EPID-based parameterized gradient method for photon beam field size determination(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2018年第11期
- Page:
- 1261-1268
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- EPID-based parameterized gradient method for photon beam field size determination
- Author(s):
- HU Jinyan1; ZHANG Liyuan2; LIU Lele1; WANG Xuemin3; PEI Yuntong1; GUO Yuexin1
- 1. Department of Radiation Oncology, the First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China; 2. Department of Radiation Oncology, Zhengzhou Central Hospital, Zhengzhou 450052, China; 3. Department of Radiotherapy, Shaanxi Provincial Cancer Hospital, Xi’an 710061, China
- Keywords:
- ; Keywords: photon beam; electronic portal image dosimetry; parameterized gradient method; field size determination; quality assurance
- PACS:
- R312；R811.1
- DOI:
- DOI:10.3969/j.issn.1005-202X.2018.11.005
- Abstract:
-
Abstract: Objective To investigate the feasibility of using parameterized gradient method (PGM) to determine photon beam field size based on electronic portal image dosimetry (EPID). Methods Profile penumbra region was fitted by PGM via a modified hyperbolic tangent function. Varian EDGE aS1200 detector was used to collect the EPID data of 6 MV and 10 MV flattening-filter (FF) and flattening-filter-free (FFF) photon beams, while TrueBeam aS1000 detector was used to obtain the EPID data of 6 MV FF photon beams. Gamma analysis with 1 mm/1% criterion was used to quantitatively assess the consistency between Profile penumbra region fitted by PGM and that measured by EPID. The FF photon beam field sizes calculated by full-width at half-maximum method and those determined by PGM were compared, and the FFF photon beam field sizes obtained by maximum slope method and those obtained by PGM were also compared. By varying beam energies and types of EPID detectors and introducing Jaw position errors, the robustness and scalability of PGM for photon beam field size determination were evaluated. Results Pearson correlation coefficient between penumbra region fitted by PGM and data measured by EPID was greater than 0.999 and γ was less than 0.2. For FF beams, the field size calculated with full-width at half-maximum method were larger than that obtained with PGM, and even larger as the field size increasing. However, after subtracting the umbra region from profile, the differences in measurements between two methods were significantly reduced. For FFF beams, the differences between the field sizes calculated with maximum slope method and those obtained with PGM were within 0.1 mm. PGM achieved a stable measurement of field size at different beam energies, modalities, independent of EPID detector characteristics, and is effective in detecting Jaw errors which was within ±1 mm. Conclusion PGM can be universally applied to EPID photon beam of all modalities for quality assurance (QA).
Last Update: 2018-11-22