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This trial was a prospective, single centre, non-blinded, randomised controlled trial. It included patients with prostate cancer undergoing external beam radiation therapy radically to an intact prostate, as well as salvage or adjuvant radiation therapy to the prostate bed, with or without the inclusion of the pelvic lymph nodes. 30 patients were randomised 1:1 to the simethicone or no intervention arm. Patients in the simethicone arm had a dose of 100mg three times per day for three days prior to their planning scan, restarted simethicone three days prior to treatment commencement and continued throughout treatment. Cone beam computed tomography (CBCT) scans were performed daily for the first 3 fractions, then weekly until completion. RV and GV were measured using volume delineation on Varian Eclipse on the planning CT and each CBCT (Figure 1). Standard deviations (SDs) were calculated for each patient for timepoints 1-10. To assess the effect of time on the outcome, these were grouped into timepoints 1-5 and 6-10 for comparison. Toxicity data was collected at baseline and weekly from week 4 using the International Prostate Symptom Score (IPSS), EORTC Quality of Life Questionnaire Prostate Cancer Module (EORTC QLQ PR25) and EORTC QLQ C30 Quality of Life Questionnaire.

264 CBCTs were analyzed. The simethicone group was not significantly different from the control group in terms of RV and GV at each time point (p>0.05) after adjusting for baseline values as a covariate. The simethicone group showed an average reduction in RV and GV of 10% and 21% respectively when compared to the control group, without reaching statistical significance. SDs were calculated for each patient over 10 time points, representing the first two weeks of radiation therapy versus subsequent weeks. These were not significantly different between the two groups (p>0.05). However, there was a statistically significant decrease in the variability of RV at time points 6-10 compared with time points 1-5 within the simethicone group (p=0.012), but no significant difference between these grouped time points in the control group (p=0.581). Baseline characteristics were similar across both arms. The toxicity questionnaires showed no significant difference between the two groups. 

Simethicone appears to significantly decrease the variability of RV when taken at least 2 weeks prior to radiation therapy, without affecting toxicity. These results support further investigation into the efficacy of simethicone in reducing RV and GV variability, with earlier commencement of simethicone and a larger number of patients.