Rectal preparation is commonly used before prostate radiotherapy to improve anatomical consistency and reduce gastrointestinal toxicity.
However, new data suggest that routine rectal preparation may not provide meaningful benefit in modern ultra hypofractionated prostate SBRT.
A study published in Technical Innovations & Patient Support in Radiation Oncology evaluated different rectal preparation strategies in patients receiving five-fraction stereotactic body radiotherapy for low- or intermediate-risk prostate cancer.
The findings showed that none of the evaluated strategies consistently improved rectal volume stability, reduced delivered dose to rectal structures, or lowered acute gastrointestinal toxicity compared with no preparation.
Why This Study Matters
Ultra hypofractionated SBRT has become a standard treatment option for selected patients with low- and intermediate-risk prostate cancer.
Because SBRT delivers high doses per fraction over only five treatments, anatomical precision is essential. Rectal filling can influence prostate position, target coverage, and organ-at-risk exposure.
For this reason, many centers use bowel or rectal preparation protocols, including laxatives, dietary changes, enemas, or other strategies.
Yet the evidence supporting these approaches remains inconsistent, especially in the SBRT setting. Much of the previous evidence comes from conventionally fractionated radiotherapy and focuses on surrogate measures such as rectal volume or gas, rather than patient-centered outcomes such as toxicity and comfort.
Study Design
The retrospective study included 56 patients with low- or intermediate-risk prostate cancer treated between February 2021 and November 2024.
All patients received ultra hypofractionated SBRT with 5 fractions of 7.25 Gy, delivered every other day using volumetric modulated arc therapy.
The investigators compared four rectal preparation strategies:
No rectal preparation.
Laxatives plus a high-fiber diet before planning CT and during treatment.
Laxatives before planning CT only, without laxatives during treatment and without diet.
Laxatives before planning CT and during treatment, without diet.
Each group included 14 patients.
A total of 280 pre-treatment cone-beam CT scans were analyzed, with five scans per patient.
The study evaluated rectal volume changes, dosimetric parameters, intrafractional motion, patient-reported gastrointestinal toxicity, and physician-reported gastrointestinal toxicity.
Rectal Volume Stability
Rectal volumes varied across treatment fractions.
The group receiving diet plus laxatives had the most stable median rectal volume between planning CT and treatment.
The no-preparation group had the highest median rectal volume at planning CT, which decreased significantly during treatment.
In contrast, the groups receiving laxatives before planning CT only or laxatives during treatment showed significant increases in rectal volume during treatment compared with planning CT.
Intergroup analysis showed better rectal volume stability in the no-preparation and diet plus laxatives groups compared with the laxative-based groups.
However, this did not translate into consistent dosimetric or toxicity benefits.
Dose Delivery Findings
Most dosimetric parameters were similar across the four groups.
The maximum dose to the anorectum and anorectal wall was higher during treatment than on planning CT in all groups, but there were no significant differences between preparation strategies.
Only the laxatives group showed a significant increase in anal canal V25 and maximum anal canal dose during treatment.
The magnitude of this difference was small, and its clinical relevance remains uncertain.
Overall, the study did not show a clear dosimetric advantage for any rectal preparation strategy.
Intrafractional Motion
Intrafractional motion was assessed using cone-beam CT imaging between the two treatment arcs.
Repositioning due to displacement of at least 1 mm was least frequent in the diet plus laxatives group and most frequent in the group that received laxatives before planning CT only.
However, in the context of modern image-guided radiotherapy, daily CBCT and intratreatment correction can help manage anatomical variation during treatment.
The authors emphasized that image guidance and adaptive radiotherapy may reduce the practical value of routine rectal preparation.
Gastrointestinal Toxicity
Patient-reported gastrointestinal toxicity was assessed using modified RTOG/EORTC acute radiation morbidity questionnaires.
At the end of treatment, grade 2 or higher gastrointestinal toxicity occurred in small numbers across all groups.
At three months, grade 2 or higher toxicity had resolved in the no-preparation group and was reported by only one patient in the diet plus laxatives group and one patient in the laxatives group.
In the group receiving laxatives before planning CT only, three patients continued to report grade 2 or higher gastrointestinal symptoms at three months.
These differences were not statistically significant.
The most common patient-reported symptoms were loose urge, cramping urge, and mucus discharge.
Physician-reported toxicity was also low overall. The incidence of grade 2 or higher CTCAE gastrointestinal toxicity was 7.1%, with no significant difference between groups.
One grade 3 gastrointestinal toxicity occurred in the diet plus laxatives group and was related to a prostate abscess after fiducial implantation.
Patient Burden and Laxative Use
An important finding was that laxative-based regimens were associated with gastrointestinal symptoms such as diarrhea, abdominal discomfort, and cramps.
These symptoms were documented as being associated with laxative use in 36% of patients receiving diet plus laxatives and 29% of patients receiving laxatives during treatment.
This matters because rectal preparation protocols can increase patient burden, reduce comfort, and require more clinical resources.
If they do not clearly improve toxicity or dosimetry, routine use may be difficult to justify.
Clinical Interpretation
The study suggests that routine rectal preparation may not be necessary for all patients receiving modern prostate SBRT.
In daily CBCT-guided workflows, anatomical changes can be monitored and corrected during treatment. In adaptive radiotherapy, treatment plans can also be adjusted to the anatomy of the day.
This reduces the potential added value of intensive preparation strategies.
The findings support a more selective, individualized approach rather than mandatory rectal preparation for every patient.
Less invasive strategies, such as approaches targeting rectal gas rather than total rectal volume, may deserve further study.
Limitations
The study included a small number of patients, with only 14 patients in each preparation group.
The design was retrospective, and the four preparation strategies were implemented in successive cohorts, which may introduce selection bias.
Questionnaire response rates were incomplete, with patient-reported data available in about 64% of cases.
The study did not assess prostate target coverage or oncologic outcomes.
Because of the small sample size, the toxicity analysis was mainly descriptive.
Despite these limitations, the study is valuable because it combines imaging, dosimetry, patient-reported outcomes, and physician-reported toxicity.
Clinical Takeaway
In this study of patients receiving five-fraction prostate SBRT, rectal preparation did not consistently improve rectal volume stability, provide dosimetric benefit, or reduce gastrointestinal toxicity compared with no preparation.
Laxative-based regimens may add gastrointestinal discomfort and patient burden without clear clinical benefit.
For modern daily CBCT-guided and adaptive radiotherapy workflows, routine rectal preparation should be reconsidered.
Future studies should focus on patient-centered outcomes, comfort, adherence, quality of life, and less invasive strategies that preserve treatment accuracy while reducing unnecessary burden.
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