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Dosimetric Impact of Patients Irregular Breathing Patterns On Dose Distribution for Liver SBRT Patient in Respiratory-Gated Radiotherapy

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T Kurosawa

T Kurosawa1*, H Tachibana2 , S Moriya3 , M Sato1 , (1) Graduate school of Health Science, Komazawa University, Setagaya, Tokyo, (2) National Cancer Center, Kashiwa, chiba, (3) University of Tsukuba, Tsukuba, Ibaraki


MO-RAM-GePD-T-6 (Monday, July 31, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Lounge

Purpose: The dosimetric error in respiratory-gated radiotherapy would increase because of patient’s irregular breathing patterns. The impact of the dose differences between gated and ungated treatment was evaluated for dose distribution of liver SBRT patient with a QA system for respiratory-gated radiotherapy using pulse information from linac.

Methods: In our QA system, which can estimate dose error derived from short beam on time in the gated radiation, the dose estimation models were generated to associate the irradiated dose and the pulse information of irradiation from the linac. To evaluate the accuracy of the estimation for our QA system, respiratory-gated irradiation was performed using five regular respiratory patterns and two irregular patterns. The dose error (Dgate) between gated and non-gated treatment was measured using the 0.6cc Farmer chamber. During the gated irradiation with each respiratory pattern, our system calculated estimation dose error (EDgate) using the estimation model. In addition, the dosimetric impact of dose error in respiratory-gated radiotherapy was evaluated for a liver SBRT patient. At first, the plan including dose error was generated using EDgate that multiplied the MUs of each field and dose calculation was performed. Second, The plan including dose error was compared with the non-gated plan.

Results: The results of the estimation accuracy show good agreement within 1.7%. Compare to non-gated plan, the high dose region in the PTV of the plan was reduced by 2.0%. The PTV D95% was decreased by 2.1%. On the other hand, normal organ doses were similar.

Conclusion: We evaluated the impact of the dosimetric error in respiratory-gated radiotherapy because of patient’s irregular breathing patterns using our QA system. Tumor coverage would be reduced when gated irradiation includes dose error derived from irregular breathing patterns.

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