Authors: Nguyen Van Nam, Nguyen Van Han, Tran Ba Bach, Doan Trung Hiep.
Research published in: Vietnam Journal of Oncology - No. 5/2019, pp. 235-242.
SUMMARY
Purpose: Evaluation of the impact of bladder volume changes on patient setting errors before radiotherapy for pelvic tumors at Vinmec Times City Hospital.
Subjects and methods: A total of 7 patients with pelvic cancer (low rectal cancer, cervical cancer, ovarian cancer) were assigned to postoperative radiotherapy at Vinmec Times City General Hospital from January 2018 to July 2019. Patients were instructed to prepare their bladders before radiation according to standard guidelines with a drinking volume of 250-400 mL and a bladder filling waiting time of 15- 30 minutes before starting radiation therapy.
To evaluate the pretreatment setting error and the influence of bladder volume changes on the daily setting error, patients were scanned with 2D-kV images daily and 3D-CBCT twice a week to assess the stability and determine the repositioning of the bladder filling position before radiation therapy and to analyze the pelvic setting error related to the change in bladder filling volume.
A total of 187 2D-kV image sequences and 75 3D-CBCT image sequences were acquired and evaluated offline on the software system to determine the setting error and the change in the bladder filling volume of the patients before treatment. Evaluation of patient setting errors on 2D-kV and 3D-CBCT images in 3 directions: AP (anterior-posterior), LR (left-right), and SI (upper-lower). Error data and bladder volume changes were stored on the ARIA system (Varian Medical System, CA, USA). These data were used to evaluate the influence of bladder volume changes on setting errors in LR, SI, and AP directions before treatment.
Results:
The mean pre-treatment setting errors of all patients were: 0.21mm ± 0.63mm (AP), -0.18mm ± 0.65mm (SI), -1.22mm ± 0.83mm (LR), and 0.38mm ± 1.02mm (AP), -1.36mm ± 0.47mm (SI), and -1.61mm ± 0.81mm (LR) for 2D-kV and 3D-CBCT, respectively.
The average bladder filling volume of patients: 269.34 ml ± 105.83 ml compared with CT simulation: 315.84 ml ± 101.85 ml, and the bladder preparation water volume for patients: 285.71 ml ± 58.03 ml; the volume change is 14.72% and 5.72%, respectively.
The allowable tolerance of bladder volume is enough to maintain stability without affecting the determination of patient setting errors in the LR, SI, and AP directions.
Conclusion: The change in bladder filling volume is 14.72% within the standard to ensure the reproducibility and maintenance of bladder volume stability in treatment without affecting daily setting errors. The bladder preparation protocol for patients is 250-350 mL. Pre-radiation patient setup error for pelvic tumors was within acceptable limits.
