PMID- 34796120 OWN - NLM STAT- PubMed-not-MEDLINE LR - 20220428 IS - 2234-943X (Print) IS - 2234-943X (Electronic) IS - 2234-943X (Linking) VI - 11 DP - 2021 TI - Evaluation of Daily CT for EPID-Based Transit In Vivo Dosimetry. PG - 782263 LID - 10.3389/fonc.2021.782263 [doi] LID - 782263 AB - PURPOSE: The difference in anatomical structure and positioning between planning and treatment may lead to bias in electronic portal image device (EPID)-based in vivo dosimetry calculations. The purpose of this study was to use daily CT instead of planning CT as a reference for EPID-based in vivo dosimetry calculations and to analyze the necessity of using daily CT for EPID-based in vivo dosimetry calculations in terms of patient quality assurance. MATERIALS AND METHODS: Twenty patients were enrolled in this study. The study design included eight different sites (the cervical, nasopharyngeal, and oral cavities, rectum, prostate, bladder, lung, and esophagus). All treatments were delivered with a CT-linac 506c (UIH, Shanghai) using 6 MV photon beams. This machine is equipped with diagnosis-level fan-beam CT and an amorphous silicon EPID XRD1642 (Varex Imaging Corporation, UT, USA). A Monte Carlo algorithm was developed to calculate the transmit EPID image. A pretreatment measurement was performed to assess system accuracy by delivering based on a homogeneous phantom (RW3 slab, PTW, Freiburg). During treatment, each patient underwent CT scanning before delivery either once or twice for a total of 268 fractions obtained daily CT images. Patients may have had a position correction that followed our image-guided radiation therapy (IGRT) procedure. Meanwhile, transmit EPID images were acquired for each field during delivery. After treatment, all patient CTs were reviewed to ensure that there was no large anatomical change between planning and treatment. The reference of transmit EPID images was calculated based on both planning and daily CTs, and the IGRT correction was corrected for the EPID calculation. The gamma passing rate (3 mm 3%, 2 mm 3%, and 2 mm 2%) was calculated and compared between the planning CT and daily CT. Mechanical errors [ +/- 1 mm, +/- 2 mm, +/- 5 mm multileaf collimator (MLC) systematic shift and 3%, 5% monitor unit (MU) scaling] were also introduced in this study for comparing detectability between both types of CT. RESULT: The average (standard deviation) gamma passing rate (3 mm 3%, 2 mm 3%, and 2 mm 2%) in the RW3 slab phantom was 99.6% +/- 1.0%, 98.9% +/- 2.1%, and 97.2% +/- 3.9%. For patient measurement, the average (standard deviation) gamma passing rates were 87.8% +/- 14.0%, 82.2% +/- 16.9%, and 74.2% +/- 18.9% for using planning CTs as reference and 93.6% +/- 8.2%, 89.7% +/- 11.0%, and 82.8% +/- 14.7% for using daily CTs as reference. There were significant differences between the planning CT and daily CT results. All p-values (Mann-Whitney test) were less than 0.001. In terms of error simulation, nonparametric test shows that there were significant differences between practical daily results and error simulation results (p < 0.001). The receiver operating characteristic (ROC) analysis indicated that the detectability of mechanical delivery error using daily CT was better than that of planning CT. AUC(Daily CT) = 0.63-0.96 and AUC(Planning CT) = 0.49-0.93 in MLC systematic shift and AUC(Daily CT) = 0.56-0.82 and AUC(Planning CT) = 0.45-0.73 in MU scaling. CONCLUSION: This study shows the feasibility and effectiveness of using two-dimensional (2D) EPID portal image and daily CT-based in vivo dosimetry for intensity-modulated radiation therapy (IMRT) verification during treatment. The daily CT-based in vivo dosimetry has better sensitivity and specificity to identify the variation of IMRT in MLC-related and dose-related errors than planning CT-based. CI - Copyright (c) 2021 Feng, Yu, Mo, Chen, Zhao, Wang and Hu. FAU - Feng, Bin AU - Feng B AD - Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China. AD - Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China. AD - Shanghai Key Laboratory of Radiation Oncology, Shanghai, China. FAU - Yu, Lei AU - Yu L AD - Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China. AD - Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China. AD - Shanghai Key Laboratory of Radiation Oncology, Shanghai, China. FAU - Mo, Enwei AU - Mo E AD - Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China. AD - Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China. AD - Shanghai Key Laboratory of Radiation Oncology, Shanghai, China. FAU - Chen, Liyuan AU - Chen L AD - Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China. AD - Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China. AD - Shanghai Key Laboratory of Radiation Oncology, Shanghai, China. FAU - Zhao, Jun AU - Zhao J AD - Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China. AD - Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China. AD - Shanghai Key Laboratory of Radiation Oncology, Shanghai, China. FAU - Wang, Jiazhou AU - Wang J AD - Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China. AD - Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China. AD - Shanghai Key Laboratory of Radiation Oncology, Shanghai, China. FAU - Hu, Weigang AU - Hu W AD - Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China. AD - Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China. AD - Shanghai Key Laboratory of Radiation Oncology, Shanghai, China. LA - eng PT - Journal Article DEP - 20211102 PL - Switzerland TA - Front Oncol JT - Frontiers in oncology JID - 101568867 PMC - PMC8592931 OTO - NOTNLM OT - EPID OT - IMRT verification OT - Monte Carlo method OT - portal dosimetry OT - quality assurance COIS- The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. EDAT- 2021/11/20 06:00 MHDA- 2021/11/20 06:01 PMCR- 2021/01/01 CRDT- 2021/11/19 06:58 PHST- 2021/09/24 00:00 [received] PHST- 2021/10/14 00:00 [accepted] PHST- 2021/11/19 06:58 [entrez] PHST- 2021/11/20 06:00 [pubmed] PHST- 2021/11/20 06:01 [medline] PHST- 2021/01/01 00:00 [pmc-release] AID - 10.3389/fonc.2021.782263 [doi] PST - epublish SO - Front Oncol. 2021 Nov 2;11:782263. doi: 10.3389/fonc.2021.782263. eCollection 2021.