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Pecić S, Vićić M, Belča I, Stojadinović S, Nidžović B, Kurij L, Dević S. Physical wedge as a tool for radiochromic film calibration. Z Med Phys 2023:S0939-3889(23)00077-6. [PMID: 37393128 DOI: 10.1016/j.zemedi.2023.05.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 05/17/2023] [Accepted: 05/31/2023] [Indexed: 07/03/2023]
Abstract
Reliable calibration is one of the major challenges in using radiochromic films (RCF) for radiation dosimetry. In this study the feasibility of using dose gradients produced by a physical wedge (PW) for RCF calibration was investigated. The aim was to establish an efficient and reproducible method for calibrating RCF using a PW. Film strips were used to capture the wedge dose profile for five different exposures and the acquired scans were processed to generate corresponding net optical density wedge profiles. The proposed method was compared to the benchmark calibration, following the guidelines for precise calibration using uniform dose fields. The results of the benchmark comparison presented in this paper showed that using a single film strip for measuring wedge dose profile is sufficient for estimating a reliable calibration curve within the recorded dose range. Furthermore, the PW calibration can be extrapolated or extended by using multiple gradients for the optimal coverage of the desired calibration dose range. The method outlined in this paper can be readily replicated using the equipment and expertise commonly found in a radiotherapy center. Once the dose profile and central axis attenuation coefficient of the PW are determined, they can serve as a reference for a variety of calibrations using different types and batches of film. This investigation demonstrated that the calibration curves obtained with the presented PW calibration method are within the bounds of the measurement uncertainty evaluated for the conventional uniform dose field calibration method.
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Affiliation(s)
- Stevan Pecić
- Faculty of Physics, University of Belgrade, Studentski trg 12-16, Belgrade 11000, Serbia.
| | - Miloš Vićić
- Faculty of Physics, University of Belgrade, Studentski trg 12-16, Belgrade 11000, Serbia
| | - Ivan Belča
- Faculty of Physics, University of Belgrade, Studentski trg 12-16, Belgrade 11000, Serbia
| | - Strahinja Stojadinović
- Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas 75390, TX, United States
| | - Borko Nidžović
- Institute of Oncology and Radiology of Serbia, Pasterova 14, Belgrade 11000, Serbia
| | - Ljubomir Kurij
- University Clinical Center of Serbia, Center for Neurooncology, Gamma Knife, Koste Todorovića 4, Belgrade 11000, Serbia
| | - Slobodan Dević
- Medical Physics Unit, McGill University, Montreal H4A 3J1, QC, Canada; Department of Radiation Oncology, SMBD Jewish General Hospital, Montreal H3T 1E2, QC, Canada
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Resch AF, Padilla Cabal F, Regodic M, Lechner W, Heilemann G, Kuess P, Georg D, Palmans H. Accelerating and improving radiochromic film calibration by utilizing the dose ratio in photon and proton beams. Med Phys 2022; 49:6150-6160. [PMID: 35754376 PMCID: PMC9543697 DOI: 10.1002/mp.15828] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 06/08/2022] [Accepted: 06/09/2022] [Indexed: 11/12/2022] Open
Abstract
Purpose Radiochromic films are versatile 2D dosimeters with high‐resolution and near tissue equivalence. To assure high precision and accuracy, a time‐consuming calibration process is required. To improve the time efficiency, a novel calibration method utilizing the ratio of the same dose profile measured at different monitor units (MUs) is introduced and tested in a proton and photon beam. Methods The calibration procedure employs the dose ratio of film measurements of the same relative profile for different absolute dose values. Hence, the ratio of the dose is constant at any point of the profile, but the ratio of the net optical densities is not constant. The key idea of the method is to optimize the calibration function until the ratio of the calculated doses is constant. The proposed method was tested in the dose range between 0.25–12 and 1–6 Gy in a proton and photon beam, respectively. A radial symmetric profile and a rectangular profile were created, both having a central plateau region of about 3 cm diameter and a dose falloff of about 1.5 cm at larger distances. The dose falloff region was used as input for the optimization method and the central plateau region served as dose reference points. Only the plateau region of the highest dose entered the optimization as an additional objective. The measured data were randomly split into differently sized training and test sets. The optimization was repeated 1000 times with random start value initialization using the same start values for the standard and the gradient method. Finally, a proton plan with four dose levels was created, which were separated spatially, to test the possibility of a full calibration within a single measurement. Results Parameter estimation was possible with as low as one dose ratio used for optimization in both the photon and the proton case, yet exhibiting a high sensitivity on the dose level. The root mean squared deviation (RMSD) of the dose was less than 1% when the dose ratio was in the order of 20, whereas the median RMSD of all optimizations was 1.7%. Using four dose levels for optimization resulted in a median RMSD of 1% when randomly selecting the dose levels. Having at least one dose ratio of about 20 included in the optimization considerably improved the RMSD of the calibration function. Using six or eight dose levels reduced the sensitivity on the dose level selection and the median RMSD was 0.8%. A full calibration was possible in a single measurement having four dose levels in one plan but spatially separated. Conclusions The number of measurements required to obtain an EBT3 film calibration function could be reduced using the proposed dose ratio method while maintaining the same accuracy as with the standard method.
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Affiliation(s)
- Andreas F. Resch
- Division Medical Radiation PhysicsDepartment of Radiation OncologyMedical University of Vienna/AKH WienViennaAustria
| | - Fatima Padilla Cabal
- Division Medical Radiation PhysicsDepartment of Radiation OncologyMedical University of Vienna/AKH WienViennaAustria
| | - Milovan Regodic
- Division Medical Radiation PhysicsDepartment of Radiation OncologyMedical University of Vienna/AKH WienViennaAustria
| | - Wolfgang Lechner
- Division Medical Radiation PhysicsDepartment of Radiation OncologyMedical University of Vienna/AKH WienViennaAustria
| | - Gerd Heilemann
- Division Medical Radiation PhysicsDepartment of Radiation OncologyMedical University of Vienna/AKH WienViennaAustria
| | - Peter Kuess
- Division Medical Radiation PhysicsDepartment of Radiation OncologyMedical University of Vienna/AKH WienViennaAustria
| | - Dietmar Georg
- Division Medical Radiation PhysicsDepartment of Radiation OncologyMedical University of Vienna/AKH WienViennaAustria
| | - Hugo Palmans
- MedAustron Ion Therapy CentreWiener NeustadtAustria
- Medical Radiation ScienceNational Physical LaboratoryTeddingtonUnited Kingdom
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Rodríguez C, García-Pinto D, Martínez LC, López-Fernández A. A new analytical model for the response curve in megavoltage photon beams of the radiochromic EBT3 films measured with flatbed scanners. J Appl Clin Med Phys 2022; 23:e13654. [PMID: 35580051 PMCID: PMC9359044 DOI: 10.1002/acm2.13654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 04/21/2022] [Accepted: 04/25/2022] [Indexed: 11/16/2022] Open
Abstract
Purpose The aim of this work is to study a new analytical model which describes the dose–response curve in megavoltage photon beams of the radiochromic EBT3 film measured with two commercially available flatbed scanners. This model takes into account the different increase of the number of two types of absorbents in the film with absorbed dose and it allows to identify parameters that depend on the flatbed scanner and the film model, and parameters that exclusively depend on the production lot. In addition, the new model is also compared with other models commonly used in the literature in terms of its performance in reducing systematic calibration uncertainties. Methods and materials The new analytical model consists on a linear combination of two saturating exponential functions for every color channel. The exponents modeling the growing of each kind of absorbent are film model and scanner model‐dependent, but they do not depend on the manufacturing lot. The proposed model considers the different dose kinetics of each absorbent and the apparent effective behavior of one of the absorbents in the red color channel of the scanner. The dose–response curve has been measured using EBT3 films, a percentage depth dose (PDD) calibration method in a dose range between 0.5 and 25 Gy, and two flatbed scanners: a Microtek 1000 XL and an EPSON 11000 XL. The PDD calibration method allows to obtain a dense collection of calibration points which have been fitted to the proposed response curve model and to other published models. The fit residuals were used to evaluate the performance of each model compared with the new analytical model. Results The model presented here does not introduce any systematic deviations up to the degree of accuracy reached in this work. The residual distribution is normally shaped and with lower variance than the distributions of the other published models. The model separates the parameters reflecting specific characteristics of the dosimetry system from the linear parameters which depend only on the production lot and are related to the relative abundance of each type of absorbent. The calibration uncertainty is reduced by a mean factor of two by using this model compared with the other studied models. Conclusions The proposed model reduces the calibration uncertainty related to systematic deviations introduced by the response curve. In addition, it separates parameters depending on the flatbed scanner and the film model from those depending on the production lot exclusively and therefore provides a better characterization of the dosimetry system and increases its reliability.
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Affiliation(s)
- César Rodríguez
- Medical Physics, Radiology Department, Complutense University, Madrid, Spain.,Medical Physics and Radiation Protection Service, Fuenlabrada University Hospital, Fuenlabrada, Spain
| | - Diego García-Pinto
- Medical Physics, Radiology Department, Complutense University, Madrid, Spain
| | - Luis Carlos Martínez
- Medical Physics and Radiation Protection Service, Doce de Octubre University Hospital, Madrid, Spain
| | - Alfonso López-Fernández
- Medical Physics and Radiation Protection Service, Fuenlabrada University Hospital, Fuenlabrada, Spain
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Microdosimetric modeling of the sensitometric curve of GafChromic films in the photon fields. Phys Med 2020; 69:170-175. [PMID: 31918369 DOI: 10.1016/j.ejmp.2019.12.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2019] [Revised: 12/01/2019] [Accepted: 12/19/2019] [Indexed: 11/20/2022] Open
Abstract
The sensitometric curve of EBT3 GafChromic film located at a depth 5 cm of RW3 water-equivalent phantom exposed to 6 MV X-rays is investigated. Variation of optical density for absorbed doses less than 2 Gy is determined by the experimental measurement together with the microdosimetric one-hit detector model. It is found that this model needs two fitting parameters, a maximum optical density and a saturation parameter. Both of them depend on the film structure as well as the photon spectrum. Meanwhile, the saturation parameter is a function of the microdosimetric single-event distribution of specific energy, i.e., f1(z). To calculate this distribution, irradiation of the films is simulated by the Geant4 toolkit. A sample of EBT3 film with 2 mm × 2 mm area is simulated. Active layer of the film is considered to contain 5000 cylindrical sensitive targets (SV) with 9.4 μm length and 1.62 μm diameter, located in random positions with different axial directions. The results obtained show that below an absorbed dose 1 Gy the maximum difference between the measured and the calculated optical densities is about 11%, while for the doses above 1 Gy the discrepancy is at most 3%. Eventually, it can be concluded that the sensitometric curve of EBT3 GafChromic film can satisfactorily be determined by the microdosimetric one-hit detector model, especially in the dose range above 1 Gy.
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Aldelaijan S, Devic S, Papaconstadopoulos P, Bekerat H, Cormack RA, Seuntjens J, Buzurovic IM. Dose-response linearization in radiochromic film dosimetry based on multichannel normalized pixel value with an integrated spectral correction for scanner response variations. Med Phys 2019; 46:5336-5349. [PMID: 31529516 DOI: 10.1002/mp.13818] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 09/02/2019] [Accepted: 09/05/2019] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To introduce a model that reproducibly linearizes the response from radiochromic film (RCF) dosimetry systems at extended dose range. To introduce a correction method, generated from the same scanned images, which corrects for scanner temporal response variation and scanner bed inhomogeneity. METHODS Six calibration curves were established for different lot numbers of EBT3 GAFCHROMIC™ film model based on four EPSON scanners [10000XL (2 units), 11000XL, 12000XL] at three different centers. These films were calibrated in terms of absorbed dose to water based on TG51 protocol or TRS398 with dose ranges up to 40 Gy. The film response was defined in terms of a proposed normalized pixel value ( n P V RGB ) as a summation of first-order equations based on information from red, green, and blue channels. The fitting parameters of these equations are chosen in a way that makes the film response equal to dose at the time of calibration. An integrated set of correction factors (one per color channel) was also introduced. These factors account for the spatial and temporal changes in scanning states during calibration and measurements. The combination of n P V RGB and this "fingerprint" correction formed the basis of this new protocol and it was tested against net optical density ( n e t O D X = R , G , B ) single-channel dosimetry in terms of accuracy, precision, scanner response variability, scanner bed inhomogeneity, noise, and long-term stability. RESULTS Incorporating multichannel features (RGB) into the normalized pixel value produced linear response to absorbed dose (slope of 1) in all six RCF dosimetry systems considered in this study. The "fingerprint" correction factors of each of these six systems displayed unique patterns at the time of calibration. The application of n P V RGB to all of these six systems could achieve a level of accuracy of ± 2.0% in the dose range of interest within modeled uncertainty level of 2.0%-3.0% depending on the dose level. Consistent positioning of control and measurement film pieces and integrating the multichannel correction into the response function formalism mitigated possible scanner response variations of as much as ± 10% at lower doses and scanner bed inhomogeneity of ± 8% to the established level of uncertainty at the time of calibration. The system was also able to maintain the same level of accuracy after 3 and 6 months post calibration. CONCLUSIONS Combining response linearity with the integrated correction for scanner response variation lead to a sustainable and practical RCF dosimetry system that mitigated systematic response shifts and it has the potential to reduce errors in reporting relative information from the film response.
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Affiliation(s)
- Saad Aldelaijan
- Department of Radiation Oncology, Dana Farber/Brigham and Women's Cancer Center, Harvard Medical School, Boston, MA, 02115, USA
- Department of Biomedical Engineering, Montreal Neurological Institute, McGill University, Montréal, QC, H3A 2B4, Canada
- Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
- Department of Radiation Oncology, SMBD Jewish General Hospital, Montréal, QC, H3T 1E2, Canada
- Biomedical Physics Department, King Faisal Specialist Hospital & Research Centre, Riyadh, 12713, Saudi Arabia
| | - Slobodan Devic
- Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
- Department of Radiation Oncology, SMBD Jewish General Hospital, Montréal, QC, H3T 1E2, Canada
| | | | - Hamed Bekerat
- Department of Radiation Oncology, SMBD Jewish General Hospital, Montréal, QC, H3T 1E2, Canada
| | - Robert A Cormack
- Department of Radiation Oncology, Dana Farber/Brigham and Women's Cancer Center, Harvard Medical School, Boston, MA, 02115, USA
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
| | - Ivan M Buzurovic
- Department of Radiation Oncology, Dana Farber/Brigham and Women's Cancer Center, Harvard Medical School, Boston, MA, 02115, USA
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