Intraoperative electron beam radiotherapy and human ureteral obstruction

Abstract

To better quantify the risk of ureteral injury following intraoperative electron beam radiotherapy (IOERT), a review of patients receiving IOERT to the ureter in the course of treatment for locally advanced and/or inoperable pelvic and abdominal malignancies at Mayo Clinic Rochester was performed. Between April 1981 and February 2003, 146 patients with locally advanced malignancies deemed initially unresectable for cure underwent treatment with external beam radiotherapy (EBRT), surgery, and IOERT in which a portion of one or both ureters (164 ureters) were within the IOERT field. Five patients were excluded from analysis because of preexisting hydronephrosis and kidney atrophy. Ninety-two of 141 patients had colorectal/anal malignancies, 26 of 141 had gynecological malignancies, 21 of 141 had retroperitoneal sarcomas, and 2 patients had miscellaneous tumors. IOERT energy ranged from 6 to 20 MeV (median, 12 MeV). IOERT dose ranged from 7.5 to 30.0 Gy (median, 15 Gy). 132 of 141 patients received EBRT either before or after their IOERT procedure at doses of 19.8 to 68.9 Gy (median, 50.0 Gy). 32 (23%) patients had evidence of ureteral obstruction prior to treatment. Follow-up was available in 138 of 141 patients (range: 0.0 to 19.3 years, median 2.1 years). Rates of ureteral obstruction were analyzed for: Type 1.) any cause of obstruction after IOERT; Type 2.) treatment related obstruction secondary to surgery, EBRT, and/or IOERT (excludes patients with documented tumor progression and/or abscess formation obstructing the ureter); Type 3.) delayed obstruction occurring at least one month after surgery and IOERT, (excludes patients with clear tumor progression, abscess formation or patients with stents placed at the time of surgery that were never removed.) See table below. Univariate and multivariate analysis revealed that IOERT dose (P < 0.015) and the presence of ureteral obstruction prior to IOERT (P < 0.001) were associated with an increased risk for ureteral obstruction related to any cause (Type 1.). Prior ureteral obstruction (P < 0.0001) was the only variable associated with an increased risk of ureteral obstruction related to treatment (Type 2.). However, IOERT dose and prior obstruction were not associated with an increased risk of delayed ureteral obstruction (Type 3.) External beam radiotherapy dose, histology, tumor site, size of the IOERT field, and number of IOERT fields had no correlation with an increased risk of ureteral obstruction. The risk of ureteral obstruction following IOERT treatment of the ureter is significant and continues to increase with time, but this risk appears to be less than previously estimated. Patients with previous ureteral involvement are at higher risk for obstruction in the period immediately following resection, IOERT, and EBRT, but they appear to not be at higher risk for late development of ureteral obstruction unrelated to tumor growth or abscess formation. The presence of IOERT dose as a risk factor in this analysis for obstruction related to any cause, including tumor progression, but not to delayed obstruction secondary to chronic radiation effect may reflect that patients with incompletely resected tumors with a higher risk for progression and obstruction of the ureter received higher IOERT doses. In contrast to previous reports from our institution (Shaw, Rad and Onc 18:247–55, 1990), the risk of ureteral obstruction is relatively constant within the range of IOERT doses conventionally employed (10 to 20 Gy).