A dosimetric analysis of lung tissue in early stage non-small cell lung cancer patients treated by Cyberknife radiotherapy

Abstract

Objective To analyze the radiation dose to the normal lung tissue of patients with early stage of non-small cell lung cancer treated by Cyberknife. Methods A retrospective analysis was conducted by summarizing the treatment plans of 264 patients with early stage non-small cell lung cancer from January 2011 to December 2013 in Tianjin Medical University Cancer Institute and Hospital. Sorted by the tumor volumes and locations, the Cyberknife plans were evaluated by means of dose volume histograms (DVH), homogeneity indexes (HI), percentage volumes receiving at least x Gy (Vx) of dose, i. e., V5, V10, V20, and V30 of the ipsilateral and contralateral lungs. For the tumors approximate to the hilus, the contralateral lungs were included in the optimization process, and the dose-volume metrics were analyzed for the contralateral and bilateral lungs. Results For the tumors close to the chest wall, V5≥(15.21±3.12)% in ipsilateral lung tissue and V5≥(1.34±0.67)% in contralateral lung tissue were observed. For the tumors near the hilus, V5≥(39.4±11.90) % in ipsilateral lung tissue and V5≥(1.48±0.34) % in contralateral lung tissue were observed. The irradiated volume ratios of both ipsilateral and contralateral lung tissue increased with the enlargement of tumor sizes. After including the contralateral lung tissue into the optimization, the irradiated volume ratios of the contralateral and bilateral lung tissue (V5, V10) decreased significantly(t=2.44, 4.81, 3.53, 3.17, P<0.05). Conclusions Higher risk of radiation injury in both ipsilateral and contralateral lung tissue can be expected for tumors near the hilus than near the chest wall. After including contralateral lung tissue into the planning optimization, lower dose to the contralateral and whole lung tissue was achieved, indicating a better protection of normal lung tissue. Key words: CyberKnife; Non-small cell lung cancer; Treatment plan; Volume percentage; Radiation pneumonitis