Abstract
BackgroundThe aim of this study was to analyze the influence of volumetric changes of bladder and rectum filling on the 3D dose distribution in prostate cancer radiotherapy.MethodsA total of 314 cone-beam CT (CBCT) image data sets from 19 patients were enrolled in this study. For each CBCT, the bladder and rectum were contoured and volume sizes were normalized to those on their original CT. The daily delivered dose was recalculated on the CBCT images and the doses to bladder and rectum were investigated. Linear regression analysis was performed to identify the mean dose change of the volume change using SPSS 19.ResultsThe data show that the variances of the normalized volume of the bladder and the rectum are 0.13–0.58 and 0.12–0.50 respectively. The variances of V70Gy, V60Gy, V50Gy, V40Gy and V30Gy of bladder are bigger than those of rectum for 17 patients. The linear regression analysis indicates a 10 % increase in bladder volume will cause a 5.6 % (±4.9 %) reduction in mean dose (p <0.05).ConclusionsThe bladder’s volume change is more significant than that of the rectum for the prostate cancer patient. The rectum volume variations are not significant except for air bubbles, which change the shape and the position of the rectum. The bladder volume variations may cause dose changes proportionately. Monitoring the bladder’s volume before fractional treatment delivery will be crucial for accurate dose delivery.
Highlights
The aim of this study was to analyze the influence of volumetric changes of bladder and rectum filling on the 3D dose distribution in prostate cancer radiotherapy
Most radiotherapy patients with prostate cancer are treated with intensity modulated radiotherapy (IMRT)
Volumetric modulated arc therapy (VMAT) helps to get highly conformal dose distributions for the planning target volume (PTV) while minimizing the dose given to the organs at risk and with short delivery time
Summary
The aim of this study was to analyze the influence of volumetric changes of bladder and rectum filling on the 3D dose distribution in prostate cancer radiotherapy. Most radiotherapy patients with prostate cancer are treated with intensity modulated radiotherapy (IMRT). Volumetric modulated arc therapy (VMAT) helps to get highly conformal dose distributions for the planning target volume (PTV) while minimizing the dose given to the organs at risk and with short delivery time. Treatment uncertainties include daily patient setup errors and internal organ motion and deformation. Studies on prostate motion have shown that both the position and Currently, CBCT is a popular imaging method that provides valuable 3D information of the patient in treatment position [6,7,8]. Hu et al showed the feasibility of using a region-of-interest (ROI) mapping method for accurate CBCT-based dose calculation [10]
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