Exhibit Hall | Forum 3
Purpose: Ventricular tachycardia (VT) is a cardiac arrhythmia that is life threatening. A new approach to the treatment of VT uses stereotactic body radiation therapy (SBRT). In this approach, a single fraction of 25 Gy dose is delivered to ablate the foci of the tachycardia. Given the precision approach to this treatment and the proximity to various organs at risk (OARs) the accuracy of dose calculation is essential. In this study a superposition convolution algorithm was compared against a linear Boltzmann radiation transport equation solver dose calculation algorithm.
Methods: Forty-eight patient plans previously calculated and treated using Varian’s Analytic Anisotropic Algorithm (AAA) were recalculated using Varian’s Acuros XB algorithm. The D98% volume of the PTV and ITV were compared as well as the max dose and the V23.75Gy to the PTV. OAR comparisons were also conducted including maximum dose to stomach and esophagus, and mean dose and volume receiving 16Gy to the heart.
Results: The mean(max) difference in max dose, PTV D98% and V23.75Gy was -0.44%(3.05%), 1.75%(3.26%), 0.28%(1.12%), respectively. The mean(max) D98% difference in the ITV was 1.88%(8.34%). The mean(max) dose difference in the maximum dose to stomach and esophagus was 12cGy(130cGy) and 18cGy(214cGy). The mean(max) difference in heart mean and V16Gy doses was 18cGy(30cGy) and 6cc(17cc).
Conclusion: The mean discrepancies in the PTV and ITV are all under 2%. The relatively low maximum differences in the PTV also suggest both algorithms estimate similar dose coverage, though the ITV has a few instances of a large discrepancy in D98%. The mean differences in the OAR doses are also relatively small, however in some cases the discrepancy can be large (stomach max dose difference is over 2Gy in one patient). This suggests that for OAR evaluation the choice of dose algorithm should be carefully chosen on a case by case basis