The development and testing of a novel spherical radiotherapy phantom system for the commissioning and patient-specific quality assurance of mono-isocentric multiple mets SRS plans.

PURPOSE: To develop a single radiotherapy phantom system capable of performing both patient-specific quality assurance (QA) measurements and commissioning measurements for mono-isocentric LinAc-based stereotactic radiosurgery ("mLSRS") treatment plans. METHODS: Design A 20-cm diameter spherical phantom was designed which contained within it a film cartridge. The surface of the sphere was machined to display a set of angular markings at both the equator and the meridian representing a spherical coordinate system. A stand was designed which allows for free rotation about any vector passing through the center of the sphere. A program was created using Python 3 to: (a) Compute the measurement setup necessary to intersect exactly one film plane with three user specified dicom points contained within the QA plan; (b) Extract the intersection dose plane from the three dimensional DICOM dose file and; (c) Generate a synthetic computed tomography (CT) in the exact measurement geometry which is subsequently used for phantom positioning during the QA measurement. TESTING: To assess the functionality of the phantom system dynamic conformal arc mLSRS plans that were generated by a clinically commissioned multiple metastasis treatment planning system (BrainLab Elements version 2.0) using patient-specific data. A total of seven patient plans were created that contained a total of 31 targets { = (0.382 ± 0.534) cc: Range [0.051, 2.05] cc,  = (30 ± 16) mm: Range[0, 55] mm} 27 of which were directly measured with film and analyzed. Each planned isocenter was mapped to the phantom's center and the dose was recomputed. From the phantom dose distribution dicom points of interest were selected in sets of three and input into the provided software. The software computed the plane that intersects with the entered three points and instructed the user on the setup geometry to place the film in the intersecting plane. The software then generated a synthetic CT scan with embedded fiducial markers rotated into the setup orientation. This CT was then used as the setup reference image in ExacTrac image guidance system (tolerance 0.7 mm & 0.5deg). All plans were delivered on a Varian Truebeam linear accelerator with HDMLC, Exactrac and a 6 degree of freedom couch. After delivery of each test plan a 10 × 10 reference field was delivered to a known dose approximately equal to the maximum dose contained within the plan for film calibration. The test film was scanned simultaneously with the 10 × 10 reference film and a film that received zero dose using an Epson 10000XL flatbed scanner after waiting 24 hours. The test film was scaled according to the reference film and analyzed via the gamma analysis (3%, 1 mm, 10%) implemented in Ashland Film QA Pro software. RESULTS: The spherical phantom system was able to perform validation measurements on a variety of patient-specific plan geometries. The average gamma pass-rate γ(3%, 1 mm,10%) for all measurements was 96.7% (σ = 3.6%). CONCLUSIONS: A novel spherical radiotherapy phantom system has been designed and tested on clinically relevant test plans.

A Multidisciplinary Team Approach to Brain and Spine Stereotactic Radiosurgery Conferences: A Unique Institutional Model.

OBJECTIVE: The use of multidisciplinary teams (MDTs) comprised of all members of the patient care team is becoming increasingly popular in the field of oncology. We present a single-center experience exploring the utility and uniqueness of an MDT in the care of patients undergoing brain and spine stereotactic radiosurgery (SRS). METHODS: The weekly SRS conference brought together neurosurgeons, radiation oncologists, neuroradiologists, physicists, dosimetrists, therapists, advanced practice providers, and trainees in these fields as well as researchers from a variety of disciplines with a goal of optimizing patient care. A survey of 20 conference attendees from 7 different facets of the MDT was conducted for feedback. RESULTS: The survey results revealed that most respondents believed the SRS conference increased educational opportunities, provided opportunities for research and collaborations, helped streamline patient care, and was beneficial to their practice. CONCLUSIONS: We present our institutional MDT model, a framework and workflow that can be incorporated at other large academic centers. We believe that the SRS conference has educational, academic, and patient care value.