Forward- and Inverse-Planned Intensity-Modulated Radiotherapy in the CHHiP Trial: A Comparison of Dosimetry and Normal Tissue Toxicity

Abstract

Aims

The CHHiP (Conventional or Hypofractionated High-dose Intensity Modulated Radiotherapy In Prostate Cancer; CRUK/06/016) trial investigated hypofractionated radiotherapy for localised prostate cancer. Forward- (FP) or inverse-planned (IP) intensity-modulated techniques were permitted. Dose–volume histogram and toxicity data were compared to explore the effects of planning method.

Materials and methods

In total, 337 participants with intermediate-risk disease and prospectively collected toxicity data were included. Patients were matched on prostate and rectum/bladder volumes and on radiotherapy dose for toxicity comparisons. The primary outcome was grade 2 or higher Radiation Therapy Oncology Group (RTOG) bowel or bladder toxicity at 2 years.

Results

IP patients had smaller volumes of rectum irradiated to 50–70 Gy ( P < 0.001); FP patients had smaller volumes of bladder irradiated to 74 Gy ( P = 0.001). Acute grade 2 + bowel toxicity was worse with FP (27/53 [52%]; 11/53 [21%] IP; P = 0.0002); with no significant differences in acute urinary toxicity. At 2 years, RTOG grade 2 + bowel toxicity rates were FP 0/53 and IP 2/53 and RTOG grade 2 + bladder rates were FP 0/54 and IP 1/57.

Conclusions

Significant differences were found between dose–volume histograms from FP and IP methods. IP may result in small reductions in acute bowel toxicity but both techniques were associated with low rates of late radiotherapy side-effects.

Highlights

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  Inverse planning resulted in smaller volumes of the rectum irradiated to 50–70 Gy.

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  Inverse planning resulted in larger volumes of the bladder irradiated to 74 Gy.

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  Inverse-planned patients had less acute bowel toxicity.

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  Late toxicity was low for forward and inverse planning.