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Preoperative radiation for cancer of the rectum with extrarectal fixation
180
Radiation Oncology, Biology, Physics
October 1990, Volume 19, Supplement
1
107 PREOPERATIVE Robert Thomas
L. Tobin, Jefferson
RADIATION
FOR CANCER OF THE RECTUM WITH EXTRARECTAL
M.D. and Mohammed University
Hospital,
Mohiuddin, Philadelphia,
FIXATION
M.D. PA
19107
Between 1976-1988, 220 patients have been consecutively treated with high dose preoperative radiotherapy at our institution. Selection of these patients for radiotherapy has been based on the preoperative clinical and pathological features with the following criteria. These include location, grade, and the presence or absence of extrarectal fixation or tethering During this time period, 134 patients were clinically determined by the surgeon and radiotherapist to have extrarectal tumor fixation and are the subject of this review. The patient population can be further divided into two subgroups which include 49 patients with clinical tethering/partial fixation, and 85 patients with completely fixed tumors. The pathological findings, patterns of failure, complications, and dose response relationships are reviewed. The present study includes 66 male and 68 females with an age range of 29-81. 121 out of 132 (92%) were located at the O-6 cm level, After appropriate staging work-up, the patients were treated with 4-field pelvic radiotherapy to 45 Gy in 25 fractions. Depending on location and degree of fixation, a localized boost dose was delivered to the tumor plus a 2 cm margin for an additional 4.8-9.6 Gy using opposed high-energy lateral fields. Surgical resection was instituted 4-6 weeks (median 5.2 weeks) post completion of radiotherapy. Sphincter-saving surgery was employed in a majority of patients, including 44/49 (90%) of the clinically tethered tumors, and 60/85 (70%) of the patients with pre-radiotherapy fixed rectal Resected specimens were examined pathologically and appropriately staged by Astler-Coller criteria. Post tumors. radiation staging revealed resected specimens would be staged as follows: 21% A/B1 , 40% B2, 29% Cl/C2. and 10% stage D. The five year actuarial survival of these patients was 65% and 70% in the clinically tethered and fixed tumor subgroups respectively. Corresponding disease-free survival is 56% and 42%. Ultimate local pelvic control was demonstrated in 90% of the patients in the tethered subgroup (2 isolated local recurrences, 3 local recurrences plus distant The patients with fixed tumors experienced 84% local control using metastasis) and distant metastatic rate of 14%. radiotherapy preoperatively (6 isolated local recurrences, 8 local plus distant). Distant metastases were noted in 13%. By pathological stage, local recurrence occurred in 4% of 28 stage O,A,Bl patients, and 16% in 99 B2 and C patients. Overall five year survival for our post-radiation B2/C patients is 63%. which is superior to published surgical series. Radiation grade III/IV complications were limited to 6% of the patient population and included four patients with post surgical bowel obstruction requiring operative lysis of adhesions, two cases of delayed wound healing, and two anastomatic breakdowns There was no treatment-related mortality. which were both successfully reconstituted. We conclude preoperative radiotherapy for rectal carcinomas with clinical extrarectal fixation provides optimal presurgical cytoreduction and excellent survival. This review also demonstrates that sphincter function can be maintained in a majority of patients with appropriate attention to patient selection, radiotherapy, and operative techniques, without compromising local control or survival. We are presently exploring the addition of chemotherapy to clinically fixed tumors and expanding our selection criteria for high-dose preoperative boost to further enhance local control and ultimate survival,
108 VERIFICATION
OF COMPUTER
FABRICATED
COMPENSATING
FILTERS
Robert M. Smith, James M.Galvin University of Pennsylvania Philadelphia, PA 19104
Medical School, Hospital of the University of Pennsylvania,
Department of Radiation Oncology,
Nonuniform dose distribution can result from irregularities in the patient’s contour, the particular arrangement of the fields, the presence of inhomogeneities, or the characteristics of the radiation beam. The dose distribution can often be improved by adding compensating filters to the treatment fields and techniques for designing compensators and calculating the resulting dose distribution have been devised. The fabrication of true 3D compensators is labor intensive, and in the past simple “digitized” compensators (e.g., copper sheets or “Ellis” blocks) have been used. With the recent development of computer controlled milling machines complex 3D compensators can now be manufactured in a relatively short period of time. Software routines are available to calculate the resulting dosedistribution, but methods for checking the design and mounting of the compensator are not available. Possible errors in the fabrication include: 1) right/left superior/inferior directions flipped; 2) comuensation factor for the wrong material was used: 3) milling machine was not-setup correctly and the wrong depths were milled: 4) milling bit was too large &r small) and too much (or too little) material was removed, 5) compensator was positioned incorrectly relative to the beam’s central axis; 6) divergence was not accounted for in the design process; 7) incorrect source-to-tray distance was used; and 9) “fill” material was poured to the wrong thickness or air bubbles present. A method has been developed for checking 3D compensators by experimentally determining a “thickness map” for comparison to the thicknesses used in the design process. The thicknesses were determined using radiographs of the compensator. The test film is obtained with the compensator mounted on a support tray and securely positioned on the treatment unit. A second film is taken with a step wedge constructed from the same material as the compensator. The films are processes together and scanned with a computer driven microdensitometer. Processor variations and film response characteristics are automatically incorporated into the thickness versus density curve. A thickness versus density curve found using the step wedge results and this information is entered into the film scanning system in place of the dose versus density response curve. An isoheight map can be plotted. Tests with compensators with arbitrary shapes indicated an accuracy of 2mm for the thickness at any point. Data will be presented for compensators with shapes of varying complexities and for different compensating materials.
Radiation Oncology, Biology, Physics
October 1990, Volume 19, Supplement
1
107 PREOPERATIVE Robert Thomas
L. Tobin, Jefferson
RADIATION
FOR CANCER OF THE RECTUM WITH EXTRARECTAL
M.D. and Mohammed University
Hospital,
Mohiuddin, Philadelphia,
FIXATION
M.D. PA
19107
Between 1976-1988, 220 patients have been consecutively treated with high dose preoperative radiotherapy at our institution. Selection of these patients for radiotherapy has been based on the preoperative clinical and pathological features with the following criteria. These include location, grade, and the presence or absence of extrarectal fixation or tethering During this time period, 134 patients were clinically determined by the surgeon and radiotherapist to have extrarectal tumor fixation and are the subject of this review. The patient population can be further divided into two subgroups which include 49 patients with clinical tethering/partial fixation, and 85 patients with completely fixed tumors. The pathological findings, patterns of failure, complications, and dose response relationships are reviewed. The present study includes 66 male and 68 females with an age range of 29-81. 121 out of 132 (92%) were located at the O-6 cm level, After appropriate staging work-up, the patients were treated with 4-field pelvic radiotherapy to 45 Gy in 25 fractions. Depending on location and degree of fixation, a localized boost dose was delivered to the tumor plus a 2 cm margin for an additional 4.8-9.6 Gy using opposed high-energy lateral fields. Surgical resection was instituted 4-6 weeks (median 5.2 weeks) post completion of radiotherapy. Sphincter-saving surgery was employed in a majority of patients, including 44/49 (90%) of the clinically tethered tumors, and 60/85 (70%) of the patients with pre-radiotherapy fixed rectal Resected specimens were examined pathologically and appropriately staged by Astler-Coller criteria. Post tumors. radiation staging revealed resected specimens would be staged as follows: 21% A/B1 , 40% B2, 29% Cl/C2. and 10% stage D. The five year actuarial survival of these patients was 65% and 70% in the clinically tethered and fixed tumor subgroups respectively. Corresponding disease-free survival is 56% and 42%. Ultimate local pelvic control was demonstrated in 90% of the patients in the tethered subgroup (2 isolated local recurrences, 3 local recurrences plus distant The patients with fixed tumors experienced 84% local control using metastasis) and distant metastatic rate of 14%. radiotherapy preoperatively (6 isolated local recurrences, 8 local plus distant). Distant metastases were noted in 13%. By pathological stage, local recurrence occurred in 4% of 28 stage O,A,Bl patients, and 16% in 99 B2 and C patients. Overall five year survival for our post-radiation B2/C patients is 63%. which is superior to published surgical series. Radiation grade III/IV complications were limited to 6% of the patient population and included four patients with post surgical bowel obstruction requiring operative lysis of adhesions, two cases of delayed wound healing, and two anastomatic breakdowns There was no treatment-related mortality. which were both successfully reconstituted. We conclude preoperative radiotherapy for rectal carcinomas with clinical extrarectal fixation provides optimal presurgical cytoreduction and excellent survival. This review also demonstrates that sphincter function can be maintained in a majority of patients with appropriate attention to patient selection, radiotherapy, and operative techniques, without compromising local control or survival. We are presently exploring the addition of chemotherapy to clinically fixed tumors and expanding our selection criteria for high-dose preoperative boost to further enhance local control and ultimate survival,
108 VERIFICATION
OF COMPUTER
FABRICATED
COMPENSATING
FILTERS
Robert M. Smith, James M.Galvin University of Pennsylvania Philadelphia, PA 19104
Medical School, Hospital of the University of Pennsylvania,
Department of Radiation Oncology,
Nonuniform dose distribution can result from irregularities in the patient’s contour, the particular arrangement of the fields, the presence of inhomogeneities, or the characteristics of the radiation beam. The dose distribution can often be improved by adding compensating filters to the treatment fields and techniques for designing compensators and calculating the resulting dose distribution have been devised. The fabrication of true 3D compensators is labor intensive, and in the past simple “digitized” compensators (e.g., copper sheets or “Ellis” blocks) have been used. With the recent development of computer controlled milling machines complex 3D compensators can now be manufactured in a relatively short period of time. Software routines are available to calculate the resulting dosedistribution, but methods for checking the design and mounting of the compensator are not available. Possible errors in the fabrication include: 1) right/left superior/inferior directions flipped; 2) comuensation factor for the wrong material was used: 3) milling machine was not-setup correctly and the wrong depths were milled: 4) milling bit was too large &r small) and too much (or too little) material was removed, 5) compensator was positioned incorrectly relative to the beam’s central axis; 6) divergence was not accounted for in the design process; 7) incorrect source-to-tray distance was used; and 9) “fill” material was poured to the wrong thickness or air bubbles present. A method has been developed for checking 3D compensators by experimentally determining a “thickness map” for comparison to the thicknesses used in the design process. The thicknesses were determined using radiographs of the compensator. The test film is obtained with the compensator mounted on a support tray and securely positioned on the treatment unit. A second film is taken with a step wedge constructed from the same material as the compensator. The films are processes together and scanned with a computer driven microdensitometer. Processor variations and film response characteristics are automatically incorporated into the thickness versus density curve. A thickness versus density curve found using the step wedge results and this information is entered into the film scanning system in place of the dose versus density response curve. An isoheight map can be plotted. Tests with compensators with arbitrary shapes indicated an accuracy of 2mm for the thickness at any point. Data will be presented for compensators with shapes of varying complexities and for different compensating materials.