Potential Benefits of Volumetric Modulated Arc Therapy to Reduce the Incidence of Grade 2 Radiation Pneumonitis in Radiotherapy for Locally Advanced Non-Small Cell Lung Cancer Patients

Abstract

<h3>Purpose/Objective(s)</h3> Although the use of volumetric modulated arc therapy (VMAT) is widespread, there are few reports on the impact of using VMAT on radiation pneumonitis (RP) in radiotherapy for locally advanced non-small cell lung cancer (NSCLC) patients especially for Asians. The administration of durvalumab after radical chemoradiotherapy has been shown to improve the outcome of locally advanced NSCLC; however, it cannot be used when grade 2 or higher radiation pneumonitis occurs. Therefore, it is extremely important to identify the predictive factors of grade 2 RP. The purpose of this study was to identify the factors that caused grade 2 RP and evaluate the impact of using VMAT on the incidence of grade 2 RP in Japanese population whose risk of RP is higher than other areas. <h3>Materials/Methods</h3> We retrospectively evaluated 124 patients who underwent radical radiotherapy for locally advanced NSCLC at our hospital from 2008 to 2019. RP was evaluated using the common terminology criteria for adverse events version 5.0. In order to analyze predictive factors of grade 2 RP, the mean lung dose and V5 Gy–V70 Gy were analyzed as the lung DVH parameters. The other predictive factors for grade 2 RP examined in this study were age, gender, performance status, vital capacity (VC), forced expiratory volume in one second (FEV1.0), lung volume, Brinkman index, presence of interstitial lung disease, presence of pulmonary emphysema, CRP, KL-6, tumor site (upper/middle vs lower lobe), planning target volume (PTV), total dose (≥ 70 Gy vs < 70 Gy). Fisher's exact test and logistic regression analysis was used to compare the incidence of grade 2 RP between the two groups for univariate analysis (UVA) and multivariate analysis (MVA), respectively. <i>P</i> values < 0.05 were considered statistically significant. Predictive performance of the predictor as a continuous variable was evaluated using the area under the receiver operator characteristic (ROC) curve (AUC). <h3>Results</h3> Eighty-four patients underwent 3D-CRT (3D-CRT group), and 40 patients underwent VMAT (VMAT group). Of the 124 cases, grade 2 or higher RP was observed in 51 cases (41.1%). The incidence of grade 2 or higher RP was significantly lower in the VMAT group compared with 3D-CRT group (25.0% vs. 48.8%, <i>P</i> = 0.0185). As for predictive factors of grade 2 RP, all lung DVH parameters were related to grade 2 RP. Among these factors, V30 which had the highest AUC value (0.787) was used as a representative value of lung DVH, and examined together with the other prognostic factors of RP in MVA. Both the UVA and MVA showed that the treatment methods (3D-CRT, <i>P</i> = 0.0097 in MVA), tumor site (lower lobe, <i>P</i> = 0.0011 in MVA), total dose (≥ 70 Gy, <i>P</i> = 0.0008 in MVA), and V_30Gy (≥ 19%, <i>P</i> < 0.0001 in MVA) were associated with grade 2 or higher RP. <h3>Conclusion</h3> We identified the predictive factors for grade 2 or higher RP in radiotherapy for locally advanced NSCLC patients. It was suggested that the use of VMAT could reduce the incidence of grade 2 RP.