A Multi-Staged Treatment Planning Framework for Large-Volume Ventricular Tachycardia Stereotactic Ablation.

Purpose/Objective(s) Stereotactic ablative radiotherapy (SAbR) is emerging as a non-invasive ventricular tachycardia (VT) ablation treatment regimen (SAbR-VT) and has attained initial success of reducing VT that is refractory to drugs and standard catheter ablation. However, a single-fraction biological potent dose (25 Gy) ablating a large planning target volume (PTV, median 98.9cc, range 60.9–298.8cc in ENCORE-VT trial) has high risk of radiation toxicity. We propose a multi-stage SAbR-VT treatment planning strategy to mitigate radiation risk. Materials/Methods The principle of multi-staged SAbR-VT is to divide a large treatment volume into multiple stages with each stage irradiating a sub-target while minimizing the overall organ at risk (OARs) biological effective dose (BED)and toxicity. The N-staged planning problem is stated: given a set of sub-targets {T1, ..., TN}, and their respective prescription doses {p1, ..., pN}, and treatment sequence {t1, ..., tN}, finding treatment plans {x1, ..., xN} such that each plan xn delivers the prescription dose pn to target Tn in a single treatment session, and the total dose of all plans satisfies the OAR dose constraints Ck of the kth OAR for all OARs {O1, ..., OK}. We formulate this problem as a constrained optimization. Let dTn(xn) denote the dose function of target Tn of plan xn and dOk(xn)denote the OAR dose function of OAR Ok of plan, the constrained optimization problem can be written as min f = ∑wk·BED({dOk},{tn}) s.t. dTn(xn)≥ pn, ∀n∈{1,..., N} and ∑dOk(xn)≤ Ck, ∀k∈{1,..., k} The objective f is the weighted sum of OARs’ BED, where is the weighting factor wk for the kth OAR. BED of OAR is the function of both physical dose distribution {dOk} and treatment sequence {tn}. Results One of the VT cases we treated has PTV of 188.2cc. In a single-stage treatment plan, the maximum doses to stomach and esophagus are 20.46Gy and 21. 57Gy. Under a 3-stage treatment strategy, the single-stage-equivalent-doses to stomach and esophagus are estimated as 14.85Gy and 15.63Gy, respectively, which is a decrease of 28 percent. Conclusion A multi-staged SAbR-VT planning framework has the potential to significantly reduce OAR BED and consequently radiation toxicity.