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Dosimetric Changes During Radiotherapy in Lung Cancer Patients with Atelectasis

C Guy

C Guy1*, E Weiss1, N Jan1, L Reshko1, G Christensen2, G Hugo1, (1) Virginia Commonwealth University, Richmond, VA, (2) University of Iowa, Iowa City, IA


SU-F-J-67 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Large geometric changes which occur during thoracic radiotherapy alter normal anatomy and target position and may induce clinically important dose changes. This study investigates variation of organ-at-risk (OAR) dose caused by atelectasis resolution during radiotherapy.

Methods: 3D IMRT treatment plans were obtained for 14 non-small-cell lung cancer patients. Dose of the clinical plan was recalculated on a baseline scan in which lung was collapsed and on a mid-treatment scan in which lung re-aeration had occurred. The changes in OAR doses were compared between the two time points. RTOG-0617 and in-house dose-volume constraints were chosen for investigation and included spinal cord, esophagus, heart, and healthy lung.

Results: 17 dose metrics were evaluated. The mean (SD) of change in mean lung dose, from baseline to mid-treatment (average taken across all patients), was 0.2 Gy (2.2 Gy) and ranged from -3.2 Gy to 6.0 Gy. 50% of patients experienced relative changes in mean lung dose of greater than 5% of baseline value. The mean (SD) of changes in heart V₄₀, V₄₅, and V₆₀ were 3.2% (3.4%), 3.0% (2.9%), and 1.4% (2.1%), respectively, and were significant for the study cohort (Wilcoxon signed-rank test, p=0.0107 for V₄₀, p=0.0052 for V₄₅, and p= 0.0353 for V₆₀. Ranges in changes of Heart V₄₀, V₄₅, and V₆₀ were -1.9% to 8.6%, -1.7% to 7.5%, and -2.1% to 4.5%, respectively. The mean (SD) of changes in Esophagus PRV Dmean and V₆₀ were 0.3 Gy (3.3 Gy) and 0.8% (7.7%), respectively, and ranged from -4.8 Gy to 6.8 Gy for Dmean and -15.2% to 14.6% for V₆₀.

Conclusion: Patients with atelectasis present at the start of radiotherapy experience significant increases in heart dose. Substantial increases in mean lung dose also occur in a subset of patients.

Funding Support, Disclosures, and Conflict of Interest: This work supported by the National Cancer Institute of National Institutes of Health under Award Number R01CA166119. Disclosures: Phillips Medical systems (Hugo, Weiss), National Institutes of Health (Hugo, Weiss, Christensen), and Roger Koch (Christensen) support, UpToDate (Weiss) royalties, and Varian Medical Systems (Hugo, Weiss) license. No potential conflicts of interest.

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