Analysis of dosimetric impact of intrafraction translation and rotation during respiratory‐gated stereotactic body radiotherapy with real‐time tumor monitoring of the lung using a novel six degrees‐of‐freedom robotic moving phantom

Abstract

This study aimed to develop a six degrees-of-freedom (6DoF) robotic moving phantom for evaluating the dosimetric impact of intrafraction rotation during respiratory-gated radiotherapy with real-time tumor monitoring in the lung. Materials and Methods: Fifteen patients who had undergone respiratory-gated stereotactic body radiotherapy (SBRT) with the SyncTraX system for lung tumors were enrolled in this study. A waterequivalent phantom (WEP) was set at the tip of the robotic arm. A log file that recorded the three-dimensional positions of three fiducial markers implanted near the lung tumor was used as the input to the 6DoF robotic moving phantom. Respiratory-gated radiotherapy was performed for the WEP, which was driven using translational and rotational motions of the lung tumor. The accuracy of the 6DoF robotic moving phantom was calculated as the difference between the actual and the measured positions. To evaluate the dosimetric impact of intrafraction rotation, the absolute dose distributions under conditions involving gating and movement were compared with those under static conditions. Results: For the sinusoidal patterns, the mean AE standard deviation (SD) of the root mean square errors (RMSEs) of the translation and rotation positional errors was <0.40 mm and 0.30°, respectively, for all directions. For the respiratory motion patterns of 15 patients, the mean AE SD of the RMSEs of the translation and rotation positional errors was <0.55 mm and 0.85°, respectively, for all directions. The c 3%/2mm values under translation with/without gating were 97.6 AE 2.2%/ 80.9 AE 18.1% and 96.8 AE 2.3%/80.0 AE 17.0% in the coronal and sagittal planes, respectively. Further, the c 3%/2mm values under rotation with/without gating were 91.5 AE 6.5%/72.8 AE 18.6% and 90.3 AE 6.1%/72.9 AE 15.7% in the coronal and sagittal planes, respectively. Conclusions: The developed 6DoF robotic phantom system could determine the translational and rotational motions of lung tumors with high accuracy. Further, respiratory-gating radiotherapy with real-time tumor monitoring using an internal surrogate marker was effective in compensating for the translational motion of lung tumors but not for correcting their rotational motion.

A dose perturbation tool for robotic radiosurgery: Experimental validation and application to liver lesions

“…Several methods have been proposed to evaluate the dosimetric impact of delivery errors. [1][2][3][4][5][6][7][8] Lujan et al 1 proposed a convolution method to estimate the dose delivered to liver lesions subject to intrafractional motion. They convolved planned dose with an organ motion probability distribution function, based on a simple mathematical breathing model, expressed as a function of position rather than a function of time.…”

“…To our knowledge, few studies have quantified the dosimetric effects of target rotations for stereotactic body radiation therapy (SBRT) liver treatments . 4, 5 Shiinoki et al 7 assessed the dosimetric impact of errors in respiratory gated beam delivery with real time motion monitoring of implanted fiducials for lung tumors. They used a high precision robotic arm to translate and rotate the phantom based on the observed motions of patients during conventional gantry mounted linac beam delivery.…”

“…Treatment delivery errors due to target motion and deformation in radiation therapy may result in insufficient dose to targets and excessive dose to organs at risk (OARs). Several methods have been proposed to evaluate the dosimetric impact of delivery errors 1–8 . Lujan et al 1 …”

“…To our knowledge, few studies have quantified the dosimetric effects of target rotations for stereotactic body radiation therapy (SBRT) liver treatments 4,5 . Shiinoki et al 7 . assessed the dosimetric impact of errors in respiratory gated beam delivery with real time motion monitoring of implanted fiducials for lung tumors.…”

“…Several methods have been proposed to evaluate the dosimetric impact of delivery errors. 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 Lujan et al. 1 proposed a convolution method to estimate the dose delivered to liver lesions subject to intrafractional motion.…”