Radiobiological modeling of two stereotactic body radiotherapy schedules in patients with stage I peripheral non-small cell lung cancer

Abstract

This study aims to compare the radiobiological response of two stereotactic body radiotherapy (SBRT) schedules for patients with stage I peripheral non-small cell lung cancer (NSCLC) using radiobiological modeling methods. Volumetric modulated arc therapy (VMAT)-based SBRT plans were designed using two dose schedules of 1 × 34 Gy (34 Gy in 1 fraction) and 4 × 12 Gy (48 Gy in 4 fractions) for 19 patients diagnosed with primary stage I NSCLC. Dose to the gross target volume (GTV), planning target volume (PTV), lung and chest wall (CW) were converted to biologically equivalent dose in 2 Gy fraction (EQD2) for comparison. Five different radiobiological models were employed to predict the tumor control probability (TCP) value. Three additional models were utilized to estimate the normal tissue complication probability (NTCP) value for the lung and the modified equivalent uniform dose (mEUD) value to the CW. Our result indicates that the 1 × 34 Gy dose schedule provided a higher EQD2 dose to the tumor, lung and CW. Radiobiological modeling revealed that the TCP value for the tumor, NTCP value for the lung and mEUD value for the CW were 7.4% (in absolute value), 7.2% (in absolute value) and 71.8% (in relative value) higher on average, respectively, using the 1 × 34 Gy dose schedule.

Keywords: dose schedule; non-small cell lung cancer; radiobiological modeling; stereotactic body radiotherapy.

Figure 1. DVH of the GTV, PTV-GTV, lung and CW after EQD₂ conversion

(A) DVH of the GTV, (B) DVH of the PTV-GTV, (C) DVH of the lung, and (D) DVH of the CW. GTV = gross target volume; PTV = planning target volume; PTV-GTV = PTV minus GTV; CW = chest wall; EQD₂ = biologically equivalent dose in 2 Gy fractions.

Figure 2. Dose distribution from the transversal, coronal and sagittal views between the two dose schedules

The dose color wash slider was set at 15 Gy for the 1 × 34 Gy schedule and 23.59 Gy for the 4 × 12 Gy schedule (the same EQD₂ dose). (A) Dose distribution of the 1 × 34 Gy schedule. (B) Dose distribution of the 4 × 12 Gy schedule.

Figure 3. Flow chart of the radiobiological modeling

cDVH = cumulative dose volume histogram; dDVH = differential dose volume histogram; EQD₂ = biologically equivalent dose in 2 Gy fractions; TCP = tumor control probability; NTCP = normal tissue complication probability; Mar = Martel model; Fen = Fenwick model; WN = Webb-Nahum model; EUD = equivalent uniform dose model; Nitin = Nitin model; LKB = Lyman-Kutcher-Burman (LKB) model; mEUD = modified equivalent uniform dose model; CW = chest wall.