A Dosimetric Comparison of Stereotactic Body Radiation Therapy Delivery Techniques for Lung Cancer: Adaptive Versus Conventional
C Ding*, A Godley, K Westover, R Timmerman, J Park, The University of Texas Southwestern Medical Ctr, Indianapolis, IN
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PO-GePV-M-89 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: To compare dosimetric effect of stereotactic body radiation therapy (SBRT) using adaptive and conventional techniques on the Ethos system.
Methods: A comparison for a stage T3N0 lung cancer patient is presented. This patient was originally treated on a linac using SBRT with a prescription dose of 50Gy in 5 fractions covering at least 95% of PTV. Cone beam CT (CBCT) was performed to setup the patient each fraction. Retrospectively, an SBRT plan with the same dose prescription and similar target and normal tissue constrains was generated using the Ethos planning system (Varian, Palo Alto). Simulated dose deliveries were performed using the Ethos emulator based on the CBCTs of each clinical treatment. Two treatment delivery schemes were compared, Conventional: five regular treatments using the initial plan, Adaptive: five treatments adapted by Ethos to match the target on the clinical CBCTs. Delivered dose was deformed back to the planning CT to compare the distributions on target and normal tissue for these two schemes.
Results: The PTV volume and shape changed during the 5 fractions SBRT treatment process. The volume started at 120.3cm³, which is close to the planning CT volume of 121.4cm³, then increased to 134.9cm³ at the second fraction, and dropped to 84.8cm³ at the fifth fraction. The delivered PTV coverage of prescription dose is 92.9% for adaptive delivery and 88.1% for conventional delivery. The lung receiving 12.5Gy or more is 121cm³ for both delivery schemes. The maximum dose to heart is 54.4Gy and 55.5Gy for adaptive and conventional delivery scheme respectively.
Conclusion: The adaptive dose delivery managed to maintain planning target coverage, while keeping equivalent normal tissue sparing to the conventional dose delivery.
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