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Watson PGF, Popovic M, Liang L, Tomic N, Devic S, Seuntjens J. Clinical Implication of Dosimetry Formalisms for Electronic Low-Energy Photon Intraoperative Radiation Therapy. Pract Radiat Oncol 2020; 11:e114-e121. [PMID: 32795615 DOI: 10.1016/j.prro.2020.07.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Revised: 05/27/2020] [Accepted: 07/27/2020] [Indexed: 11/26/2022]
Abstract
PURPOSE Intraoperative radiation therapy (IORT) using the INTRABEAM, a miniature x-ray source, has shown to be effective in treating breast cancer. However, recent investigations have suggested a significant deviation between the reported and delivered doses. In this work, the dose delivered by INTRABEAM in the TARGIT breast protocol was investigated, along with the dose from the Xoft Axxent, another source used in breast IORT. METHODS AND MATERIALS The absorbed dose from the INTRABEAM was determined from ionization chamber measurements using: (a) the manufacturer-recommended formula (Zeiss V4.0 method), (b) a Monte Carlo calculated chamber conversion factor (CQ method), and (c) the formula consistent with the TARGIT breast protocol (TARGIT method). The dose from the Xoft Axxent was determined from ionization chamber measurements using the Zeiss V4.0 method and calculated using the American Association of Physicists in Medicine TG-43 formalism. RESULTS For a nominal TARGIT prescription of 20 Gy, the dose at the INTRABEAM applicator surface ranged from 25.2 to 31.7 Gy according to the CQ method for the largest (5 cm) and smallest (1.5 cm) diameter applicator, respectively. The Zeiss V4.0 method results were 7% to 10% lower (23.2 to 28.6 Gy). At 1 cm depth, the CQ and Zeiss V4.0 absorbed doses were also larger than those predicted by the TARGIT method. The dose at 1 cm depth from the Xoft Axxent for a surface dose of 20 Gy was slightly less than INTRABEAM (3%-7% compared with CQ method). An exception was for the 3 cm applicator, where the Xoft dose was appreciably lower (31%). CONCLUSIONS The doses delivered in the TARGIT breast protocol with INTRABEAM were significantly greater than the prescribed 20 Gy and depended on the size of spherical applicator used. Breast IORT treatments with the Xoft Axxent received less dose compared with TARGIT INTRABEAM, which could have implications for studies comparing clinical outcomes between the 2 devices.
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Affiliation(s)
| | - Marija Popovic
- Medical Physics Unit, McGill University, Montreal, QC, Canada
| | - Liheng Liang
- Medical Physics Unit, Department of Radiation Oncology, SMBD Jewish General Hospital, McGill University, Montreal, QC, Canada
| | - Nada Tomic
- Medical Physics Unit, Department of Radiation Oncology, SMBD Jewish General Hospital, McGill University, Montreal, QC, Canada
| | - Slobodan Devic
- Medical Physics Unit, Department of Radiation Oncology, SMBD Jewish General Hospital, McGill University, Montreal, QC, Canada
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montreal, QC, Canada
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Liang LH, Tomic N, Vuong T, Aldelaijan S, Bekerat H, DeBlois F, Seuntjens J, Devic S. Physics aspects of the Papillon technique-Five decades later. Brachytherapy 2017; 17:234-243. [PMID: 29102741 DOI: 10.1016/j.brachy.2017.09.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Revised: 09/26/2017] [Accepted: 09/26/2017] [Indexed: 12/15/2022]
Abstract
PURPOSE The Papillon technique using 50-kVp soft X-rays to treat rectal adenocarcinomas was developed and clinically implemented in the 1960s. We describe differences between accurate dosimetry and clinical implementation of this technique that is extending from its very inception to date. METHODS AND MATERIALS A renaissance of the Papillon technique occurred with two recently introduced 50-kVp systems: Papillon+ by Ariane and a custom-made rectal applicator (consisting of a surface applicator inserted into a proctoscope) by iCAD's Xoft Axxent Electronic Brachytherapy (eBT) System (iCad, Inc., Sunnyvale, CA). In contrast to the initial design, we investigated the impact of introducing a plastic lid, which would provide more reproducible and more accurate dose delivery across the rectal adenocarcinoma patient population. We use both parallel-plate chamber and radiochromic film dosimeters to determine differences in basic dosimetry characteristics (beam half-value layers, outputs, percent depth doses, and profiles) between the Xoft Electronic Brachytherapy rectal applicator system with and without the plastic lid in place. RESULTS Compared to the open-cone applicator, the proposed applicator with the plastic lid produces a slightly harder (more penetrating) beam quality (half-value layer of 1.4 vs. 1.3-mm Al), but with reduced output (by 33%), and a slightly broader beam with flatness not worse than 3% and symmetry not worse than 2%. CONCLUSIONS In addition to characterizing beam properties modified by the possible introduction of the plastic cap, we also pointed out and addressed misconceptions in the use of radiochromic films for dose measurements at low-energy photon beams.
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Affiliation(s)
- Li Heng Liang
- Radiation Oncology Department, Jewish General Hospital, Montreal, Quebec, Canada; Medical Physics Unit, McGill University, Montreal, Quebec, Canada
| | - Nada Tomic
- Radiation Oncology Department, Jewish General Hospital, Montreal, Quebec, Canada; Medical Physics Unit, McGill University, Montreal, Quebec, Canada
| | - Te Vuong
- Radiation Oncology Department, Jewish General Hospital, Montreal, Quebec, Canada; Oncology Department, McGill University, Montreal, Quebec, Canada
| | - Saad Aldelaijan
- Medical Physics Unit, McGill University, Montreal, Quebec, Canada; Biological & Biomedical Engineering Department, Montreal Neurological Institute, Montréal, Québec, Canada; Biomedical Physics Department, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia
| | - Hamed Bekerat
- Radiation Oncology Department, Jewish General Hospital, Montreal, Quebec, Canada; Medical Physics Unit, McGill University, Montreal, Quebec, Canada
| | - Francois DeBlois
- Radiation Oncology Department, Jewish General Hospital, Montreal, Quebec, Canada; Medical Physics Unit, McGill University, Montreal, Quebec, Canada
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montreal, Quebec, Canada; Oncology Department, McGill University, Montreal, Quebec, Canada
| | - Slobodan Devic
- Radiation Oncology Department, Jewish General Hospital, Montreal, Quebec, Canada; Medical Physics Unit, McGill University, Montreal, Quebec, Canada; Segal Cancer Centre, Jewish General Hospital, McGill University, Montréal, Québec, Canada.
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