Abstract Book

S1019

ESTRO 37

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.

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.

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. EP-1883 Class-solution for Pinnacle Autoplan using dual arc VMAT for head and neck cancer J. Van Santvoort 1 , D. Reijtenbagh 1 , H. Rozema 2 , M. Van Dalum 2 , R. Gangabisoensingh 2 , M. De Goede 1 , R. Wiggenraad 2 , M. Mast 2 1 Haaglanden Medical Centre, Medical Physics, Leidschendam, The Netherlands 2 Haaglanden Medical Centre, Radiotherapy, Leidschendam, The Netherlands Purpose or Objective Automated planning (Autoplan) can play a significant role to improve efficiency and plan quality and consistency, but a class-solution is important for successful implementation. High target coverage and adequate Organ At Risk (OAR) sparing must be achieved, each with the right priorities, making fine tuning afterwards unnecessary. Pinnacle Autoplan was used during the introduction of Volumetric Arc Therapy (VMAT) for head and neck (H&N) cancer patients in our clinic. We developed a class- solution to create dual arc VMAT plans with a Simultaneously Integrated Boost (SIB) technique that, without fine tuning, had similar or better target coverage and OAR sparing compared to the clinically used Intensity Modulated Radiotherapy (IMRT) plans. Material and Methods An Autoplan treatment technique was designed, based on the clinical protocol. For patients with malignancies on both sides a dual arc of 178-182 degrees was selected. For patients with a tumour on one side a 350-150 or 220- 10 degree dual arc was used, depending on the location of the tumour. Treatment goals were added to improve plan quality. The radiation oncologists approved the developed treatment plans, based on coverage, conformality, OAR sparing and overall quality. Finally,