Evaluation of How Daily Variation of Organs at Risk Changes Organ Doses and Immune Suppression From the Treatment Plan During SBRT Treatment to Lung
B Walker1*, C Nguyen2,P Read3, T Showalter4, J Larner5, K Wijesooriya6, (1) University of Virginia, Charlottesville, VA, (2) University of Virginia, Charlottesville, VA, (3) University Of Virginia, Dept. Radiation Oncology, ,,(4) University Of Virginia Health Systems, ,,(5) University of Virginia Health Systems, Charlottesville, VA
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PO-GePV-M-137 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Treatment related immune suppression (TRIS) is associated with decreased overall survival for a range of solid tumors including lung cancer. Currently there is no computational model or data available to predict dose differences for organs at risk (OAR) or immune cell kill changes due to daily variations of OAR’s during treatment. We evaluated the variation of dosimetric criteria for all blood rich OARs such as the heart, aorta, vena cava, pulmonary artery, and lymphoid OARs such as thoracic spine, and lymph nodes in the thorax with daily alignment of the tumor and how it leads to changes in immune suppression during lung SBRT treatments.
Methods: We have analyzed a set of 42 IGRT data sets for 7 early stage lung cancer patients who received five treatment fractions via SBRT under an IRB prospective clinical trial. For each fraction, dose reconstruction was performed based on OAR location with respect to the tumor in the pre-treatment CBCT. Dose delivered to OARs was computed utilizing rigid registration of all 5 CBCTs with six degrees of freedom of the tumor. Accordingly, organ structures were propagated with respect to the ITV using Velocity(Varian). These shifted organ structures were fed into an in-house python algorithm to evaluate the changes in immune cell kill and compared to measurement.
Results: Mean and standard deviations of the dosimetric changes of example organs are: aorta( max(0.2±1.0Gy), V10.0(0.7±1.8cc), V15(-0.1±0.5cc), and V20(0.0±0.1cc)), thoracic spine( max(-0.7±1.4Gy), V10.0(0.4±1.7cc), V15(1.2±2.3cc), and V20(0.6±1.7cc)), and thoracic lymph nodes (max(0.8±2.2Gy), V10.0(0.2±2.9cc), V15(-0.6±1.8cc), and V20(-0.3±0.9cc)). Mean and standard deviations of the differences of the immune cell kill are delivered(-0.04±0.25 x10^9 cells/L).
Conclusion: During lung SBRT treatments, when aligning to the tumor in 6D leads to reasonable shifting of the blood rich and immune rich organs, while overall immune cell kill is robust to these changes.
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