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Two-Year Outcomes of the SPARC Phase II Trial: Simultaneous Focal Boost With Stereotactic Radiation Therapy for
Binnaz Yasar1, Yae-Eun Suh2, Ewan Chapman3
1Royal Marsden NHS Foundation Trust, London, UK; The Institute of Cancer Research, London, UK.
International Journal of Radiation Oncology, Biology, Physics
|January 13, 2026
Summary
Stereotactic body radiotherapy (SBRT) with a focal boost for high-risk prostate cancer is well-tolerated, showing low late toxicity. This CyberKnife-based SBRT approach demonstrates favorable outcomes with minimal impact on quality of life.
Area of Science:
- Oncology
- Radiation Oncology
- Urologic Oncology
Background:
- High-risk localized prostate cancer requires effective treatment to improve outcomes.
- Stereotactic body radiotherapy (SBRT) with a focal boost to the dominant intraprostatic lesion (DIL) is a strategy to enhance efficacy while minimizing toxicity.
- CyberKnife-based SBRT offers precise radiation delivery for prostate cancer treatment.
Purpose of the Study:
- To assess late toxicity and quality of life (QOL) following CyberKnife-based SBRT with a simultaneous integrated boost in localized prostate cancer patients.
- To evaluate genitourinary (GU) and gastrointestinal (GI) toxicity, sexual function, and overall QOL at 2 years post-treatment.
- To determine the biochemical outcomes at 2 years.
Main Methods:
- Patients with unfavorable intermediate- to high-risk localized prostate cancer received 36.25 Gy in 5 fractions with a simultaneous focal boost up to 47.5 Gy using CyberKnife.
- All participants received androgen deprivation therapy.
- Late toxicity (RTOG-assessed), IPSS, urinary QOL, IIEF-5 sexual function, EQ5D-5L QOL, and biochemical outcomes were assessed at 2 years.
Main Results:
- Twenty participants were enrolled with a median follow-up of 54 months.
- At 2 years, the cumulative rate of grade ≥ 2 GU toxicity was 35% and GI toxicity was 5%. No grade 3 late toxicity was observed.
- No significant worsening in EQ5D-5L QOL or IPSS scores was noted; however, sexual function (IIEF-5) scores decreased. One biochemical relapse occurred.
Conclusions:
- CyberKnife-based SBRT with a simultaneous integrated boost is well-tolerated in high-risk prostate cancer patients at 2 years.
- The observed cumulative rates of grade ≥ 2 GU and GI toxicity (35% and 5%) are consistent with contemporary SBRT trials.
- This treatment approach shows promise for managing localized prostate cancer with acceptable toxicity and QOL preservation.
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