BACKGROUND-Case studies have suggested the efficacy of catheter-free, electrophysiologyguided noninvasive cardiac radioablation for ventricular tachycardia (VT) using stereotactic body radiation therapy (SBRT), though prospective data is lacking. METHODS-We conducted a prospective phase I/II trial of noninvasive cardiac radioablation in adults with treatment-refractory episodes of VT or cardiomyopathy related to premature ventricular contractions (PVCs). Arrhythmogenic scar regions were targeted by combining noninvasive anatomic and electrical cardiac imaging with a standard SBRT workflow followed by delivery of a single fraction of 25 Gray (Gy) to the target. The primary safety endpoint was treatment-related serious adverse events (SAE) in the first 90 days. The primary efficacy endpoint was any reduction in VT episodes (tracked by indwelling ICDs) or any reduction in PVC burden

Helical tomotherapy is a relatively new modality with integrated treatment planning and delivery hardware for radiation therapy treatments. In view of the uniqueness of the hardware design of the helical tomotherapy unit and its implications in routine quality assurance, the Therapy Physics Committee of the American Association of Physicists in Medicine commissioned Task Group 148 to review this modality and make recommendations for quality assurance related methodologies. The specific objectives of this Task Group are: ͑a͒ To discuss quality assurance techniques, frequencies, and tolerances and ͑b͒ discuss dosimetric verification techniques applicable to this unit. This report summarizes the findings of the Task Group and aims to provide the practicing clinical medical physicist with the insight into the technology that is necessary to establish an independent and comprehensive quality assurance program for a helical tomotherapy unit. The emphasis of the report is to describe the rationale for the proposed QA program and to provide example tests that can be performed, drawing from the collective experience of the task group members and the published literature. It is expected that as technology continues to evolve, so will the test procedures that may be used in the future to perform comprehensive quality assurance for helical tomotherapy units.

The first clinical MR-IGRT system was validated for real-time tracking and gating capabilities and shown to be reliable and accurate. Patient workflow methods were developed for efficient treatment. Periodic quality assurance tests can be efficiently performed with commercially available equipment to ensure accurate system performance.

The requirement of an independent verification of the monitor units ͑MU͒ or time calculated to deliver the prescribed dose to a patient has been a mainstay of radiation oncology quality assurance. The need for and value of such a verification was obvious when calculations were performed by hand using look-up tables, and the verification was achieved by a second person independently repeating the calculation. However, in a modern clinic using CT/MR/PET simulation, computerized 3D treatment planning, heterogeneity corrections, and complex calculation algorithms such as convolution/superposition and Monte Carlo, the purpose of and methodology for the MU verification have come into question. In addition, since the verification is often performed using a simpler geometrical model and calculation algorithm than the primary calculation, exact or almost exact agreement between the two can no longer be expected. Guidelines are needed to help the physicist set clinically reasonable action levels for agreement. This report addresses the following charges of the task group: ͑1͒ To re-evaluate the purpose and methods of the "independent second check" for monitor unit calculations for non-IMRT radiation treatment in light of the complexities of modernday treatment planning. ͑2͒ To present recommendations on how to perform verification of monitor unit calculations in a modern clinic. ͑3͒ To provide recommendations on establishing action levels for agreement between primary calculations and verification, and to provide guidance in addressing discrepancies outside the action levels. These recommendations are to be used as guidelines only and shall not be interpreted as requirements.

In this manuscript, the authors detail the complete workflow for cardiac stereotactic body radiation therapy that was performed to treat patients with refractory ventricular tachycardia on a recently completed phase 1/2 trial. Included in this report are the dose-volume metrics Purpose: A prospective phase 1/2 trial for electrophysiologic guided noninvasive cardiac radioablation treatment of ventricular tachycardia (ENCORE-VT) demonstrating efficacy for arrhythmia control has recently been reported. The treatment workflow, report dose-volume metrics, and overall process improvements are described here. Methods and Materials: Patients receiving 25 Gy in a single fraction to the cardiac ventricular tachycardia substrate (identified on presimulation multimodality imaging) on the phase 1/2 trial were included for analysis. Planning target volume (PTV), R50, monitor unit ratio, and gradient measure values were compared over time using statistical process control. Outlier values in the dose-volume histogram (DVH) for PTV and organs at risk were identified by calculating inner fences based on the interquartile range. Median heart substructure doses are also reported.