2358: Establishment of Intensity-Modulated Radiation Therapy for Whole Pelvic Irradiation in Cervical Carcinoma Patients After Hysterectomy

Abstract

To establish the technique of intensity-modulated radiation therapy (IMRT) for whole pelvic irradiation in cervical carcinoma patients after hysterectomy, the following questions should be answered: (1). What was the optimum irradiation position? (2). How was the target volume delineated? (3). What was the optimum irradiation plan? This study was designed to answer these questions. All patients enrolled in this study were cervical carcinoma after hysterectomy with high-risk of pelvic recurrence. (1) Patients were immobilized by vacuum-lock with both supine and prone positions, respectively, and set-up errors were measured three times a week at both irradiation positions by comparison of DRR and EPID. Doses to bladder, intestine and colon were evaluated when bladder was full or empty. The set-up errors were also measured at prone position with full and empty bladder. (2) CTV was defined as regional pelvis lymph nodes and tumor bed, and was delineated by contouring pelvis vessels with 1 cm margin surrounding vessels. (3) Dosimetric parameter comparisons were carried out among irradiation plans, which included 3DCRT with 2-field, 3-field, 4-field 5-field and 6-field, and IMRT of 5-field, 7-field, 9-field, 11-field and 13-field. The goal was to deliver 45 Gy to >97% PTV. (1) From 2004 to 2005, 10 patients enrolled for irradiation position study. The set-up errors were 3.0mm ± 0.7mm and 8.2mm ± 1.4mm at anterior-posterior direction (p=.02), 2.2mm ± 0.5mm and 5.1mm ± 1.2mm at cranial-caudal direction (p=.04) and 1.5mm ± 0.2mm and 3.8mm ± 1.3mm at left-right direction (p=.05), respectively for prone and supine position. Five patients were selected for study of bladder status. Comparisons of DVH of bladder, intestine and colon less doses to above organs were found with full bladder than empty bladder (p=.02, .04 and .03, respectively). With prone position and full bladder, the random error for set-up errors was 3.1 mm ± 1.2 mm, system error was 6.7 mm ± 1.1 mm, and total uncertainty was 7.4 mm ± 1.6 mm. For 95% confidence interval, the margin added from CTV to PTV could be 10 mm based on total uncertainty. (2) A guideline for delineation of CTV was proposed. (3) Dosimetric parameter, including target coverage, conformity index (CI), doses to bladder, intestine, colon, rectum, head of femur, spinal cord, and irradiated MU as well as beamlits were compared. 90 irradiation plans had been generated for 10 patients. Overall, IMRT plans were better than 3DCRT plans in terms of target coverage, doses to normal organs and CI. For IMRT, as the number of fields increased, all dosimetric parameters improved, but beamlits and number of irradiation MU were also increased. IMRT with 9-field plan was recommended because beyond 9-field plan no more significant improvement was noticed, whereas beamlits and number of MU increased. (1) Prone position with full bladder was the best irradiation condition. (2) Guideline of contouring CTV was established. (3) IMRT with 9-field plan was appropriate.