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Impact of the Interplay Effect On 4D Dose Distribution in Respiratory-Gated VMAT-SBRT for Hepatocellular Carcinoma

R Takahashi*, H Tachibana , K Hotta , H Baba , K Motegi , T Akimoto , National Cancer Center Hospital East, Kashiwa


(Tuesday, 7/16/2019) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 3

Purpose: To assess the influence of residual motion in respiratory gated VMAT-SBRT for Hepatocellular carcinoma (HCC) using 4D-dose reconstruction method.

Methods: Three patient plans for HCC were collected, in which VMAT-SBRT with respiratory gating were generated using Eclipse (Varian Medical Systems, Palo Alto, CA). DICOM-RT plan file of the each plan, including gantry angle, MLC position, dose rate, MUs on each control point (CP), was divided into respiratory-phased plan files. Residual motion of the tumor during the gating irradiation were measured using the 4DCT. The gated dose distributions were created as summation of doses for each phase plans. The gated dose distribution was compared with that of the original plan on static CT using dosimetric parameters and dose differences. In addition to it, film measurement in the verification plan was performed using a dynamic phantom operated with sin wave form assuming free-breathing and conventional and 4D reconstructed dose distributions were compared using gamma evaluation.

Results: The residual motions of the patients was 4.0+/-3.9mm, 1.1+/-1.3mm and 1.2+/-1.7mm, respectively. The difference between the original and gated doses was 18% at the maximum in GTV, and 48.4% outside GTV. However, there were no significant difference of the dose indices of GTV D95% and Liver-GTV V10Gy. The reconstructed doses showed better agreement with measurement compared to conventional doses.

Conclusion: Our approach visualizes interplay effect during VMAT delivery without measurement process in plan approval process and clinical impact of dose discrepancies due to the interplay effect could be evaluated in the patient CT images.


Dosimetry, Gating, Respiration


TH- External beam- photons: Quality Assurance - VMAT

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