Proceedings of the 41st Annual ASTRO Meeting 21 I 123 INTENSITY MODULATED RADIATION THERAPY (IMRT) MAY REDUCE SMALL BOWEL, RECTUM, AND BLADDER COMPLICATIONS IN PATIENTS WITH CERVICAL CANCER TREATED TO THE PELVIS AND PARAAORTIC AREA Portelance L. Chao C, Grigsby PW. Bennet H Mallinckrodt Institute of Radiology, St. Louis, MO, USA Purpose: The prevalence of the combined-modality approach (chemotherapy and irradiation) to treat patients with locally advanced cervical cancer is increasing because of the recently published RTOG 90-01 results. However, alarming higher gastrointestinal (GI) and genitourological (GU) complications were documented in patients who received chemoirradiation. Measures that allow adequate doses to the tumor and lymphatic drainage while sparing normal structures will greatly improve complication-free disease control. Theoretically, IMRT has the potential not only to achieve these objectives but also to permit dose escalation to the grossly enlarged metastatic lymph nodes in the pelvis and paraaortic area without increasing GI/GU complications. However, information in this area has been scarce. In this study, we assess whether IMRT can effectively deliver prescribed doses to the different lymph node regions in the pelvic and paraaortic areas while more effectively sparing small bowel, rectum, and bladder. Methods and Materials: Ten patients with cervical cancer underwent computed tomography (CT) simulation. The archived CT images were retrieved to a Voxel-Q computer for target contouring. The target volumes (paraaortic, common iliac, external iliac, internal iliac lymph nodes, and cervix/uterus) and the pertinent normal structures were also defined. These images and contours were transferred to both an IMRT planning system (Corvus 2.0, Nomos) and a 3-D planning system (Focus, CMS). IMRT plans were compared with conventional two- (2CF) and four-(4CF) field techniques following the guidelines of the RTOG 90-01 protocol for pelvic and paraaortic treatments. IMRT was planned to be delivered by dynamic multileaf collimators using a step-n-shoot technique. Three IMRT field arrangements (4, 7, and 9 fields) were tested in each patient. For this comparative study, we prescribed 45 Gy in 25 fractions using a 18 MV photon beam to all targets. The IMRT treatment plans were designed to cover the target by at least 95% of the prescribed dose. A Student-T test was performed to compute the statistical significance in the fraction of normal tissue (rectum, small bowel, bladder) receiving 66%, 88%, and 100% of the prescribed dose between IMRT and conventional beam arrangements. Results: The amount of small bowel receiving the prescribed dose with the IMRT technique was: 4 fields, 11.01 + 5.67%; 7 fields, 15.05 i 6.76%; 9 fields, 13.56 2 5.30%. These were all significantly better than with 2CF (35.28 i 13.84%) and 4CF (34.24 i- 17.82%) (pcO.05). The fraction of rectal volume receiving a dose greater than the prescribed dose was: 4 fields, 8.55 I 4.64%; 7 fields, 6.37 I 5.19%; 9 fields, 3.34 2 3.0%, in contrast to 84.01 i 18.37% with 2CF (p=O.OOl) and 46.37 i 24.97% with 4CF (p=O.OOl). Similarly, the fractional volume of bladder receiving the prescribed dose was: 4 fields, 30.29 i 4.64%; 7 fields, 31.66 t 8.26%; 9 fields, 26.91 f 5.57%. It was significantly worse with 2CF (92.89 ? 35.26%) (pcO.05) and with 4CF (60.48 t 31.80%) (p<O.O5). No statistically significant difference was observed among the three IMRT techniques. Conclusions: When compared with the conventional external beam arrangements, conformal irradiation using a dynamic multileaf collimator to deliver IMRT treatment can potentially decrease GI and GU toxicity. Clinical implementation of inverse planning IMRT may improve the therapeutic outcome of patients with locally advanced cervical cancer, especially when chemotherapy is added or pelvic/paraaortic lymph nodes are grossly enlarged and a higher radiation dose is required. i 24 TREATMENT OF HIGH RISK UTERINE CANCER WITH WHOLE ABDOMINOPELVIC RADIATION THERAPY Smith RS, Teng NN, Kapp DS Stanford University, Stanford, CA, USA Purpose: To evaluate the treatment outcomes in patients with optimally debulked advanced stage (FIG0 stage III or IV) endometrial adenocarcinoma (ACA), or stages I to IV uterine papillary serous (UPS) or clear cell (CC) uterine cancer treated postoperatively with whole abdominopelvic irradiation (WAPI). Materials and Methods: Between 1979 and 1998, 48 patients received adjuvant WAPI at our institution. Twenty-two patients had FIG0 stage III (n= 18) or stage IV (n=4) endometrial ACA and 26 patients had FIG0 stages I to IV disease with UPS or CC histologies (stage 1~6: 11=2, III=13 and IV=5). The average age of the patients was 62.1 years (59 and 64.7 years in the ACA and UPS/CC groups, respectively). The treatment goal was 30 Gy to the upper abdomen (mean delivered dose of 27.5 Gy) and 50 Gy to the pelvis (mean delivered dose of 48.3 Gy). Twenty-one patients received a boost to the paraaortic nodes and/or diaphragm to a mean total dose of 42 Gy. Twenty-three patients received a boost to the vaginal mucosa by either low-dose rate or high dose rate brachytherapy. The Kaplan-Meier method was used in the survival analysis. The mean duration of follow-up was 36 months (2.4 to 135 months). The association of age, stage, grade, depth of myometrial invasion, histology, and nodal involvement with outcome were tested in univariate and multivariate analyses. Results: The 3.year actuarial disease free (DFS) and overall survival (OS) rates for the entire group were 60% and 75%, respectively. Analysis by histology revealed 3-year actuarial DFS of 74% and 49%, and OS of 84% and 68% for the ACA and UPS/CC groups, respectively. Early stage patients (stage I and II) with UPS/CC histologies had DFS and OS of 87%. However, those with advanced stage UPS/CC histologies (stage III and IV), had DFS and OS of 36% and 61%. Four patients in the ACA group failed, all with extraabdominal recurrences. Eleven of the 26 patients in the UPS/CC group recurred: 2 in the abdomen, 2 in the lungs, 2 with simultaneous failures in the abdomen and lungs, 3 at the vaginal apex and 2 in the supraclavicular nodes. Ten of these 11 patients had stage III or IV disease. A total of 10 patients experienced acute treatment related toxicity (3 with GI toxicities and 7 due to hematologic suppression) which required a treatment break of one week or more (n=8) or discontinuation of WAPI (n=2). No treatment related deaths occurred. One patient developed a small bowel obstruction requiring surgery 25 months following completion of treatment. The 3-year actuarial complication rate was 5%. Univariate analysis of factors prognostic for DFS and OS revealed that only age (either as a continuous variable or dichotomized at the mean age of 62 years) was statistically significant, with older patients having poorer survival. Multivariate analysis confirmed that age was the only significant prognostic factor.