Refining the definition of biochemical failure in the era of stereotactic body radiation therapy for

Refining the definition of biochemical failure in the era of stereotactic body radiation therapy ...

Prostate

Refining the definition of biochemical failure in the era of stereotactic body radiation therapy for prostate cancer: The Phoenix definition and beyond - PDF Version

Ma TM, Roy S, Wu X, Mantz C, Fuller D, Miszczyk L, Napieralska A, Namysł-Kaletka A, Bagshaw HP, Buyyounouski MK, Glicksman R, Loblaw DA, Katz A, Upadhyaya SK, Nickols N, Steinberg ML, Philipson R, Aghdam N, Suy S, Pepin A et al

Radiotherapy and Oncology: Volume 166, January 2022, Pages 1-7

DOI: 10.1016/j.radonc.2021.11.005

BACKGROUND AND PURPOSE

The Phoenix definition for biochemical failure (BCF) after radiotherapy uses nadir PSA (nPSA) + 2.0 ng/mL to classify a BCF and was derived from conventionally fractionated radiotherapy, which produces significantly higher nPSAs than stereotactic body radiotherapy (SBRT). We investigated whether an alternative nPSA-based threshold could be used to define post-SBRT BCFs.

MATERIALS AND METHODS

PSA kinetics data on 2038 patients from nine institutions were retrospectively analysed for low- and intermediate-risk PCa patients treated with SBRT without ADT. We evaluated the performance of various nPSA-based definitions. We also investigated the relationship of relative PSA decline (rPSA, PSA18month/PSA6month) and timing of reaching nPSA + 2 with BCF.

RESULTS

Median follow-up was 71.9 months. BCF occurred in 6.9% of patients. Median nPSA was 0.16 ng/mL. False positivity of nPSA + 2 was 30.2%, compared to 40.9%, 57.8%, and 71.0% for nPSA + 1.5, nPSA + 1.0, and nPSA + 0.5, respectively. Among patients with BCF, the median lead time gained from an earlier nPSA + threshold definition over the Phoenix definition was minimal. Patients with BCF had significantly lower rates of early PSA decline (mean rPSA 1.19 vs. 0.39, p < 0.0001) and were significantly more likely to reach nPSA + 2 ≥ 18 months (83.3% vs. 21.1%, p < 0.0001). The proposed criterion (rPSA ≥ 2.6 or nPSA + 2 ≥ 18 months) had a sensitivity and specificity of 92.4% and 81.5%, respectively, for predicting BCF in patients meeting the Phoenix definition and decreased its false positivity to 6.4%.

CONCLUSION

The Phoenix definition remains an excellent definition for BCF post-SBRT. Its high false positivity can be mitigated by applying additional criteria (rPSA ≥ 2.6 or time to nPSA + 2 ≥ 18 months).