Effects of Bladder Filling and Rectal Gas on Number of CBCT Scans and Treatment Time for Prostate Cancer Patients Undergoing EBRT.

PURPOSE/OBJECTIVE(S) Prostate cancer patients undergoing EBRT may be treated with a full bladder and empty rectum to maintain a consistent prostate position. To optimize setup for hypofractionated regimens, cone beam CT (CBCT) scans may be performed to assess the level of bladder filling and the amount of rectal gas before each treatment. However, achieving a precise bladder volume and minimizing rectal gas prior to radiation treatment can be difficult and time-consuming. This process often leads to repeated CBCT scans, treatment delays, and an unpleasant patient experience. We prospectively evaluated the interplay between bladder filling, rectal gas, number of CBCT scans, and the total in-department time. We evaluated whether there was sufficient clinical evidence to justify the use of an alternative imaging technique to reduce the number of CBCT scans and improve treatment efficiency. MATERIALS/METHODS For bladder and bowel preparation, patients drank 8 oz of water 45-60 mins prior to CBCT scans and took simethicone twice daily and psyllium supplementation daily throughout the treatment course in addition to a saline enema 2-3 hours before CBCT. Inadequate bladder filling prompted oral administration of 8 oz of water and a 20-30-minute delay. Excess rectal gas was passed either voluntarily or via a rectal tube. Relevant data, such as patient arrival time, the number of CBCT scans, and total in-department time, were recorded. RESULTS We evaluated 475 individual treatments among 194 patients. A total of 34.3% of treatments had bladder filling events, 17.7% had rectal gas events, and 10.5% had both events. The number of CBCT scans had a right-skewed Poisson distribution, with mean 1.43 ± 0.88 (range 0-5). 47.4% of treatments had 1 CBCT scan, 31.8% had 2 CBCT scans, 7.8% had 3 CBCT scans, 1.7% had 4 CBCT scans, and 0.4% had 5 CBCT scans. The distribution of the number of retries (taken off the table) heavily clustered in 0 and 1. 66% of treatments had 0 retries, 19% had 1 retries, 13% had 2 retries, and 2% had 3 retries. The mean and median actual in-department times were 68.9 ± 41.9 and 60.0 mins, while the mean and median scheduled appointment times were 30.1 ± 16.6 and 20 mins. The actual in-department time had a range of 18-245 mins. The median actual in-department time was significantly different from the median scheduled appointment time (P = 2.2e-16). The difference between the two was 40.0 mins. CONCLUSION Our findings demonstrate that the level of bladder filling affected the number of CBCT scans, number of retries, and ultimately the total in-department time. There was sufficient clinical evident to support the use of an alternative imaging technique, such as bladder ultrasound, to reduce the number of repeat CBCT scans and improve the overall treatment efficiency of prostate cancer.