KEY POINTS
- Retrospective dosimetric analysis of 30 clinically N0M0 prostate cancer patients treated with cone-beam computed tomography-based online adaptive simultaneous integrated boost stereotactic body radiotherapy in 5 fractions.
- Two dose cohorts were analyzed: 15 patients received 30 Gy to prostate plus seminal vesicles and 35 Gy to prostate; 15 received 30 Gy to prostate plus seminal vesicles and 37.5 Gy to prostate.
- Across 150 treatment sessions, the scheduled plan was selected only 3 times (2%); otherwise, the daily adapted plan was used.
- Target coverage significantly favored adaptive plans across all evaluated target-volume parameters (p < 0.001); median prostate planning target volume V100% improved from 89.9% with scheduled plans to 95.1% with adaptive plans.
- Organ-at-risk effects were mixed. Several bladder, rectum, penile bulb, sigmoid colon, and femoral head parameters differed significantly, but adaptation did not produce a consistent organ-at-risk sparing benefit across the whole cohort.
CLINICAL TAKEAWAY
Daily cone-beam computed tomography-based online adaptation appears most useful for preserving prostate stereotactic body radiotherapy target coverage when anatomy changes fraction to fraction. The organ-at-risk story is less clean: adaptation kept doses acceptable but did not consistently lower them. This is clinically relevant dosimetric evidence, not proof of improved toxicity, local control, or survival.