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Dose Measurements of Modulated Spot-Scanning Particle Beams with Beam-Gating of Respiratory-Phase

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Z Huang

W Hsi , Z Huang*, w wang , Y SHENG , Y Deng , Shanghai Proton and Heavy Ion Center (SPHIC), Shanghai, Shanghai


SU-E-T-281 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

To present dosimetric variations due to target movements with beam-gating windows of various respiratory-phase in homogeneous phantom irradiated by modulated spot-scanning carbon-ions and protons in Siemens IONTRIS system.

For the safety and efficacy of proton therapy to treat three patients with lung cancer during our clinical trial, residual motion was required within 5mm. To study dosimetric variations due to respiratory movement, a target of 4.0cmx4.0cm with 2cm thick was moved with distances of 3.5mm, 4.4mm, 6.0mm, 8.3mm, and 11.0mm with beam-gating windows between various phases of inhalation or exhalation at a sin-wave breathing pattern. The target was irritated at 110mm depth by modulated carbon-ions with focus sizes of 4.1mm to 4.6mm, and a grid size of 1mm between spots. And, by modulated protons with focus sizes of 11.4mm to 13.6mm, and a grid size of 1.9mm between spots. A 4.0cmx4.0cm field size was used for both beams. EBT3 films was placed at the center of target for measurements. Delivery dose was 5.0 Gy with >1.0% uniformity over target. The uniformity and field size of each measured 2D lateral profiles were extracted.

By irradiating films to a doses at linear region of dose response, the uniformity and field size were extracted by measured optical density. The measured deviations from calculated field width and dose increase with increased motion amplitude. Larger non-uniformity was observed for carbon-ion with smaller focus size in comparing with protons. For movements of 4.4mm and 6.0mm, Optical Density uniformity of 3.80% and 5.66%were observed for carbon beam. But, is 3.46% for protons with 11.4mm movement.

Our investigations showed that 5% optical density uniformity for carbon-ions and protons might be acceptable for treatments with 8.3mm movements in homogeneous phantoms. Dose variation introduced in complex anatomy of real patients need further investigation.

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