Room: Exhibit Hall
Purpose: This study was to investigate the prostate motion model and dose variation during radiotherapy using a 4D transperineal ultrasound system (4D-TPUS).
Methods: From July 2014 through December 2017, 131 prostate cancer patients were enrolled. During treatment delivering, 4D-TPUS were used to collect data of prostate's real-time motion . Then, the real delivered doses were calculated according to the real-time motion data and the leaf sequences/MUs. The delivered doses were compared with the planned doses by using the clinical acceptance criteria.
Results: A total of 3387 fractions were evaluated. The mean (Â±SD) of the infraction displacements were [mm]: SI: (0.03 Â± 0.92); LR: (0.12 Â± 1.03); and AP: (-0.01 Â± 1.37), respectively. There were 41, 29, and 66 fractions with deviation exceeded 3 mm in the SI, LR, and AP directions, respectively. The AP direction has the largest extent of prostate displacement. We classified our patients into three groups according to the motion model: stable (n=78), irregular (n=13) and intention (n=40). The intention group was defined as persistent deviation to the same direction (the maximal displacement should exceed 3 mm) that repeated in at least 50% fractions. All these patients had obviously anxiety and urinary frequency and urgency. Delivered doses showed that all the 4 patients in the intention group did not meet our clinical requirements.
Conclusion: The present study demonstrated that for over 90% of fractions, a CTV-PTV margin of 3 mm would be good coverage with the planned prescribed dose. However, it is important to identify the patients belonging to the intention group. Pre-treatment with anti-anxiety drugs and Î± receptor blocker may be useful in relief the prostate motion.