15 patients over 122 fractions undergoing radiotherapy to thoracic (10) and abdominopelvic (5) regions on True Beam STx 2.0 lineal accel- erator with 6D couch ...
E702
International Journal of Radiation Oncology Biology Physics
between PBM discrepancy and tidal volume has an R2 value of 0.51 over the patient pool. Conclusion: 4DCT imaging was found to be capable of measuring changes in pulmonary perfusion due to respiration. A difference in PBM with respiration was found in all cases; we’ve found that the PBM increased with inhalation, and decreased with exhalation. There was a correlation between PBM loss and tidal volume found. The 4DCT derived respiratory induced PBM signal will provide a new window to investigate pulmonary circulation in health and diseases (e.g. pulmonary emboli). Author Disclosure: N.k. Myziuk: None. T.M. Guerrero: None. E. Castillo: None. D. Solis: None. J. Zhang: None. G. Sakthivel: None. R. Guerra: None.
Conclusion: Set up errors documented by OSMS and CBCT positively correlate. OSMS has an added advantage of documenting intrafraction motion. Author Disclosure: A. Nachankar: None. R. Patil: None. P. Dandekar: None. V. Mhatre: None. P.T. Patwe: None.
3671 Set-Up Errors Detected By 3D Optical Surface Monitoring System Positively Correlate with Cone Beam CT Values. A. Nachankar,1 R. Patil,1 P. Dandekar,2 V. Mhatre,1 and P.T. Patwe3; 1Sir H N Reliance Foundation Hospital, MUMBAI, India, 2Sir H N Reliance Foundation Hospital, Mumbai, India, 3Sir HN Reliance Foundation Hospital & RC, Mumbai, India Purpose/Objective(s): Image guidance is recommended for accurate positioning in high precision radiotherapy delivery and also to account for organ motion. Most image guidance tools available use ionizing radiation for imaging. Few newer tools can track organ motion in real time which involve implantation of fiducials. Three dimensional optical surface monitoring system (OSMS) uses optically visible light to track patient surface. The reflecting light from patient’s body surface is captured by 3 cameras to continuously monitor patient movement during treatment. We compared data of OSMS with on board cone beam CT (CBCT) for setup accuracy and documented intrafraction set up errors. Materials/Methods: We retrospectively analyzed patient positioning of 15 patients over 122 fractions undergoing radiotherapy to thoracic (10) and abdominopelvic (5) regions on True Beam STx 2.0 lineal accelerator with 6D couch. Patient was aligned to the isocenter with lasers based on skin reference tattoos marked at simulation. Set up errors were calculated by OSMS prior to acquiring CBCT by comparing surface data to planning CT scan. All the patients underwent CBCT based soft tissue matching for correction of set up errors. OSMS continuously monitored intrafraction motion and threshold for beam holding for translational motion was 5 mm and rotational motion was 3 degrees. Results: For thoracic sites, translational errors documented by CBCT vs OSMS (pre-correction) were comparable, (5 2mm vs 4 mm in vertical, 3.2 2 vs 3.1 4 longitudinal, 4.42.8 vs 3.4 3 lateral, respectively). Rotational errors for thoracic sites documented by CBCT vs surface imaging (pre-correction) were (0.9 0.8 degree vs 0.8 0.7 degree pitch, 0.8 0.7 vs 1 0.7 roll, 0.8 0.8 vs 1.1 0.8 rotation, respectively). For abdominopelvic sites, translational errors documented by CBCT vs OSMS were comparable (3.1 2.5 mm vs 3.52.5 mm vert, 2.1 1.6 vs 3 3.5 long, and 3.8 3.2 vs 3.7 3 lat, respectively). Rotational errors for abdominopelvic sites documented by CBCT vs OSMS (pre-correction) were (0.6 0.68 degree vs 2.2 2 degree pitch, 0.6 0.5 vs 0.9 0.6 roll, 0.5 0.5 vs 1.25 1.43 rotation, respectively). We calculated Pearson’s correlation coefficient for set up errors documented by OSMS and CBCT. For thoracic sites Pearson’s correlation coeficient was (r Z 0.6) in vert, (rZ0.64) in lat, (r Z 0.4) in long, (rZ 0.05) in rotation, (rZ 0.5) in pitch and (r Z 0.4) in roll. For abdominopelvic sites Pearson’s correlation coeficient was (r Z 0.3) in vert, (r Z 0.02) in long, (rZ0.8) in lat, (rZ -0.1) in pitch, (r Z 0.5) in roll and (rZ 0.6) in rotation. Overall, Pearson’s correlation coefficient showed positive correlation between OSMS and CBCT values (0
