Overview of medical physics education and research programs in a non-academic environment.

Northwest Medical Physics Center (NMPC) is a nonprofit organization that provides clinical physics support to over 35 radiation therapy facilities concentrated in the Pacific Northwest. Although clinical service is the primary function of NMPC, the diverse array of clinical sites and physics expertise has allowed for the establishment of structured education and research programs, which are complementary to the organization's clinical mission. Three clinical training programs have been developed at NMPC: a therapy medical physics residency program accredited by the Commission on Accreditation of Medical Physics Education Programs (CAMPEP), an Applied Physics Technologist (APT) program, and a summer undergraduate internship program. A partnership has also been established with a major radiation oncology clinical vendor for the purposes of validating and testing new clinical devices across multiple facilities. These programs are managed by a dedicated education and research team at NMPC, made up of four qualified medical physicists (QMPs). The education and research work has made a significant contribution to the organization's clinical mission, and it has provided new training opportunities for early-career physicists across many different clinical environments. Education and research can be incorporated into nonacademic clinical environments, improving the quality of patient care, and increasing the number and type of training opportunities available for medical physicists.

Determination of commissioning criteria for multileaf-collimator, stereotactic radiosurgery treatments on Varian TrueBeam and Edge machines using a novel anthropomorphic phantom.

An anthropomorphic phantom has been developed by Varian Medical Systems for commissioning multileaf-collimator (MLC), stereotactic radiosurgery (SRS) treatments on Varian TrueBeam and Edge linear accelerators. Northwest Medical Physics Center (NMPC) has collected end-to-end data on these machines, at six independent clinical sites, to establish baseline dosimetric and geometric commissioning criteria for SRS measurements with this phantom. The Varian phantom is designed to accommodate four interchangeable target cassettes, each designed for a specific quality assurance function. End-to-end measurements utilized the phantom to verify the coincidence of treatment isocenter with a hidden target in a Winston-Lutz cassette after localization using cone-beam computed tomography (CBCT). Dose delivery to single target (2 cm) and single-isocenter, multitarget (2 and 1 cm) geometries was verified using ionization chamber and EBT3 film cassettes. A nominal dose of 16 Gy was prescribed for each plan using a site's standard beam geometry for SRS cases. Measurements were performed with three Millennium and three high-definition MLC machines at beam energies of 6-MV and 10-MV flattening-filter-free energies. Each clinical site followed a standardized procedure for phantom simulation, treatment planning, quality assurance, and treatment delivery. All treatment planning and delivery was performed using ARIA oncology information system and Eclipse treatment planning software. The isocenter measurements and irradiated film were analyzed using DoseLab quality assurance software; gamma criteria of 3%/1 mm, 3%/0.5 mm, and 2%/1 mm were applied for film analysis. Based on the data acquired in this work, the recommended commissioning criteria for end-to-end SRS measurements with the Varian phantom are as follows: coincidence of treatment isocenter and CBCT-aligned hidden target < 1 mm, agreement of measured chamber dose with calculated dose ≤ 5%, and film gamma passing > 90% for gamma criteria of 3%/1 mm after DoseLab auto-registration shifts ≤ 1 mm in any direction.

Localized irradiation of tumors prior to synthetic dsRNA therapy enhanced the resultant anti-tumor activity.

BACKGROUND AND PURPOSE: Despite the potent tumoricidal activity of the synthetic dsRNA in culture, its in vivo anti-tumor activity has proven to be limited. We sought to devise and validate a new strategy to improve the in vivo anti-tumor activity by integrating localized irradiation into dsRNA therapy. MATERIALS AND METHODS: Using a mouse lung cancer model and a mouse melanoma model in immuno-competent mice or athymic nude mice, we evaluated the combined anti-tumor activity using a synthetic dsRNA, polyinosine-cytosine (poly(I:C)). RESULTS: Localized irradiation of tumors prior to the poly(I:C) therapy significantly delayed the tumor growth as compared to monotherapies using the radiation or poly(I:C) alone. The poly(I:C) enhanced the tumor response to radiation with a dose modification factor as large as 20. The combined effect was synergistic only in immuno-competent mice with highly immunogenic tumors. The anti-tumor activity of the combination therapy was significantly impaired when the type I interferons in the mice were neutralized. CONCLUSIONS: This combination modality may represent a promising approach to exploit synthetic dsRNA in cancer therapy and to enhance tumor response to radiation. T cell-mediated immunity was likely responsible for the combined synergistic effect. Type I interferons contributed significantly to the combined anti-tumor activity.

Dosimetric uncertainties of three-dimensional dose reconstruction from two-dimensional data in a multi-institutional study.

Inconsistencies in the treatment planning process leading to dosimetric uncertainties may affect conclusions drawn from interinstitutional radiation oncology clinical trials. The purpose of this study was to assess the dosimetric uncertainties resulting from the process of reconstructing three-dimensional dose distributions from two-dimensional treatment plan information provided by participating institutions in a randomized clinical trial. This study was based on American College of Radiology Protocol #427, Locally Advanced Multi-Modality Protocol; a multi-institutional phase II randomized study involving radiation therapy for patients with inoperable non-small cell lung cancer. Several sources of dosimetric uncertainty were identified and analyzed, including image quality of hard-copy computed tomography (CT) images, slice spacing of CT scans, treatment position, interpretations of target volumes by radiation oncologists, the contouring of normal anatomic structures, and the use of common beam models for all dose calculations. Each source of uncertainty was investigated using a set of plans, with the ideal characteristics of digital images with 3-mm axial slice spacing and a flat couch, consisting of eight cases from Vanderbilt University Medical Center with electronically transferred CT data. The target volume DVH values were dependent on the additional uncertainty introduced by differences in delineation of the target volumes by the participating radiation oncologists. The DVH values for the lungs and heart were dependent on image quality and treatment position. Esophagus DVH values were not dependent on any of the sources of uncertainty. None of the structure DVH values were dependent on slice thickness or variations in the contouring of normal anatomic structures. Reconstruction of three-dimensional dose distributions from two-dimensional treatment plan information may be useful in cases for which digital CT data is not available or for historical data review. However, dosimetric accuracy will depend on image quality of the treatment planning CT data and consistency in the delineation of tumor volumes.