Patient-Reported Rectal QOL with Pelvic Nodal Irradiation ± Involved Pelvic Nodal Boost to 75 Gy EQD2 in Men with Prostate Cancer

Abstract

<h3>Purpose/Objective(s)</h3> The study was designed to compare patient-reported acute and late rectal function quality of life (RQOL) between men with local or regional prostate cancer treated with or without an involved pelvic nodal simultaneous integrated boost (SIB). It is hypothesized that men receiving pelvic nodal radiotherapy at 50.4 Gy in 28 fractions (Pelv50) have similar RQOL as men receiving the same pelvis dose plus the addition of involved pelvic nodal SIB to 67.2 Gy in 28 fractions (Pelv67). <h3>Materials/Methods</h3> Rectal toxicity was assessed using the Merrick Rectal Function Assessment Score (R-FAS). The R-FAS consists of nine questions and a scoring range of 0-27, with higher scores indicating poorer bowel function. Patients with measures -180 days and up to 730 days from the start of RT were included in the analysis. SIB targets included radiographically apparent nodal GTVs plus a 5mm margin. Pelvic nodal contours extended from aortic bifurcation through the bilateral obturator nodes. An EQD2 of 75 Gy to involved nodal targets was calculated for the Pelv67 group based on 28 fractions of 2.4 Gy with an α/β ratio of 1.5. Patients were dichotomized by treatment received (Pelv50 vs. Pelv67). Non-parametric kernel regression was modeled with R-FAS score as the dependent variable and time from RT and treatment cohort as the independent variables, with improved Akaike information criterion to determine optimal bandwidth. Marginal means and 95% confidence intervals were predicted at 90-day intervals from timepoint 0 with 50 bootstrapping replications. <h3>Results</h3> There was no difference in baseline age or baseline Charlson Comorbidity Index between the two cohorts. There was no significant difference in mean R-FAS over the entire time interval between the two cohorts (Pelv67 vs. Pelv50: 0.4 points, p=0.17). There is no significant difference in R-FAS score at any discrete timepoint between Pelv67 and Pelv50 as the 95% confidence intervals overlap (Table). <h3>Conclusion</h3> Pelvic nodal irradiation with a simultaneous integrated boost to 67.2 Gy in 28 fractions (EQD2=75 Gy) was associated with similar rates of RQOL compared to standard pelvic irradiation from the patient's perspective. This study suggests that dose escalation using a pelvic nodal SIB technique to 75Gy EQD2 is safe despite the proximity of the rectum and bowel to SIB targets.