To quantify the effect of interfractional movements of the prostate, seminal vesicles (SVs) and rectum on prostate proton treatment using full sets of in-room CT images.
We analyzed 1483 sets of daily CT images acquired throughout the proton therapy treatment for 40 patients with four times higher statistics than the one of our published results . We evaluated daily movements of pelvic anatomies by simulating image-matching strategies, and estimated means, systematic and random errors of each anatomies. The change of the mean and errors were also studied by referring daily CT-images as a reference to evaluate the optimum period of re-acquiring the CT-images for re-planning.
The data confirmed our previous results and the prostate-rectum matching showed the smaller errors. The mean and systematic errors of the anterior and posterior sides of SVs decreased, when the daily CT-images acquired around 10 days after the first irradiation were used as a reference in comparison to the simulator CT-images, as did the rectum’s anterior region. Figure 1 shows the mean and errors of the rectal daily movement over the superior-inferior (SI) position by referring sequential daily CT-images for each image matching method. The positive mean values around SVs region, which means the movement toward the anterior side, decreased gradually as the reference CT number increases.
The re-planning with the reference CT after 10 days might reduce the rectal dose around SV region. The effect of daily movement on proton dose will be presented based on several planning scenarios.
Y.Maeda,et al. Medical Physics,45(5),1844(2018).