ESTRO 37 Abstract book

S1020

ESTRO 37

MC based log file reconstructions will provide accurate estimates of the actually delivered dose, and by being fed-back to the daily optimisation process, could also allow to compensate for fraction-specific delivery or calculational uncertainties. EP-1882 Volume-based algorithm for optimal lung dose preceding automated planning K.H. Lin 1,2 , C.X. Hsu 1,2 , C.H. Chang 1 , H.J. Tien 1,2 , C.W. Yu 1,2 , P.W. Shueng 1,3 , T.H. Wu 2 1 Far Eastern Memorial Hospital, Radiation Oncology, New Taipei City, Taiwan 2 National Yang-Ming University, Department of Biomedical Imaging and Radiological Sciences, Taipei, Taiwan 3 National Yang-Ming University, Department of Medicine- School of Medicine, Taipei, Taiwan Purpose or Objective To prevent potential complications such as radiation pneumonitis and radiation pericarditis in the radiotherapy, the surrounding normal organs must be considered in the well-designed treatment planning. The radiotherapy treatment planning(RTP) can vary in quality due to the experience of the medical physicists and institutional-protocols. It is time-consuming to decide the parameter of optimization. In this study, we aim to create a volume-based algorithm that can provide the gantry rotating angle before the automated planning and rapidly reduce the lung dose. Material and Methods An anthropomorphic phantom study was simulated in RTP. A planning target volume (PTV)(50 Gy in 25 fractions) was contoured with 17 cm in length, 7.08 cm in width. We set several partial arc angles and its related restricted angles in the RTP. The restricted angle in lung could further form a restricted volume to spare the primary beam (Figure 1A). 15 RTP were performed using different restricted angles (from 0° to 280°, with increment of 20°) and the related arc angles. We developed the volume-based algorithm that could automatically calculate the restrict angle, arc angle, predicted lung V5 and related lung dose. The dosimetric index of PTV, organs at risk (OAR) including lung, heart, spinal cord, dose distribution, and dose-volume histogram (DVH) from volumetric modulated arc therapy (VMAT) and Tomotherapy were analyzed (Figure 1B-G). Accuracy of predicted lung V5 and actual lung V5 was assessed.

Results 45 RTP included Tomotherapy (n=15), VMAT with 20 iterations (n=15), VMAT with 40 iterations (n=15). The results showed that the increasing of restricted angle would significantly reduce the mean lung dose and slightly decrease mean heart dose. The arc angle, restricted angle, and restricted volume showed strong correlation with mean lung dose (r = - 0.998) and lung V5 (r = - 0.993). R2 value between actual lung V5 and predicted lung V5 was 0.97 (Figure 2). The predicted lung V5 using volume-based algorithm was successfully achieved within 20 iterations by 5 mins during the automated planning.

Conclusion The volume-based algorithm preceding automated planning successfully provides the optimal arc angle and reduces lung dose. The predicted lung V5 can be achieved rapidly and accurately. We will further validate this volume-based algorithm in all kinds of tumors.