RAIDER Trial Results Shed Light on Radiotherapy Toxicity Profiles, Adverse Events

By Emily Menendez - Last Updated: May 18, 2023

Radiotherapy is commonly utilized to treat muscle-invasive bladder cancer (MIBC), often in combination with other treatments. Adding concurrent chemotherapy to radiotherapy treatment has been shown to improve outcomes for patients with MIBC. A recent exploratory analysis examined patients with MIBC who were given 20 or 32 fractions of radical radiotherapy during the RAIDER clinical trial.

Patients in the RAIDER trial were randomized 1:1:2 to receive standard radiotherapy or standard-dose or escalated-dose adaptive radiotherapy. Neoadjuvant chemotherapy and concomitant therapy were allowed. Researchers analyzed acute toxicity by concomitant therapy-fractionation schedule combination.

A total of 345 patients (163 receiving 20 fractions and 182 receiving 32 fractions) with MIBC were recruited from 46 different medical centers between September 2015 and April 2020. Each patient had unifocal bladder cancer staged T2-T4a N0 M0.

Acute toxicity was assessed weekly during radiotherapy and 10 weeks after the start of treatment. Fisher’s exact tests were used to compare patients reporting treatment grade 2 or worse genitourinary, gastrointestinal, or other adverse events (AEs) at any point in the acute period.

Of the 345 total patients, 49% received neoadjuvant chemotherapy and 71% received concomitant therapy, with 5-fluorouracil/mitomycin C being the most common. A total of 44 of 114 (39%) patients received 20 fractions, while 94 of 130 (72%) received 32 fractions. Acute grade 2+ gastrointestinal toxicity rates were higher in patients who received concomitant therapy compared with those who received radiotherapy alone in the 20-fraction cohort (54/111 [49%] vs 7/49 [14%]; P<.001) but not in the 32-fraction cohort (P=.355).

Grade 2+ gastrointestinal toxicity rates were the highest for gemcitabine. Significant differences were noted among therapies in the 32-fraction cohort (P=.006), while no significant differences were found in the 20-fraction cohort (P=.099). No differences were found in grade 2+ genitourinary toxicities between concomitant therapies in either the 20- or 32-fraction cohorts.

The RAIDER trial demonstrated that grade 2+ AEs are common during radiotherapy treatment. The toxicity profile varies by the type of concomitant therapy received, with higher gastrointestinal toxicity rates in patients who received gemcitabine.