Evaluation Of Intra-Fraction Motion Of Prostate Gland During Moderately Hypofractionated External Beam Radiotherapy Using Four Dimensional Trans Perineal Ultrasound (TPUS)

Abstract

The purpose of the study is to monitor the intra fraction movements of prostate during hypo fractionated EBRT in real time using noninvasive 4D trans perineal ultra sound (Elekta clarity TPUS auto scan system). A total of 1986 trans perineal ultrasound sound (TPUS) monitorings were studied. We analyzed TPUS monitoring data of 100 treatment sessions from five of our patients treated with 60Gy/20 fractions over four weeks. Planning CT scan and reference TPUS was acquired in same position. Bladder and rectal protocols were reproduced in all treatment sessions. Treatment was delivered with VMAT technique under TPUS guidance with Gating. During treatment continuous monitoring of prostate motion is done with TPUS in three direction Superior- Inferior (SI), Right-Left (RL), Anterior-Posterior (AP). The treatment time for each session ranged from 220 to 660 seconds. The prostate displacement in every 20 second interval was taken for evaluation in this study. The mean, median, maximum displacements in each direction were calculated. Percentage of time the prostate moved within 1mm, 3mm, 6mm, 10mm, >10mm and percentage of time prostate moved in SI, RL, AP direction were assessed for each patient. The treatment was automatically stopped (gating) if the displacement of prostate is more than 3mm for more than 3 seconds. The mean prostate displacement of (1.14±0.80) mm, (-1.77±2.57) mm, (-1.96±1.46) mm were observed in SI, RL, AP directions. The prostate moved within 3mm in 88.58%, 90.16% ,75.76% and within 6 mm in 98.94%, 97.24%, 92.96% of treatment time in SI, RL, AP directions respectively. Prostate displacement was noted in inferior: superior (86%:13.9%); right: left (47.02%:52.98%); anterior: posterior (11.64%:88.36%) directions respectively. The maximum duration of prostate displacement was seen in posterior and inferior direction. Maximum displacement up to 13.65 mm was detected. Deviations more than 10mm in SI, RL, AP directions were 0%, 0.2% and 3.5% respectively. Maximum displacement was seen in AP direction. Maximum duration of prostate displacement was seen in inferior and superior direction. Real time monitoring of prostate motion during treatment is warranted during hypo fractionated radiotherapy while using tight margins.