Abstract
AIM: To compare the radiotherapy technique used in a randomised trial with VMAT and an in-house technique for prostate cancer. BACKGROUND: Techniques are evolving with volumetric modulated arc therapy (VMAT) commonly used. The CHHiP trial used a 3 PTV forward planned IMRT technique (FP_CH). Our centre has adopted a simpler two PTV technique with locally calculated margins. MATERIALS AND METHODS: 25 patients treated with FP_CH to 60 Gy in 20 fractions were re-planned with VMAT (VMAT_CH) and a two PTV protocol (VMAT_60/52 and VMAT_60/48). Target coverage, conformity index (CI), homogeneity index (HI), monitor units (MU) and dose to the rectum, bladder, hips and penile bulb were compared. RESULTS: PTV coverage was high for all techniques. VMAT_CH plans had better CI than FP_CH (p ≤ 0.05). VMAT_60/52/48 plans had better CI than VMAT_CH. FP_CH had better HI and fewer MU than VMAT (p ≤ 0.05). More favourable rectum doses were found for VMAT _CH than FP_CH (V(48.6), V(52.8), V(57), p ≤ 0.05) with less difference for bladder (p ≥ 0.05). Comparing VMAT_CH to VMAT_60/52/48 showed little differences for the bladder and rectum but VMAT_CH had larger penile bulb doses (V(40.8), V(48.6), mean, D(2,) p ≤ 0.05). Femoral head doses (V(40.8)) were similarly low for all techniques (p = ≥ 0.05). CONCLUSION: VMAT produced more conformal plans with smaller rectum doses compared to FP_CH albeit worse HI and more MU. VMAT_60/52 and VMAT_60/48 plans had similar rectal and bladder doses to VMAT_CH but better CI and penile bulb doses which may reduce toxicity.