Rasoul Shahmohamadi 1, Hadi Taleshi Ahangari 1*, Ali Akhavan 2 1 Department of Medical Physics, Faculty of Medicine, Semnan University of Medical Sciences, Semnan, Iran 2 Department of Medical Physics, Faculty of Medicine, Isfahan University of Medical Sciences , Isfahan , Iran

PO-GePV-P-5 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Respiratory movement of the diaphragm can affect dosimetry. The aim of this study was to calculate dose uncertainty due to respiratory movements in proton therapy of non-small cell lung cancer for tumors located in the anterior wall of the lung.

Methods: For this purpose, the GATE Monte Carlo code and 4D NCAT phantom were employed with a realistic breathing model to simulate the respiratory cycles of a patient to assess the displacement of the tumor. An adult male was modeled via NCAT phantom generator software with a height of 195 cm, a weight of 95 kg, a respiratory rhythm of 15 breathing per minut, heart rate of 60 beats per minute, and the chest diaphragm movement of 2 cm. 10 phantoms with 10 different breathing cycle states in equal time intervals were modeled.. five tumor groups with spherical shape based on NTM groupings as T1a group (d=1cm), T1b group(d=2cm), T2a group(d=4cm); T2b group(d=6cm), and group T3(d=8cm) are created in each phantom (50 different phantom-tumor states in total) in the anterior wall of the lung and are irradiated with pencil beam proton. The uncertainty was calculated by calculating D95 Value changes.

Results: Uncertainty value changes from 19% to 95% percent for different group sizes T1a, T1b, T2a, T2b, T3, respectively. Although the error rate decreases with increasing tumor size, in all groups the error is more than 3% (which is the criterion for the correctness of treatment in radiotherapy).

Conclusion: In all tumor groups, the uncertainty value is more than 3%. Treatment of anterior lung wall tumors with proton therapy is not possible without the use of adjuvant techniques such as IGPT due to its high uncertainty.

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