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Impact of 4D-CT Ventilation Image-Based Proton Radiotherapy for Stereotactic Body Radiotherapy

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Y Ieko

Y Ieko1*, N Kadoya1 , T Kanai1,2 , Y Nakajima1,3 , K Arai1,4 , T Kato4 , K Ito1 , Y Miyasaka1 , K Takeda1 , K Jingu1 , (1) Tohoku University Graduate School of Medicine, Sendai, Japan, (2) Yamagata University Faculty of Medicine, Yamagata, Japan, (3) Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo, Japan, (4) Southern Tohoku Proton Therapy Center, Koriyama, Japan


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

Purpose: The purpose of this study was to clarify the impact of 4D-CT ventilation image-based functional treatment planning with passive scattering proton therapy (PSPT) for SBRT compared with 3D-CRT and VMAT using photon beams.

Methods: Ten early-stage lung cancer patients with a peripheral tumor (tumor size < 5 cm) were studied. 4D-CT ventilation was calculated using the patient’s 4D-CT data, deformable image registration and a density-change-based algorithm. For each patient, three functional plans were generated using non-coplanar 3D-CRT with 6-8 beams, VMAT with two coplanar full arcs and PSPT with 2-4 coplanar beams. The prescribed dose and dose constraint were based on RTOG0618 (60Gy(E) /3fr). Dose constraints for the functional lung were applied for high-functional lung regions (>20th percentile). To analyze the irradiated dose to the functional lung, we calculated dose functional histogram-based dosimetric parameters for the functional lung (fMLD, fV5, fV10 and fV20). fMLD, fV5, fV10 and fV20 were defined as the percentage of the total ventilation contained within the volume receiving ≥5 Gy, 10 Gy and 20 Gy, respectively.

Results: For the functional 3D-CRT, VMAT and PSPT, fV5 was 26.8%, 24.7% and 11.9%, fV10 was 15.4%, 12.8% and 10.0%, fV20 was 6.6%, 6.9% and 7.4%, and fMLD were 5.3 Gy, 5.1 Gy and 3.8 Gy, respectively. All DVH parameters of each functional plan met the dose constraints of RTOG 0618. The results showed that PSPT led to significant reductions in fV5, fV10 and fMLD, though there was no significant reduction in fV20.

Conclusion: Because of the physical characteristics of the Bragg peak, PSPT reduced the high-functional lung regions, especially for regions with a moderate or low dose, compared with 3D-CRT and VMAT, indicating that 4D-CT ventilation image-based PSPT may have lower lung toxicity.

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