Radiosensitivity of orthotopic ileal neobladders.

350 Background: A prior report from our institution documented that Kock ileal reservoirs can tolerate doses of 45-50.4Gy. This study provides retrospective information on the radiosensitivity of orthotopic neobladders by reviewing the acute and late toxicity in patients who underwent post-operative radiotherapy following radical cystoprostatectomy with orthotopic ileal neobladder reconstruction. Methods: The USC bladder cancer database was queried for all patients who underwent cystoprostatectomy and neobladder reconstruction followed by adjuvant radiation therapy related to their bladder cancer. The original patient charts and radiation therapy records were reviewed to determine the dose of radiation received by the neobladder. The patient charts were also reviewed to determine acute and late toxicity related to radiation. Results: From 1980 to 2013, 1,742 patients underwent radical cystoprostatectomy with orthotopic neobladder reconstruction. Of those 1,742 patients, 10 patients met the criteria of the study. The median age of the patients who received post-operative radiotherapy was 66.9 years. Forty percent of the study population received a dose of 50.4Gy, 50% received a dose of 45-46.8Gy and one patient, while prescribed a dose of 61.2Gy, only received 39.6Gy secondary to progression of disease on treatment that required termination of RT. All patients received 1.7-1.8Gy per fraction. The most common indications for radiotherapy were close or positive surgical margins. Two patients were treated with IMRT while the rest of the patients received 4 field or AP-PA beam arrangements. Of the patients that completed radiation, 3 had grade 2 or less CTCAE v4.0 acute GI toxicity; no patients reported acute GU toxicity. Two patients reported chronic grade 1 GU toxicity, likely related to their neobladders, with no reports of chronic GI toxicity. No patients experienced neobladder perforation, leak, or fistula. Conclusions: The use of moderate doses of pelvic radiotherapy (45-50.4Gy) was well tolerated among the 10 patients who had radiotherapy following cystoprostatectomy with orthotopic neobladder creation. This data supports the use of post-operative radiotherapy to moderate doses in this patient population when clinically indicated.