Dosimetric factors predicting radiation pneumonitis after CyberKnife stereotactic body radiotherapy for peripheral lung cancer

Abstract

Objective:The aims of this study were to investigate the frequency of symptomatic radiation pneumonitis (RP) after CyberKnife lung stereotactic body radiotherapy (SBRT) and to evaluate predictive factors of symptomatic RP.Methods:56 patients with peripheral non-small-cell lung cancer were treated using the CyberKnife® VSI™ System (Accuracy Inc., Sunnyvale, CA) between May 2013 and September 2015. Total radiation doses ranged from 48 to 56 Gy, as delivered in four equal fractions. Symptomatic RP was defined as a grade of ≥2. Predictive factors for symptomatic RP were evaluated using univariate and multivariate analyses.Results:With a median follow-up duration of 12.5 months (range, 3–27 months), symptomatic RP was observed in 6 (10.7%) of the 56 patients. In the univariate analysis, percent vital capacity (p < 0.05), maximum tumour diameter (p < 0.05), gross tumour volume (p < 0.05), planning target volume (p < 0.01), mean lung dose (p < 0.01) and a normal lung volume receiving 5–50 Gy of radiation (V5–50) (p < 0.01) were identified as significant predictive factors for symptomatic RP. In the multivariate analysis, only a V25 >3.4% (p = 0.011) was identified as a significant predictive factor of symptomatic RP.Conclusion:The incidence of symptomatic RP after CyberKnife SBRT was almost identical to the incidences reported in the linear accelerator-based SBRT. A significant association was observed between a V25 >3.4% and the risk of developing symptomatic RP.Advances in knowledge:This is the first report that has investigated prognostic factors for symptomatic RP after CyberKnife SBRT for lung cancer. The newly developed scoring system may help to predict symptomatic RP.

Pretreatment Factors Influencing Radiation Pneumonitis after Stereotactic Body Radiation Therapy in the Treatment of Lung Cancer

“…RP is a relatively common yet troublesome toxicity in patients treated with radiation for lung cancer. The rate of developing symptomatic RP in our study sample was 16%, which is similar to other published rates for patients treated with SBRT [11][12][13][14][15][16]. Our study also identified that SBRT treatment in patients with a history of prior lung-directed therapy and treatment to the right lung, specifically the RLL, are at greater risk of developing symptomatic RP.…”

“…The cause of increased toxicity in treating these patients likely corresponds to the fact that a greater proportion of their remaining viable lung is being treated as compared to patients without lung-directed therapy. A correlation between the ratio of treated lung volume to untreated lung volume and the increased risk of pneumonitis was not directly assessed in our study, but has been reported previously [11,[13][14][15][16][17].…”

“…There has been a number of studies evaluating dosimetric data that correlates with the risk of symptomatic RP. Nakamura et al reviewed data patients treated with Cyberknife-based SBRT for lung cancer [11]. They assessed the dosimetric data of 56 patients to find potential correlations with symptomatic RP.…”

“…Pretreatment patient factors including patient age, cancer location, smoking status, chemotherapy schedule and medical comorbidities have been identified as clinical risk factors for the development of symptomatic RP in patients treated with conventionally fractionated radiation therapy [10]. In patients treated with SBRT, dosimetric factors including gross tumor volume, planning target volume, total volume of lung receiving 5 Gy (TLV5), 20 Gy (TLV20), contralateral V5, and mean lung dose (MLD) were found to be associated with the development of symptomatic RP [6,11]. However, there is limited data evaluating pretreatment, patient-specific factors that influence the development of RP in patients receiving SBRT.…”

Correlation of dosimetric factors with the development of symptomatic radiation pneumonitis in stereotactic body radiotherapy

“…Symptomatic radiation pneumonitis (RP) is a wellknown subacute side effect of SBRT with reported occurrences ranging from approximately 10-20% of patients treated with commonly used fractionation schemes [4][5][6][7]. Symptomatic RP generally occurs within 1 year, typically within 3-6 months, following completion of SBRT, [8][9][10][11]. Although radiation-induced lung toxicities (RILTs) are commonly asymptomatic or manageable, some cases are symptomatic with a risk of mortality [12][13][14].…”