Room: Karl Dean Ballroom C
Purpose: Locally-advanced non-small cell lung cancer (LA-NSCLC) patients are treated with chemoradiotherapy (CRT); however, approximately 15-20% of these patients develop significant morbidity with radiation pneumonitis (RP). Currently, the most acceptable dosimetric predictors assume homogenous underlying lung function. This study correlates the radiation dose in high-ventilation portions of the lung with RP outcome for patients treated with proton (PR) and photon (PH) radiotherapy.
Methods: This was a case-control retrospective study. 48 patients (24 proton, 24 photon) with LA-NSCLC treated with concurrent CRT were identified, of whom 24 exhibited RP (graded using CTCAE v4.0) after proton or photon radiotherapy, and 24 were negative controls (matched based on age, smoking, tumor location, total dose and modality). The inhale and exhale simulation CT scans were deformed using clinically validated Advanced Normalization Tools. The 3D lung ventilation maps were derived from the deformation matrix and partitioned into low, medium and high ventilation zones for dosimetric analysis. A two-tailed studentâ€™s t-test was used to correlate dose in each ventilation zone with risk of RP.
Results: In the low-ventilation portion of the lung, similar dose distribution was observed for V20áµ¥ (ventilation volume receiving â‰¥ 20Gy) for both treatment modalities between the RP (PH:11.4Â±1.9%, PR:9.9Â±2.8%) and non-RP (PH:11.0Â±3.6%, PR:9.1Â±1.9%) groups (PH:p=0.759, PR:p=0.461). V5áµ¥ was also not significantly different. However, in the high-ventilation portions, the RP group had significantly higher V20áµ¥ (PH:11.6Â±2.6% vs. 7.6Â±3.6%, p=0.006, PR:10.5Â±2.1% vs. 6.9Â±3.7%, p=0.007) and V5áµ¥ (PH:19.1Â±3.0% vs. 14.5Â±5.2%, p=0.016, PR:13.0Â±1.9% vs. 8.7Â±4.1%, p=0.004). Furthermore, the mean dose in the high-ventilation portions for RP patients was significantly higher than that of the non-RP patients (PH:p=0.004, PR:p=0.011), while the low-ventilation portions didnâ€™t show differentiation.
Conclusion: Our data supports findings that dose to the high-ventilated lung might serve as a predictor of RP and is the first study to demonstrate this in patients treated with protons.