Intrafraction motion assessment in SBRT for prostate cancer: a prospective study

Transient excursions, typically within 20 seconds duration, and drifts of the prostate gland were observed during treatment. Spatial displacements > 11 mm in the cranial-caudal direction were identified in 1 patient, > 4 mm in the cranial-caudal and anterior-posterior directions in 3 patients, < 4 mm in the remaining patients. Evaluated CTV-to-PTV margins are shown in Table 1. Concerning robustness plan analysis, more than 98% of PTV is covered by 95% of prescription dose. The mean values of the DVH uncertainty ranges (upper / lower range bound with respect to the planned dose) is (+1.5% ; -2% ) and (+2.7%;-13.1%) at V 68Gy for rectum and at V 60Gy for bladder respectively.