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Immobilization and Treatment of Patients Receiving Radiation Therapy for Extremity Soft-Tissue Sarcoma
0
Third Place Smithers/AAMD
1992 Writing Competition
IMMOBILIZATION AND TREATMENT OF PATIENTS RECEIVING RADIATION THERAPY FOR EXTREMITY SOFT-TISSUE SARCOMA KIML. Department
of Radiation
LIGHT,
R.T.T., C.M.D.
Oncology, Duke University Medical Center, Durham, NC 277 10. U.S.A.
Abstract-The treatment of extremity soft-tissue sarcoma has evolved considerably over the years. Previously, the preferred treatment was radical resection or amputation. Recently, radiation therapy combined with conservative resection has been shown to provide adequate tumor control while preserving a functional limb. Often, a large volume of tissue is irradiated in a manner that requires the patient to be in a reproducible position. Minimizing patient movement is imperative to ensure that the prescribed dose is delivered to the designated target volume. At our institution, Alpha Cradles @*have been routinely used for eight years to aid in positioning extremity sarcoma patients. The positioning of the patient for tumors at different locations in the extremity and the Alpha Cradle@ fabrication is described. The positioning device is comfortable for the patient and the accuracy is verified by comparison of simulation films with weekly port films. Key Words: Extremity sarcoma, Radiation therapy, Immobilization, Reproducibility.
INTRODUCTION
sulted in a local recurrence rate as high as 77% in a group of 218 patients analyzed by Martin et al.’ at M. D. Anderson Hospital. Amputations at the joint above the tumor were then frequently employed to obtain clear margins. These tumors were not even considered for radiation therapy because they were considered radioresistant. Function sparing procedures that combined a more limited resection with pre- or postoperative radiation therapy are now the predominant treatment. Local recurrence rates have dropped to approximately 20% with this approach.3 With the increased use of radiation therapy for the treatment of extremity soft-tissue sarcomas, careful attention to radiation delivery is essential. Optimal precision in radiation oncology is influenced by knowledge of the dose prescribed, accurate measurements of machine output and beam parameters, as well as ensuring that the treatment beam accurately transverses the desired anatomy during every treatment. The ability to reproduce the patient position from day to day can be a major problem in radiation oncology. A reduction of as much as 10% in dose from the prescribed dose could occur if the tumor was missed due to inaccurate setup once or twice during a treatment course or if there is movement of the tumor
Soft-tissue sarcoma arises from mesenchymal tissue and accounts for less than 1% of cancers treated in most oncology centers. These tumors show no prevalence in any particular sex nor is there any clear age predominance, although some histologic types seem to be more common in either the younger or older patient. ’ The most common site for initial presentation is the extremity. The most common presenting symptom is a painless, palpable mass.* An effective management plan requires precise preoperative evaluation to assess the primary tumor as well as evaluation of possible metastatic disease. Conventional x-rays are useful in evaluating large tumors, although computerized tomography (CT) or magnetic resonance imaging (MRI) are considered the optimal imaging modalities in the evaluation of soft-tissue sarcomas. Management of extremity soft-tissue sarcomas has evolved considerably over the years.2-7 It was initially thought that tumor control could be obtained with a wide local excision. Local excision alone re* Alpha Cradle@-Smithers
Medical Products, Inc.
I35
136
Medical Dosimetry
Volume 17, Number 3, 1992
out of the field during an individual treatment.* Precise positioning is required to minimize this problem. When setting up the radiation treatment fields, 5to IO-cm margins are given longitudinally to the tumor due to its growth pattern, while a smaller margin is used circumferentially. A strip of soft tissue along the circumference of the extremity is spared to avoid edema, radiation fibrosis, and loss of function.3 A smaller margin is acceptable unless the tumor is advanced, since involvement through the fascia of the muscle conipartment is unlikely for localized tumors. For advanced tumors, more margin is needed and can usually be obtained with oblique fields and customized blocking to ensure some normal tissue sparing. Due to the sometimes complex field arrangement necessary for treatment of these patients, precise repositioning of the extremity is essential. A variety of immobilization techniques for other treatment sites are well described in the literature.8-‘6 Although it is recognized that immobilization is necessary for treating extremity sarcoma patients, there is little information in the literature detailing the positioning and immobilization technique.3*‘7
METHODS
AND MATERIALS
Patient positioning Fifty extremity soft-tissue sarcoma patients were treated with radiation therapy at our institution from 1984 to 199 1. Forty-seven of these patients had sarcomas of the lower extremity and three had sarcomas of the upper extremity. Alpha Cradle@* immobilization devices were used on all patients. The location of the tumor in the affected extremity determines the position of the patient in the Alpha Cradle@. Soft-tissue sarcoma occurs most often in the thigh. Tumor involvement can be extensive before a mass becomes palpable, thus large treatment volumes are usually necessary. The muscles in the thigh are divided into three groups: the anterior, medial, and posterior compartments. ‘* For anteriolateral tumors, treatment is usually given via parallel opposed oblique fields directed from the medial to the lateral aspect of the thigh. Anteriomedial tumors can usually be treated with AP-PA or slightly angled fields. If the tumor is proximal, the legs are separated to avoid radiation to the opposite extremity. Due to the wider field that is needed proximally, customized field shaping is used to spare normal tissue along the inferiolateral aspect of the thigh. Patients are generally positioned prone, with the involved extremity rotated, or placed on their side with their thighs separated when irradiating the posterior compartment of the thigh. At our insti* Smithers Medical Products, Inc.
Fig. 1. Alpha Cradle@ used when treating thigh sarcomas includes immobilization from the pelvis to the foot to ensure reproducible rotation of the extremity.
tution, we have found that the patient’s position can best be maintained by immobilizing from the pelvis to the foot (Fig. 1). This adequately stabilizes the joint above and below the tumor site and maintains the same volume of tissue in the treatment field daily. The muscles in the lower leg are divided into three groups: the anterior, lateral, and posterior compartments. I8 The anterior compartment of the lower leg can be irradiated with parallel opposed oblique fields while the lateral compartment can usually be treated with an AP-PA arrangement. The posterior compartment is best treated with parallel opposed lateral fields, with the involved extremity elevated by the Alpha Cradle@. The elevation of the affected leg avoids irradiation of the opposite extremity. The Alpha Cradle@ should include the foot and knee to avoid variable rotation of the leg from day to day. The arm is more difficult to irradiate due to the difficulty in moving the arm far enough away from the trunk of the body. The involved muscle compartment is irradiated by rotating the arm in a position to minimize the gantry angle and spare normal tissue along the circumference of the arm. An increased gantry angle may cause the trunk of the body to be in
Immobilization
for soft-tissue sarcoma 0 K. LIGHT
the entrance or exit of the beam. The Alpha Cradle@ should include the affected arm as well as the chest and shoulders. Alpha CradlP fabrication and use The patient’s position and method of immobilization are determined prior to obtaining a treatment planning CT. Alpha Cradle@ supplies that are needed are the slotted board, dividers, chemicals (Bottles “1” and “2”). plastic bag, Styrofoam pieces, and protective gloves. The plastic bag is tapered to the patient’s width and positioned on the slotted board. Styrofoam pieces are inserted in the bag where the chemicals will be poured to help produce a sturdy base for the Alpha Cradle.@ The patient is instructed to lie down on the bag in the desired position to check the width and length of the bag and check positioning of the styrofoam pieces in the bag. The patient moves off the bag while the chemicals are prepared. Usually, two sets of 325-cc chemicals and one set of 250-cc chemicals are used for immobilization of the lower extremity since immobilization from the pelvis to the foot is needed to ensure reproducible rotation of the extremity. When immobilizing the upper extremity, one set of 325-cc chemicals and one set of 250-1~~chemicals are used. The Alpha Cradle@ includes the affected arm as well as the chest and shoulders. A piece of cylindrical Styrofoam is placed in the plastic bag to form a handle for the patient to hold onto during each treatment.
137
The immobilization of the chest and handle for the hand helps to ensure proper placement and rotation of the arm on a daily basis. Protective gloves are worn and Bottle “ 1” is poured into Bottle “2” according to the instruction sheet furnished by the supplier. Bottle “2” is shaken vigorously for 15 seconds, with the cap pointing down. The mixture is poured into the bag and as much air as possible is forced out of the bag with the hand. The bag is folded at the open end and taped with 2-inch-wide tape to avoid spillage. The patient is then instructed to lie on the bag in the desired position and the dividers are placed to press the rising foam against the patient. The temperature of the foam during the chemical reaction is warm and comfortable to the patient. The patient then lies motionless for about 15 minutes while the foam solidifies with the dividers in place. During this time, the physician comes into the CT room and marks the palpable tumor or the surgical scar with a catheter. He also will mark the approximate length of the treatment field and give instructions about the number of CT scans needed for treatment planning. Typically, the scan spacing is 1 cm through the tumor and 2 cm through the remainder of the field. The patient is aligned with the long axis of the extremity parallel to the laser, and a reference catheter is placed on the line extending through the entire scan volume. The center of the scan volume is marked on the patient’s skin, and the
Fig. 2. Marks are placed on the patient and the Alpha Cradle@ to ensure set-up reproducibility.
138
Medical Dosimetry
marks are extended down to both sides of the Alpha Cradle@. This helps to keep the alignment of the Alpha Cradle@ consistent from CT to simulation. During simulation, the setup lasers and treatment fields are carefully marked on the Alpha Cradle@-’ wherever possible to ensure setup accuracy for daily treatment (Fig. 2). As previously mentioned, AP-PA or oblique fields are usually the best field arrangement. Oblique fields may need to be combined with wedges to minimize the dose variation within the tumor (Fig. 3). The fields are routinely treated with a 4- or 6-MV photon beam. Bolus may be needed to increase the dose to the incision. No adverse reactions have been noted on the patients’ skin, even when treating through several centimeters of the Alpha Cradle.@ Most patients receiving preoperative radiation therapy at our institution for palpable tumors also received hyperthermia and were entered onto a protocol with hyperthermia randomized to one-versus-two treatments per week. I9 The Alpha Cradle6 constructed for immobilization during the radiation treatment were also used on selected patients for immobilization during their hyperthermia treatment. Patients treated with a coupling ultrasound hyperthermia applicator also had an Alpha Cradle@ constructed to create a rigid foam block to assist in positioning the applicator over the tumor area. The Alpha Cradle@ has made the setup for subsequent hyperthermia treatments quickly reproducible and also aids in accurate replacement of thermometry sensors.2o RESULTS All patients treated at our institution for extremity soft-tissue sarcoma in the past eight years have had Alpha Cradles@ constructed for immobilization. Before 1984, a consistent treatment policy including radiation therapy was not followed. For these reasons, comparison of setup accuracy with and without Alpha Cradle@ use was not possible. A retrospective review of simulation and port films of the last ten patients treated in our department for extremity soft-tissue sarcoma revealed that no changes.in the treatment fields were indicated on the port films in six out of the ten patients studied. The maximum shift in the remaining four patients was 0.5 cm and the average shift was 0.45 cm. These port films were taken on a weekly basis and reviewed by the radiation oncologist. This demonstrates the reproducibility of the daily setup when using Alpha Cradle@immobilization. DISCUSSION The optimum approach to treatment of extremity soft-tissue sarcoma involves a multidisciplinary
Volume 17, Number 3, 1992
Fig. 3. Dose distribution for oblique wedged fields demonstrating normal tissue sparing (6 MV, 100 cm SAD, Open and 15’ wedged fields).
team to determine a treatment plan for each patient. Radiation therapy combined with conservative surgery can be effective and is optimal if tumor control and limb sparing are achieved. A good functional result is more likely to be obtained when the prescribed dose is accurately delivered. Large fields with customized blocking are often used for extremity sarcoma patients. These fields are more difficult to reproduce on a daily basis. Setup errors can cause underdosing of the target volume or deliver dose to normal tissue not intended to be in the treatment field. All efforts should be made to improve positioning and immobilization if maximum tumor response is to be achieved. The immobilization technique described increases the comfort of the patient as well as controlling rotation of the extremity, thus improving the accuracy of the treatment delivery. REFERENCES 1. Sears, H.F. Soft tissue sarcoma: A historical overview. Semin. Oncol. 3:129-132; 1981. 2. Shiu, M.H.; Hajdu, S.I. Management of soft tissue sarcoma of the extremitv. Semin. Oncol. 8: 172- 179: 198 1. 3. Tepper, J.E:; Suit, H.D. The role of radiation therapy in the treatment of sarcoma of soft tissue. Cancer Invest. 3:587-592; 1985. 4. Tepper, J.E.; Rosenberg, S.A.; Glatstein, E. Radiation therapy technique in soft tissue sarcomas of the extremity-Policies of treatment at the National Cancer Institute. Int. J. Radiat. Oncol. Biol. Phys. 8:263-273; 1982. 5. Tepper, J.E.; Suit, H.D. Radiation therapy alone for sarcoma of soft tissue. Cancer 56:475-479; 1985. 6. Selch, M.T.; Kelly, K.H.; Ferreiro, G.A.; Mirra, J.M.; Parker, R.G.; Eilber, R.F. Limb salvage therapy for soft tissue sarcomas of the foot. Int. J. Radiat. Oncol. Biol. Phys. 19:41-48; 1990. 7. Martin, R.G.; Butler, J.J.; Albares-Saavedra, J. Soft tissue tumors: Surgical treatment and results. In: Tumors ofbone and soft tissues. Chicago: Year Book Medical Publisher. 333-347, 1965.
Immobilization
for soft-tissue sarcoma 0 K. LIGHT
8. Hendrickson, F.R. Precision in radiation oncology. Int. .I. Ru&at. Oncool.Biol. Phys. 8:311-312; 1982. 9. Verhey, L.J.; Goiten, M.; McNulty, P.; Munzemida, J.E.; Suit, H.D. Precise positioning of patients for radiation therapy. Int. J. Radial. Oncol. Biol. Phys. 8:289-294; 1982. 10. Rabinowitz, 1.; Broomberg, J.; Goiten, M.; McCarthy, K.: Leong, J. Accuracy of radiation field alignment in clinical practice. Int. J. Radiat. Oncol. Biol. Phys. 11:1857-1867; 1985. I I. Weller, M.K.; Muller, P.L.; Sugai. S.; Leverick, J. Immobilization techniques and dosimetric aspects for pituitary tumors. Med. Dosim. 16:127-135; 1991. 12. Bentel. G.C. Positioning and immobilization device for patients receiving radiation therapy for carcinoma of the breast. Med. Dosim. 15:3-6; 1990. 13. Bentel, G.C.; Nelson, C.E.; Noel, K.T. Treatment planning and dose calculation in radiation oncology. 4th ed. Elmsford. NY: Pergamon Press; 1989. 14. Goldschmidt, E.J.: Hoist. R.J. Medulloblastoma immobilization and treatment considerations. Med. Dosim. 157-l I; 1990.
139
15. Bentel, G. Positioning and immobilization of patients undergoing radiation therapy for Hodgkin’s disease. Med. Dosim. 16:l I l-l 17: 1991. 16. McCane, K.; Parsons, L.; Schoenfeld, L.; Maddeford, A. A technique for evaluating cast foam positioning and immobilization devices used in breast cancer radiotherapy. Med. Dosim. 16:119-125: 1991. 17. Buscher. M. The building of free-form customized immobilizers. Med. Dosim. 15: 17- 18; 1990. 18. Moore. K.L. Clinically oriented anatomy. 2nd ed. Baltimore. MD: Williams and Wilkins; 1985. 19. Leopold, K.A.; Harrelson, J.; Prosnitz. L.: Samulski, T.V.; Dewhirst. M.W.: Oleson, J.R. Preoperative hyperthennia and radiation for soft tissue sarcomas: Advantage of two vs. one hyperthermia treatments per week. Int. J. Radial. Oncol. Biol. PIzw. 16:107-l 15: 1989. 20. Oleson, J.R.: Samulski, T.V. Improved coupling of ultrasound hyperthermia applicators to patients. Inr. J. Radial. Oncol. Biol. Phys. 16:1-4; 1989.
Third Place Smithers/AAMD
1992 Writing Competition
IMMOBILIZATION AND TREATMENT OF PATIENTS RECEIVING RADIATION THERAPY FOR EXTREMITY SOFT-TISSUE SARCOMA KIML. Department
of Radiation
LIGHT,
R.T.T., C.M.D.
Oncology, Duke University Medical Center, Durham, NC 277 10. U.S.A.
Abstract-The treatment of extremity soft-tissue sarcoma has evolved considerably over the years. Previously, the preferred treatment was radical resection or amputation. Recently, radiation therapy combined with conservative resection has been shown to provide adequate tumor control while preserving a functional limb. Often, a large volume of tissue is irradiated in a manner that requires the patient to be in a reproducible position. Minimizing patient movement is imperative to ensure that the prescribed dose is delivered to the designated target volume. At our institution, Alpha Cradles @*have been routinely used for eight years to aid in positioning extremity sarcoma patients. The positioning of the patient for tumors at different locations in the extremity and the Alpha Cradle@ fabrication is described. The positioning device is comfortable for the patient and the accuracy is verified by comparison of simulation films with weekly port films. Key Words: Extremity sarcoma, Radiation therapy, Immobilization, Reproducibility.
INTRODUCTION
sulted in a local recurrence rate as high as 77% in a group of 218 patients analyzed by Martin et al.’ at M. D. Anderson Hospital. Amputations at the joint above the tumor were then frequently employed to obtain clear margins. These tumors were not even considered for radiation therapy because they were considered radioresistant. Function sparing procedures that combined a more limited resection with pre- or postoperative radiation therapy are now the predominant treatment. Local recurrence rates have dropped to approximately 20% with this approach.3 With the increased use of radiation therapy for the treatment of extremity soft-tissue sarcomas, careful attention to radiation delivery is essential. Optimal precision in radiation oncology is influenced by knowledge of the dose prescribed, accurate measurements of machine output and beam parameters, as well as ensuring that the treatment beam accurately transverses the desired anatomy during every treatment. The ability to reproduce the patient position from day to day can be a major problem in radiation oncology. A reduction of as much as 10% in dose from the prescribed dose could occur if the tumor was missed due to inaccurate setup once or twice during a treatment course or if there is movement of the tumor
Soft-tissue sarcoma arises from mesenchymal tissue and accounts for less than 1% of cancers treated in most oncology centers. These tumors show no prevalence in any particular sex nor is there any clear age predominance, although some histologic types seem to be more common in either the younger or older patient. ’ The most common site for initial presentation is the extremity. The most common presenting symptom is a painless, palpable mass.* An effective management plan requires precise preoperative evaluation to assess the primary tumor as well as evaluation of possible metastatic disease. Conventional x-rays are useful in evaluating large tumors, although computerized tomography (CT) or magnetic resonance imaging (MRI) are considered the optimal imaging modalities in the evaluation of soft-tissue sarcomas. Management of extremity soft-tissue sarcomas has evolved considerably over the years.2-7 It was initially thought that tumor control could be obtained with a wide local excision. Local excision alone re* Alpha Cradle@-Smithers
Medical Products, Inc.
I35
136
Medical Dosimetry
Volume 17, Number 3, 1992
out of the field during an individual treatment.* Precise positioning is required to minimize this problem. When setting up the radiation treatment fields, 5to IO-cm margins are given longitudinally to the tumor due to its growth pattern, while a smaller margin is used circumferentially. A strip of soft tissue along the circumference of the extremity is spared to avoid edema, radiation fibrosis, and loss of function.3 A smaller margin is acceptable unless the tumor is advanced, since involvement through the fascia of the muscle conipartment is unlikely for localized tumors. For advanced tumors, more margin is needed and can usually be obtained with oblique fields and customized blocking to ensure some normal tissue sparing. Due to the sometimes complex field arrangement necessary for treatment of these patients, precise repositioning of the extremity is essential. A variety of immobilization techniques for other treatment sites are well described in the literature.8-‘6 Although it is recognized that immobilization is necessary for treating extremity sarcoma patients, there is little information in the literature detailing the positioning and immobilization technique.3*‘7
METHODS
AND MATERIALS
Patient positioning Fifty extremity soft-tissue sarcoma patients were treated with radiation therapy at our institution from 1984 to 199 1. Forty-seven of these patients had sarcomas of the lower extremity and three had sarcomas of the upper extremity. Alpha Cradle@* immobilization devices were used on all patients. The location of the tumor in the affected extremity determines the position of the patient in the Alpha Cradle@. Soft-tissue sarcoma occurs most often in the thigh. Tumor involvement can be extensive before a mass becomes palpable, thus large treatment volumes are usually necessary. The muscles in the thigh are divided into three groups: the anterior, medial, and posterior compartments. ‘* For anteriolateral tumors, treatment is usually given via parallel opposed oblique fields directed from the medial to the lateral aspect of the thigh. Anteriomedial tumors can usually be treated with AP-PA or slightly angled fields. If the tumor is proximal, the legs are separated to avoid radiation to the opposite extremity. Due to the wider field that is needed proximally, customized field shaping is used to spare normal tissue along the inferiolateral aspect of the thigh. Patients are generally positioned prone, with the involved extremity rotated, or placed on their side with their thighs separated when irradiating the posterior compartment of the thigh. At our insti* Smithers Medical Products, Inc.
Fig. 1. Alpha Cradle@ used when treating thigh sarcomas includes immobilization from the pelvis to the foot to ensure reproducible rotation of the extremity.
tution, we have found that the patient’s position can best be maintained by immobilizing from the pelvis to the foot (Fig. 1). This adequately stabilizes the joint above and below the tumor site and maintains the same volume of tissue in the treatment field daily. The muscles in the lower leg are divided into three groups: the anterior, lateral, and posterior compartments. I8 The anterior compartment of the lower leg can be irradiated with parallel opposed oblique fields while the lateral compartment can usually be treated with an AP-PA arrangement. The posterior compartment is best treated with parallel opposed lateral fields, with the involved extremity elevated by the Alpha Cradle@. The elevation of the affected leg avoids irradiation of the opposite extremity. The Alpha Cradle@ should include the foot and knee to avoid variable rotation of the leg from day to day. The arm is more difficult to irradiate due to the difficulty in moving the arm far enough away from the trunk of the body. The involved muscle compartment is irradiated by rotating the arm in a position to minimize the gantry angle and spare normal tissue along the circumference of the arm. An increased gantry angle may cause the trunk of the body to be in
Immobilization
for soft-tissue sarcoma 0 K. LIGHT
the entrance or exit of the beam. The Alpha Cradle@ should include the affected arm as well as the chest and shoulders. Alpha CradlP fabrication and use The patient’s position and method of immobilization are determined prior to obtaining a treatment planning CT. Alpha Cradle@ supplies that are needed are the slotted board, dividers, chemicals (Bottles “1” and “2”). plastic bag, Styrofoam pieces, and protective gloves. The plastic bag is tapered to the patient’s width and positioned on the slotted board. Styrofoam pieces are inserted in the bag where the chemicals will be poured to help produce a sturdy base for the Alpha Cradle.@ The patient is instructed to lie down on the bag in the desired position to check the width and length of the bag and check positioning of the styrofoam pieces in the bag. The patient moves off the bag while the chemicals are prepared. Usually, two sets of 325-cc chemicals and one set of 250-cc chemicals are used for immobilization of the lower extremity since immobilization from the pelvis to the foot is needed to ensure reproducible rotation of the extremity. When immobilizing the upper extremity, one set of 325-cc chemicals and one set of 250-1~~chemicals are used. The Alpha Cradle@ includes the affected arm as well as the chest and shoulders. A piece of cylindrical Styrofoam is placed in the plastic bag to form a handle for the patient to hold onto during each treatment.
137
The immobilization of the chest and handle for the hand helps to ensure proper placement and rotation of the arm on a daily basis. Protective gloves are worn and Bottle “ 1” is poured into Bottle “2” according to the instruction sheet furnished by the supplier. Bottle “2” is shaken vigorously for 15 seconds, with the cap pointing down. The mixture is poured into the bag and as much air as possible is forced out of the bag with the hand. The bag is folded at the open end and taped with 2-inch-wide tape to avoid spillage. The patient is then instructed to lie on the bag in the desired position and the dividers are placed to press the rising foam against the patient. The temperature of the foam during the chemical reaction is warm and comfortable to the patient. The patient then lies motionless for about 15 minutes while the foam solidifies with the dividers in place. During this time, the physician comes into the CT room and marks the palpable tumor or the surgical scar with a catheter. He also will mark the approximate length of the treatment field and give instructions about the number of CT scans needed for treatment planning. Typically, the scan spacing is 1 cm through the tumor and 2 cm through the remainder of the field. The patient is aligned with the long axis of the extremity parallel to the laser, and a reference catheter is placed on the line extending through the entire scan volume. The center of the scan volume is marked on the patient’s skin, and the
Fig. 2. Marks are placed on the patient and the Alpha Cradle@ to ensure set-up reproducibility.
138
Medical Dosimetry
marks are extended down to both sides of the Alpha Cradle@. This helps to keep the alignment of the Alpha Cradle@ consistent from CT to simulation. During simulation, the setup lasers and treatment fields are carefully marked on the Alpha Cradle@-’ wherever possible to ensure setup accuracy for daily treatment (Fig. 2). As previously mentioned, AP-PA or oblique fields are usually the best field arrangement. Oblique fields may need to be combined with wedges to minimize the dose variation within the tumor (Fig. 3). The fields are routinely treated with a 4- or 6-MV photon beam. Bolus may be needed to increase the dose to the incision. No adverse reactions have been noted on the patients’ skin, even when treating through several centimeters of the Alpha Cradle.@ Most patients receiving preoperative radiation therapy at our institution for palpable tumors also received hyperthermia and were entered onto a protocol with hyperthermia randomized to one-versus-two treatments per week. I9 The Alpha Cradle6 constructed for immobilization during the radiation treatment were also used on selected patients for immobilization during their hyperthermia treatment. Patients treated with a coupling ultrasound hyperthermia applicator also had an Alpha Cradle@ constructed to create a rigid foam block to assist in positioning the applicator over the tumor area. The Alpha Cradle@ has made the setup for subsequent hyperthermia treatments quickly reproducible and also aids in accurate replacement of thermometry sensors.2o RESULTS All patients treated at our institution for extremity soft-tissue sarcoma in the past eight years have had Alpha Cradles@ constructed for immobilization. Before 1984, a consistent treatment policy including radiation therapy was not followed. For these reasons, comparison of setup accuracy with and without Alpha Cradle@ use was not possible. A retrospective review of simulation and port films of the last ten patients treated in our department for extremity soft-tissue sarcoma revealed that no changes.in the treatment fields were indicated on the port films in six out of the ten patients studied. The maximum shift in the remaining four patients was 0.5 cm and the average shift was 0.45 cm. These port films were taken on a weekly basis and reviewed by the radiation oncologist. This demonstrates the reproducibility of the daily setup when using Alpha Cradle@immobilization. DISCUSSION The optimum approach to treatment of extremity soft-tissue sarcoma involves a multidisciplinary
Volume 17, Number 3, 1992
Fig. 3. Dose distribution for oblique wedged fields demonstrating normal tissue sparing (6 MV, 100 cm SAD, Open and 15’ wedged fields).
team to determine a treatment plan for each patient. Radiation therapy combined with conservative surgery can be effective and is optimal if tumor control and limb sparing are achieved. A good functional result is more likely to be obtained when the prescribed dose is accurately delivered. Large fields with customized blocking are often used for extremity sarcoma patients. These fields are more difficult to reproduce on a daily basis. Setup errors can cause underdosing of the target volume or deliver dose to normal tissue not intended to be in the treatment field. All efforts should be made to improve positioning and immobilization if maximum tumor response is to be achieved. The immobilization technique described increases the comfort of the patient as well as controlling rotation of the extremity, thus improving the accuracy of the treatment delivery. REFERENCES 1. Sears, H.F. Soft tissue sarcoma: A historical overview. Semin. Oncol. 3:129-132; 1981. 2. Shiu, M.H.; Hajdu, S.I. Management of soft tissue sarcoma of the extremitv. Semin. Oncol. 8: 172- 179: 198 1. 3. Tepper, J.E:; Suit, H.D. The role of radiation therapy in the treatment of sarcoma of soft tissue. Cancer Invest. 3:587-592; 1985. 4. Tepper, J.E.; Rosenberg, S.A.; Glatstein, E. Radiation therapy technique in soft tissue sarcomas of the extremity-Policies of treatment at the National Cancer Institute. Int. J. Radiat. Oncol. Biol. Phys. 8:263-273; 1982. 5. Tepper, J.E.; Suit, H.D. Radiation therapy alone for sarcoma of soft tissue. Cancer 56:475-479; 1985. 6. Selch, M.T.; Kelly, K.H.; Ferreiro, G.A.; Mirra, J.M.; Parker, R.G.; Eilber, R.F. Limb salvage therapy for soft tissue sarcomas of the foot. Int. J. Radiat. Oncol. Biol. Phys. 19:41-48; 1990. 7. Martin, R.G.; Butler, J.J.; Albares-Saavedra, J. Soft tissue tumors: Surgical treatment and results. In: Tumors ofbone and soft tissues. Chicago: Year Book Medical Publisher. 333-347, 1965.
Immobilization
for soft-tissue sarcoma 0 K. LIGHT
8. Hendrickson, F.R. Precision in radiation oncology. Int. .I. Ru&at. Oncool.Biol. Phys. 8:311-312; 1982. 9. Verhey, L.J.; Goiten, M.; McNulty, P.; Munzemida, J.E.; Suit, H.D. Precise positioning of patients for radiation therapy. Int. J. Radial. Oncol. Biol. Phys. 8:289-294; 1982. 10. Rabinowitz, 1.; Broomberg, J.; Goiten, M.; McCarthy, K.: Leong, J. Accuracy of radiation field alignment in clinical practice. Int. J. Radiat. Oncol. Biol. Phys. 11:1857-1867; 1985. I I. Weller, M.K.; Muller, P.L.; Sugai. S.; Leverick, J. Immobilization techniques and dosimetric aspects for pituitary tumors. Med. Dosim. 16:127-135; 1991. 12. Bentel. G.C. Positioning and immobilization device for patients receiving radiation therapy for carcinoma of the breast. Med. Dosim. 15:3-6; 1990. 13. Bentel, G.C.; Nelson, C.E.; Noel, K.T. Treatment planning and dose calculation in radiation oncology. 4th ed. Elmsford. NY: Pergamon Press; 1989. 14. Goldschmidt, E.J.: Hoist. R.J. Medulloblastoma immobilization and treatment considerations. Med. Dosim. 157-l I; 1990.
139
15. Bentel, G. Positioning and immobilization of patients undergoing radiation therapy for Hodgkin’s disease. Med. Dosim. 16:l I l-l 17: 1991. 16. McCane, K.; Parsons, L.; Schoenfeld, L.; Maddeford, A. A technique for evaluating cast foam positioning and immobilization devices used in breast cancer radiotherapy. Med. Dosim. 16:119-125: 1991. 17. Buscher. M. The building of free-form customized immobilizers. Med. Dosim. 15: 17- 18; 1990. 18. Moore. K.L. Clinically oriented anatomy. 2nd ed. Baltimore. MD: Williams and Wilkins; 1985. 19. Leopold, K.A.; Harrelson, J.; Prosnitz. L.: Samulski, T.V.; Dewhirst. M.W.: Oleson, J.R. Preoperative hyperthennia and radiation for soft tissue sarcomas: Advantage of two vs. one hyperthermia treatments per week. Int. J. Radial. Oncol. Biol. PIzw. 16:107-l 15: 1989. 20. Oleson, J.R.: Samulski, T.V. Improved coupling of ultrasound hyperthermia applicators to patients. Inr. J. Radial. Oncol. Biol. Phys. 16:1-4; 1989.