Evaluate Daily Bladder Dose Volume Histograms In Prostate Cancer Patients

Objective:To analyze the impact of the bladder filling states on the radiation dose received by bladder itself in image guided radiation therapy(IGRT)for prostate cancer.Methods:This paper studied 9 cases of prostate cancer patients who received IGRT in the radiotherapy department of Henan Province People's Hospital from August 2017 to May 2018.Before radiotherapy treatment every day,cone-beam computed tomography(CBCT)scans were performed to all the 9 patients.A total of 257 images were collected and sent back to the Pinnacle planning system of Philips Corporation.The same radiotherapist delineated the contours of treatment target area and surrounding organs at risk on basis of images collected,adopted original radiotherapy plan and make recalculations.Finally,the dose distribution of the bladder during the actual treatment was obtained.Results:(1)Based on the experimental data,the bladder volumes of 9 patients during treatment for total 257 times averagely decreased by 13% when compared with those volumes indicated on localized CT.(2)The experimental results show that,when the standardized bladder volume(standardized bladder volume=actual bladder volume per day/bladder volume during CT simulation)changed to 0.87±0.22,the standard bladder dose(standard bladder dose=actual bladder dose per day/bladder dose as original treatment plan)would change to 1.01±0.08.The study adopted the linear regression to analyze the correlation between standardized bladder volume and standard bladder dose of 9 patients in 257 times of treatments.The results observed were y=?0.155x+1.136,R2=0.310.Conclusion:(1)The doses to the bladder are influenced by different bladder filling status in IGRT for prostate cancer.(2)According to recommendations from the International Committee on Radiation Units and Measurement(ICRU),the acceptable bladder radiotherapy dose error in clinical trials is 5%.In this linear regression model,when the bladder volume X ranged from 0.55 to 1.2,the bladder dose Y would have a variation from 1.05% to 0.95% compared with the original treatment plan,within the tolerance range of 5%.When the bladder volumes of patients vary within the range of-45% to +20% if compared with those of CT location,the error of bladder dose can be ensured within the allowable range of 5%.