Stereotactic body radiotherapy Noninferior to Conventional Radiotherapy for Low-to-Intermediate Risk Prostate Cancer: Study

This was a study of 874 patients with localized prostate cancer stages T1 or T2, a Gleason score of 3+4 or less, and PSA levels of no higher than 20 ng per milliliter. There were a total of 62 patients who were randomly assigned to one of two arms: SBRT in a cumulative dose of 36.25 Gy in 5 fractions over 1-2 weeks or conventional radiotherapy, administered to a total dose of 78 Gy in 39 fractions over 7.5 weeks or 62 Gy in 20 fractions over 4 weeks. Importantly, this was not an androgen-deprivation therapy (ADT) study but a study designed to directly look at the effect of radiation modalities per se. From August 2012 through January 2018, participants were enrolled at 38 centers, and analyses were done with the intention to treat.

Results

• During a median follow-up of 74.0 months, results of the trial confirmed that for SBRT, in comparison to conventional radiotherapy, freedom from biochemical or clinical failure was non-inferior for the primary outcome.

• The 5-year biochemical or clinical failure-free rate was 95.8% (95% CI, 93.3 to 97.4) in the SBRT group and 94.6% (95% CI, 91.9 to 96.4) in the control group, with an unadjusted hazard ratio of 0.73 (90% CI, 0.48 to 1.12; P=0.004 for noninferiority).

• These findings indicate that a shorter, easier SBRT course was not associated with an increased risk of prostate cancer recurrence or progression and thus could be an acceptable treatment strategy for many patients.

• Although SBRT was not inferior according to the standards of cancer control, the trial also measured levels of toxicity.

• It was seen that cumulative incidence of late Radiation Therapy Oncology Group grade 2 or higher genitourinary toxic effects at 5 years was significantly higher in SBRT group, 26.9% (95% CI, 22.8 to 31.5) than in the control radiotherapy group, 18.3% (95% CI, 14.8 to 22.5; P<.001).

• Cumulative incidence of late gastrointestinal toxic effects (RTOG grade 2 or higher) was comparable for the two arms: 10.7% (95% CI, 8.1 to 14.2) for SBRT and 10.2% (95% CI, 7.7 to 13.5) for controls (P=0.94).

In conclusion, this phase II randomized trial showed that five-fraction SBRT is equivalent to conventional radiotherapy in preventing biochemical and clinical failure of low-intermediate risk localized prostate cancer. This study provides very strong evidence to demonstrate the use of SBRT as a highly efficacious alternative in the management of localized prostate cancer.

Reference:

van As, N., Griffin, C., Tree, A., Patel, J., Ostler, P., van der Voet, H., Loblaw, A., Chu, W., Ford, D., Tolan, S., Jain, S., Camilleri, P., Kancherla, K., Frew, J., Chan, A., Naismith, O., Armstrong, J., Staffurth, J., Martin, A., … Hall, E. (2024). Phase 3 trial of stereotactic body radiotherapy in localized prostate cancer. The New England Journal of Medicine, 391(15), 1413–1425.https://doi.org/10.1056/nejmoa2403365