Toxicity and second primary cancer estimate for hypo-and-conventionally fractionated Volumetric Modulated Arc-Therapy of prostate carcinoma.

The aim of this study is to evaluate the toxicity (NTCP: normal tissue complication probability) and estimate the risk of induced second primary cancer (EAR: Excess Absolute Risk) following volumetric modulated arc therapy using different regimens. A cohort of twenty prostate cancer patients, median age of 71 years and various stages, was biologically evaluated for organs at risk (rectum, bladder, and small intestine) using different schedules. This was done according to Lyman-Kutcher-Burman (NTCP) and EAR modeling. For each patient, three treatment plans were created and evaluated for dose schedules of 76 Gy/2 Gy/F, 70/2.5 Gy/F and 60 Gy/3 Gy/F. The biological effective dose (BED), was performed, using α/β = 1.5 for the tumour (prostate), and α/β = 3 for organs at risk. The results for the conventional and hypo-fractionated dose deliveryscheduleswere: for rectum, the NTCP (rectal bleeding endpoint) was 9.5 % for 2 Gy fractions, and 10.24 % and 7.6 % for hypo-fractionated total doses of 70 Gy and 60 Gy, respectively. Lower toxicity for the bladder, estimated at 0.05 %, 0.07 %, and 0.01 % for 76 Gy, 70 Gy, and 60 Gy with 2Gy, 2.5 Gy, and 3Gy per fraction, respectively. Linear relationship between the 2nd primary cancer and the "OED" for the linear Exponential model (Bell shape) was obtained for the bladder. In case of the small intestine and bladder, the EAR Mechanistic (Full) model was: 2.10 and 1.96, respectively, at 60 Gy; 2.04 and 2.73 at 70 Gy; and 6.30 and 2.18 at 76 Gy. Hypo-fractionated (HF schedules were beneficial in terms of decreasing the toxicity and the risk of induced second primary cancer.