Reinforcing treatment and evaluation workflow of stereotactic ablative body radiotherapy for refractory ventricular tachycardia

Abstract

Purpose: Cardiac radioablation is a novel, non-invasive treatment for ventricular tachycardia (VT), involving a single fractional stereotactic ablative body radiotherapy (SABR) session with a prescribed dose of 25 Gy. This complex procedure requires a detailed workflow and stringent dose constraints compared to conventional radiation therapy. This study aims to establish a consistent institutional workflow for single-fraction cardiac VT-SABR, emphasizing robust plan evaluation and quality assurance.

Materials and methods: The study developed a consistent institutional workflow for VT-SABR, including computed tomography (CT) simulation, target volume definition, treatment planning, robust plan evaluation, quality assurance, and image-guided strategy. The workflow was implemented for two patients with cardiac arrhythmia. Accurate target volume definition using planning CT images and electronic anatomical mapping was critical. A four-dimensional (4D) cone-beam CT (CBCT) and breath-hold electrocardiographic gated CT images reliably detected target motion.

Results: The resulting plans exhibited a conformity index greater than 0.7 and a gradient index around G4.0. Dose constraints for the planning target volume (PTV) aimed for 95% or higher PTV dose coverage, with a maximum dose of 200% or lower. However, one case did not meet the PTV dose coverage due to the proximity of the PTV to gastrointestinal organs. Plans adhered to dose constraints for organs at risk near the heart, but meeting constraints for specific cardiac sub-structures was challenging and dependent on PTV location.

Conclusion: The plans demonstrated robustness against respiratory motion and patient positional uncertainty through a robust evaluation function. The 4D and intra-fractional CBCT were effective in verifying target motion and setup stability.

Keywords: Stereotactic ablative radiotherapy; Treatment planning; Ventricular tachycardia.

Fig. 1.

Flowchart of VT-SABR established in our institution illustrating the steps from CT simulation to image-guided radiation therapy. VT, ventricular tachycardia; SABR, stereotactic ablative body radiotherapy; CT, computed tomography; ECG, electrocardiogram; 4D, four-dimensional; 3D, three-dimensional; GTV, gross tumor volume; ITV, internal target volume; PTV, planning target volume; EAM, electronic anatomical mapping; OAR, organ-at-risk; HI, homogeneity index; CI, conformity index; CBCT, cone-beam CT; QA, quality assurance; IMRT, intensity modulated radiation therapy.

Fig. 2.

Target volume delineation (right column) with reference to the regions activated in electronic anatomical mapping for two cases: (A) case 1 and (B) case B. PTV, planning target volume; CT, computed tomography.

Fig. 3.

(Top row) Dose distributions, (Bottom row) dose-volume histograms for PTV and organs-at-risk produced from treatment plans of (A) case 1 and (B) case 2. PTV, planning target volume; LAD, left anterior descending artery; LCX, left circumflex artery; LV, left ventricle; L, left; R, right; LA, left atrium; RA, right atrium.

Fig. 4.

Dose volume histograms from the dose recalculated on the inhale (top) and exhale (bottom) phases of the four-dimensional (4D) computed tomography images investigating the degree of dosimetry impact from the respiratory motion: (A) case 1 and (B) case 2.

Fig. 5.

Robust evaluation of patient set-up uncertainty: comparing DVHs (solid) from patient set-up errors in six different scenarios (1 mm shift in each direction) to DVHs (dashed) from the original plan: (A) case 1 and (B) case 2. DVH, dose volume histogram; LAD, left anterior descending artery; LCX, left circumflex artery; LV, left ventricle; PTV, planning target volume.

Fig. 6.

Cone-beam computed tomography (CBCT) image acquisitions for image-guided radiation therapy for ventricular tachycardia stereotactic ablative body radiotherapy of the first patient case: (A) planning CT image, (B) 4D CBCT image, and (C) intra-fractional CBCT image. 4D, four-dimensional.