Planning target volume D95 and mean dose should be considered for optimal local control for stereotactic ablative radiotherapy

Publication date: Available online 18 March 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Lina Zhao, Shouhao Zhou, Peter Balter, Chan Shen, Daniel R. Gomez, James D. Welsh, Steve H. Lin, Joe Y. Chang
PurposeTo identify the optimal dose parameters predictive for local/lobar control after stereotactic ablative radiotherapy (SABR) in early stage non–small cell lung cancer (NSCLC).Methods and MaterialsThis study encompasses a total of 1092 patients (1200 lesions) with NSCLC of clinical stage T1-T2 N0M0 who were treated with SABR of 50 Gy in 4 fractions or 70 Gy in 10 fractions, depended on tumor location/size, using CT based heterogeneity corrections and a convolution superposition calculation algorithm. Patients were monitored by chest CT or PET/CT and/or biopsy after SABR. Factors predicting local/lobar recurrence (LR) were determined by competing risk multivariate analysis. Continuous variables were divided into 2 subgroups at cut-off values identified by receiver operating characteristic curves.ResultsAt a median follow-up time of 31.7 months (interquartile range 14.8-51.3 months), the 5-year time to local recurrence within the same lobe, and overall survival rates were 93.8% and 44.8%, respectively. Total cumulative numbers of patients experiencing LR were 40 (3.7%), occurring at the median times of 14.4 months (range 4.8-46). Using multivariate competing risk analysis, independent predictive factors for LR after SABR were minimum biologically effective dose (BED10) to 95% of planning target volume (PTVD95BED10) ≤ 86 Gy (corresponding to PTV D95 physics dose of 42 Gy in 4 fractions or 55Gy in 10 fractions) and gross tumor volume ≥8.3cm3. PTVmean BED10 was highly correlated with PTVD95 BED10. In univariate analysis, a cut-off of 130Gy for PTVmean BED10 (corresponding to PTVmean physics dose of 55Gy in 4 fractions or 75Gy in 10 fractions) is also significantly associated with LR.ConclusionsIn addition to gross tumor volume, higher radiation dose delivered to PTV predicts for better local/lobar control. We recommend that both PTVD95 BED10 >86 GY and PTVmean BED10 >130Gy should be considered for SABR plan optimization.

Teaser

Local recurrence risk after SABR is associated with radiation dose and tumor volume in early stage NSCLC. However, the dose received by PTV can be quite different, and is dependent on dose distribution and the choice of the prescription isodose lines. Both PTVD95 BED10 >86 GY and PTVmean BED10 >130Gy should be considered for SABR plan optimization for lesions <125 cm3 (corresponds to tumor size <6 cm). This is particularly important when implementing IMRT/VMAT based SABR.

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