Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_9_3207 - Effect of Normal Lung Definition on Lung Dosimetry and Clinical Treatment Decision Making in SBRT for Lung Cancer

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Effect of Normal Lung Definition on Lung Dosimetry and Clinical Treatment Decision Making in SBRT for Lung Cancer
R. Liu1,2, L. Y. Mei3, H. Yao4, K. Shiue5, A. Cerra-Franco5, C. He1,2, G. Bartlett4, R. C. Zellars5, T. Lautenschlaeger5, J. Y. Jin5, and F. M. Kong6; 1Department of Thoracic Radiation Oncology, Affiliated Cancer Hospital of Zhengzhou University, Henan Cancer Hospital, zhengzhou, China, 2Department of Radiation Oncology, Simon Cancer Center, Indiana University School of Medicine, indianapolis, IN, 3West China Hospital of Sichuan University, Chengdu, China, 4Department of Radiation Oncology, Simon Cancer Center, Indiana University School of Medicine, indianapolis, IN, China, 5Department of Radiation Oncology, Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN, 6Indiana University Radiation Oncology, Indianapolis, IN

Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) is the treatment of choice for inoperable early stage non-small cell lung cancer (NSCLC). Dose-volume histogram (DVH) parameters such as the lung volume receiving ≥ 5 Gy (V5), 20 Gy (V20) and mean lung dose (MLD) are routinely used to evaluate plan safety. The definition of lung volume varies from treating centers regarding the exclusion of targets. This study aims to compare lung DVH parameters among the various lung volume definitions to evaluate its effect on dosimetric limits which is important for SBRT plan evaluation.

Materials/Methods: total of 194 newly diagnosed NSCLC patients treated with SBRT without prior surgery or prior chest radiation were eligible. The gross tumor volume (GTV) and planning target volume (PTV) were defined by the treating physician and dosimetrist. PTV0.5, PTV1.0, and PTV1.5 were generated using GTV plus a 0.5 cm, 1.0 cm, and 1.5 cm uniform expansion, respectively. Lung DVHs were computed with varying exclusion of these targets. The lung V5, V20 and MLD were compared across these 5 lung volume definitions. The risk of radiation pneumonitis (RP) was assessed through DVH atlas mapping.

Results: There were significant differences in lung dosimetric parameters among the 5 lung definition methods (all p < 0.05). The maximum difference based on these methods in MLD for total lungs (TL) ranged from 1.1 Gy to 2.9 Gy, and for ipsilateral lung (IL) ranged from 1.9 Gy to 5.2 Gy, respectively. The maximum difference in V5 for TL ranged from 1.4% to 4.6%, and for IL ranged from 2.1% to 7.2%, respectively. The maximum difference in V20 for TL ranged from 2.8% to 6.4%, and for IL ranged from 3.2% to 11.9%, respectively. There was an increasing trend in the differences of MLD or V5 of all 5 lung definitions as GTV/TL volume ratio increased. V5s of IL of all methods were correlated with each other and significantly correlated with RP (p < 0.05), except when excluding GTV. DVH atlases generated from the 5 different lung definition methods showed that there were differences in risk of RP. Limiting radiation pneumonitis of grade 2 or greater (RP2) to 10%, MLD thresholds would be 7.9, 8.1, 7.6 Gy for TL-GTV, -PTV0.5, and -PTV1.5, respectively, and 11.9, 11.4, 9.3 Gy, for IL-GTV, -PTV0.5, and -PTV1.5, respectively.

Conclusion: Lung volume definition has a significant and clinical meaningful effect on lung dosimetric limits. Clinicians should take the lung volume definition into consideration while assessing DVH parameters for SBRT plan.

Author Disclosure: R. Liu: None. L.Y. Mei: None. A. Cerra-Franco: None. C. He: None. G. Bartlett: None. R. Zellars: Board Member; Indiana University Health Physicians. T. Lautenschlaeger: None. J. Jin: Employee; Indiana University Health. Research Grant; Varian medical system, Xstrahl Inc. Honoraria; Varian medical system. Board memebr; SANTRO. F.(. Kong: Research Grant; Varian, NCI/NIH. Founding President and Board of Director; Sino-American Network for Therapeutic Radiation On. President 2015; American Association of Women Radiologists (AAWR). President 2012-2013; Association for Chinese Professors. Founding Board Member; Sino-American Network for Therapeutic Radiology.

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