ABSTRACT
Objective:To analyze the clinically acceptable and reproducible bladder and rectum volumes of prostate cancer patients during radiotherapy under bladder and bowel preparation, aiming to provide quantitative indicators for bowel and bladder preparation before and after radiotherapy.Methods:Clinical data of 275 prostate cancer patients with strict bladder and bowel preparation and completion of whole course radical radiotherapy at Sun Yat-sen University Cancer Center from April 2015 to December 2020 were retrospectively analyzed. Patients were scanned with cone beam CT (CBCT) before each treatment and the setup error was recorded. Sixty-six patients were selected by simple random sampling and the bladder and rectum on daily CBCT was outlined using MIM software. The relationship between the ratio of daily bladder or rectum volume to the planned bladder or rectum volume (relative value of volume) and setup error was analyzed. Quantitative data were expressed as mean±SD. Normally distributed data were analyzed by paired t-test while non-normally distributed data were assessed by Kruskal-Wallis test.Results:The bladder and rectum volume on planning CT were (370.87±110.04) ml and (59.94±25.07) ml of 275 patients. The bladder and rectum volumes on planning CT were (357.51±107.38) ml and (65.28±35.37) ml respectively of the 66 selected patients with 1611 sets of CBCT images. And the bladder and rectum volumes on daily CBCT were (258.96±120.23) ml and (59.95 ± 30.40) ml. The bladder volume of patients was decreased by 3.59 ml per day on average during the treatment and 0.37 ml for the rectum volume. According to the bladder volume on planning CT, all patients were divided into three groups: <250 ml, 250-450 ml and >450 ml groups. The relative value of volume in the 250-450 ml group during the course of radiotherapy was the smallest. And the setup error in the superior and inferior (SI) direction was (0.28±0.24) cm and (0.19±0.17) cm in the left and right (LR) direction, significantly lower than those in the other two groups (both P≤0.027). According to the rectum volume on planning CT, all patients were divided into four groups: <50 ml, 50-<80 ml, 80-120 ml and >120 ml groups. The <50 ml group had the smallest relative value of volume during radiotherapy, and the setup error in the SI direction was (0.26±0.22) cm and (0.24±0.22) cm in the anterior and posterior (AP) direction, significantly smaller than those in the other groups (both P≤0.003). The setup errors in the SI, LR, AP directions of the enrolled 66 patients were (0.30±0.25) cm, (0.20±0.18) cm and (0.28±0.27) cm, respectively. Among them, the relative value of bladder volume in the AP direction was (0.73±0.37) in the setup error <0.3 cm group, which was statistically different from those in the setup error 0.3-0.5 cm and >0.5 cm groups (both P<0.05). Conclusion:Under the bladder and bowel preparation before planning CT, the appropriate bladder and rectum volumes are in the range of 250-450 ml and <50 ml, which yields higher reproducibility and smaller setup error.
ABSTRACT
Objective:To provide evidence for the selection of fixation devices and CTV to PTV margins (M ptv) in precision radiotherapy for pelvic tumors by analyzing three fixation devices in precision radiotherapy for prostate cancer. Methods:From April 2015 to December 2020, 133 prostate cancer patients treated with pelvic drainage area irradiation in our center were retrospectively analyzed. The patients were fixed with 1.2m vacuum bag (n=39), 1.8m vacuum bag (n=44) and personalized prone plate by our center (n=50). Each patient was asked to complete our bowel and bladder preparation process before positioning and radiotherapy. The registration of CBCT to planned CT before each treatment adopted the same registration box and algorithm. Setup errors in the SI, LR and AP directions under qualified bowel and bladder conditions were recorded. Setup errors in three directions under three fixation devices and corresponding M ptv values were analyzed. The correlation between setup errors with age and body mass index (BMI) was analyzed. Results:Analysis of 3333 setup errors data showed: in the SI and LR directions, the mean setup errors of 1.2m vacuum bag (3.26mm, 2.34mm) were greater than those of 1.8m vacuum bag (2.51mm, P<0.001; 1.90mm, P<0.001), and personalized prone plate (3.07mm, P=0.066; 2.10 mm, P=0.009). In the AP direction, the mean setup errors of 1.2m vacuum bag (supine)(2.20mm) were smaller than those of 1.8m vacuum bag (3.33mm, P<0.001) and personalized prone plate (3.61mm, P<0.001). The setup errors of 1.8m vacuum bag in all directions were smaller than those of personalized prone plate (P≤0.028). According to Van Herk's expansion formula, the M ptv of 1.2m vacuum bag in three directions was approximately 4 mm. The M ptv of 1.8m vacuum bag and personalized prone plate in the SI and LR directions was approximately 3 mm, and more than 5 mm in the AP direction. The setup errors were not correlated with age or BMI. Conclusions:From the setup errors results of three devices, 1.8m vacuum bag is the best, followed by personalized prone plate. And supine position is better than prone position in the AP direction.