- Email: [email protected]
Analysis of interstitial breast brachytherapy plan using dose volume histogram
Abstracts / Brachytherapy 6 (2007) 77e118 3
UTHSCSA, San Antonio, TX; Texas Cancer Clinic, San Antonio, TX. Purpose: The first clinical trial of permanent Cs-131 seed implants for monotherapeutic treatment of early stage prostate cancer is nearing completion (80 of a targeted 100 patients). While the clinical results are of paramount importance, the physics and dosimetry framework provides the foundation without which interpretation of the data is meaningless. Presented here are the techniques that were developed and the dosimetric results obtained from this seven-institution trial. Methods and Materials: A protocol was developed which established methods for performing and documenting implants performed with Cs131. Forms and images were submitted electronically and stored within a centralized database. Dosimetric analysis focused on post implant dosimetry from CT scans performed two weeks post procedure. Anatomical contouring was performed by the submitting institution. Results: Despite the similarity of the practices followed by the participating institutions, the resultant implants were quite different. For each individual institution, total source strength was highly correlated to target volume, but overall correlation throughout the database was poor. Dosimetrically, targetvolume ratios ranged from 1.2 to 2.8. Prostate volumes were compared to ultrasound-generated pre-implant volumes, highlighting the difference in practitioner’s interpretation of the glandular borders. Average post-to-pre implant ratios ranged from 1.05 to 1.81. For this isotope and the dose distributions achieved by the participating institutions, V150 was very low (40.8 11.0%), V100 and D90 acceptable (91.8 + 5.4% and 104.6 8.6 Gy, respectively). Urethra U150 were low at 0.03 cm3. Rectal R100 were comparable to those achieved with I-125 implantation at 0.35 cm3 on the average. Conclusions: Implant differences can be tolerated and highlighted in a multi-institutional trial. These differences offer an opportunity for study of the various aspects of the procedure, allowing for informed recommendation with regard to technique and implant targets. This has been successfully done for this Cs-131 permanent prostate brachytherapy trial. Analysis of the clinical outcome data and the correlation to dosimetric quantifiers is the subject of a companion paper. Study supported by Isoray Medical, manufacturer of the sources used in the study.
OR-32 Presentation Time: 9:20 AM Advances in calibration of high-dose-rate brachytherapy sources Larry A. DeWerd, Ph.D.1 Stephen Davis, M.sc.2 Wes Culberson, Ph.D.1 1 Medical Physics, University of Wisconsin, Madison, WI; 2Medical Radiation Research Center, University of Wisconsin, Madison, WI. Purpose: High-dose-rate (HDR) brachytherapy Ir-192 sources have been in existence for more than 15 years. The calibration of HDR Ir-192 was first developed at the University of Wisconsin, using what has come to be termed the seven-distance technique. Since its inception multiple manufacturers of this source have entered the marketplace. The design of these sources consists of a single pellet or 2 pellets encapsulated in different materials. There are different afterloaders used to deliver the source through a catheter to a patient. Another high dose rate source with low energy (50 keV) is a miniature x-ray source. The intent of the lower energy is a better dose distribution and less transmission through the patient into the room. A miniature x-ray source was calibrated using a free air chamber designed for energies at 50 keV or less. Methods and Materials: Each of the manufacturer sources for Ir-192 and another high-dose-rate source, Yb-169, have been measured with the 7distance apparatus. The calibration method for the energies involved for the ion chamber will be described, including the changes in the NIST air kerma standard for the cesium calibration point. The high dose rate x-ray source has been calibrated with a free air chamber. Results: Comparison of sources from different Ir-192 manufacturers, including the new design versus the older design, and the subsequent use of well chambers to determine the air kerma strength will be explained. The calibrations for all the manufacturers of this source agree within 1% and well chambers can be calibrated to air kerma strength within the total
89
uncertainty of 2% (k 5 2). All the HDR Ir-192 sources agree with the present value within +0.5%. The x-ray sources agree within +2%. Conclusions: New advances in sources used for high-dose-rate brachytherapy utilize lower energies and source modifications of the Ir192 nuclide. The air kerma strength of all of these sources has been made allowing subsequent well chamber calibrations to be performed. All sources can now be calibrated to air kerma strength. Owner Standard Imaging.
OR-33 Presentation Time: 9:30 AM A 3D forward treatment planning algorithm using pre-calculated Monte Carlo data sets for HDR/PDR tandem and ovoid intracavitary systems Michael J. Price, B.S. Firas Mourtada, Ph.D. Radiation Physics, The University of Texas M D Anderson Cancer Center, Houston, TX. Purpose: To develop an algorithm for forward planning of Ir-192 FletcherWilliamson (FW) HDR/PDR ICBT cervical carcinoma procedures using a database of validated Monte Carlo (MC) dose distributions. Methods and Materials: The algorithm utilizes treatment parameters (i.e., source strength, dwell positions and times) as well as defined patient geometric points of interest (e.g. Points A and B, ICRU rectal and bladder points, etc.) extracted from Nucletron’s Plato TPS. Dose distributions for a variety of FW inter-colpostat Ir-192 source dwell positions were simulated using experimentally-validated MCNPX MC models. An opposing, source-less FW ovoid is included in each simulation to approximately account for perturbations in dose due to the paired applicator system. An additional MC model was constructed of the source in a tandem tube segment. Using source coordinates derived from Plato, dose distributions were translated and rotated so that MC generated dose distributions correspond to the digitized source positions. Dose rate distributions were then converted to absolute dose and superimposed with respect to the patient-defined coordinate system. Dose delivered to pointsof-interest were calculated and compared to doses calculated by the Plato TPS. Results: Preliminary results indicate that the proposed algorithm is able to calculate 3D dose distributions limited only by the statistical uncertainty of the MC dose estimate (z3%). This has been achieved by accurately modeling the colpostat’s components (i.e. steel shaft, set screw, air gap, and polysulfone cap) as well as the tungsten shields. Insufficient consideration of these components has been shown by the authors to introduce an overestimation of dose (6% and 40%). Conclusions: The proposed, precalculated MC-based, forward planning algorithm is useful in reporting more accurate dose distributions administered in ICBT HDR/PDR treatments.
OR-34 Presentation Time: 9:40 AM Analysis of interstitial breast brachytherapy plan using dose volume histogram Murali Nair, Ph.D., Rufus J. Mark, M.D., Paul J. Anderson, M.D., Thomas R. Neumann, M.D., Steven Gurley, C.M.D., David White, C.M.D., Joseph Britt Colenda, M.S. Radiation Oncology, Joe Arrington Cancer Center, Lubbock, TX. Purpose: The purpose of this presentation is to discuss the results of the quality assurance analysis of high dose rate (HDR) interstitial breast brachytherapy plans. The criteria used for this analysis along with the results and the criteria used for the template design are discussed. Methods and Materials: We have treated about 98 patients with HDR interstitial brachytherapy. The age group of patients treated with this technique range from 46 to 89 with a median age of 71 years (N 5 25). The patients were selected for this treatment following tylectomy. The 6 French flexi catheters were implanted under image guidance using a custom made template, such that the planning target volume (PTV) covered 2- to 2.5-cm margin from the site of the surgical boundary. The reference dose (RD) delivered to the PTV was 34 Gy in 10 fractions over
90
Abstracts / Brachytherapy 6 (2007) 77e118
5 days. The template was redesigned with grid spacing of 10 mm between columns and 10 mm between the rows, in order to achieve uniform coverage and to minimize high dose gradient within the implant volume. The neighboring 3 grid holes formed the vertices of a triangle for better dosimetry. We have used the following quality assurance criteria for analysis. Total of 28 patient plans treated with the new template were analyzed in this study using the dose volume histograms (DVH). The coverage uniformity must be such that 95 to 100% of the PTV will cover 100% of RD. The volume receiving 1.5 times RD, must be less than or equal to 30% of PTV (1.5RD < 0.3 PTV). The volume receiving 2 times RD must be less than or equal to 10% of PTV (2RD < 0.1 PTV). Results: The PTV ranged from 20 to 220 cc. The criteria #1 was met in 95% (N 5 27) of the plans analyzed. One plan had criteria #1 reaching 40% of PTV. The criteria #2 was met in 70% (N 5 20) of the plans analyzed, 9% (N 5 3) of the plans were at 20% of PTV and the rest (N 5 5) were within 10% to 15% of PTV. The deviation from the criteria was due to irregular shape of PTV and less was due to less number of catheters available for optimization. Conclusions: The number of catheters and the spacing between the catheters were critical for reducing the high dose gradient inside the PTV and thereby reducing the chances of fat necrosis. Based on our clinical observation, it was very essential to keep the volume receiving high dose gradient, 1.5 RD (5.10 Gy) !30% of PTV and the dose gradient 2 RD (6.8 Gy) !10% of PTV. For reducing the high dose gradient volume, it was important to maintain the spacing between the sources to 10 mm and was possible with more catheters available for optimization. Also for uniformity of coverage along the PTV, it was essential to place a source at least 5 mm inside the boundary of the PTV. OR-35 Presentation Time: 9:50 AM Postoperative urethral dose assessment of I-125 prostate implants using in vivo MOSFET detectors Bradley R. Prestidge, M.D.1,2 Ines Jurkovic, M.S.1,2 Amir G. Sadeghi, Ph.D.1,2 Leticia Salinas, M.S.2 William S. Bice, Ph.D.1,2,3 1Radiation Oncology, Texas Cancer Clinic, San Antonio, TX; 2Radiological Sciences, UT Health Sciences Center of San Antonio, San Antonio, TX; 3Southwest Cancer Foundation, San Antonio, TX. Purpose: Although prostate low-dose-rate (LDR) brachytherapy treatment planning systems provide point dose information, verification of the actual dose received within the volume in real time has not been previously studied. A commercially available MOSFET (Metal Oxide Silicon Field Effect Transistor) system (TN-502LA5, high sensitivity) has been investigated for performing in-vivo dosimetry during permanent LDR prostate implants. The study results are presented. Methods and Materials: The MOSFET system was calibrated for I-125 in both solid water and in a water phantom using single high activity sources. Measurements were performed for 29 consecutive, I-125 patients, by inserting the linear array consisting of five individual MOSFETs (2 cm apart) into the patient’s Foley catheter. Detector locations were determined from a custom radio-opaque marker array inserted prior to a CT scan performed immediately after the procedure. This scan was also used for Day-0 post-operative dosimetric evaluation of the implant. MOSFET positions included: 1) Within the bladder neck (0 cm), 2) At the prostate base (2 cm), 3) Approximately mid-glad (4 cm), and 4) At the prostatic apex or beyond (6 cm). Data were collected while the patients were in post-operative recovery. Patient measurements were collected for one hour and compared to doses calculated from the postimplant CT scan. Results: As calculated in the post implant treatment plan, the dose increased with the distance from the bladder, reached its maximum inside the prostatic urethra and decreased again at the apex of the gland. The measured values for the I-125 implants ranged from 0.0005 to 0.129 Gy/hr. Differences between measured and calculated dose rates ranged from 0 to 27.1% different from the calculated value. The overall correlation between the measured and calculated values was 0.993. Extra care must be taken when using MOSFET in the harsh environments encountered during invivo measurement. Calibration factors were seen to vary widely between
dosimeters, emphasizing the need for careful measurement and record keeping. Precise positioning for calibration and patient measurements is critical, particularly in higher dose regions where there are large dose gradients. Conclusions: Overall, in-vivo measurements agreed well with the postimplant values obtained from the treatment planning system. Measurements were felt to be a useful quality assurance procedure, helpful in identifying potential issues with regard to implant quality and another means of conducting the post implant evaluation. PROSTATE PAPER SESSION Tuesday May 1, 2007 11:30 AMe12:30 PM OR-36 Presentation Time: 11:30 AM Long-term urinary function following Iodine-125 prostate brachytherapy Juanita M. Crook, M.D.1 Chris Roberts, B.Sc.1 Neil Fleshner, M.D.2 1 Radiation Oncology, Princess Margaret Hospital, Toronto, ON, Canada; 2 Surgical Oncology, University Health Network, Toronto, ON, Canada. Purpose: To describe long term urinary function in men treated with Iodine125 without the use of supplemental beam irradiation. Methods and Materials: At the Princess Margaret Hospital/University Health Network, 473 men with favorable-risk prostate cancer have been treated with Iodine-125 prostate brachytherapy (BT), with a followup ranging from 12 to 84 months. A short course of hormonal therapy (2e6 months) was used in 15% prior to BT to reduce prostate size. Implants were preplanned using transrectal ultrasound (TRUS) and performed using preloaded needles under TRUS and fluoroscopy guidance. Postplan assessment was performed at 1 month using MR-CT fusion. Urinary function was assessed prior to implant by the International Prostate Symptom Score (IPSS) and a voiding study, and following BT by IPSS at each followup visit. Urinary retention and catheterization, urgency and urge incontinence, persistently elevated IPSS, stricture and the need for surgical intervention are reported. Severity was scored according to the CTCAE 3.0. Results: Median patient age was 63 years (45e83). Median prostate volume was 38 cc (14e62). T stage was T1c in 65% and T2a in 35%; 93.5% were Gleason 6 and the median pretreatment PSA was 5.6 ng/mL. Median baseline IPSS was 6 (0e24). Median V100 was 93%, V150 57%, D90 160 Gy. Mean urethral D30 was 191 Gy and D5 214 Gy. No significant urinary sequelae were reported in 80.1% of men after 1 year. IPS scores O15 and at least 5 points above their baseline were reached in 9%. Flares in the IPSS last a median of 3.9 mo. Symptoms of retention requiring either catheterization or surgical intervention were seen in 3.4% (1.7% stricture, 0.4% TURP, 3.1% catheter). Of the 15 men requiring catheterization at any time after one year, only 3 (0.6%) remain dependent on intermittent self catheterization. The median duration of catheter use for those which resolved is 24 weeks. Moderate to severe urinary urgency occurred in 8.0%, but in only 0.8% was it unresponsive to anti-cholinergics. Conclusions: In this practice 20% of men experienced some degree of late urinary morbidity following Iodine-125 prostate brachytherapy. Rates may vary according to technique and selection factors. The majority respond well to medical or surgical intervention, with only 0.8% persistent urgency, and 0.6% catheter dependence. OR-37 Presentation Time: 11:40 AM Long-term urinary and rectal toxicity evaluation after permanent prostate brachytherapy monotherapy Kevin Stephans, M.D.1 Eric A. Klein, M.D.2 Kenneth Angermeier, M.D.2 James Ulchaker, M.D.2 Nabil Chihade, M.D.3 Andrew Altman, M.D.3 Chandana Reddy, M.S.1 Jay P. Ciezki, M.D.1 1Radiation Oncology, Cleveland Clinic, Cleveland, OH; 2Glickman Urological Institute, Cleveland Clinic, Cleveland, OH; 3Kaiser Urology, Kaiser Permanente, Cleveland, OH. Purpose: Assessment of long-term urinary and rectal toxicity in patients with at least 5 years potential followup after prostate brachytherapy (PI).
UTHSCSA, San Antonio, TX; Texas Cancer Clinic, San Antonio, TX. Purpose: The first clinical trial of permanent Cs-131 seed implants for monotherapeutic treatment of early stage prostate cancer is nearing completion (80 of a targeted 100 patients). While the clinical results are of paramount importance, the physics and dosimetry framework provides the foundation without which interpretation of the data is meaningless. Presented here are the techniques that were developed and the dosimetric results obtained from this seven-institution trial. Methods and Materials: A protocol was developed which established methods for performing and documenting implants performed with Cs131. Forms and images were submitted electronically and stored within a centralized database. Dosimetric analysis focused on post implant dosimetry from CT scans performed two weeks post procedure. Anatomical contouring was performed by the submitting institution. Results: Despite the similarity of the practices followed by the participating institutions, the resultant implants were quite different. For each individual institution, total source strength was highly correlated to target volume, but overall correlation throughout the database was poor. Dosimetrically, targetvolume ratios ranged from 1.2 to 2.8. Prostate volumes were compared to ultrasound-generated pre-implant volumes, highlighting the difference in practitioner’s interpretation of the glandular borders. Average post-to-pre implant ratios ranged from 1.05 to 1.81. For this isotope and the dose distributions achieved by the participating institutions, V150 was very low (40.8 11.0%), V100 and D90 acceptable (91.8 + 5.4% and 104.6 8.6 Gy, respectively). Urethra U150 were low at 0.03 cm3. Rectal R100 were comparable to those achieved with I-125 implantation at 0.35 cm3 on the average. Conclusions: Implant differences can be tolerated and highlighted in a multi-institutional trial. These differences offer an opportunity for study of the various aspects of the procedure, allowing for informed recommendation with regard to technique and implant targets. This has been successfully done for this Cs-131 permanent prostate brachytherapy trial. Analysis of the clinical outcome data and the correlation to dosimetric quantifiers is the subject of a companion paper. Study supported by Isoray Medical, manufacturer of the sources used in the study.
OR-32 Presentation Time: 9:20 AM Advances in calibration of high-dose-rate brachytherapy sources Larry A. DeWerd, Ph.D.1 Stephen Davis, M.sc.2 Wes Culberson, Ph.D.1 1 Medical Physics, University of Wisconsin, Madison, WI; 2Medical Radiation Research Center, University of Wisconsin, Madison, WI. Purpose: High-dose-rate (HDR) brachytherapy Ir-192 sources have been in existence for more than 15 years. The calibration of HDR Ir-192 was first developed at the University of Wisconsin, using what has come to be termed the seven-distance technique. Since its inception multiple manufacturers of this source have entered the marketplace. The design of these sources consists of a single pellet or 2 pellets encapsulated in different materials. There are different afterloaders used to deliver the source through a catheter to a patient. Another high dose rate source with low energy (50 keV) is a miniature x-ray source. The intent of the lower energy is a better dose distribution and less transmission through the patient into the room. A miniature x-ray source was calibrated using a free air chamber designed for energies at 50 keV or less. Methods and Materials: Each of the manufacturer sources for Ir-192 and another high-dose-rate source, Yb-169, have been measured with the 7distance apparatus. The calibration method for the energies involved for the ion chamber will be described, including the changes in the NIST air kerma standard for the cesium calibration point. The high dose rate x-ray source has been calibrated with a free air chamber. Results: Comparison of sources from different Ir-192 manufacturers, including the new design versus the older design, and the subsequent use of well chambers to determine the air kerma strength will be explained. The calibrations for all the manufacturers of this source agree within 1% and well chambers can be calibrated to air kerma strength within the total
89
uncertainty of 2% (k 5 2). All the HDR Ir-192 sources agree with the present value within +0.5%. The x-ray sources agree within +2%. Conclusions: New advances in sources used for high-dose-rate brachytherapy utilize lower energies and source modifications of the Ir192 nuclide. The air kerma strength of all of these sources has been made allowing subsequent well chamber calibrations to be performed. All sources can now be calibrated to air kerma strength. Owner Standard Imaging.
OR-33 Presentation Time: 9:30 AM A 3D forward treatment planning algorithm using pre-calculated Monte Carlo data sets for HDR/PDR tandem and ovoid intracavitary systems Michael J. Price, B.S. Firas Mourtada, Ph.D. Radiation Physics, The University of Texas M D Anderson Cancer Center, Houston, TX. Purpose: To develop an algorithm for forward planning of Ir-192 FletcherWilliamson (FW) HDR/PDR ICBT cervical carcinoma procedures using a database of validated Monte Carlo (MC) dose distributions. Methods and Materials: The algorithm utilizes treatment parameters (i.e., source strength, dwell positions and times) as well as defined patient geometric points of interest (e.g. Points A and B, ICRU rectal and bladder points, etc.) extracted from Nucletron’s Plato TPS. Dose distributions for a variety of FW inter-colpostat Ir-192 source dwell positions were simulated using experimentally-validated MCNPX MC models. An opposing, source-less FW ovoid is included in each simulation to approximately account for perturbations in dose due to the paired applicator system. An additional MC model was constructed of the source in a tandem tube segment. Using source coordinates derived from Plato, dose distributions were translated and rotated so that MC generated dose distributions correspond to the digitized source positions. Dose rate distributions were then converted to absolute dose and superimposed with respect to the patient-defined coordinate system. Dose delivered to pointsof-interest were calculated and compared to doses calculated by the Plato TPS. Results: Preliminary results indicate that the proposed algorithm is able to calculate 3D dose distributions limited only by the statistical uncertainty of the MC dose estimate (z3%). This has been achieved by accurately modeling the colpostat’s components (i.e. steel shaft, set screw, air gap, and polysulfone cap) as well as the tungsten shields. Insufficient consideration of these components has been shown by the authors to introduce an overestimation of dose (6% and 40%). Conclusions: The proposed, precalculated MC-based, forward planning algorithm is useful in reporting more accurate dose distributions administered in ICBT HDR/PDR treatments.
OR-34 Presentation Time: 9:40 AM Analysis of interstitial breast brachytherapy plan using dose volume histogram Murali Nair, Ph.D., Rufus J. Mark, M.D., Paul J. Anderson, M.D., Thomas R. Neumann, M.D., Steven Gurley, C.M.D., David White, C.M.D., Joseph Britt Colenda, M.S. Radiation Oncology, Joe Arrington Cancer Center, Lubbock, TX. Purpose: The purpose of this presentation is to discuss the results of the quality assurance analysis of high dose rate (HDR) interstitial breast brachytherapy plans. The criteria used for this analysis along with the results and the criteria used for the template design are discussed. Methods and Materials: We have treated about 98 patients with HDR interstitial brachytherapy. The age group of patients treated with this technique range from 46 to 89 with a median age of 71 years (N 5 25). The patients were selected for this treatment following tylectomy. The 6 French flexi catheters were implanted under image guidance using a custom made template, such that the planning target volume (PTV) covered 2- to 2.5-cm margin from the site of the surgical boundary. The reference dose (RD) delivered to the PTV was 34 Gy in 10 fractions over
90
Abstracts / Brachytherapy 6 (2007) 77e118
5 days. The template was redesigned with grid spacing of 10 mm between columns and 10 mm between the rows, in order to achieve uniform coverage and to minimize high dose gradient within the implant volume. The neighboring 3 grid holes formed the vertices of a triangle for better dosimetry. We have used the following quality assurance criteria for analysis. Total of 28 patient plans treated with the new template were analyzed in this study using the dose volume histograms (DVH). The coverage uniformity must be such that 95 to 100% of the PTV will cover 100% of RD. The volume receiving 1.5 times RD, must be less than or equal to 30% of PTV (1.5RD < 0.3 PTV). The volume receiving 2 times RD must be less than or equal to 10% of PTV (2RD < 0.1 PTV). Results: The PTV ranged from 20 to 220 cc. The criteria #1 was met in 95% (N 5 27) of the plans analyzed. One plan had criteria #1 reaching 40% of PTV. The criteria #2 was met in 70% (N 5 20) of the plans analyzed, 9% (N 5 3) of the plans were at 20% of PTV and the rest (N 5 5) were within 10% to 15% of PTV. The deviation from the criteria was due to irregular shape of PTV and less was due to less number of catheters available for optimization. Conclusions: The number of catheters and the spacing between the catheters were critical for reducing the high dose gradient inside the PTV and thereby reducing the chances of fat necrosis. Based on our clinical observation, it was very essential to keep the volume receiving high dose gradient, 1.5 RD (5.10 Gy) !30% of PTV and the dose gradient 2 RD (6.8 Gy) !10% of PTV. For reducing the high dose gradient volume, it was important to maintain the spacing between the sources to 10 mm and was possible with more catheters available for optimization. Also for uniformity of coverage along the PTV, it was essential to place a source at least 5 mm inside the boundary of the PTV. OR-35 Presentation Time: 9:50 AM Postoperative urethral dose assessment of I-125 prostate implants using in vivo MOSFET detectors Bradley R. Prestidge, M.D.1,2 Ines Jurkovic, M.S.1,2 Amir G. Sadeghi, Ph.D.1,2 Leticia Salinas, M.S.2 William S. Bice, Ph.D.1,2,3 1Radiation Oncology, Texas Cancer Clinic, San Antonio, TX; 2Radiological Sciences, UT Health Sciences Center of San Antonio, San Antonio, TX; 3Southwest Cancer Foundation, San Antonio, TX. Purpose: Although prostate low-dose-rate (LDR) brachytherapy treatment planning systems provide point dose information, verification of the actual dose received within the volume in real time has not been previously studied. A commercially available MOSFET (Metal Oxide Silicon Field Effect Transistor) system (TN-502LA5, high sensitivity) has been investigated for performing in-vivo dosimetry during permanent LDR prostate implants. The study results are presented. Methods and Materials: The MOSFET system was calibrated for I-125 in both solid water and in a water phantom using single high activity sources. Measurements were performed for 29 consecutive, I-125 patients, by inserting the linear array consisting of five individual MOSFETs (2 cm apart) into the patient’s Foley catheter. Detector locations were determined from a custom radio-opaque marker array inserted prior to a CT scan performed immediately after the procedure. This scan was also used for Day-0 post-operative dosimetric evaluation of the implant. MOSFET positions included: 1) Within the bladder neck (0 cm), 2) At the prostate base (2 cm), 3) Approximately mid-glad (4 cm), and 4) At the prostatic apex or beyond (6 cm). Data were collected while the patients were in post-operative recovery. Patient measurements were collected for one hour and compared to doses calculated from the postimplant CT scan. Results: As calculated in the post implant treatment plan, the dose increased with the distance from the bladder, reached its maximum inside the prostatic urethra and decreased again at the apex of the gland. The measured values for the I-125 implants ranged from 0.0005 to 0.129 Gy/hr. Differences between measured and calculated dose rates ranged from 0 to 27.1% different from the calculated value. The overall correlation between the measured and calculated values was 0.993. Extra care must be taken when using MOSFET in the harsh environments encountered during invivo measurement. Calibration factors were seen to vary widely between
dosimeters, emphasizing the need for careful measurement and record keeping. Precise positioning for calibration and patient measurements is critical, particularly in higher dose regions where there are large dose gradients. Conclusions: Overall, in-vivo measurements agreed well with the postimplant values obtained from the treatment planning system. Measurements were felt to be a useful quality assurance procedure, helpful in identifying potential issues with regard to implant quality and another means of conducting the post implant evaluation. PROSTATE PAPER SESSION Tuesday May 1, 2007 11:30 AMe12:30 PM OR-36 Presentation Time: 11:30 AM Long-term urinary function following Iodine-125 prostate brachytherapy Juanita M. Crook, M.D.1 Chris Roberts, B.Sc.1 Neil Fleshner, M.D.2 1 Radiation Oncology, Princess Margaret Hospital, Toronto, ON, Canada; 2 Surgical Oncology, University Health Network, Toronto, ON, Canada. Purpose: To describe long term urinary function in men treated with Iodine125 without the use of supplemental beam irradiation. Methods and Materials: At the Princess Margaret Hospital/University Health Network, 473 men with favorable-risk prostate cancer have been treated with Iodine-125 prostate brachytherapy (BT), with a followup ranging from 12 to 84 months. A short course of hormonal therapy (2e6 months) was used in 15% prior to BT to reduce prostate size. Implants were preplanned using transrectal ultrasound (TRUS) and performed using preloaded needles under TRUS and fluoroscopy guidance. Postplan assessment was performed at 1 month using MR-CT fusion. Urinary function was assessed prior to implant by the International Prostate Symptom Score (IPSS) and a voiding study, and following BT by IPSS at each followup visit. Urinary retention and catheterization, urgency and urge incontinence, persistently elevated IPSS, stricture and the need for surgical intervention are reported. Severity was scored according to the CTCAE 3.0. Results: Median patient age was 63 years (45e83). Median prostate volume was 38 cc (14e62). T stage was T1c in 65% and T2a in 35%; 93.5% were Gleason 6 and the median pretreatment PSA was 5.6 ng/mL. Median baseline IPSS was 6 (0e24). Median V100 was 93%, V150 57%, D90 160 Gy. Mean urethral D30 was 191 Gy and D5 214 Gy. No significant urinary sequelae were reported in 80.1% of men after 1 year. IPS scores O15 and at least 5 points above their baseline were reached in 9%. Flares in the IPSS last a median of 3.9 mo. Symptoms of retention requiring either catheterization or surgical intervention were seen in 3.4% (1.7% stricture, 0.4% TURP, 3.1% catheter). Of the 15 men requiring catheterization at any time after one year, only 3 (0.6%) remain dependent on intermittent self catheterization. The median duration of catheter use for those which resolved is 24 weeks. Moderate to severe urinary urgency occurred in 8.0%, but in only 0.8% was it unresponsive to anti-cholinergics. Conclusions: In this practice 20% of men experienced some degree of late urinary morbidity following Iodine-125 prostate brachytherapy. Rates may vary according to technique and selection factors. The majority respond well to medical or surgical intervention, with only 0.8% persistent urgency, and 0.6% catheter dependence. OR-37 Presentation Time: 11:40 AM Long-term urinary and rectal toxicity evaluation after permanent prostate brachytherapy monotherapy Kevin Stephans, M.D.1 Eric A. Klein, M.D.2 Kenneth Angermeier, M.D.2 James Ulchaker, M.D.2 Nabil Chihade, M.D.3 Andrew Altman, M.D.3 Chandana Reddy, M.S.1 Jay P. Ciezki, M.D.1 1Radiation Oncology, Cleveland Clinic, Cleveland, OH; 2Glickman Urological Institute, Cleveland Clinic, Cleveland, OH; 3Kaiser Urology, Kaiser Permanente, Cleveland, OH. Purpose: Assessment of long-term urinary and rectal toxicity in patients with at least 5 years potential followup after prostate brachytherapy (PI).