Comparison of Patient-Reported Quality-of-Life between Spot Scanned Proton Stereotactic Body Radiation Therapy and Conventional Proton Therapy after Radiotherapy for Intermediate-Risk Prostate Cancer: A Single-Center Prospective Registry Experience

Abstract

<h3>Purpose/Objective(s)</h3> Proton stereotactic body proton therapy (SBPT) for prostate cancer takes advantage of biologic advantages with hypofractionation and the technical advances of spot scanning. We report toxicities and quality-of-life (QOL) in patients treated with SBPT versus conventional proton therapy (CPT) in a single-institution prospective registry. <h3>Materials/Methods</h3> Patients (Pt) with localized intermediate-risk prostate cancer (PC) were treated with proton radiation (RT) from 2016 to 2018 on an IRB approved prospective registry. Treatment included SBPT (≥6 Gy/fx) or CPT (<2 Gy/fx) per physician choice. Expanded Prostate Cancer Index Composite (EPIC), AUASI, SF-12, Promis10, FACIT-COST, and PRO-CTCAE QOL were administered pre-RT, end-of-treatment, 3, 6, 12 months post RT, and then annually. Toxicities were recorded according to CTCAE v5. Fisher's Exact and Kruskal-Wallis tests were utilized to compare pt characteristics between groups. Effect of treatment were analyzed using logistic regression (toxicity), Kaplan-Meier statistics, and repeated measure mixed models (QOL) with all events were baseline adjusted. <h3>Results</h3> 191 pts were included with a median follow-up of 43.2 months (SBPT:39.9, CPT: 44.9). SBPT (38 Gy/5 fxs) was used in 47 pts (24.6%) while CPT used in 144 pts (75.6%) ranged from 75.6-79.2 Gy in 39-44 fx. At baseline, SBPT pts, tended to be younger, higher BMI, lower Gleason score, lower T stage, less likely to have had prior or treatment concurrent ADT, and less likely to have had concurrent urinary medications. There was no significant difference between arms in terms of survival (p=0.22) and development of new primary cancers (p=0.63). At last follow-up, there were 1x failures for SBPT and 4x failure for CPT (p=0.92). Grade 2+ AE were experienced by 12.8% SBPT versus 11.1% CPT (p=0.76). When adjusted for baseline toxicity, neither acute (≤3 months) grade 2+ (p=0.3) nor chronic grade 2+ (p=0.24) AEs were significantly different between the arms. No significant differences occurred between the arms for Promis10 overall (p=0.76), Physical (p=0.75), or Social (p=0.79) domains, PRO-CTCAE (p>0.73), or FACIT-COST (p=0.92). In regard to EPIC domains, SBPT pts fared significantly (all p<0.05) better in: urinary, bowel, urinary function, urinary bother, urinary irritative/obstructive, bowel bother, and Mental SF12. All other domains did not approach statistical significance (all p>0.1). <h3>Conclusion</h3> There was no significant difference in PC patients treated with SBPT versus CPT except for an improvement in prostate specific QOL in SBPT patients. SBPT appears safe and effective, while providing improved QOL over CPT.