S. Sudo Sr, N. Kita, N. Tomita, T. Takaoka, M. Ukai, D. Okazaki, M. Niwa, A. Torii, S. Takano, M. Oguri, A. Matsuura, and A. Hiwatashi; Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan
Purpose/Objective(s): In the treatment of non-small cell lung cancers, there is an increasing demand for less invasive stereotactic body radiotherapy (SBRT) compared to surgery. Local recurrence (LR) significantly impacts prognosis, and factors such as histological type and tumor size have been considered as LR risks. In this study, we retrospectively examined LR risks from the perspective of dose coverage to the target. Materials/
Methods: Patients with clinical stage IA1-IIA squamous cell carcinoma (SCC) or adenocarcinoma (ADC), who were treated with SBRT, were included in the analysis. Doses of 44–52 Gy were prescribed to the isocenter of planning target volume (PTV) according to the respective tumor diameters. The primary endpoint was LR. Age, sex, performance status, smoking, forced expiratory volume 1L, tumor diameter, biologically effective doses (BED) in a/ß = 10 were evaluated for the clinical factors. As for dose parameters, mean, minimum, and maximum doses, D99, D98, D95, D90, D80, D50, and homogeneity index (HI) of the gross tumor volume (GTV), internal target volume (ITV), and PTV were evaluated. To evaluate the relationship between risk factors and LR, the univariate analyses were performed with the Gray test for clinical factors and with the Fine-Gray model for dose parameters. The multivariate analysis was conducted using the Fine-Gray model. Results: Among the 198 patients analyzed, median age was 77 years. Of these, 63 and 135 patients were in the SCC and ADC groups, respectively. Mean, minimum, and maximum doses, D99, D98, D95, D90, D80, D50, and HI were 99.8, 95.4, 102.6, 96.5, 96.9 97.4, 98.1, 98.7, 99.9, and 1.1 in GTV, 99.5, 92.6, 102.9, 95.0, 95.6, 96.3, 97.1, 98.1, 99.6, and 1.1 in ITV, and 98.5, 83.5, 102.9, 89.6, 90.9, 93.0, 94.8, 96.4, 98.9, and 1.2 in PTV, respectively. The median follow-up period was 48.5 months. The 3-year LR rates of all patients, SCC and ADC groups were 13.4%, 23.0%, and 9.3%, respectively. In the univariate analysis of clinical factors, tumor diameter, BED, histological type were associated with LR in all patients (p = 0.023, 0.025, and 0.013, respectively). No factor was associated with LR in the ADC group, while BED was associated with LR in the SCC group (p = 0.034). In the univariate analysis of dose parameters, no factor was associated with LR in all patients and the SCC group, while only HI of GTV was associated with LR in the ADC group (p = 0.027). In the multivariate analysis, no factor was associated with LR in all patients. ITV mean, ITV D90, ITV D80, ITV D50, and PTV D50 were associated with LR in the SCC group (p = 0.011, 0.044, 0.031, 0.013, and 0.037, respectively), while GTV minimum and GTV HI were associated with LR in the ADC group (p = 0.029 and 0.015, respectively). Conclusion: In the SCC group, the coverage of PTV D50 and several parameters of ITV showed a significant correlation with LR after SBRT. The coverage of ITV is considered particularly crucial in SBRT for SCC tumors.
