Initial experience with stereotactic body radiation therapy for localized prostate cancer using helical tomotherapy

Single-institution single-arm prospective study. Endpoint: To assess whether there are more than 5 % of men having grade 3 GU or any grade 3 GI acute toxicity during stereotactic body radiation therapy (SBRT) for prostate cancer using helical tomotherapy.

Since May 2012, 17 prostate cancer patients were treated with helical tomotherapy. The exclusion criteria used are the following: Gleason score ≥8, PSA >20 ng/ml, cT3b-4, IPSS ≥20 and history of acute urinary retention. CTV included the prostate gland and 1 cm of seminal vesicles in the low-risk group (LR) or the seminal vesicles completely in the intermediate (IR) and high-risk (HR) NCCN groups. CTV margins ranged from 2 to 8 mm, while PTV margins were 2 to 9 mm. Patients received eight fractions of 5.48 Gy (LR) or 5.65 Gy (IR, HR) on alternate days. Total equivalent doses at 2 Gy per fraction are 87.4 for LR and 92.3 Gy for IR-HR using an α/β value of 1.5. Correspondent figures for a α/β of 3 are 74.3 Gy and 78.2 Gy, respectively. Megavoltage CT (MVCT) for on-line correction was taken before every fraction.

The patient distribution by risk group is 29, 47 and 24 % for LR, IR and HR, respectively. 82 % received neoadjuvant-concomitant hormonal therapy. Acute GU toxicity grade 1, 2 and 3 was found in 70, 6 and 0 % of men. GI toxicity was observed in 50, 0 and 0. After 136 MVCT, the standard deviation of the mean individual corrections in the anterior-posterior direction was 2.5 mm.

SBRT for prostate cancer using helical tomotherapy is feasible. Initial results show an early toxicity profile no worse than SBRT delivered with robotic radiosurgery or conventionally fractionated radiotherapy.