one of the major drawbacks in using I-125 in temporary implants. Our net cost has been $20-2 1 per seed; and, thus, reuse of I- 125 seeds is imperative. Each institution must maintain a proper inventory, which takes into account how often to order new seeds, how many seeds to order, and what activity to or-
I
19mm[’ Fig. 1. An Ir- 192 plastic afterloading tube is compared to an I125 afterloading tube.
* Best Industries.
October 1988, Volume 15, Number 4
] 125mm aled
Fig. 2. An Ir- 192 ribbon is compared with an I- 125 ribbon. Unlike Ir- 192 ribbons where the seeds are fixed in position, the I125 seeds have a variable spacing. der. We are currently ordering 200 seeds every 6 weeks
at 5 mCi per seed. This allows us to load two to three implants simultaneously. To optimize reuse in the treatment of breast cancer, we found it helpful to use a fixed dose rate in our breast boost technique.16 In combination with 4500 cGy to the whole breast, our policy had been to deliver a 1500 cGy boost at 35-50 cGy per hour. Excluding high risk patients, we continue to deliver the same minimal tumor dose of 1500 cGy at a fixed rate of 62.5 cGy per hour, thereby limiting the treatment time to 24 hr. for these patients. This allows maximal recycling of the I- 125 seeds. High risk patients who have positive margins, moderate to extensive intraductal cancer, or young patients with high grade infiltrative lesions may receive a higher boost dose of 1800-2200 cGy at 40-50 cGy/hr. For those patients who received their implant after the external beam irradiation, it was common for them to be admitted to the hospital on the morning of the implant and leave the following afternoon. Many patients have their breast implant at the time of re-exicision and/or axillary dissection. Contamination. I- 125 is coated onto a silver wire and has a thin titanium encapsulation. The isotope is both water soluble and volatile; and thus, if a seed were crushed, a significant radiation contamination problem could occur.’ Since, Ir-192 seeds are metallic, contamination is not a risk. Extreme care is mandatory in the handling and reuse of I- 125 seeds. Calibration. Since the seeds are of high activity and are reused, it is essential that the initial activity of each seed not vary from that which is stated by the manufacturer. Currently each seed is calibrated by 3M and is guaranteed to be within 4% of the stated activity. In addition, we purchase two calibration seeds with each order. Their stated activity is an average of ten measurements made on each seed. We are currently assaying at least 25% of the seeds received with each order. If variations greater than 5% of the stated activity are detected, all of the seeds are assayed. Normal tissue doses. Of concern is the high absorption of low energy photons on bony surfaces due to photoelectric interactions. A high periosteal dose could result in an increased incidence of exposed bone and/or osteo-
Temporary I-I 25 implants 0 D. H. CLARKE etal.
radionecrosis. This is particularly applicable to head and neck and sarcoma implants. To minimize the risk in head and neck implants, when applicable we have attempted to shield the mandible. Since there is a decreased attenuation of low energy photons (30% to 40%) in fat,13 there may be an increase in the anticipated skin dose in breast implants, particularly in post-menopausal patients or patients with fatty breasts. This could result in telangectasia formation and/ or skin retraction compromising the cosmetic result. On the other hand, the decreased photon absorption in fat may be beneficial, resulting in a lower incidence of fat necrosis* or a decrease in breast fibrosis.4
Advantages of Z-125 I- 125 is an attractive substitute for iridium 192 in temporary plastic tube implants for several reasons: (a) I- 125 is easy to shield; (b) Radiation safety is facilitated; (c) There are dosimetric advantages; (d) The dose to sensitive organs close to the implant is lower; (e) The use of any private room facilitates the development of a centralized brachytherapy ward. Obviously, all of these advantages are to some degree interrelated; however, each remains a distinct entity and will be discussed separately. Shielding. The half value layer of I- 125 in lead is only l/40 of a mm. Flexible lead rubber can be secured with tape or a kerlex roll over the implant, effectively eliminating radiation exposure to hospital personnel and visitors.*’ We have routinely surveyed patients with and without the lead rubber shield (Table 1). With shielding, the exposure rates at one meter have not exceeded 2.0 mR/hr. The mean exposure rate at one meter was decreased from 18.50 mR/hr to 0.58 mR/hr with shielding. Lead aprons may be worn as proposed by Genest et al.’in those situations where lead rubber shielding is not practical (large head and neck or laryngeal implants). Either of these simple protective devices obviate the need for cumbersome bedside shields which are difficult to
Table 1. Exposure rates near I- 125patients Mean Activity (mCi) At 1 meter (mR/h) Shielded Unshielded At surface (mR/h) Shielded Unshielded At bedside (mR/h) Shielded Unshielded
373 0.6 18.5 24 2396 5 112
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move, create storage problems, and interfere with good nursing care. Unlike Ir- 192 and Cs- 137, I- 125 does not require large heavy containers. This facilitates both the storage and the transport of I- 125 seeds. Shielding of surrounding normal tissues can be achieved in some situations. An example is the ability to shield the mandible in intraoral implants. Thin lead can be embedded into a dental appliance (Fig. 3) and worn during the implant, thereby partially shielding those portions of the mandible and gingiva which are adjacent to the tumor. Care should be taken to avoid displacing the implant or shielding any portion of the target volume. Intraoral protective appliances have been used routinely in our department with iridium implants, but its importance when I- 125 seeds are used cannot be overemphasized. Radiation safety. The major advantage of substituting I-125 seeds for h-192 seeds is the resultant decrease in radiation exposure to hospital personnel. As a consequence, the patient may likely receive better nursing care. This is particularly important for those patients who have had a laparotomy, radical neck dissection, en bloc resection of a sarcoma or other major surgery in conjunction with their implant. The feelings of isolation are reduced, and patient apprehensions regarding the safety of the implant are minimized. Secondly, there is little radiation exposure to visitors. Visitors can stay throughout the duration of visiting hours, which allows more patient contact and further alleviates any feelings of isolation. However, we do continue to restrict visitation by pregnant women and children.
(30 patients) Range 240-606 o-2 6-38 5-52 900-6300 o-17 7-190
* The bedside dose rate was measured at a location where a nurse would stand to administer nursing care. These dose rates are highly variable and are dependent upon the location of the implant.
Fig. 3. A patient presented with a T-2 lateral tongue lesion and was treated with 5000 cGy external beam irradiation and an I125 interstitial implant. An oral protective appliance with lead (Pb) imbedded into the right side is illustrated.
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Thirdly, there is a decreased radiation exposure to the patient at sites distant from the implant. We have been concerned about incidental radiation to the contralateral breast and the thyroid in breast implants, and to the thyroid and the eye in head and neck implants. Radiation induced thyroid tumors, both benign and malignant, are dose related.6 Brachytherapy ward. Since we are able to use any standard private room, we have been able to develop a brachytherapy ward. Costly specially shielded patient rooms or the use of end rooms scattered throughout the hospital can be avoided. Our Ir- 192 remote afterloader units,? and our isotope room are now conveniently located on the brachytherapy ward. This floor is staffed by specialized nurses, who have been instructed in the care of brachytherapy patients. They are knowledgeable about radiation and our implant techniques. We believe that this has resulted in superior nursing care for our implanted patients. Dosimetry. I- 125 seeds provide a much more dynamic dosimetric approach to implant planning and therapy than do Ir- 192 seeds.33sBecause the spacing of the seeds is individualized for each patient, there is full control over the dose rate after the implant is performed. The physician prescribes the treatment time, dose rate, and total dose for each patient and the seed spacing is then determined. Additionally, the spacing within the implant can be varied (40% of cases), to correct for dose inhomogeneities (hot spots or cold spots), which may have resulted from variations in ribbon spacing or ribbon deviation. This feature may be particularly powerful in complex head and neck implants.3 Furthermore, there are inherent dosimetric properties of I- 125, which are advantageous. The isodose distributions within the implanted volume are very similar to those which are observed in an iridium implant (Fig. 4). However, at some distance from the implant, outside of the target volume, the dose from an I- 125 implant is considerably less than that of an Ir-192 implant, thereby sparing normal tissues. A detailed description of our dosimetric approach will be the subject of another publication. Technique The afterloading plastic tubes and seed ribbons used in I- 125 implants have important differences in their construction when compared to the plastic tubes and seed ribbons used in Ir-192 implants. It is essential to fully understand the differences since the I-125 seeds, unlike Ir- 192 seeds, are loose within the seed-ribbon assembly. Plastic tubepreparation in the o. r. As illustrated in Figure 1, the afterloading plastic tube used in the I- 125 implants has a slightly greater outer diameter than those tubes used for iridium implants (1.9 mm. versus 1.7
-f Microselectron,
Nucletron
Corporation,
Holland.
October
1988,
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I-125
4
lr-192
Fig. 4. Comparison of an I- 125 and Ir- I92 isodose distribution. mm.). Therefore, modified buttons* with a larger central hole are required when securing the plastic tubes skin-toskin in the operating room. While it is technically possible to place standard Ir- 192 buttons onto the I- 125 afterloading plastic tubes, if the modified I-125 buttons are not used, it is technically impossible to afterload the I125 ribbons. There are two factors involved: (a) The standard Ir-192 buttons create a slight but significant constriction in the plastic tubes designed for I- 125 ribbons; and, (b) Unlike Ir-192 ribbons, which slide very loosely into the afterloading tubes, the I- 125 ribbons fit quite snugly into their afterloading plastic tubes; consequently the ribbon cannot pass the point of constriction. An inner support tube, within the I-125 plastic tube, was designed to prevent tube stretching during the implant procedure, to avoid compromise of the tube lumen. We have been able to afterload all patients without any difficulty with the exception of two patients, where standard Ir- 192 buttons were inadvertently threaded onto the afterloading tubes. In those cases, the iridium buttons had to be removed and were replaced by the modified Henschke button. In the operating room, we customarily use radiopaque barium buttons to secure the plastic tubes skin-to-skin at the entry and exit points. A metal Henschke button is then inserted over the leader end of the plastic tube prior to cutting the plastic tubes. Thus, each plastic tube has two buttons threaded onto the open end. The metal Henschke buttons are needed to secure the I- 125 seed ribbons within the afterloading plastic tubes to prevent seed movement after the implant has been loaded. The leader end and the excess tubing is cut in the standard fashion and the inner support tube is withdrawn from the plastic tube. This is accomplished by inserting either the leader end of an afterloading tube or a stylet into the cut end of the afterloading tube. The inner support tube, which is hollow, attaches and is withdrawn as illustrated in Figure 5.
Temporary I- 125 implants 0 D. H. CLARKE et al.
Fig. 5. The inner support tube is removed after placement the plastic afterloading catheters into the patient.
of
Our inventory of I- 125 afterloading tubes includes those illustrated in Figure 6: (a) The standard blind end tube is used in breast implants, sarcomas, etc.; (b) A smooth rounded blind end tube has been designed for surgical field implants; (c) A double leader tube is used for loops.
Preparation of the I-125 seed-ribbon assembly in the isotope room. When Ir-192 ribbons are ordered from the manufacturer, the seeds are firmly fixed in position. For most implants a standard spacing of 1 cm., from the center of one seed to the center of the next seed, is used. Special orders with seeds back-to-back or with variable spacing are available. However, once the iridium ribbons have been ordered, one cannot change the spacing of the seeds nor increase the number of seeds within a given ribbon. On the other hand, the I- 125 seed ribbons are prepared individually for each patient. When preparing the ribbons, spacers are inserted between the I- 125 seeds. The seed spacing is dependent upon the seed activity and the desired dose rate. Since the seeds are reused multiple times and the seedribbons individually constructed for each patient, the seeds must be loose within the seed ribbon. Therefore, one must assure that the seeds are not displaced, lost or damaged’ during source transport, patient loading, or source removal. Once the seeds and spacers have been freely inserted, a “pusher” is inserted into the ribbon to secure the seeds and spacers in position (Fig. 2). The brachytherapy dosimetrist trims the excess pusher flush with the ribbon and the end is heat sealed with a solder-
Fig. 6. The three types of afterloading tubes which are currently available are demonstrated.
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ing iron. This completes the preparation of the seed-ribbon assembly in the isotope room. It should be emphasized that at the time of loading, after the ribbon has been inserted into the afterloading tube and trimmed, the pusher is again loose within the ribbon and is at risk of becoming dislodged. It must again be heat sealed to hold it and the seeds in position. An alternative technique using hemostatic clips has been described.” Because of structural differences, the I-125 ribbon is considerably more rigid than the Ir- 192 ribbon. After the seeds, spacers, and pusher have been inserted into the I125 ribbon, the structural integrity is analogous to that of the plastic tube which is used to afterload cesium into a Fletcher-Suit tandem. Technique of loading the implant. A breast implant will be used to illustrate the differences between an Ir192 and an I- 125 loading. The I- 125 seed-ribbon assembly with its pusher is inserted into the afterloading tube until it reaches the end of the tube at the barium button (Fig. 7). A tip spacer has been placed at the end of the ribbon at the time of ribbon preparation so that the first seed is positioned at the prescribed distance from the skin. The tip spacer also serves as a safety feature so that the active end of the seed-ribbon assembly can be safely cut after the implant is completed at the time of ribbon disassembly. The metal button is now crimped to secure the outer wall of the ribbon assembly to the afterloading tube (Figs. 7,8). Initially we attempted to use hemoclips; however, because the I- 125 ribbons are much more rigid than Ir-192 ribbons, we found that hemoclips did not form a tight bond between the ribbon and afterloading tube. The metal Henschke buttons when crimped form a far superior seal. After the seed-ribbon assembly is secured to the afterloading catheter some of the excess ribbon and pusher material is cut. It is essential that a small portion of the ribbon and pusher material protrude through the end of the afterloading tube to facilitate later ribbon removal (Figs. 7,9). Finally, the end of the ribbon-pusher assembly is heat sealed with a soldering iron to prevent the pusher and
Fig. 7. The technique of inserting and securing the seed-ribbon assembly into the afterloading tubes is shown.
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enhanced by heat sealing the ribbon and pusher to prevent the ribbon contents from being dislodged. Ribbon removal. Calibrated pliers are used to reopen the metal buttons (Fig. lo), and the ribbon assembly is removed. Both ends of the ribbon assembly have been heat sealed; and, therefore, the risk of losing an I-125 seed is minimal. Prior to removing the plastic tubes, the patient is surveyed, and the ends of the plastic tubes are meticulously cleaned with peroxide or betadine. Lastly, the seeds are returned to the appropriate batch for reuse.
CONCLUSIONS Fig. 8. A two plane breast implant has been performed. Both a barium button and a metal Henschke button have been in-
serted onto the plastic tube. Arrows point to metal Henschke buttons that have been crimped to secure the outer ribbon assembly to the afterloading tube. Note that there is excess pusher ribbon material protruding from the ends of the plastic tubes. This facilitates later ribbon removal. the underlying seeds from becoming dislodged during or
after the implant (Figs. 7, 9). If the ribbon did not protrude it would become heat sealed to the plastic tube, making later ribbon removal very difficult. Recall that the pusher and seeds within the ribbon are loose. Hence, it is imperative that the end of the ribbon-pusher apparatus be bonded. This additional step is not required with the Ir-192 plastic tube technique. This completes the preparation of the I- 125 seed-ribbon-afterloading tube assembly. To summarize, a triple component assembly must be secured: (a) The afterloading tube; (b) The I- 125 ribbon; (c) The loose components within the I- 125 ribbon (I- 125 seeds, spacers and pusher). Barium buttons are used to secure the afterloading tube skin-to-skin. A Henschke button is used to secure the ribbon assembly to the afterloading tube. The structural integrity of the assembly is
Fig. 9. The final step in securing the seed-ribbon assembly is shown. Heat sealing the end of the ribbon bonds the pusher to the outer wall of the ribbon and prevents dislodgement of the pusher, seeds or spacers from the ribbon.
Temporary I- 125 implants offer several important advantages over Ir- 192 when using the afterloading plastic tube technique. Radiation safety is the most obvious and important advantage. Furthermore, I- 125 lends itself to easy shielding of personnel, visitors, and radiosensitive normal tissues distant from the implanted area. The use of I- 125 seeds has facilitated the development of a brachytherapy ward with skilled nurses who are specially trained in caring for brachytherapy patients and who have a good understanding of radiation therapy. I- 125 seeds provide a flexible and dynamic dosimetric program since the seed-ribbons are individually prepared after the implant is done. This allows us to have full control over the dose rate and allows for correction of either hot spots or cold spots within the implanted volume. We have found that the technique can easily be adapted to any site where the afterloading plastic tube technique is used. We have observed no untoward or unexpected effects. The acute reactions observed thus far do not appear to differ from those seen after Ir- 192 implants. This confirms the findings of others.‘*” Ofcourse, we must wait for longer follow-up before assessing the impact on chronic or long term sequelae. It should be emphasized that before initiating such a program, a complete understanding of the technique is imperative. There are significant differences between I125 and Ir- 192 implants in regards to the afterloading tube construction, seed-ribbon assembly preparation, se-
Fig. 10. At the time of removal of the seed-ribbon assembly, calibrated pliars are used to uncrimp the metal button.
Temporary I- 125 implants 0 D. H. CLARKE etal.
curing the seed-ribbon-afterloading tube assembly, and dosimetric planning. Thus far, it appears that the advan-
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tages far outweigh our early concerns or any of the potential disadvantages discussed above.
REFERENCES 1. Broga, D., Gilbert, M.: A review of three incidents involving the release of I- 125 from seeds interstitially implanted within the prostate gland. Health Phys. 45: 593-597, 1983. 2. Clarke, D.H., Curtis, J.L., Martinez, A., Fajardo, L., Goffinet, D.: Fat necrosis ofthe breast simulating recurrent carcinoma after primary radiotherapy in the management of early stage breast carcinoma. Cancer52: 442-445, 1983. 3. Clarke, D.H., Edmundson, G.K., Matter, R.C., Martinez, A.: The superiority of I- 125 seeds in temporary plastic tube implants (Abstr.). Endocuriether. Hyperther. Oncol. 4: 86,
15. Martinez, A., Edmundson, G.K., Cox, R.S., Gunderson, L.L., Howes, A.E.: Combination of external beam irradiation and multiple-site perineal applicator (MUPIT) for treatment of locally advanced or recurrent prostatic, anorectal, and gynecologic malignancies. Int. J. Radiat. Oncol. Biol. Phys. 11: 391-398, 1985. 16. Matter, R.C., Vicini, F., Clarke, D.H., Martinez, A., Edmundson, G.K.: Preliminary results utilizing I-125 seeds as a substitute for Ir- 192 seeds in plastic tube afterloading breast implants (Abst.). Endocuriether. Hyperther. Oncol. 4: 86, 1988.
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4. Clarke, D.H., Martinez, A., Cox, R.S.: Analysis of cosmetic results and complications in patients with stage I and II breast cancer treated by biopsy and irradiation. Znt. J.
17. Meertens, H., Bartelink, H.: First experience with the microselectron in breast conserving therapy implants. In Brachytherapy, Proceedings 3rd International Selectron Users Meeting, Mould, R.F. (Ed.). Innsbruck, Austria,
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5. Edmundson, G.K., Clarke, D.H., Martinez, A., Matter, R.C.: An activity-compensated approach to Iodine- 125 temporary implant dosimetry. (Abstr). Endocuriether. Hyperther. Oncol. 2: 2 10, 1986.
6. Fjalling, M., Tisell, L., Carlsson, S., Hansson, G., Lundberg, L., Oden, A.: Benign and malignant thyroid nodules after neck irradiation. Cancer 58: 12 19- 1224, 1986. 7. Genest, P., Hilaris, B.S., Nori, D., Batata, M., Vikram, B., Hopfan, S., St. Get-main, J., Anderson, L.L., Kim, J.H., Alfieri, A.: Iodine-125 as a substitute for Iridium-192 in temporary interstitial implants. Endocuriether. Hyperther. Oncol. 1: 223-228, 1985. 8. Girinsky, T., van Limbergen, E., Gerbaulet, A., Haie, C., Chassagne, D.: Different dose-rates in preoperative intracavitary curietherapy for cervical carcinoma. In Brachytherapy, Proceedings 3rd International Meeting, Mould, R.F. (Ed.). Innsbruck,
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servative Management of Breast Cancer. New Surgical and Radiotherapeutic Techniques, Harris, J.R., Hellman, S.,
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tron Trading BV. 1984, pp. 229-232. 9. Goffinet, D.R., Fee, W.E., Wells, J., Austin-Seymour, M., Clarke, D.H., Mariscal, J.M., Goode, R.L.: 192 Ir Pharyngoepiglottic fold interstitial implants: The key to successful treatment of base tongue carcinoma by radiation therapy. Cancer55:
Nucletron Trading BV. 1984, pp. 27 l-276. 18. Nori, D., Hilaris, B.S., Chadha, M., Bains, M., Jain, S., Hopfan, S., Anderson, L.L.: Clinical applications of a remote afterloader. Endocuriether. Hyperther. Oncol. 1: 193-200,1985. 19. Pierquin, B.: Conservative treatment for carcinoma of the breast: Experience of Creteil-Ten-year-results. In Con-
941-948,1985.
10. Goffinet, D.R., Ling, C.C., Mar&al, M.: Preliminary clinical experience with removable Iodine- 125 breast implant boosts. (Abstr). Endocuriether. Hyperther. Oncol. 2: 2 16, 1986. 11. Hilaris, B.S., Nori, D., Horowitz, B.S., Beattie, E.J., Martini, N.: Perioperative brachytherapy in the management of non-oat cell lung cancer. In Brachytherapy Oncology1982: Advances in Lung and Other Cancers, Hilaris, B.S., Nori, D. (Eds.). New York, Memorial Sloan-Kettering Cancer Center. 1982, pp. 33-40. 12. Hilaris, B.S., Shiu, M.H., Nori, D., Anderson, L.L., Manolatos, S.: Limbsparing therapy for locally advanced softtissue sarcomas. Endocuriether. Hyperther. Oncol. 1: 1724, 1985. 13. Johns, H.E., Cunningham, J.R.: Appendices A-Basic Data. Table 3c and 3e. In The Physics of Radiology 4th edition, Johns, H.E., Cunningham, J.R. (Eds.). Springfield, Illinois, Charles C. Thomas. 1983, pp. 724-725. 14. Martinez, A., Clarke, D.H.: Treatment results, cosmesis, and complications in stages I and II breast cancer patients treated by excisional biopsy and irradiation. In Current Controversies in Breast Cancer, Ames, F.C., Blumenschien, G.R., Montague, E.D. (Eds.). Austin, Texas, U. of Texas Press. 1984, pp. 369-38 1.
21.
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Silen, W. (Eds.). Philadelphia, JB Lippincott Co. 1983, pp. 11-14. Puthawala, A.A., Syed, A.M.N., Eads, D.L., Neblett, D., Gillin, L., Gates, T.C.: Limited external irradiation and interstitial 192 iridium implant in the treatment of squamous cell carcinoma of the tonsillar region. Znt. J Radiat. Oncol. Biol. Phys. 11: 1595-1602, 1985. Puthawala, A.A., Syed, A.M.N., Tansey, L.A., Shanberg, A., Austin, P.A., McNamara, C.S.: Temporary iridium192 implant in the management of carcinoma of the prostate. “An anaylsis of treatment results and complications in the first one hundred patients”. Endocuriether. Hyperther. Oncol. 1: 25-34, 1985. Schray, M.F., Braun, J.S., Vetter, R.J., Yeakel, P.: Personnel exposure in brachytherapy (Abstr.). Endocuriether. Hyperther. Oncol. 2: 2 12, 1986. Shank, B.: Breast preservation and brachytherapy. Endocuriether. Hyperther. Oncol. 2: S- 17-S-24, 1986. Syed, A.M.N., Puthawala, A.A., Neblett, D., Disaia, P.J., Berman, M.L., Rettenmaier, M., Nalick, R., McNamara, C.: Transperineal interstitital-intracavitary “Syed-Neblett” applicator in the treatment of carcinoma of the uterine cervix. Endocuriether. Hyperther. Oncol. 2: 1-13, 1986. van Bunningen, B.N.F., Battermann, J.: Experience with selectron afterloading in the Antoni van Leeuwenhoek Hospital. In Brachytherapy, Proceedings 3rd International Selectron Users Meeting, Mould, R.F. (Ed.). Innsbruck, Austria, Nucletron Trading BV. 1984, pp. 6- 12. Vikram, B., Strong, E., Shah, J., Spiro, R., Gerold, F., et al.: A nonlooping afterloading technique for base oftongue implants. Results in the first 20 patients. Znt. J. Radiat. Oncol. Biol. Phys. 11: 1853-1855, 1985. Warmelink, C., Edmundson, G.K., Martinez, A., Clarke, D.H., Matter, R.C.: The use of lead-rubber shielding in temporary Iodine- 125 Implants (Abstr.). Endocuriether. Hyperther. Oncol. 4: 86, 1988.
0360-3016/88 $3.00 + .OO Copyright 0 1988 Pergamon Press plc
??Technical Innovations and Notes
THE UTILIZATION OF I-125 SEEDS AS A SUBSTITUTE FOR h-192 SEEDS IN TEMPORARY INTERSTITIAL IMPLANTS: AN OVERVIEW AND A DESCRIPTION OF THE WILLIAM BEAUMONT HOSPITAL TECHNIQUE DANIEL H. CLARKE, M.D., GREGORY K. EDMUNDSON, R.T.(T), ALVARO MARTINEZ, RICHARD C. MATTER, M.D. AND CATHY WARMELINK, M.S.
M.D.,
Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI In August of 1986, the Department of Radiation Oncology at William Beaumont Hospital (WBH) initiated the routine use of high activity I-125 seeds as a substitute for B-192 seeds in temporary implants where the afterloading plastic tube technique was used. Through March 6,1987,42 temporary I-125 implants were performed as a boost for curative therapy (38 breasts, 2 sarcomas, 2 tongues). Thus far, we have observed no differences in acute toxicity. Sources ranging from 2 to 5 mCi were utilized. The advantages of I-125 are as follows: (a) Easy to shield; (b) Radiation safety; (c) Decreased exposure to sensitive organs in close proximity to the implanted site; (d) Dosimetric advantages both intrinsic and extrinsic; and (e) Any private room can be used for these patients allowing a central brachytherapy ward to be established. While the advantages were obvious, we anticipated potential disadvantages and shortcomings and these will be discussed in detail. Furthermore because of significant differences in tube and ribbon construction, the I-125 afterloading plastic tube technique has important differences from that technique used with Ir-192. These modifications must be fully understood to maintain the integrity of the I125 seed-ribbon afterloading tube assembly. A detailed description of the technique will be emphasized. Iodine 125 seeds, Interstitial temporary implants, Brachytherapy, Radiation safety.
and this further increased the number of implants performed.4.14.1%23These changes resulted in higher radiation exposure for hospital employees.22 Because of the large number of brachytherapy cases currently being performed in the Radiation Oncology Department at WBH, we have implemented the routine use of I-125 seeds as a substitute for Ir-192 seeds where the afterloading plastic tube technique is used. While radiation safety was the overriding factor for making this change, there were other significant advantages which will be described below. The I-125 implant technique will be described.
INTRODUCTION
In the U.S., during the mid to late 1970’s, there was a renewed interest in brachytherapy when it became apparent that the high energy linear accelerator was not an ample substitute for implant therapy. With an increasing awareness of the importance of radiation safety, afterloading techniques (Cs- 137 for intracavitary and Ir- 192 for interstitial implants) became routine to decrease radiation exposure. Further refinements included the introduction of remote afterloaders for both intracavitaryE, 18.25 and interstitial implants.’ 7 As complex interstitial techniques evolved, such as those used in head and neck tumors9’20’26and gynecologic templates’5.2’,24 and as the indications for brachytherapy expanded, as in soft tissue sarcomas’2 and thoracic tumors, ’’both the number of interstitial implants as well as the implanted volumes increased dramatically. In the late 1970’s and early 1980’s breast conservation therapy, in lieu of mastectomy, became widely accepted,
METHODS
AND
MATERIALS
Between August 1986 and March 6, 1987,42 temporary I-125 implants were performed. All patients were undergoing curative therapy. The implant served as a boost either prior to or after external beam radiation
Presented at the 9th Annual Mid-Winter Meeting of the American Endocurietherapy Society, San Juan, Puerto Rico, December 1986. Reprint requests to: Daniel H. Clarke, M.D., 3601 W. 13 Mile Road, Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48072.
Acknowledgement-We would like to thank Glenda Noble, C.P.S. for her secretarial assistance in the preparation of this manuscript and the Radiation Oncology Residents for helping in the care of these patients. We would also like to thank Pat Banks for her outstanding artistic work. Accepted for publication 2 1 April 1988. 1027
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therapy (38 breasts, 2 sarcomas, 1 base of tongue, 1 oral tongue). Our breast implant technique uses a generous target volume around the tumor bed. All patients have had a 2, 3, or 4 plane implant to a full breast quadrant or an equivalent thereof, which provides a substantial margin around the operative bed. I6 The minimal tumor dose rate line is that isodose line, calculated in a plane perpendicular to the ribbons at the center of the implant, which continuously encompasses the target volume without significant irregularities. Most breast implants had lo12 ribbons (5-6/plane). The activity ranged from 200 mCi to 900 mCi (mean 400 mCi).27 Initial concerns Increasedplastic tube diameter. Figure 1 illustrates the differences between an I-l 25 and an Ir- 192 afterloading plastic tube. It is evident that the outer diameter of the I125 plastic tube is slightly greater than that of the iridium afterloading tube. However, the I-125 seed ribbon has a significantly greater diameter than does the iridium seed ribbon (Fig. 2). Therefore, unlike afterloading an Ir- 192 implant, there is a very snug fit between the I-125 seed ribbon and the I- 125 plastic tube. We had several concerns regarding the I- 125 plastic tubes: (a) We felt that the larger tube diameter might result in clinically significant soft tissue injury, particularly in head and neck implants; (b) Since many of our patients undergo breast implants under local anesthesia, we were concerned about the possibility of increased patient discomfort during implantation necessitating general anesthesia; (c) If the plastic tube was stretched at the time of the implant, there could be difficulties afterloading the sources because of the snug tube-ribbon fit. To avoid this potential problem the afterloading catheters were designed with an inner support tube.* (Fig. 1) Cost. Cost has been one of the major drawbacks in using I-125 in temporary implants. Our net cost has been $20-2 1 per seed; and, thus, reuse of I- 125 seeds is imperative. Each institution must maintain a proper inventory, which takes into account how often to order new seeds, how many seeds to order, and what activity to or-
I
19mm[’ Fig. 1. An Ir- 192 plastic afterloading tube is compared to an I125 afterloading tube.
* Best Industries.
October 1988, Volume 15, Number 4
] 125mm aled
Fig. 2. An Ir- 192 ribbon is compared with an I- 125 ribbon. Unlike Ir- 192 ribbons where the seeds are fixed in position, the I125 seeds have a variable spacing. der. We are currently ordering 200 seeds every 6 weeks
at 5 mCi per seed. This allows us to load two to three implants simultaneously. To optimize reuse in the treatment of breast cancer, we found it helpful to use a fixed dose rate in our breast boost technique.16 In combination with 4500 cGy to the whole breast, our policy had been to deliver a 1500 cGy boost at 35-50 cGy per hour. Excluding high risk patients, we continue to deliver the same minimal tumor dose of 1500 cGy at a fixed rate of 62.5 cGy per hour, thereby limiting the treatment time to 24 hr. for these patients. This allows maximal recycling of the I- 125 seeds. High risk patients who have positive margins, moderate to extensive intraductal cancer, or young patients with high grade infiltrative lesions may receive a higher boost dose of 1800-2200 cGy at 40-50 cGy/hr. For those patients who received their implant after the external beam irradiation, it was common for them to be admitted to the hospital on the morning of the implant and leave the following afternoon. Many patients have their breast implant at the time of re-exicision and/or axillary dissection. Contamination. I- 125 is coated onto a silver wire and has a thin titanium encapsulation. The isotope is both water soluble and volatile; and thus, if a seed were crushed, a significant radiation contamination problem could occur.’ Since, Ir-192 seeds are metallic, contamination is not a risk. Extreme care is mandatory in the handling and reuse of I- 125 seeds. Calibration. Since the seeds are of high activity and are reused, it is essential that the initial activity of each seed not vary from that which is stated by the manufacturer. Currently each seed is calibrated by 3M and is guaranteed to be within 4% of the stated activity. In addition, we purchase two calibration seeds with each order. Their stated activity is an average of ten measurements made on each seed. We are currently assaying at least 25% of the seeds received with each order. If variations greater than 5% of the stated activity are detected, all of the seeds are assayed. Normal tissue doses. Of concern is the high absorption of low energy photons on bony surfaces due to photoelectric interactions. A high periosteal dose could result in an increased incidence of exposed bone and/or osteo-
Temporary I-I 25 implants 0 D. H. CLARKE etal.
radionecrosis. This is particularly applicable to head and neck and sarcoma implants. To minimize the risk in head and neck implants, when applicable we have attempted to shield the mandible. Since there is a decreased attenuation of low energy photons (30% to 40%) in fat,13 there may be an increase in the anticipated skin dose in breast implants, particularly in post-menopausal patients or patients with fatty breasts. This could result in telangectasia formation and/ or skin retraction compromising the cosmetic result. On the other hand, the decreased photon absorption in fat may be beneficial, resulting in a lower incidence of fat necrosis* or a decrease in breast fibrosis.4
Advantages of Z-125 I- 125 is an attractive substitute for iridium 192 in temporary plastic tube implants for several reasons: (a) I- 125 is easy to shield; (b) Radiation safety is facilitated; (c) There are dosimetric advantages; (d) The dose to sensitive organs close to the implant is lower; (e) The use of any private room facilitates the development of a centralized brachytherapy ward. Obviously, all of these advantages are to some degree interrelated; however, each remains a distinct entity and will be discussed separately. Shielding. The half value layer of I- 125 in lead is only l/40 of a mm. Flexible lead rubber can be secured with tape or a kerlex roll over the implant, effectively eliminating radiation exposure to hospital personnel and visitors.*’ We have routinely surveyed patients with and without the lead rubber shield (Table 1). With shielding, the exposure rates at one meter have not exceeded 2.0 mR/hr. The mean exposure rate at one meter was decreased from 18.50 mR/hr to 0.58 mR/hr with shielding. Lead aprons may be worn as proposed by Genest et al.’in those situations where lead rubber shielding is not practical (large head and neck or laryngeal implants). Either of these simple protective devices obviate the need for cumbersome bedside shields which are difficult to
Table 1. Exposure rates near I- 125patients Mean Activity (mCi) At 1 meter (mR/h) Shielded Unshielded At surface (mR/h) Shielded Unshielded At bedside (mR/h) Shielded Unshielded
373 0.6 18.5 24 2396 5 112
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move, create storage problems, and interfere with good nursing care. Unlike Ir- 192 and Cs- 137, I- 125 does not require large heavy containers. This facilitates both the storage and the transport of I- 125 seeds. Shielding of surrounding normal tissues can be achieved in some situations. An example is the ability to shield the mandible in intraoral implants. Thin lead can be embedded into a dental appliance (Fig. 3) and worn during the implant, thereby partially shielding those portions of the mandible and gingiva which are adjacent to the tumor. Care should be taken to avoid displacing the implant or shielding any portion of the target volume. Intraoral protective appliances have been used routinely in our department with iridium implants, but its importance when I- 125 seeds are used cannot be overemphasized. Radiation safety. The major advantage of substituting I-125 seeds for h-192 seeds is the resultant decrease in radiation exposure to hospital personnel. As a consequence, the patient may likely receive better nursing care. This is particularly important for those patients who have had a laparotomy, radical neck dissection, en bloc resection of a sarcoma or other major surgery in conjunction with their implant. The feelings of isolation are reduced, and patient apprehensions regarding the safety of the implant are minimized. Secondly, there is little radiation exposure to visitors. Visitors can stay throughout the duration of visiting hours, which allows more patient contact and further alleviates any feelings of isolation. However, we do continue to restrict visitation by pregnant women and children.
(30 patients) Range 240-606 o-2 6-38 5-52 900-6300 o-17 7-190
* The bedside dose rate was measured at a location where a nurse would stand to administer nursing care. These dose rates are highly variable and are dependent upon the location of the implant.
Fig. 3. A patient presented with a T-2 lateral tongue lesion and was treated with 5000 cGy external beam irradiation and an I125 interstitial implant. An oral protective appliance with lead (Pb) imbedded into the right side is illustrated.
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Thirdly, there is a decreased radiation exposure to the patient at sites distant from the implant. We have been concerned about incidental radiation to the contralateral breast and the thyroid in breast implants, and to the thyroid and the eye in head and neck implants. Radiation induced thyroid tumors, both benign and malignant, are dose related.6 Brachytherapy ward. Since we are able to use any standard private room, we have been able to develop a brachytherapy ward. Costly specially shielded patient rooms or the use of end rooms scattered throughout the hospital can be avoided. Our Ir- 192 remote afterloader units,? and our isotope room are now conveniently located on the brachytherapy ward. This floor is staffed by specialized nurses, who have been instructed in the care of brachytherapy patients. They are knowledgeable about radiation and our implant techniques. We believe that this has resulted in superior nursing care for our implanted patients. Dosimetry. I- 125 seeds provide a much more dynamic dosimetric approach to implant planning and therapy than do Ir- 192 seeds.33sBecause the spacing of the seeds is individualized for each patient, there is full control over the dose rate after the implant is performed. The physician prescribes the treatment time, dose rate, and total dose for each patient and the seed spacing is then determined. Additionally, the spacing within the implant can be varied (40% of cases), to correct for dose inhomogeneities (hot spots or cold spots), which may have resulted from variations in ribbon spacing or ribbon deviation. This feature may be particularly powerful in complex head and neck implants.3 Furthermore, there are inherent dosimetric properties of I- 125, which are advantageous. The isodose distributions within the implanted volume are very similar to those which are observed in an iridium implant (Fig. 4). However, at some distance from the implant, outside of the target volume, the dose from an I- 125 implant is considerably less than that of an Ir-192 implant, thereby sparing normal tissues. A detailed description of our dosimetric approach will be the subject of another publication. Technique The afterloading plastic tubes and seed ribbons used in I- 125 implants have important differences in their construction when compared to the plastic tubes and seed ribbons used in Ir-192 implants. It is essential to fully understand the differences since the I-125 seeds, unlike Ir- 192 seeds, are loose within the seed-ribbon assembly. Plastic tubepreparation in the o. r. As illustrated in Figure 1, the afterloading plastic tube used in the I- 125 implants has a slightly greater outer diameter than those tubes used for iridium implants (1.9 mm. versus 1.7
-f Microselectron,
Nucletron
Corporation,
Holland.
October
1988,
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I-125
4
lr-192
Fig. 4. Comparison of an I- 125 and Ir- I92 isodose distribution. mm.). Therefore, modified buttons* with a larger central hole are required when securing the plastic tubes skin-toskin in the operating room. While it is technically possible to place standard Ir- 192 buttons onto the I- 125 afterloading plastic tubes, if the modified I-125 buttons are not used, it is technically impossible to afterload the I125 ribbons. There are two factors involved: (a) The standard Ir-192 buttons create a slight but significant constriction in the plastic tubes designed for I- 125 ribbons; and, (b) Unlike Ir-192 ribbons, which slide very loosely into the afterloading tubes, the I- 125 ribbons fit quite snugly into their afterloading plastic tubes; consequently the ribbon cannot pass the point of constriction. An inner support tube, within the I-125 plastic tube, was designed to prevent tube stretching during the implant procedure, to avoid compromise of the tube lumen. We have been able to afterload all patients without any difficulty with the exception of two patients, where standard Ir- 192 buttons were inadvertently threaded onto the afterloading tubes. In those cases, the iridium buttons had to be removed and were replaced by the modified Henschke button. In the operating room, we customarily use radiopaque barium buttons to secure the plastic tubes skin-to-skin at the entry and exit points. A metal Henschke button is then inserted over the leader end of the plastic tube prior to cutting the plastic tubes. Thus, each plastic tube has two buttons threaded onto the open end. The metal Henschke buttons are needed to secure the I- 125 seed ribbons within the afterloading plastic tubes to prevent seed movement after the implant has been loaded. The leader end and the excess tubing is cut in the standard fashion and the inner support tube is withdrawn from the plastic tube. This is accomplished by inserting either the leader end of an afterloading tube or a stylet into the cut end of the afterloading tube. The inner support tube, which is hollow, attaches and is withdrawn as illustrated in Figure 5.
Temporary I- 125 implants 0 D. H. CLARKE et al.
Fig. 5. The inner support tube is removed after placement the plastic afterloading catheters into the patient.
of
Our inventory of I- 125 afterloading tubes includes those illustrated in Figure 6: (a) The standard blind end tube is used in breast implants, sarcomas, etc.; (b) A smooth rounded blind end tube has been designed for surgical field implants; (c) A double leader tube is used for loops.
Preparation of the I-125 seed-ribbon assembly in the isotope room. When Ir-192 ribbons are ordered from the manufacturer, the seeds are firmly fixed in position. For most implants a standard spacing of 1 cm., from the center of one seed to the center of the next seed, is used. Special orders with seeds back-to-back or with variable spacing are available. However, once the iridium ribbons have been ordered, one cannot change the spacing of the seeds nor increase the number of seeds within a given ribbon. On the other hand, the I- 125 seed ribbons are prepared individually for each patient. When preparing the ribbons, spacers are inserted between the I- 125 seeds. The seed spacing is dependent upon the seed activity and the desired dose rate. Since the seeds are reused multiple times and the seedribbons individually constructed for each patient, the seeds must be loose within the seed ribbon. Therefore, one must assure that the seeds are not displaced, lost or damaged’ during source transport, patient loading, or source removal. Once the seeds and spacers have been freely inserted, a “pusher” is inserted into the ribbon to secure the seeds and spacers in position (Fig. 2). The brachytherapy dosimetrist trims the excess pusher flush with the ribbon and the end is heat sealed with a solder-
Fig. 6. The three types of afterloading tubes which are currently available are demonstrated.
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ing iron. This completes the preparation of the seed-ribbon assembly in the isotope room. It should be emphasized that at the time of loading, after the ribbon has been inserted into the afterloading tube and trimmed, the pusher is again loose within the ribbon and is at risk of becoming dislodged. It must again be heat sealed to hold it and the seeds in position. An alternative technique using hemostatic clips has been described.” Because of structural differences, the I-125 ribbon is considerably more rigid than the Ir- 192 ribbon. After the seeds, spacers, and pusher have been inserted into the I125 ribbon, the structural integrity is analogous to that of the plastic tube which is used to afterload cesium into a Fletcher-Suit tandem. Technique of loading the implant. A breast implant will be used to illustrate the differences between an Ir192 and an I- 125 loading. The I- 125 seed-ribbon assembly with its pusher is inserted into the afterloading tube until it reaches the end of the tube at the barium button (Fig. 7). A tip spacer has been placed at the end of the ribbon at the time of ribbon preparation so that the first seed is positioned at the prescribed distance from the skin. The tip spacer also serves as a safety feature so that the active end of the seed-ribbon assembly can be safely cut after the implant is completed at the time of ribbon disassembly. The metal button is now crimped to secure the outer wall of the ribbon assembly to the afterloading tube (Figs. 7,8). Initially we attempted to use hemoclips; however, because the I- 125 ribbons are much more rigid than Ir-192 ribbons, we found that hemoclips did not form a tight bond between the ribbon and afterloading tube. The metal Henschke buttons when crimped form a far superior seal. After the seed-ribbon assembly is secured to the afterloading catheter some of the excess ribbon and pusher material is cut. It is essential that a small portion of the ribbon and pusher material protrude through the end of the afterloading tube to facilitate later ribbon removal (Figs. 7,9). Finally, the end of the ribbon-pusher assembly is heat sealed with a soldering iron to prevent the pusher and
Fig. 7. The technique of inserting and securing the seed-ribbon assembly into the afterloading tubes is shown.
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enhanced by heat sealing the ribbon and pusher to prevent the ribbon contents from being dislodged. Ribbon removal. Calibrated pliers are used to reopen the metal buttons (Fig. lo), and the ribbon assembly is removed. Both ends of the ribbon assembly have been heat sealed; and, therefore, the risk of losing an I-125 seed is minimal. Prior to removing the plastic tubes, the patient is surveyed, and the ends of the plastic tubes are meticulously cleaned with peroxide or betadine. Lastly, the seeds are returned to the appropriate batch for reuse.
CONCLUSIONS Fig. 8. A two plane breast implant has been performed. Both a barium button and a metal Henschke button have been in-
serted onto the plastic tube. Arrows point to metal Henschke buttons that have been crimped to secure the outer ribbon assembly to the afterloading tube. Note that there is excess pusher ribbon material protruding from the ends of the plastic tubes. This facilitates later ribbon removal. the underlying seeds from becoming dislodged during or
after the implant (Figs. 7, 9). If the ribbon did not protrude it would become heat sealed to the plastic tube, making later ribbon removal very difficult. Recall that the pusher and seeds within the ribbon are loose. Hence, it is imperative that the end of the ribbon-pusher apparatus be bonded. This additional step is not required with the Ir-192 plastic tube technique. This completes the preparation of the I- 125 seed-ribbon-afterloading tube assembly. To summarize, a triple component assembly must be secured: (a) The afterloading tube; (b) The I- 125 ribbon; (c) The loose components within the I- 125 ribbon (I- 125 seeds, spacers and pusher). Barium buttons are used to secure the afterloading tube skin-to-skin. A Henschke button is used to secure the ribbon assembly to the afterloading tube. The structural integrity of the assembly is
Fig. 9. The final step in securing the seed-ribbon assembly is shown. Heat sealing the end of the ribbon bonds the pusher to the outer wall of the ribbon and prevents dislodgement of the pusher, seeds or spacers from the ribbon.
Temporary I- 125 implants offer several important advantages over Ir- 192 when using the afterloading plastic tube technique. Radiation safety is the most obvious and important advantage. Furthermore, I- 125 lends itself to easy shielding of personnel, visitors, and radiosensitive normal tissues distant from the implanted area. The use of I- 125 seeds has facilitated the development of a brachytherapy ward with skilled nurses who are specially trained in caring for brachytherapy patients and who have a good understanding of radiation therapy. I- 125 seeds provide a flexible and dynamic dosimetric program since the seed-ribbons are individually prepared after the implant is done. This allows us to have full control over the dose rate and allows for correction of either hot spots or cold spots within the implanted volume. We have found that the technique can easily be adapted to any site where the afterloading plastic tube technique is used. We have observed no untoward or unexpected effects. The acute reactions observed thus far do not appear to differ from those seen after Ir- 192 implants. This confirms the findings of others.‘*” Ofcourse, we must wait for longer follow-up before assessing the impact on chronic or long term sequelae. It should be emphasized that before initiating such a program, a complete understanding of the technique is imperative. There are significant differences between I125 and Ir- 192 implants in regards to the afterloading tube construction, seed-ribbon assembly preparation, se-
Fig. 10. At the time of removal of the seed-ribbon assembly, calibrated pliars are used to uncrimp the metal button.
Temporary I- 125 implants 0 D. H. CLARKE etal.
curing the seed-ribbon-afterloading tube assembly, and dosimetric planning. Thus far, it appears that the advan-
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tages far outweigh our early concerns or any of the potential disadvantages discussed above.
REFERENCES 1. Broga, D., Gilbert, M.: A review of three incidents involving the release of I- 125 from seeds interstitially implanted within the prostate gland. Health Phys. 45: 593-597, 1983. 2. Clarke, D.H., Curtis, J.L., Martinez, A., Fajardo, L., Goffinet, D.: Fat necrosis ofthe breast simulating recurrent carcinoma after primary radiotherapy in the management of early stage breast carcinoma. Cancer52: 442-445, 1983. 3. Clarke, D.H., Edmundson, G.K., Matter, R.C., Martinez, A.: The superiority of I- 125 seeds in temporary plastic tube implants (Abstr.). Endocuriether. Hyperther. Oncol. 4: 86,
15. Martinez, A., Edmundson, G.K., Cox, R.S., Gunderson, L.L., Howes, A.E.: Combination of external beam irradiation and multiple-site perineal applicator (MUPIT) for treatment of locally advanced or recurrent prostatic, anorectal, and gynecologic malignancies. Int. J. Radiat. Oncol. Biol. Phys. 11: 391-398, 1985. 16. Matter, R.C., Vicini, F., Clarke, D.H., Martinez, A., Edmundson, G.K.: Preliminary results utilizing I-125 seeds as a substitute for Ir- 192 seeds in plastic tube afterloading breast implants (Abst.). Endocuriether. Hyperther. Oncol. 4: 86, 1988.
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4. Clarke, D.H., Martinez, A., Cox, R.S.: Analysis of cosmetic results and complications in patients with stage I and II breast cancer treated by biopsy and irradiation. Znt. J.
17. Meertens, H., Bartelink, H.: First experience with the microselectron in breast conserving therapy implants. In Brachytherapy, Proceedings 3rd International Selectron Users Meeting, Mould, R.F. (Ed.). Innsbruck, Austria,
Radiat. Oncol. Biol. Phys. 9: 1807- 18 13, 1983.
5. Edmundson, G.K., Clarke, D.H., Martinez, A., Matter, R.C.: An activity-compensated approach to Iodine- 125 temporary implant dosimetry. (Abstr). Endocuriether. Hyperther. Oncol. 2: 2 10, 1986.
6. Fjalling, M., Tisell, L., Carlsson, S., Hansson, G., Lundberg, L., Oden, A.: Benign and malignant thyroid nodules after neck irradiation. Cancer 58: 12 19- 1224, 1986. 7. Genest, P., Hilaris, B.S., Nori, D., Batata, M., Vikram, B., Hopfan, S., St. Get-main, J., Anderson, L.L., Kim, J.H., Alfieri, A.: Iodine-125 as a substitute for Iridium-192 in temporary interstitial implants. Endocuriether. Hyperther. Oncol. 1: 223-228, 1985. 8. Girinsky, T., van Limbergen, E., Gerbaulet, A., Haie, C., Chassagne, D.: Different dose-rates in preoperative intracavitary curietherapy for cervical carcinoma. In Brachytherapy, Proceedings 3rd International Meeting, Mould, R.F. (Ed.). Innsbruck,
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servative Management of Breast Cancer. New Surgical and Radiotherapeutic Techniques, Harris, J.R., Hellman, S.,
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tron Trading BV. 1984, pp. 229-232. 9. Goffinet, D.R., Fee, W.E., Wells, J., Austin-Seymour, M., Clarke, D.H., Mariscal, J.M., Goode, R.L.: 192 Ir Pharyngoepiglottic fold interstitial implants: The key to successful treatment of base tongue carcinoma by radiation therapy. Cancer55:
Nucletron Trading BV. 1984, pp. 27 l-276. 18. Nori, D., Hilaris, B.S., Chadha, M., Bains, M., Jain, S., Hopfan, S., Anderson, L.L.: Clinical applications of a remote afterloader. Endocuriether. Hyperther. Oncol. 1: 193-200,1985. 19. Pierquin, B.: Conservative treatment for carcinoma of the breast: Experience of Creteil-Ten-year-results. In Con-
941-948,1985.
10. Goffinet, D.R., Ling, C.C., Mar&al, M.: Preliminary clinical experience with removable Iodine- 125 breast implant boosts. (Abstr). Endocuriether. Hyperther. Oncol. 2: 2 16, 1986. 11. Hilaris, B.S., Nori, D., Horowitz, B.S., Beattie, E.J., Martini, N.: Perioperative brachytherapy in the management of non-oat cell lung cancer. In Brachytherapy Oncology1982: Advances in Lung and Other Cancers, Hilaris, B.S., Nori, D. (Eds.). New York, Memorial Sloan-Kettering Cancer Center. 1982, pp. 33-40. 12. Hilaris, B.S., Shiu, M.H., Nori, D., Anderson, L.L., Manolatos, S.: Limbsparing therapy for locally advanced softtissue sarcomas. Endocuriether. Hyperther. Oncol. 1: 1724, 1985. 13. Johns, H.E., Cunningham, J.R.: Appendices A-Basic Data. Table 3c and 3e. In The Physics of Radiology 4th edition, Johns, H.E., Cunningham, J.R. (Eds.). Springfield, Illinois, Charles C. Thomas. 1983, pp. 724-725. 14. Martinez, A., Clarke, D.H.: Treatment results, cosmesis, and complications in stages I and II breast cancer patients treated by excisional biopsy and irradiation. In Current Controversies in Breast Cancer, Ames, F.C., Blumenschien, G.R., Montague, E.D. (Eds.). Austin, Texas, U. of Texas Press. 1984, pp. 369-38 1.
21.
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Silen, W. (Eds.). Philadelphia, JB Lippincott Co. 1983, pp. 11-14. Puthawala, A.A., Syed, A.M.N., Eads, D.L., Neblett, D., Gillin, L., Gates, T.C.: Limited external irradiation and interstitial 192 iridium implant in the treatment of squamous cell carcinoma of the tonsillar region. Znt. J Radiat. Oncol. Biol. Phys. 11: 1595-1602, 1985. Puthawala, A.A., Syed, A.M.N., Tansey, L.A., Shanberg, A., Austin, P.A., McNamara, C.S.: Temporary iridium192 implant in the management of carcinoma of the prostate. “An anaylsis of treatment results and complications in the first one hundred patients”. Endocuriether. Hyperther. Oncol. 1: 25-34, 1985. Schray, M.F., Braun, J.S., Vetter, R.J., Yeakel, P.: Personnel exposure in brachytherapy (Abstr.). Endocuriether. Hyperther. Oncol. 2: 2 12, 1986. Shank, B.: Breast preservation and brachytherapy. Endocuriether. Hyperther. Oncol. 2: S- 17-S-24, 1986. Syed, A.M.N., Puthawala, A.A., Neblett, D., Disaia, P.J., Berman, M.L., Rettenmaier, M., Nalick, R., McNamara, C.: Transperineal interstitital-intracavitary “Syed-Neblett” applicator in the treatment of carcinoma of the uterine cervix. Endocuriether. Hyperther. Oncol. 2: 1-13, 1986. van Bunningen, B.N.F., Battermann, J.: Experience with selectron afterloading in the Antoni van Leeuwenhoek Hospital. In Brachytherapy, Proceedings 3rd International Selectron Users Meeting, Mould, R.F. (Ed.). Innsbruck, Austria, Nucletron Trading BV. 1984, pp. 6- 12. Vikram, B., Strong, E., Shah, J., Spiro, R., Gerold, F., et al.: A nonlooping afterloading technique for base oftongue implants. Results in the first 20 patients. Znt. J. Radiat. Oncol. Biol. Phys. 11: 1853-1855, 1985. Warmelink, C., Edmundson, G.K., Martinez, A., Clarke, D.H., Matter, R.C.: The use of lead-rubber shielding in temporary Iodine- 125 Implants (Abstr.). Endocuriether. Hyperther. Oncol. 4: 86, 1988.