HDR Focal Boost with Whole Gland SBRT in Localized Prostate Cancer: Assessment of Acute Toxicity and Early Quality of Life

Abstract

<h3>Purpose/Objective(s)</h3> The dominant intraprostatic lesion (or GTV) is recognized as a possible site of radioresistance, potentially increasing the risk of relapse following prostate radiotherapy. We evaluated an approach of HDR focal boost to the GTV followed by dose-adjusted whole gland SBRT, and report the acute toxicity and early quality of life (QoL). <h3>Materials/Methods</h3> Patients with intermediate- to high-risk localized prostate cancer with GTV(s) identified on MR were enrolled into this non-randomized phase II trial. All patients received MR-guided HDR focal boost to the GTV(s), 15 Gy in single fraction, and whole gland prostate SBRT (33 Gy in 5 fractions to CTV; 30 Gy in 5 fractions to PTV). SBRT was delivered on conventional Linac (CL) or MRLinac (MRL). Rectal spacer was placed at the discretion of the treating physician. Toxicity and QoL assessments included CTCAE v4.0 and EPIC questionnaire at baseline, 1, 3 and 6 months, and 1, 2, 3, and 5 years. <h3>Results</h3> Ninety-five patients enrolled between 2016 and 2021 with ≥6-month follow-up were included in this analysis. Majority (83%) had intermediate-risk; 17% had high-risk disease. Median age was 70 years (range; 56 – 79). Seventy-five patients were treated on CL and 20 on MRL. Rectal spacer was placed in 68 patients. Acute G1 and G2 GU toxicity were 53% and 25%, respectively; G1 and G2 GI toxicity was 24% and 4%, where 74% had a rectal spacer. Mean percentage change in EPIC urinary score at 1 month was -9.3; -11.8 on CL and 0.5 on MRL. At 6 months this improved to -0.6. Mean EPIC bowel score reduced by -4.4 at 1 month; -5.3 on CL and -0.5 on MRL. Six-month bowel score was 0.7. Presence of rectal spacer did not appear to influence the bowel score. <h3>Conclusion</h3> An approach of HDR focal boost with whole gland prostate SBRT was well tolerated with minimal acute toxicity, and recovery by 6 months. Further follow up will determine the study primary endpoint of local control, and late toxicity and QoL outcomes, using this treatment approach.