Helical tomotherapy-based hypofractionated radiotherapy for prostate cancer: a report on the procedure, dosimetry and preliminary clinical outcome.

Context: Hypofractionated intensity-modulated radiotherapy (IMRT) under image guidance using helical tomotherapy for prostate cancer improves therapeutic ratio. Aims: To report on clinical and dosimetric experience using hypofractionated helical tomotherapy for prostate cancer. Settings and Design: Prospective consecutive case series as feasibility study approved by Institutional Review Board (IRB) (2007-11). Materials and Methods: The staging work-up, risk stratification, simulation, contouring, planning, online matching and treatment delivery methodology are described in detail. The doses to (prostate and nodal) PTV and organs at risk (bladder, rectum, bowel and femoral heads) are described. The audit of online matching was used to determine set-up errors, PTV margins and resultant translational vector. We also report the outcomes in terms of biochemical relapse-free survival and acute toxicity. Results: Fifty-three consecutive patients were included. The baseline PSA was 23 ng/ml (1.60-100.37). The prostate BED3 ranged from 110-129 Gy (alpha/beta for prostate 1.5-3 Gy) and nodal 72-87.68 Gy. The required PTV margin by van Hark's formula for lateral, longitudinal and vertical axes were 11.30, 9.95 and 13.49 mm, respectively with resultant vectors 3-15 mm. There was 7% to 8% chance of missing part of CTV in absence of image guidance. There was only one patient requiring premature conclusion at 45 Gy due grade 3 genitourinary toxicity. At median follow-up of 23 months, biochemical relapse-free survival rate is 95.2%. Conclusions: Hypofractionated IMRT under image guidance using helical tomotherapy for prostate cancer is feasible with acceptable acute toxicity and may be advantageous in high throughput centers.