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Abstract
Purpose: Lung toxicity is a primary side effect in stereotactic radiotherapy (SBRT) for early-stage non-small cell lung cancer (NSCLC). We aimed to use a set of radiobiological models to evaluate and compare modern IMRT delivery techniques with three-dimensional conformal techniques for SBRT treatment of NSCLC in terms of lung toxicity, and aimed to compare the results from different radiobiologcal models. Methods: Ten early-stage NSCLC patients treated with SBRT were retrospectively selected. Five treatment plans were generated to deliver 50 Gy in five fractions to the planning target volume for each case: a helical tomotherapy (HT) plan, two three-dimensional cofnromal radiotherapy (3D-CRT) plans using 6-MV and 10-MV photon beams respectively, and two volumetric modulated arc therapy (VMAT) plans using one and two arc fields respectively. The lung RDV was calculated with three parallel functional sub-unit (FSU) models and two normal tissue complication probability (NTCP) models. Results: Both the HT and VMAT plans showed significantly higher contralateral mean lung dose and lower ipsilateral mean lung dose compared to the 3D-CRT plans. There was no statistically significant difference in terms of lung toxicities between the IMRT and 3D-CRT techniques using either the FSU models or the NTCP models. Based on both the FSU and the NTCP models, there was strong correlation between lung toxicity and the mean lung dose in SBRT treatment plans. Conclusions: Based on both the NTCP and parallel FSU models, both IMRT and traditional 3D-CRT delivery techniques could achieve comparable lung sparing inn SBRT treatment of early-stage lung cancer. However, the validity of the radiobiological model results should be checked by clinical data.
Highlights
In recent years, hypofractionated stereotactic body radiotherapy (SBRT) has been widely implemented as a definitive treatment modality for early-stage non-small cell lung cancer (NSCLC), especially for patients who are not candidates for surgery due to existing morbidities including cardiopulmonary complications [1] [2] [3]
We aimed to evaluate the discrepancies between existing radiobiological models in lung toxicity modeling in SBRT treatments
As to the contralateral lung, each of the three intensitymodulated radiotherapy (IMRT) techniques showed significantly higher mean lung dose compared to the 3D techniques, while there was no significant difference among the three IMRT techniques
Summary
In recent years, hypofractionated stereotactic body radiotherapy (SBRT) has been widely implemented as a definitive treatment modality for early-stage non-small cell lung cancer (NSCLC), especially for patients who are not candidates for surgery due to existing morbidities including cardiopulmonary complications [1] [2] [3]. While early-stage lung cancer patients could potentially be cured from SBRT treatments, it is imperative to minimize radiation-induced toxicities to reduce post-treatment morbidities. In the EUD model, a power-law formula is used to convert the dose-volume histogram (DVH) from a RT plan to a single equivalent dose parameter, which can be translated to normal tissue complication probability (NTCP) through a sigmoid function [7]. In contrast to the EUD concept, the parallel FSU model quantifies the percentage of lung volume damaged by RT treatment, which is potentially a clinically measurable quantity. Previous studies using the parallel FSU model indicate that this model could be relevant in evaluation of organ toxicities in RT treatments [10] [11]
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