Optimizing cardio-respiratory motion management in stereotactic arrhythmia radioablation through mid-position planning target volume.

PURPOSE/OBJECTIVE: This study proposes an implementation of the mid-position (MidP) approach to compensate for cardio-respiratory motions in the context of Stereotactic Arrhythmia Radioablation (STAR) and evaluates its benefits compared to an internal target volume (ITV) approach. MATERIALS AND METHODS: Fifteen patients who underwent STAR for refractory ventricular tachycardia in our institution were included in this retrospective planning study. For each patient, a cardiac-gated four-dimensional computed tomography (4D-CT(card)) scan and a respiratory-gated four-dimensional computed tomography (4D-CT(resp)) were acquired. All patients were treated using a volumetric modulated arc therapy technique using an in-treatment Cone-Beam CT (CBCT) image guidance. The MidP approach was implemented to compensate for uncertainties, including cardio-respiratory motions characterized using the 4D-CT(card) and 4D-CT(resp) scans, and the inter-fraction motions measured using the CBCT scans. For comparison purposes, the ITV approach was also implemented. Both approaches were compared in terms of planning target volume (PTV) volumes, doses to organs-at-risk, and clinical target volume (CTV) doses, assessed using a 4D modeling method that estimates the accumulated dose. RESULTS: Compared with the ITV method, the MidP approach resulted in a mean [min-max] relative PTV volume reduction of 30% [19%, 48%] (p < 0.001, Wilcoxon signed rank test). The mean [min-max] D95% CTV coverage was 105% [101%-114%] and 107% [101%-117%] of the prescription dose for MidP and ITV-based plans, respectively. The median dose to the whole heart was significantly lower with MidP-based plans with a mean difference of -0.5 Gy (p = 0.0084). The near-maximum dose (D1%) delivered to left coronary arteries, aorta, and stomach was systematically lower with the MidP-based plans. CONCLUSION: Compared to ITV based approach, the use of MidP strategy for treatment planning of STAR leads to significantly smaller PTV and lower surrounding OAR doses while still achieving a clinically acceptable CTV coverage.