A comparison of a moderately hypofractionated IMRT planning technique used in a randomised UK external beam radiotherapy trial with an in-house technique for localised prostate cancer.

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 ( ≤  0.05). VMAT_60/52/48 plans had better CI than VMAT_CH. FP_CH had better HI and fewer MU than VMAT ( ≤  0.05). More favourable rectum doses were found for VMAT _CH than FP_CH (V, V, V,  ≤  0.05) with less difference for bladder ( ≥  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, V, mean, D  ≤  0.05). Femoral head doses (V) were similarly low for all techniques ( = ≥ 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.