Dose-Response with Stereotactic Body Radiotherapy for Prostate Cancer

Dose-Response with Stereotactic Body Radiotherapy for Prostate Cancer: A Multi-Institutional Analysis of Prostate-Specific Antigen Kinetics and Biochemical Control:



Publication date: Available online 7 October 2020

Source: Radiotherapy and Oncology

Author(s): Rebecca G. Levin-Epstein, Naomi Y. Jiang, Xiaoyan Wang, Shrinivasa K. Upadhyaya, Sean P. Collins, Simeng Suy, Nima Aghdam, Constantine Mantz, Alan J. Katz, Leszek Miszczyk, Aleksandra Napieralska, Agnieszka Namysl-Kaletka, Nicholas Prionas, Hilary Bagshaw, Mark K. Buyyounouski, Minsong Cao, Nzhde Agazaryan, Audrey Dang, Ye Yuan, Patrick A. Kupelian



Highlights

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•Dose-escalation was associated with greater prostate ablation and PSA decay.



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•All dose groups in our study achieved median nPSAs of ≤0.2 ng/mL.



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•Dose-escalation to 40/5, but not beyond, was associated with improved BCRFS.



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•Rates of BCR were low across all dose groups, with 5-year BCRFS estimates of at least 93%





Abstract

Background and purpose

The optimal dose for prostate stereotactic body radiotherapy (SBRT) is still unknown. This study evaluated the dose-response relationships for prostate-specific antigen (PSA) decay and biochemical recurrence (BCR) among 4 SBRT dose regimens.



Materials and Methods

In 1,908 men with low-risk (50.0%), favorable intermediate-risk (30.9%), and unfavorable intermediate-risk (19.1%) prostate cancer treated with prostate SBRT across 8 institutions from 2003-2018, we examined 4 regimens (35 Gy/5 fractions [35/5, n=265, 13.4%], 36.25 Gy/5 fractions [36.25/5, n=711, 37.3%], 40 Gy/5 fractions [40/5, n=684, 35.8%], and 38 Gy/4 fractions [38/4, n=257, 13.5%]). Between dose groups, we compared PSA decay slope, nadir PSA (nPSA), achievement of nPSA ≤0.2 and ≤0.5 ng/mL, and BCR-free survival (BCRFS).



Results

Median follow-up was 72.3 months. Median nPSA was 0.01 ng/mL for 38/4, and 0.17-0.20 ng/mL for 5-fraction regimens (p<0.0001). The 38/4 cohort demonstrated the steepest PSA decay slope and greater odds of nPSA ≤0.2 ng/mL (both p<0.0001 vs. all other regimens). BCR occurred in 6.25%, 6.75%, 3.95%, and 8.95% of men treated with 35/5, 36.25/5, 40/5, and 38/4, respectively (p=0.12), with the highest BCRFS after 40/5 (vs. 35/5 hazard ratio [HR] 0.49, p=0.026; vs. 36.25/5 HR 0.42, p=0.0005; vs. 38/4 HR 0.55, p=0.037) including the entirety of follow-up, but not for 5-year BCRFS (≥93% for all regimens, p≥0.21).



Conclusion

Dose-escalation was associated with greater prostate ablation and PSA decay. Dose-escalation to 40/5, but not beyond, was associated with improved BCRFS. Biochemical control remains excellent, and prospective studies will provide clarity on the benefit of dose-escalation.



Keywords

prostate cancerstereotactic body radiation therapySBRTdose-escalationdose-responsebiochemical control