Impact of tumor position displacement during end-exhalation breath-hold condition on tumor dose in lung stereotactic body radiation therapy using volumetric modulated arc therapy.

Background And Purpose: In lung stereotactic body radiation therapy (SBRT) using a breath-holding technique, displacement of tumor during breath-holding is rarely considered. This study used four-dimensional (4D) dose calculation with cine computed tomography (CT) to evaluate the impact of unexpected tumor position displacement during breath-holding on the target dose of lung volumetric modulated arc therapy (VMAT)-SBRT.

Materials And Methods: This study included 20 cases for which tumor position displacement during end-exhalation breath-holding (range: 0.5-12.6 mm) was evaluated on cine CT. VMAT-SBRT plans (3D dose) were generated using treatment planning CT images (reference CT) acquired during end-exhalation breath-hold. For each plan, the 4D dose was calculated using deformable image registration of the cine CT images and was accumulated onto the reference CT. Dose metrics and the mean biologically effective dose at  = 10 (BED) for the gross tumor volume (GTV) were compared between 3D and 4D doses.

Results: In the 17 cases where the tumor was within the planning target volume (PTV) during breath-holding, the difference between the 3D and 4D doses was within 3 % for each dose metric. However, in 3 cases where the tumor position during breath-holding included displacement outside the PTV, both the D and mean BED of the GTV were reduced by 6.9-20.0 % and 2.1-13.8 %, respectively, in 4D doses compared to 3D doses.

Conclusion: Our study showed that tumor position displacements during breath-holding may lead to substantial tumor dose reduction.