A comparison of treatment planning techniques used in two randomised UK external beam radiotherapy trials for localised prostate cancer.

AIMS: To compare the radiotherapy planning techniques from two multicentre randomised external beam radiotherapy trials in the UK of conformal radiotherapy vs intensity-modulated radiotherapy (IMRT).

MATERIALS AND METHODS: Sixteen sequential patients with histologically confirmed localised prostate cancer treated in the conventional or hypofractionated IMRT trial (CHHiP) were planned using both the CHHiP and Medical Research Council RT-01 planning protocols to 74 Gy in 37 daily fractions. The CHHiP plan used a single phase simple forward planned three-field IMRT plan for easy multicentre adoption. The RT-01 plan used two phases: three-field conformal radiotherapy plan to 64 Gy followed by a six-field boost of 10 Gy. After coverage of the planning target volumes according to the respective trial protocols, the dose to the rectum and bladder was assessed for the two planning techniques.

RESULTS: There was acceptable planning target volume coverage by both the CHHiP and RT-01 plans. All CHHiP plans produced lower mean irradiated rectal volumes at all measured dose levels compared with the RT-01 plans, particularly for irradiated rectal volumes at 50 and 70 Gy (P<0.05). In the cases when a CHHiP plan failed to meet its own trial dose constraints, the volumes of irradiated rectum were less than if an RT-01 planning technique had been used. The CHHiP plans gave lower mean irradiated bladder volumes at both 50 and 60 Gy, but higher volumes at 74 Gy. These differences in irradiated bladder volumes were significant at the 60 and 74 Gy dose levels (P<0.05) in favour of the CHHiP and RT-01 plans, respectively.

CONCLUSION: The forward planned CHHiP IMRT planning solution gives more favourable rectal sparing than the RT-01 plan. This is important to limit any potential increase in late rectal toxicity for prostate cancer patients treated with high-dose conventional or hypofractionated schedules.