Program Information
Dosimetric Verification of Photon Robust Plan with Intra-Fraction Organ Motion
C Liu*, K Xie , D Pearson , N Sperling , E Parsai , University of Toledo Medical Center, Toledo, OH
Presentations
SU-I-GPD-T-245 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: For lung cancer patient, robust planning utilizes minimax optimization that considers moving uncertainties when optimizing the beams. For patient with intra-fraction organ motion, it has been a concern that the actual dose distribution is hard to measure because the target and surrounding tissue is moving while the QA device is static. We used an in-house made dynamic QA device to measure the “actual” robust plan dose and applied it on patient geometry.
Methods: A left lower lobe lung cancer patient previously treated with conventional ITV technique was selected and the patient was re-planed utilizes robust technique. An in-house made dynamic QA device has been used to measure the dose when motion occurs. Both plans have been delivered to the dynamic QA device. The measured data was re-calculated on patient geometry utilizing 3DVH software.
Results: For ITV based plan, the measured lung V20Gy is 6.14% higher than expected and the measured maximum dose is 9.2% lower than expected. For robust plan, the measured lung V20Gy is 4.13% higher than expected and the measured maximum dose is 0.3% lower than expected. From 3DVH estimated dose on patient geometry, we can see more dose has been delivered to surrounding tissue especially on the path of the intra-fraction organ motion.
Conclusion: Based on the evaluation we performed, we can see more dose on the traditional ITV plan in the surrounding tissue, especially on the path of the intra-fraction organ motion. This “blurring” is because the target is moving with respiration while the beam is static. When intra-fraction organ motion occurs, the ITV based plan gives the surrounding tissue more dose and less dose in internal target volume (ITV), the robust plan also delivered more dose to the surrounding tissue but it’s more constant with plan dose.
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