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D'Souza M, Nusrat H, Renaud J, Peterson G, Sarfehnia A. First-stage validation of a portable imageable MR-compatible water calorimeter. Med Phys 2020; 47:5312-5323. [PMID: 32786081 DOI: 10.1002/mp.14448] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Revised: 07/24/2020] [Accepted: 07/31/2020] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The purpose of this study is to design a water calorimeter with three goals in mind: (a) To be fully magnetic resonance (MR)-compatible; (b) To be imaged using kV cone beam computed tomography (CBCT), MV portal imaging or MRI for accurate positioning; (c) To accommodate both vertical and horizontal beam incidence, as well as volumetric deliveries or Gamma Knife®. Following this, the calorimeter performance will be measured using an accelerator-based high-energy photon beam. METHODS A portable 4°C cooled stagnant water calorimeter was built using MR-compatible materials. The walls consist of layers of acrylic plastic, aerogel-based material acting as thermal insulation, as well as tubing for coolant to flow to keep the calorimeter temperature stable at 4°C. The lid contains additional pathways for coolant to flow through as well as two hydraulically driven stirrers. The water calorimeter was positioned in an Elekta Versa using kV CBCT imaging as well as orthogonal MV image pairs. Absolute absorbed dose to water was then determined under a 6 MV flattening filter-free (FFF) beam. This was compared against reference dosimetry results that were measured under identical conditions with an Exradin A1SL ionization chamber with a calibration coefficient directly traceable to the National Research Council Canada. RESULTS The dose to water determined with the calorimeter (n = 30) agreed with the A1SL ionization chamber reference dose measurements (n = 15) to within 0.25%. The uncertainty associated with the water calorimeter absorbed dose measurement was estimated to be 0.54% (k = 1). CONCLUSIONS An MR-compatible water calorimeter was successfully built and absolute absorbed dose to water under a conventional 6 MV FFF beam was determined successfully as a first-stage validation of the system.
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Affiliation(s)
- Mark D'Souza
- Department of Physics, Ryerson University, 350 Victoria St., Toronto, ON, M5B 2K3, Canada
| | - Humza Nusrat
- Department of Radiation Oncology, University of Toronto, 2075 Bayview Ave., Toronto, ON, M4N 3M5, Canada.,Department of Medical Physics, Sunnybrook Odette Cancer Centre, 2075 Bayview Ave, Toronto, ON, M4N 3M5, Canada
| | - James Renaud
- Metrology Research Centre, National Research Council Canada, Montreal Rd., Ottawa, ON, K1A 0R6, Canada.,Medical Physics Unit, McGill University, 1001 Decarie Blvd., Montreal, QC, H4A 3J1, Canada
| | - Gerard Peterson
- Department of Medical Physics, Sunnybrook Odette Cancer Centre, 2075 Bayview Ave, Toronto, ON, M4N 3M5, Canada
| | - Arman Sarfehnia
- Department of Physics, Ryerson University, 350 Victoria St., Toronto, ON, M5B 2K3, Canada.,Department of Radiation Oncology, University of Toronto, 2075 Bayview Ave., Toronto, ON, M4N 3M5, Canada.,Department of Medical Physics, Sunnybrook Odette Cancer Centre, 2075 Bayview Ave, Toronto, ON, M4N 3M5, Canada.,Medical Physics Unit, McGill University, 1001 Decarie Blvd., Montreal, QC, H4A 3J1, Canada
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