Ureter Tolerance in Patients Treated with Stereotactic Body Radiation Therapy on Abdominopelvic Lymph Nodes: Analysis on Dose-related Late Toxicity.

PURPOSE

This study evaluated late ureteral toxicity in relation to dose in patients treated with stereotactic body radiation therapy (SBRT) on abdominopelvic lymph node (A-P LN) oligometastases and assessed differences between planned and received ureteral dose.

METHODS AND MATERIALS

Patients treated between 2011 and 2023 with SBRT on A-P LN oligometastases from various primary tumors were retrospectively reviewed. Toxicity was graded using the Common Terminology Criteria for Adverse Events version 5.0. Dose-volume histogram parameters (maximum dose to the ureter [D] maximum dose to 0.1 cc of the ureter [D], and maximum dose to 0.5 cc of the ureter [D]) from ureters receiving >10 Gy were extracted and compared with published ureteral constraints (D 108, D 108, and D 77 Gy equivalent dose of 2 Gy per fraction with a:b ratio of 3 Gy [EQD2]). Interfraction dose variation was derived from patients who were treated with online adaptive SBRT.

RESULTS

The study included 144 patients, of whom 121 had a total of 137 ureters that were treated with <10 Gy. Most patients (85%) received 45 Gy in 5 fractions. The median ureter D and D were 60 and 42 Gy EQD2, respectively. No grade (G) ≥ 4 toxicities were observed. Three patients (2%) developed G3 ureteral obstruction, with D values of 121, 97, and 74 Gy EQD2. Five patients (4%) experienced any G of late urinary toxicity, but only 1 of them exceeded the D of 108 Gy EQD2. In total, 31 (23%) patients did not experience late toxicity, despite exceeding this parameter. No significant difference was found between the planned and received ureter dose (D 25 vs 22 Gy EQD2P = .23). The median follow-up was 28 months.

CONCLUSIONS

The incidence of G3 ureteral toxicity after SBRT on A-P LN oligometastases is low (2%). Published dose constraints were violated in 23% of the patients without reported toxicity, suggesting other factors may contribute. Furthermore, no difference was found between the planned and received ureter dose, indicating that the planned dose is a reliable estimate of the dose received.