Redefining Boundaries - Safety of Radiotherapy in the Presence of Orthotopic Neobladder

<h2>Abstract</h2><h3>Introduction</h3> Pelvic radiotherapy in patients with neobladder reconstruction following cystectomy is rare but encountered in clinical practice. Its potential impact on neobladder function remains underexplored in the current literature. <h3>Methods</h3> We conducted a retrospective study of patients with urothelial carcinoma who underwent cystectomy with neobladder reconstruction, followed by pelvic radiotherapy. Radiation dosimetric data pertaining to the neobladder was analyzed. Medical records were reviewed for evidence of urinary or neobladder dysfunction. <h3>Results</h3> Twenty-one patients were found to meet inclusion criteria at our institution and were subsequently analyzed. The median age at time of cystectomy and neobladder creation was 61 years. The mean equivalent dose in 2 Gy fractions (EQD2) using an α/β ratio of 10 of the prescribed total dose was 39.1 Gy. Three patients received multiple courses of pelvic radiotherapy, all other patients received a single course. Over half of the patients received hypofractionated radiotherapy;palliation was the most common indication. Amongst available radiation dose data, the median Dmax (defined as D0.03cc) inEQD2 using an α/β ratio of 10 to neobladder was 36.5Gy (range 5.2-98.8 Gy). The median Dmean in EQD2 using an α/β ratio of 10 to neobladder was 15.7 Gy (range 0.5-49.6 Gy). The median Dmax via EQD2 using an α/β ratio of 3 to neobladder (accounting for normal tissue effect) was 38.9 Gy (range 4.6-102.9). Although three patients experienced acute genitourinary toxicity attributable to pelvic radiotherapy, none experienced Grade 3 or worse toxicity. At median post pelvic radiotherapy follow-up duration of 13.4 months, none of the 21 patients included on this study had neobladder dysfunction that could be attributed to radiotherapy. <h3>Conclusions</h3> Pelvic radiotherapy following neobladder reconstruction post-cystectomy appears to carry minimal risk of radiation-induced neobladder toxicity. Larger studies are warranted to further validate the safety profile of pelvic radiotherapy in patients with neobladder reconstruction.