Toxicity profile and clinical outcomes of stereotactic body radiotherapy with a focal boost without fiducials or perirectal hydrogel spacer for localized prostate cancer

Whole-prostate dose escalation in stereotactic body radiotherapy (SBRT) for localized prostate cancer (PCa) can improve oncological outcomes, albeit at the cost of increased toxicity. A focal boost to the dominant intraprostatic lesion (DIL) is gaining interest as an alternative approach. Herein, we investigate the safety and efficacy of this approach.

This retrospective study enrolled patients with localized PCa who underwent five-fraction SBRT with a focal boost to the DIL at our institution between May 2016 and August 2021. The prescription doses to the whole prostate were 35 and 36.25 Gy for low- to favorable intermediate-risk PCa and unfavorable intermediate- to high-risk PCa, respectively. The focal boost to the DIL was up to 115–140% of the prescribed dose. None of the patients underwent pretreatment fiducial or perirectal hydrogel spacer placement. Acute and late genitourinary (GU) and gastrointestinal (GI) toxicities and oncological outcomes were assessed.

Among the 520 patients, 44% were categorized as patients with high-risk PCa. The median follow-up period was 42.9 months. No acute or late grade ≥3 toxicities were observed. Acute and late grade 2 GU toxicities were observed in 22.3 and 6.1%, respectively, while GI toxicities were observed in 2.1 and 0.8% of the patients. The 4‑year relapse-free survival rate was 94.8% among all patients.

Our results indicate that SBRT with a focal boost without fiducials or perirectal hydrogel spacer for localized PCa has a promising toxicity profile and oncological outcomes. Longer follow-up studies are necessary to adequately evaluate late toxicities and efficacy.