Is rectal preparation necessary in contemporary image-guided prostate radiotherapy?

Introduction: Rectal preparation during prostate radiotherapy (RT) was established in the era of two-dimensional bone-based IGRT, but its necessity with contemporary three-dimensional IGRT is uncertain. We examined the impact of omitting rectal preparation on prostate inter- and intrafraction motion, rectal volume, and their relationship. Methods: Two datasets were analysed. Dataset one included patients receiving RT for de novo prostate cancer on a C-arm linear accelerator, stratified by use of micro-enema or no rectal preparation. Interfraction prostate motion was calculated from daily CBCT, and compared between preparation groups, with further stratification by rectal volume on planning CT (pCT) < 90 or ≥ 90 cm Results: Dataset one included 255 patients: 96 with and 159 without rectal preparation. Median rectal volume on pCT (proportion with rectal volume ≥ 90 cm Conclusion: Rectal preparation reduced the proportion of patients with a large rectum on pCT by only 10-15 %. A large rectum modestly increased interfraction motion but did not affect intrafraction motion. Findings suggest rectal preparation is not universally required with contemporary IGRT.