Abstract
Objective To observe the motions of the rectum and bladder by image-guided radiotherapy (IGRT) and to analyze their impact on treatment. Methods Eighteen patients with prostate cancer undergoing intensity-modulated radiotherapy (IMRT) were enrolled in the study and 247 cone-beam computed tomography (CBCT) images were obtained from this study. The clinical target volume, bladder, and rectum were contoured on all simulated CT and CBCT to examine their volume and position changes. The dose distributions were recalculated based on the data of the x-, y-, and z-axis setup errors. The doses to planning target volume (PTV) and organs at risk were calculated in the replanning, and their impact on treatment was analyzed. Comparison of the planning and replanning results was made by paired t-test. The effects of displacements and volumes of the bladder and rectum on target doses were analyzed by Pearson correlation method. Results Great changes in the volumes of the bladder and rectum were observed during the treatment. For the planning and replanning results, PTVD95% was 7777.37 cGy vs. 7628.56 cGy (P=0.027), PTVDmin was 87.91 cGy vs. 83.35 cGy (P=0.000), and RVP was 5.89% vs. 8.31%(P=0.000). There were correlations between PTVD95% and the motions of the bladder and rectum, with correlation coefficients of 0.296 and 0.177, respectively. The correlation coefficient between rectal volume and PTVD95% was 0.115, indicating a certain correlation. There is a certain correlation between and PTVDmin and bladder volume, with a correlation coefficient of-0.128. Conclusions The recovery of the state during localization for the bladder and rectum, especially the latter, has great significance to ensure the target dose and reduce exposure of the rectum in the IMRT for prostate cancer. Key words: Prostate neoplasms/intensity modulated radiotherapy; Image-guided radiotherapy; Alignment; Dosemetry
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