PII S0360-3016(00)00771-9 PHYSICS CONTRIBUTION INTENSITY-MODULATED WHOLE PELVIC RADIATION THERAPY IN PATIENTS WITH GYNECOLOGIC MALIGNANCIES JOHN C. ROESKE,PH.D.,* ANTHONY LUJAN,PH.D.,* JACOB ROTMENSCH, M.D.,* ² STEVE E.WAGGONER, M.D., ² DIANE YAMADA, M.D., ² AND ARNO J. MUNDT, M.D.* *Department of Radiation and Cellular Oncology, and ² Department of Obstetrics and Gynecology, Section of Gynecologic Oncology, University of Chicago, Chicago, IL Purpose: To evaluate the ability of intensity-modulated radiation therapy (IMRT) to reduce the volume of small bowel irradiated in women with gynecologic malignancies receiving whole pelvic radiotherapy (WPRT). Methods and Materials: Ten women with cervical (5) or endometrial (5) cancer undergoing WPRT were selected for this analysis. A planning CT scan of each patient was obtained following administration of oral, i.v., and rectal contrast. The clinical target volume (CTV) was defined as the proximal vagina, parametrial tissues, uterus (if present), and regional lymph nodes. The CTV was expanded uniformly by 1 cm in all directions to produce a planning target volume (PTV). The bladder, rectum, and small bowel were also delineated in each patient. Two plans were created: a standard “4-field box” with apertures shaped to the PTV in each beam’s eye view and an IM-WPRT plan designed to conform to the PTV while minimizing the volume of normal tissues irradiated. Both plans were normalized to deliver 45 Gy to the PTV. Isodose distributions and dose–volume histograms (DVH) were compared. Results: The IM-WPRT plan reduced the volume of small bowel irradiated in all 10 patients at doses above 30 Gy. At the prescription dose, the average volume of small bowel irradiated was reduced by a factor of two (17.4 vs. 33.8%, p  0.0005). In addition, the average volume of rectum and bladder irradiated at the prescription dose was reduced by 23% in both cases (p  0.0002 and p  0.0005, respectively). The average PTV doses delivered by the conventional and IM-WPRT plans were 47.8 Gy and 47.4 Gy, respectively. Corresponding maximum doses were 50.0 Gy and 54.8 Gy, respectively. However, on average, only 3.2% of the PTV received greater than 50.0 Gy in the IM-WPRT plans. Conclusion: Our results suggest that IM-WPRT is an effective means of reducing the volume of small bowel irradiated in women with gynecologic malignancies receiving WPRT. This approach potentially offers a method for reducing small bowel complications in patients with gynecologic malignancies. © 2000 Elsevier Science Inc. Gynecology, Whole pelvic radiation therapy, Inverse planning, Intensity modulation. INTRODUCTION Whole pelvic radiation therapy (WPRT) is commonly used in the treatment of many gynecologic malignancies, particularly cervical and endometrial carcinomas. In addition to the treat- ment of the primary site, WPRT is used to sterilize metastatic disease in the pelvic lymph nodes. Treatment of these nodes, however, entails irradiation of a considerable volume of small bowel. Unsurprisingly, small bowel sequelae are among the most important acute and chronic toxicities in these patients (1, 2). Sequelae include small bowel obstruction, enteritis, and diarrhea. However, more subtle problems including malab- sorption of vitamin B12, bile acids and lactose have been reported following small bowel irradiation (3– 6). The incidence and severity of small bowel sequelae in women undergoing WPRT can be reduced by a variety of means. The benefits of multiple fields, high energy beams, customized blocking and low daily fraction sizes are well known (2). Various agents have also been proposed as possible radioprotectors of the small bowel (7–13). Since it is a mobile structure, mechanical means have been used to displace the small bowel from the pelvis during treatment (14 –17). However, such methods are often cumbersome (on both patients and staff) and may be difficult to reproduce. Reprint requests to: Dr. John C. Roeske, Department of Radia- tion and Cellular Oncology, University of Chicago, MC 9006, 5758 South Maryland Avenue, Chicago, IL 60637. E-mail: roeske@rover.bsd.uchicago.edu Presented at the 40th annual Meeting of the American Society for Therapeutic Radiology and Oncology, Phoenix, AZ (USA), October 25–29, 1998. Acknowledgment—The authors thank Jong Kung, Ph.D., for help- ful discussions associated with the early stages of this work. The research reported in this publication is supported by a grant from the Illinois Department of Public Health. Its contents are solely the responsibility of the authors and do not necessarily reflect the official views of the Illinois Department of Public Health. Accepted for publication 10 July 2000. Int. J. Radiation Oncology Biol. Phys., Vol. 48, No. 5, pp. 1613–1621, 2000 Copyright © 2000 Elsevier Science Inc. Printed in the USA. All rights reserved 0360-3016/00/$–see front matter 1613