Dose calculation algorithm evaluation for cardiac radioablation of ventricular tachycardia

Ventricular tachycardia is a life-threatening cardiac arrhythmia that can potentially be treated using stereotactic body radiation therapy given as a single fraction. Given these characteristics, along with the delicate nature of irradiating a portion of the heart, accuracy of dose calculation in the treatment planning system is imperative. Two such calculation methods employed are superposition-convolution-based algorithms, such as Varian's Analytical Anisotropic Algorithm (AAA) and Linear Boltzmann Transport Equation solvers, such as Varian's Acuros XB (AXB). The purpose of this work is to compare these calculation algorithms in this treatment setting. Forty-eight patient plans with a nominal planning target volume prescription dose of 25 Gy that were initially calculated using AAA were recalculated using AXB without re-optimization. A third recalculation was conducted using Radformation's standalone Monte Carlo (MC) algorithm as a gold standard. Both AAA and AXB dose distributions were then compared to MC using 3D gamma analysis. Various target dose metrics in the AAA, AXB, and MC plans were compared along with organ-at-risk (OAR) dose points. Relative to MC, the median agreement rate for AAA was 89.1% and for AXB was 98.3%. The minimum agreement rate over the patient cohort was 70.4% and 93.2% for AAA and AXB, respectively. The overall gamma agreement rates were significantly higher for AXB than for AAA. With respect to the target and OAR dose comparisons, in every case, the differences in dose metrics were significantly different between AAA/MC and AXB/MC, with AXB having the superior agreement with MC. The mean differences between MC for both algorithms were lower in each case for AXB. By every metric evaluated, including target dose coverage, OAR dose endpoints, and 3D gamma dose evaluation, AXB resulted in a more precise agreement with the MC dose calculation benchmark for cardiac radioablation of ventricular tachycardia.