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Accuracy and Precision of Dynamic Tracking Irradiation with VERO-4DRT System

N Hayashi

N Hayashi1*, Y Takada2 , T Mizuno2 , H Nakae2 , T Murai3 , (1) Graduate school of Health Sciences, Fujita Health University, Tayoake, Aichi, (2) Department of Radiology, Ogaki Tokushukai Hospital, Ogaki, Gifu, (3) Department of Radiation Oncology, Nagoya City University, Nagoya, Aichi


SU-F-T-255 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

The VERO-4DRT system is able to provide dynamic tracking irradiation (DTI) for the target with respiratory motion. This technique requires enough commissioning for clinical implementation. The purpose of this study is to make sure the accuracy and precision of DTI using VERO-4DRT through commissioning from fundamental evaluation to end-to-end test.

We evaluated several contents for DTI commissioning: the accuracy of absorption dose at isocenter in DTI, the field size and penumbra of DTI, the accuracy of 4D modeling in DTI. All evaluations were performed by respiratory motion phantom (Quasar phantom). These contents were compared the results between static irradiation and DTI. The shape of radiation field was set to square from 3 cm x 3 cm to 10 cm x 10 cm. The micro 3D chamber and Gafchromic EBT3 film were used for absorbed dose and relative dose distribution measurement, respectively. The sine and irregular shaped waves were used for demonstrative respiratory motion. The visicoil was implanted into the phantom for guidance of respiratory motion. The respiration patterns of frequency and motion amount were set to 10-15 BPM and 1-2 cm, respectively.

As the result of absorbed dose of DTI in comparison with static irradiation, the average dose error at isocenter was 0.5% even though various respiratory patterns were set on. As the result of relative dose distribution, the field size (set it on 50% dose line) was not significantly changed in all respiratory patterns. However, the penumbra was larger in greater respiratory motion (up to 4.1 mm). The 4D modeling coincidence between actual and created waves was within 1%.

The DTI using VERO-4DRT can provide sufficient accuracy and precision in absorbed dose and distribution. However, the patient-specific quantitative internal margin corresponding respiratory motion should be taken into consideration with image guidance.

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