Two-Year Outcomes of the SPARC Phase II Trial: Simultaneous Focal Boost With Stereotactic Radiation Therapy for Localized Prostate Cancer.

Yasar, B.; Suh, YE.; Chapman, E.; Nicholls, L.; Henderson, D.; Jones, C.; Morrison, K.; Wells, E.; Henderson, J.; Meehan, C.; Sohaib, A.; Taylor, H.; Tree, A.; van As, N.

Two-Year Outcomes of the SPARC Phase II Trial: Simultaneous Focal Boost With Stereotactic Radiation Therapy for Localized Prostate Cancer.

All Authors

Yasar, B.

Suh, YE.

Chapman, E.

Nicholls, L.

Henderson, D.

Jones, C.

Morrison, K.

Wells, E.

Henderson, J.

Meehan, C.

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LTHT Author

Jones, Caroline

LTHT Department

Leeds Cancer Centre
Medical Physics & Engineering

Non Medic

Principal Radiotherapy Physicist

Publication Date

2026

Item Type

Journal Article

Abstract

PURPOSE: Stereotactic body radiation therapy (SBRT) with focal boost to the dominant intraprostatic lesion (DIL) provides a strategy to enhance outcomes in high-risk localized prostate cancer while minimizing toxicity. This study assessed late toxicity and quality of life (QOL) following CyberKnife-based SBRT with a simultaneous integrated boost in localized prostate cancer. METHODS AND MATERIALS: Patients with newly diagnosed, biopsy-proven unfavorable intermediate- to high-risk localized prostate cancer (at least one of the following: Gleason >= 4+3, MRI-defined T3a N0, PSA >= 20) with <=2 MRI-defined DILs were enrolled. Participants received 36.25 Gy in 5 fractions with a simultaneous focal boost <=47.5 Gy delivered using CyberKnife. All participants received androgen deprivation therapy. The current analysis reports RTOG-assessed late genitourinary (GU) and gastrointestinal (GI) toxicity, late International Prostate Symptom Score and urinary QOL, late International Index of Erectile Function 5-Questionnaire assessed sexual function, late EQ5D-5L QOL, and biochemical outcomes at 2 years. RESULTS: Between 2013 and 2023, 20 participants were enrolled with a median follow-up of 54 months (IQR, 24-108 months). The median D95 dose delivered to the DIL was 47.43 Gy. At 2 years, the cumulative rate of RTOG-assessed grade >=2 GU and GI toxicity was 35% (95% CI, 15%-59%) and 5% (95% CI, 1%-25%), respectively. The prevalence of grade 2 GU and GI toxicity at 2 years was 0% and there was no late grade 3 GU and GI toxicity. There was no clinically significant worsening of EQ5D-5L-assessed QOL, International Prostate Symptom Score score, and urinary QOL scores at 2 years compared with baseline. There was a reduction in International Index of Erectile Function 5-Questionnaire scores for sexual function at 2 years (median 10; IQR, 5-18) from baseline (median 18; IQR, 6-22). There is one case of biochemical relapse reported to date. CONCLUSIONS: CyberKnife-based SBRT delivering 36.25 Gy to the prostate with a simultaneous integrated boost <=47.5 Gy is well tolerated at 2 years. The cumulative rates of grade >=2 GU and GI toxicity were 35% and 5%, respectively, consistent with other contemporary SBRT trials with and without focal boost. Copyright © 2026 Elsevier Inc. All rights reserved.