1
|
López-Guadalupe VM, Rodríguez-Laguna A, Poitevin-Chacón MA, López-Pineda E, Brandan ME. Out-of-field mean photon energy and dose from 6 MV and 6 MV FFF beams measured with TLD-300 and TLD-100 dosimeters. Med Phys 2021; 48:6567-6577. [PMID: 34528262 DOI: 10.1002/mp.15233] [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: 03/01/2021] [Revised: 09/01/2021] [Accepted: 09/04/2021] [Indexed: 01/02/2023] Open
Abstract
PURPOSE To measure the out-of-field mean photon energy and dose imparted by the secondary radiation field generated by 6 MV and 6 MV FFF beams using TLD-300 and TLD-100 dosimeters and to use the technique to quantify the contributions from the different sources that generate out-of-field radiation. METHODS The mean photon energy and the dose were measured using the TLD-300 glow curve properties and the TLD-100 response, respectively. The TLD-300 glow curve shape was energy-calibrated with gamma rays from 99m Tc, 18 F, 137 Cs, and 60 Co sources, and its energy dependence was quantified by a parameter obtained from the curve deconvolution. The TLD-100 signal was calibrated in absorbed dose-to-water inside the primary field. Dosimeters were placed on the linac head, and on the surface and at 4.5 cm depth in PMMA at 1-15 cm lateral distances from a 10 × 10 cm2 field edge at the isocenter plane. Three configurations of dosimeters around the linac were defined to identify and quantify the contributions from the different sources of out-of-field radiation. RESULTS Typical energies of head leakage were about 500 keV for both beams. The mean energy of collimator-scattered radiation was equal to or larger than 1250 keV and, for phantom-scattered radiation, mean photon energies were 400 keV for the 6 MV and 300 keV for the 6 MV FFF beam. Relative uncertainties to determine mean photon energy were better than 15% for energies below 700 keV, and 40% above 1000 keV. The technique lost its sensitivity to the incident photon energy above 1250 keV. On the phantom surface and at 1-15 cm from the field edge, 80%-90% of out-of-field dose came from scattering in the secondary collimator. At 4.5 cm deep in the phantom and 1-5 cm from the field edge, 50%-60% of the out-of-field dose originated in the phantom. At the points of measurement, the head leakage imparted less than 0.1% of the dose at the isocenter. The 6 MV FFF beam imparted 8-36% less out-of-field dose than the 6 MV beam. These energy results are consistent with general Monte Carlo simulation predictions and show excellent agreement with simulations for a similar linac. The measured out-of-field doses showed good agreement with independent evaluations. CONCLUSIONS The out-of-field mean photon energy and dose imparted by the secondary radiation field were quantified by the applied TLD-300/TLD-100 method. The main sources of out-of-field dose were identified and quantified using three configurations of dosimeters around the linac. This technique could be of value to validate Monte Carlo simulations where the linac head design, configuration, or material composition are unavailable.
Collapse
Affiliation(s)
| | | | | | - Eduardo López-Pineda
- Instituto de Física, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
| | - María-Ester Brandan
- Instituto de Física, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
| |
Collapse
|
2
|
Massillon-Jl G. Future directions on low-energy radiation dosimetry. Sci Rep 2021; 11:10569. [PMID: 34012097 PMCID: PMC8134474 DOI: 10.1038/s41598-021-90152-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 05/05/2021] [Indexed: 01/02/2023] Open
Abstract
For more than one century, low-energy (< 100 keV) photons (x-rays and gamma) have been widely used in different areas including biomedical research and medical applications such as mammography, fluoroscopy, general radiography, computed tomography, and brachytherapy treatment, amongst others. It has been demonstrated that most of the electrons produced by low photon energy beams have energies below 10 keV. However, the physical processes by which these low energy electrons interact with matter are not yet well understood. Besides, it is generally assumed that all the energy deposited within a dosimeter sensitive volume is transformed into a response. But such an assumption could be incorrect since part of the energy deposited might be used to create defects or damages at the molecular and atomic level. Consequently, the relationship between absorbed dose and dosimeter response can be mistaken. During the last few years, efforts have been made to identify models that allow to understand these interaction processes from a quantum mechanical point of view. Some approaches are based on electron-beam − solid-state-interaction models to calculate electron scattering cross-sections while others consider the density functional theory method to localize low energy electrons and evaluate the energy loss due to the creations of defects and damages in matter. The results obtained so far could be considered as a starting point. This paper presents some methodologies based on fundamental quantum mechanics which can be considered useful for dealing with low-energy interactions.
Collapse
Affiliation(s)
- G Massillon-Jl
- Instituto de Física, Universidad Nacional Autónoma de México, 04510, Coyoacan Mexico City, Mexico.
| |
Collapse
|
3
|
Zhang Y, Yan S, Cui Z, Wang Y, Li Z, Yin Y, Li B, Quan H, Zhu J. Out-of-field dose assessment for a 1.5 T MR-Linac with optically stimulated luminescence dosimeters. Med Phys 2021; 48:4027-4037. [PMID: 33714229 PMCID: PMC8360091 DOI: 10.1002/mp.14839] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 02/04/2021] [Accepted: 03/04/2021] [Indexed: 11/06/2022] Open
Abstract
PURPOSE To assess the out-of-field surface and internal dose of the 1.5 T MR-Linac compared to the conventional external beam linac using optically stimulated luminescence dosimeters (OSLDs), and evaluate the out-of-field dose calculation accuracy of the Monaco treatment planning system (TPS) of the 1.5T MR-Linac. METHODS A cubic solid water phantom, with OSLDs on the surface, was vertically irradiated by MR-Linac square fields with different sizes. In addition, OSLDs were arranged out of the beam edges in four directions. An anthropomorphic adult phantom, with 125 cm3 simulated volume, was irradiated in four orthogonal directions by both MR-Linac and conventional linac at the head, thoracic, and pelvic sites. Out-of-field doses were measured by OSLDs on both the surface and internal emulational organs at risk (OARs). The results were compared to the simulated dose from Monaco TPS. RESULTS At different field sizes (5 × 5 to 20 × 20 cm2 ) and distances (1 to 10 cm) to beam edge, the out-of-field surface dose measured on MR-Linac varied from 0.16 % (10 cm to 5 × 5 cm2 edge) to 7.02 % (1 cm to 20 × 20 cm2 edge) of the maximum dose laterally and from 0.14 % (10 cm to 5 × 5 cm2 edge) to 8.56 % (1 cm to 20 × 20 cm2 edge) of the maximum dose longitudinally. Compared to the OSLDs measured data, the Monaco TPS presented an overestimate of the out-of-field dose of OARs at 0-2 % isodose area on both surface and internal check points, and the overestimation gets greater as the distance increases. The underestimation was found to be 0-35% at 2-5% isodose area on both surface and internal check points. Compared to the conventional linac, MR-Linac delivered higher average values of out-of-field dose on surface check points (20%, 19%, 21%) and internal simulated OARs (42%, 37%, 9%) of the anthropomorphic phantom at head, thoracic, and pelvic irradiations, respectively. CONCLUSIONS Compared to the conventional linac, MR-Linac has the same out-of-field dose distribution. However, considering the absolute dose values, MR-Linac delivered relatively higher out-of-field doses on both surface and internal OARs. Additional radiation shielding to patients undergoing MR-Linac may provide protection from out-of-field exposure.
Collapse
Affiliation(s)
- Yan Zhang
- School of Physics and Technology, Wuhan University, Wuhan, P.R. China.,Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, P.R. China
| | - Shaojie Yan
- Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, P.R. China.,School of Nuclear Science and Technology, University of South China, Hengyang, P.R. China
| | - Zhen Cui
- Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, P.R. China
| | - Yungang Wang
- Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, P.R. China
| | - Zhenjiang Li
- Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, P.R. China
| | - Yong Yin
- Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, P.R. China
| | - Baosheng Li
- Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, P.R. China
| | - Hong Quan
- School of Physics and Technology, Wuhan University, Wuhan, P.R. China
| | - Jian Zhu
- Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, P.R. China.,Shandong Medical Imaging and Radiotherapy Engineering Center, Jinan, P.R. China.,Shandong Key Laboratory of Digital Medicine and Computer Assisted Surgery, The Affiliated Hospital of Qingdao University, Qingdao, P.R. China
| |
Collapse
|
4
|
Delana A, Barbareschi A, Consorti R, Daniela Falco M. Dose calculation accuracy in proximity of a pacemaker: A multicenter study with threecommercial treatment planning systems. Phys Med 2020; 80:201-208. [DOI: 10.1016/j.ejmp.2020.10.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 10/02/2020] [Accepted: 10/22/2020] [Indexed: 11/16/2022] Open
|
5
|
García-Hernández T, Vicedo-González A, Sánchez-Nieto B, Romero-Expósito M, Roselló-Ferrando J. PERIPHERAL SURFACE DOSE FROM A LINEAR ACCELERATOR: RADIOCHROMIC FILM EXPERIMENTAL MEASUREMENTS OF FLATTENING FILTER FREE VERSUS FLATTENED BEAMS. RADIATION PROTECTION DOSIMETRY 2020; 188:285-298. [PMID: 31922571 DOI: 10.1093/rpd/ncz286] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 11/06/2019] [Accepted: 11/26/2019] [Indexed: 06/10/2023]
Abstract
There is a growing interest in the use of flattening filter free (FFF) beams due to the shorter treatment times. The reduction of head scatter suggests a better radiation protection to radiotherapy patients, considering the expected decrease in peripheral surface dose (PSD). In this work, PSD of flattened (FF) and FFF-photon beams was compared. A radiochromic film calibration method to reduce energy dependence was used. PSD was measured at distances from 2 to 50 cm to the field border for different square field sizes, modifying relevant clinical parameters. Also, clinical breast and prostate stereotactic body radiotherapy (SBRT) plans were studied. For square beams, FFF PSD is lower compared with FF PSD (differences ranging from 3 to 64%) and 10 MV FFF yields to the lowest value, for distances greater than 5 cm. For SBRT plans, near and far away from the field border, there is a reduction of PSD for FFF-beams, but the behavior at intermediate distances should be checked depending on the case.
Collapse
Affiliation(s)
| | - Aurora Vicedo-González
- Departmento de Física Médica, ERESA Hospital General Universitario de Valencia, Valencia, Spain
| | | | | | - Joan Roselló-Ferrando
- Departmento de Física Médica, ERESA Hospital General Universitario de Valencia, Valencia, Spain
- Departamento de Fisiología, Universidad de Valencia, Valencia, Spain
| |
Collapse
|
6
|
Gayen S, Kombathula SH, Manna S, Varshney S, Pareek P. Dosimetric comparison of coplanar and non-coplanar volumetric-modulated arc therapy in head and neck cancer treated with radiotherapy. Radiat Oncol J 2020; 38:138-147. [PMID: 33012157 PMCID: PMC7533406 DOI: 10.3857/roj.2020.00143] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Accepted: 04/22/2020] [Indexed: 12/25/2022] Open
Abstract
Purpose To evaluate the dosimetric variations in patients of head and neck cancer treated with definitive or adjuvant radiotherapy using optimized non-coplanar (ncVMAT) beams with coplanar (cVMAT) beams using volumetric arc therapy. Materials and Methods Twenty-two patients of head and neck cancer that had received radiotherapy using VMAT in our department were retrospectively analyzed. Each of the patients was planned using coplanar and non-coplanar orientations using an optimized couch angle and fluences. We analyzed the Conformity Index (CIRTOG), Dose Homogeneity Index (DHI), Heterogeneity Index (HIRTOG), low dose volume, target and organs-at-risk coverage in both the plans without changing planning optimization parameters. Results The prescription dose ranged from 60 Gy to 70 Gy. Using ncVMAT, CIRTOG, DHI and HIRTOG, and tumor coverage (ID95%) had improved, low dose spillage volume in the body V5Gy was increased and V10Gy was reduced. Integral dose and intensity-modulated radiation therapy factor had increased in ncVMAT. In the case of non-coplanar beam arrangements, maximum dose (Dmax) of right and left humeral head were reduced significantly whereas apex of the right and left lung mean dose were increased. Conclusion The use of ncVMAT produced better target coverage and sparing of the shoulder and soft tissue of the neck as well as the critical organ compared with the cVMAT in patients of head and neck malignancy.
Collapse
Affiliation(s)
- Sanjib Gayen
- Department of Radiation Oncology, All India Institute of Medical Sciences, Jodhpur, India
| | - Sri Harsha Kombathula
- Department of Radiation Oncology, All India Institute of Medical Sciences, Jodhpur, India
| | - Sumanta Manna
- Department of Radiation Oncology, All India Institute of Medical Sciences, Jodhpur, India
| | - Sonal Varshney
- Department of Radiation Oncology, All India Institute of Medical Sciences, Jodhpur, India
| | - Puneet Pareek
- Department of Radiation Oncology, All India Institute of Medical Sciences, Jodhpur, India
| |
Collapse
|
7
|
Kry SF, Alvarez P, Cygler JE, DeWerd LA, Howell RM, Meeks S, O'Daniel J, Reft C, Sawakuchi G, Yukihara EG, Mihailidis D. AAPM TG 191: Clinical use of luminescent dosimeters: TLDs and OSLDs. Med Phys 2019; 47:e19-e51. [DOI: 10.1002/mp.13839] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Revised: 08/27/2019] [Accepted: 08/28/2019] [Indexed: 12/20/2022] Open
Affiliation(s)
- Stephen F. Kry
- The University of Texas MD Anderson Cancer Center Houston TX USA
| | - Paola Alvarez
- The University of Texas MD Anderson Cancer Center Houston TX USA
| | | | | | | | - Sanford Meeks
- University of Florida Health Cancer Center Orlando FL USA
| | | | | | | | | | | |
Collapse
|
8
|
Miften M, Mihailidis D, Kry SF, Reft C, Esquivel C, Farr J, Followill D, Hurkmans C, Liu A, Gayou O, Gossman M, Mahesh M, Popple R, Prisciandaro J, Wilkinson J. Management of radiotherapy patients with implanted cardiac pacemakers and defibrillators: A Report of the AAPM TG-203 †. Med Phys 2019; 46:e757-e788. [PMID: 31571229 DOI: 10.1002/mp.13838] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Revised: 07/16/2019] [Accepted: 08/28/2019] [Indexed: 11/11/2022] Open
Abstract
Managing radiotherapy patients with implanted cardiac devices (implantable cardiac pacemakers and implantable cardioverter-defibrillators) has been a great practical and procedural challenge in radiation oncology practice. Since the publication of the AAPM TG-34 in 1994, large bodies of literature and case reports have been published about different kinds of radiation effects on modern technology implantable cardiac devices and patient management before, during, and after radiotherapy. This task group report provides the framework that analyzes the potential failure modes of these devices and lays out the methodology for patient management in a comprehensive and concise way, in every step of the entire radiotherapy process.
Collapse
Affiliation(s)
- Moyed Miften
- Task Group 203, Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, CO, 80045, USA
| | - Dimitris Mihailidis
- Task Group 203, University of Pennsylvania, Perelman Center for Advanced Medicine, Philadelphia, PA, 19104, USA
| | - Stephen F Kry
- Department of Radiation Physics, UT MD Anderson Cancer Center, Houston, TX, 77030, USA
| | - Chester Reft
- Department of Radiation Oncology, University of Chicago, Chicago, IL, 60637, USA
| | - Carlos Esquivel
- Department of Radiation Oncology, UT Health Sciences Center, San Antonio, TX, 78229, USA
| | - Jonathan Farr
- Division of Radiological Sciences, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA
| | - David Followill
- Department of Radiation Physics, UT MD Anderson Cancer Center, Houston, TX, 77030, USA
| | - Coen Hurkmans
- Department of Radiotherapy, Catharina Hospital, Eindhoven, the Netherlands
| | - Arthur Liu
- Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, CO, 80045, USA
| | - Olivier Gayou
- Department of Radiation Oncology, Allegheny General Hospital, Pittsburg, PA, 15212, USA
| | - Michael Gossman
- Department of Radiation Oncology, Tri-State Regional Cancer Center, Ashland, KY, 41101, USA
| | - Mahadevappa Mahesh
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, 21287, USA
| | - Richard Popple
- Department of Radiation Oncology, University of Alabama, Birmingham, AL, 35249, USA
| | - Joann Prisciandaro
- Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 48109, USA
| | | |
Collapse
|
9
|
Colnot J, Barraux V, Loiseau C, Berejny P, Batalla A, Gschwind R, Huet C. A new Monte Carlo model of a Cyberknife ® system for the precise determination of out-of-field doses. Phys Med Biol 2019; 64:195008. [PMID: 31387085 DOI: 10.1088/1361-6560/ab38e5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In a previous work, a PENELOPE Monte Carlo model of a Cyberknife system equipped with fixed collimator was developed and validated for in-field dose evaluation. The aim of this work is to extend it to evaluate peripheral doses and to determine the precision of the treatment planning system (TPS) Multiplan in evaluating the off-axis doses. The Cyberknife® head model was completed with surrounding components based on manufacturer drawings. The contribution of the different head parts on the out-of-field dose was studied. To model the attenuation and the modification of particle energy caused by components not modelled, the photon transport was modified in one of the added components. The model was iteratively adjusted to fit dose profiles measured with EBT3 films and an ionization chamber for several collimator sizes. Finally, dose profiles were calculated using the two Multiplan TPS algorithms and were compared to our simulations. The contributions to out-of-field dose were identified as scattered radiation from the phantom and head leakage and scatter originating at the secondary collimator level. Particle transport in the additional pieces was modified to model this radiation. The maximum differences between simulated and measured doses are of 20.4%. Regarding the detector responses away from axis, EBT3 films and the Farmer chamber give similar response (less than 20% difference). The TPS Monte Carlo algorithm underestimates the doses away from axis more importantly for the smaller field sizes (up to 98%). Besides, RayTracing simplifies peripheral dose to a constant value with no inclusion of particle transport. A Monte Carlo model of a Cyberknife system for the determination of out-of-field doses up to 14 cm off-axis was successfully developed and validated for different depths and field sizes in comparison with measurements. This study also confirms that TPS algorithms do not model peripheral dose properly.
Collapse
Affiliation(s)
- J Colnot
- Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Service de Recherche en Dosimétrie, Laboratoire de Dosimétrie des Rayonnements Ionisants, Fontenay-aux-Roses, France. Author to whom correspondence should be addressed
| | | | | | | | | | | | | |
Collapse
|
10
|
Qin Z, Xie T, Dai X, Zhang B, Ma Y, Khan IU, Zhang X, Li H, Yan Y, Zhao W, Li S, Chen Z, Zhang D, Xu J, Hu X, Xing L, Feng K, Lewis E, Sun W. New model for explaining the over-response phenomenon in percentage of depth dose curve measured using inorganic scintillating materials for optical fiber radiation sensors. OPTICS EXPRESS 2019; 27:23693-23706. [PMID: 31510270 DOI: 10.1364/oe.27.023693] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Accepted: 07/23/2019] [Indexed: 06/10/2023]
Abstract
Inorganic scintillating material used in optical fibre sensors (OFS) when used as dosimeters for measuring percentage depth dose (PDD) characteristics have exhibited significant differences when compared to those measured using an ionization chamber (IC), which is the clinical gold standard for quality assurance (QA) assessments. The percentage difference between the two measurements is as high as 16.5% for a 10 × 10 cm2 field at 10 cm depth below the surface. Two reasons have been suggested for this: the presence of an energy effect and Cerenkov radiation. These two factors are analysed in detail and evaluated quantitatively. It is established that the influence of the energy effect is only a maximum of 2.5% difference for a beam size 10 × 10 cm2 compared with the measured ionization chamber values. And the influence of the Cerenkov radiation is less than 0.14% in an inorganic scintillating material in the case of OFS when using Gd2O2S:Tb as the luminescent material. Therefore, there must be other mechanisms leading to over-response. The luminescence mechanism of inorganic scintillating material is theoretically analysed and a new model is proposed and validated that helps explain the over-response phenomenon.
Collapse
|
11
|
Choi HJ, Park H, Yi CY, Kim BC, Shin WG, Min CH. Determining the energy spectrum of clinical linear accelerator using an optimized photon beam transmission protocol. Med Phys 2019; 46:3285-3297. [PMID: 31055830 DOI: 10.1002/mp.13569] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 04/09/2019] [Accepted: 04/25/2019] [Indexed: 12/29/2022] Open
Abstract
PURPOSE The complex beam delivery techniques for patient treatment using a clinical linear accelerator (linac) may result in variations in the photon spectra, which can lead to dosimetric differences in patients that cannot be accounted for by current treatment planning systems (TPSs). Therefore, precise knowledge of the fluence and energy spectrum (ES) of the therapeutic beam is very important. However, owing to the high energy and flux of the beam, the ES cannot be measured directly, and validation of the spectrum modeled in the TPS is difficult. The aim of this study is to develop an efficient beam transmission measurement procedure for accurately reconstructing the ES of a therapeutic x-ray beam generated by a clinical linac. METHODS The attenuation of a 6 MV photon beam from an Elekta Synergy Platform clinical linac through different thicknesses of graphite and lead was measured using an ion chamber. The response of the ion chamber as a function of photon energy was obtained using the Monte Carlo (MC) method in the Geant4 simulation code. Using the curves obtained in the photon beam transmission measurements and the ion chamber energy response, the ES was reconstructed using an iterative algorithm based on a mathematical model of the spectrum. To evaluate the accuracy of the spectrum reconstruction method, the reconstructed ES (ESrecon ) was compared to that determined by the MC simulation (ESMC ). RESULTS The ion chamber model in the Geant4 simulation was well validated by comparing the ion chamber perturbation factors determined by the TRS-398 calibration protocol and EGSnrc; the differences were within 0.57%. The number of transmission measurements was optimized to 10 for efficient spectrum reconstruction according to the rate of increase in the spectrum reconstruction accuracy. The distribution of ESrecon obtained using the measured transmission curves was clearly similar to the reference, ESMC , and the dose distributions in water calculated using ESrecon and ESMC were similar within a 2% local difference. However, in a heterogeneous medium, the dose discrepancy between them was >5% when a complex beam delivery technique composed of 171 control points was used. CONCLUSIONS The proposed measurement procedure required a total time of approximately 1 h to obtain and analyze 20 transmission measurements. In addition, it was confirmed that the transmission curve of high-Z materials influences the accuracy of spectrum reconstruction more than that of low-Z materials. A well-designed transmission measurement protocol suitable for clinical environments could be an essential tool for better dosimetric accuracy in patient treatment and for periodic verification of the beam quality.
Collapse
Affiliation(s)
- Hyun Joon Choi
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493, Korea
| | - Hyojun Park
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493, Korea
| | - Chul Young Yi
- Center for Ionizing Radiation, Korea Research Institute of Standards and Science, Daejeon 34113, Korea
| | - Byoung-Chul Kim
- Center for Ionizing Radiation, Korea Research Institute of Standards and Science, Daejeon 34113, Korea
| | - Wook-Geun Shin
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493, Korea
| | - Chul Hee Min
- Department of Radiation Convergence Engineering, Yonsei University, 1 Yeonsedae-gil, Heungeop-myeon, Wonju, 26493, Korea
| |
Collapse
|
12
|
Kry SF, Bednarz B, Howell RM, Dauer L, Followill D, Klein E, Paganetti H, Wang B, Wuu CS, George Xu X. AAPM TG 158: Measurement and calculation of doses outside the treated volume from external-beam radiation therapy. Med Phys 2017; 44:e391-e429. [DOI: 10.1002/mp.12462] [Citation(s) in RCA: 164] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 05/17/2017] [Accepted: 05/25/2017] [Indexed: 12/14/2022] Open
Affiliation(s)
- Stephen F. Kry
- Department of Radiation Physics; MD Anderson Cancer Center; Houston TX 77054 USA
| | - Bryan Bednarz
- Department of Medical Physics; University of Wisconsin; Madison WI 53705 USA
| | - Rebecca M. Howell
- Department of Radiation Physics; MD Anderson Cancer Center; Houston TX 77054 USA
| | - Larry Dauer
- Departments of Medical Physics/Radiology; Memorial Sloan-Kettering Cancer Center; New York NY 10065 USA
| | - David Followill
- Department of Radiation Physics; MD Anderson Cancer Center; Houston TX 77054 USA
| | - Eric Klein
- Department of Radiation Oncology; Washington University; Saint Louis MO 63110 USA
| | - Harald Paganetti
- Department of Radiation Oncology; Massachusetts General Hospital and Harvard Medical School; Boston MA 02114 USA
| | - Brian Wang
- Department of Radiation Oncology; University of Louisville; Louisville KY 40202 USA
| | - Cheng-Shie Wuu
- Department of Radiation Oncology; Columbia University; New York NY 10032 USA
| | - X. George Xu
- Department of Mechanical, Aerospace, and Nuclear Engineering; Rensselaer Polytechnic Institute; Troy NY 12180 USA
| |
Collapse
|
13
|
Skrobala A, Adamczyk S, Kruszyna-Mochalska M, Skórska M, Konefał A, Suchorska W, Zaleska K, Kowalik A, Jackowiak W, Malicki J. Low dose out-of-field radiotherapy, part 2: Calculating the mean photon energy values for the out-of-field photon energy spectrum from scattered radiation using Monte Carlo methods. Cancer Radiother 2017. [PMID: 28623063 DOI: 10.1016/j.canrad.2017.04.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- A Skrobala
- Electroradiology Department, University of Medical Sciences, Poznan, Poland; Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland.
| | - S Adamczyk
- Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland
| | - M Kruszyna-Mochalska
- Electroradiology Department, University of Medical Sciences, Poznan, Poland; Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland
| | - M Skórska
- Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland
| | - A Konefał
- Department of Nuclear Physics and its Applications, Institute of Physics, Silesian University, Katowice, Poland
| | - W Suchorska
- Radiobiology Laboratories, Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland
| | - K Zaleska
- Radiobiology Laboratories, Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland
| | - A Kowalik
- Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland
| | - W Jackowiak
- Ist Radiotherapy Department, Greater Poland Cancer Centre, Poznan, Poland
| | - J Malicki
- Electroradiology Department, University of Medical Sciences, Poznan, Poland; Medical Physics Department, Greater Poland Cancer Centre, Poznan, Poland
| |
Collapse
|
14
|
Delaby N, Bellec J, Bouvier J, Jouyaux F, Perdrieux M, Castelli J, Lecouillard I, Manens JP, Lafond C. CyberKnife® M6™: Peripheral dose evaluation for brain treatments. Phys Med 2017; 37:88-96. [PMID: 28535920 DOI: 10.1016/j.ejmp.2017.04.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 03/17/2017] [Accepted: 04/12/2017] [Indexed: 10/19/2022] Open
Abstract
PURPOSE This study evaluates the peripheral dose (PD) delivered to healthy tissues for brain stereotactic radiotherapy treatments (SRT) performed with a CyberKnife M6™ Robotic Radiosurgery System and proposes a model to estimate PD before treatment. METHOD PD was measured with thermoluminescent dosimeters. Measurements were performed to evaluate the influence of distance, collimator type (fixed or Iris™) and aperture size on PD for typical brain treatment plans simulated on an anthropomorphic phantom. A model to estimate PD was defined by fitting functions to these measurements. In vivo measurements were subsequently performed on 30 patients and compared to the model-predicted PD. RESULTS PD (in cGy) was about 0.06% of MU at 15cm for a 20mm fixed collimator and 0.04% of MU for the same aperture with Iris™ collimator. In vivo measurements showed an average thyroid dose of 55mGy (σ=18.8mGy). Computed dose for thyroid, breast, umbilicus and gonads showed on average a relative difference of 3.4% with the in vivo dose (σ=12.4%). CONCLUSION PD at the thyroid with Iris™ was about a third lower than with a fixed collimator in case of brain SRT. Despite uncertainties (use of anthropomorphic PD to estimate patient specific PD, surface PD to estimate OAR PD) the model allows PD to be estimated without in vivo measurements. This method could be used to optimise PD with different planning strategies.
Collapse
Affiliation(s)
- N Delaby
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France.
| | - J Bellec
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France
| | - J Bouvier
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France
| | - F Jouyaux
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France
| | - M Perdrieux
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France
| | - J Castelli
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France; Inserm, U1099, 35000 Rennes, France; Université de Rennes-1, LTSI, 35000 Rennes, France
| | - I Lecouillard
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France
| | - J P Manens
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France; Inserm, U1099, 35000 Rennes, France; Université de Rennes-1, LTSI, 35000 Rennes, France
| | - C Lafond
- Centre Eugène Marquis, Département de Radiothérapie, rue de La Bataille Flandres Dunkerque - CS 44229, 35042 Rennes Cedex, France; Inserm, U1099, 35000 Rennes, France; Université de Rennes-1, LTSI, 35000 Rennes, France
| |
Collapse
|
15
|
Vũ Bezin J, Allodji RS, Mège JP, Beldjoudi G, Saunier F, Chavaudra J, Deutsch E, de Vathaire F, Bernier V, Carrie C, Lefkopoulos D, Diallo I. A review of uncertainties in radiotherapy dose reconstruction and their impacts on dose-response relationships. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2017; 37:R1-R18. [PMID: 28118156 DOI: 10.1088/1361-6498/aa575d] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Proper understanding of the risk of radiation-induced late effects for patients receiving external photon beam radiotherapy requires the determination of reliable dose-response relationships. Although significant efforts have been devoted to improving dose estimates for the study of late effects, the most often questioned explanatory variable is still the dose. In this work, based on a literature review, we provide an in-depth description of the radiotherapy dose reconstruction process for the study of late effects. In particular, we focus on the identification of the main sources of dose uncertainty involved in this process and summarise their impacts on the dose-response relationship for radiotherapy late effects. We provide a number of recommendations for making progress in estimating the uncertainties in current studies of radiotherapy late effects and reducing these uncertainties in future studies.
Collapse
Affiliation(s)
- Jérémi Vũ Bezin
- Inserm, Radiation Epidemiology Team, CESP-U1018, F-94807, Villejuif, France. Gustave Roussy, Villejuif, F-94805, France. Paris-Sud University, Orsay, F-91400, France
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Nelson VK, Holloway L, McLean ID. The application of thermoluminescence dosimetry in X-ray energy discrimination. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2015; 38:543-9. [PMID: 26330215 DOI: 10.1007/s13246-015-0374-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Accepted: 08/25/2015] [Indexed: 11/26/2022]
Abstract
Clinical dosimetry requires an understanding of radiation energy to accurately determine the delivered dose. For many situations this is known, however there are also many situations where the radiation energy is not well known, thus limiting dosimetric accuracy. This is the case in personnel dosimetry where thermo luminescent (TL) dosimetry is the method of choice. Traditionally beam energy characteristics in personnel dosimetry are determined through discrimination with the use of various filters fitted within a radiation monitor. The presence of scattered and characteristic radiation produced by these metallic filters, however, can compromise the results. In this study the TL response of five materials TLD100, TLD100H, TLD200, TLD400 and TLD500, was measured at various X-ray energies. The TL sensitivity ratio for various combinations of materials as a function of X-ray energy was calculated. The results indicate that in personal dosimetry a combination of three or more TL detector system has a better accuracy of estimation of effective radiation energy of an X-ray beam than some of the current method of employed for energy estimation and has the potential to improve the accuracy in dose determination in a variety of practical situations. The development of this method also has application in other fields including quality assurance of the orthovoltage therapy machines, dosimetry intercomparisons of kilovoltage X-ray beams, and measurement of the dose to critical organs outside a treatment field of a megavoltage therapy beam.
Collapse
Affiliation(s)
- V K Nelson
- Liverpool and Macarthur Cancer Therapy Centres, Therry Road, Campbelltown, NSW, 2560, Australia.
| | - L Holloway
- Liverpool and Macarthur Cancer Therapy Centres, Therry Road, Campbelltown, NSW, 2560, Australia
- Institute of Medical Physics, Sydney University, Sydney, NSW, 2000, Australia
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2560, Australia
| | - I D McLean
- Medical Physics Department, Canberra Hospital, Garran, ACT, 2605, Australia
| |
Collapse
|
17
|
Zutz H, Hupe O. Ambient dose and dose rate measurements in the vicinity of Elekta Precise accelerators for radiation therapy. RADIATION PROTECTION DOSIMETRY 2014; 162:431-437. [PMID: 24379437 DOI: 10.1093/rpd/nct356] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In radiation therapy, commercially available medical linear accelerators (LINACs) are used. At high primary beam energies in the 10-MeV range, the leakage dose of the accelerator head and the backscatter from the room walls, the air and the patient become more important. Therefore, radiation protection measurements of photon dose rates in the treatment room and in the maze are performed to quantify the radiation field. Since the radiation of the LINACs is usually pulsed with short radiation pulse durations in the microsecond range, there are problems with electronic dose (rate) meters commonly used in radiation protection. In this paper measurements with ionisation chambers are presented and electronic dosemeters are used for testing at selected positions. The measured time-averaged dose rate ranges from a few microsieverts per hour in the maze to some millisieverts per hour in the vicinity of the accelerator head and up to some sieverts per hour in the blanked primary beam and several hundred sieverts per hour in the direct primary beam.
Collapse
Affiliation(s)
- H Zutz
- Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, Braunschweig D-38116, Germany
| | - O Hupe
- Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, Braunschweig D-38116, Germany
| |
Collapse
|
18
|
Photon dosimetry methods outside the target volume in radiation therapy: Optically stimulated luminescence (OSL), thermoluminescence (TL) and radiophotoluminescence (RPL) dosimetry. RADIAT MEAS 2013. [DOI: 10.1016/j.radmeas.2013.03.004] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
|
19
|
Hälg RA, Besserer J, Schneider U. Systematic measurements of whole-body dose distributions for various treatment machines and delivery techniques in radiation therapy. Med Phys 2012; 39:7662-76. [DOI: 10.1118/1.4767773] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
20
|
Estimating dose to implantable cardioverter-defibrillator outside the treatment fields using a skin QED diode, optically stimulated luminescent dosimeters, and LiF thermoluminescent dosimeters. Med Dosim 2012; 37:334-8. [DOI: 10.1016/j.meddos.2011.11.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 09/16/2011] [Accepted: 11/08/2011] [Indexed: 11/19/2022]
|
21
|
Chofor N, Harder D, Poppe B. Non-reference condition correction factor kNR of typical radiation detectors applied for the dosimetry of high-energy photon fields in radiotherapy. Z Med Phys 2012; 22:181-96. [DOI: 10.1016/j.zemedi.2012.05.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Revised: 03/29/2012] [Accepted: 05/03/2012] [Indexed: 11/25/2022]
|
22
|
Quinn A, Holloway L, Cutajar D, Hardcastle N, Rosenfeld A, Metcalfe P. Megavoltage cone beam CT near surface dose measurements: potential implications for breast radiotherapy. Med Phys 2011; 38:6222-7. [DOI: 10.1118/1.3641867] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
23
|
Low-energy photons in high-energy photon fields – Monte Carlo generated spectra and a new descriptive parameter. Z Med Phys 2011; 21:183-97. [DOI: 10.1016/j.zemedi.2011.02.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Revised: 02/17/2011] [Accepted: 02/19/2011] [Indexed: 12/22/2022]
|
24
|
Wagner D, Anton M, Vorwerk H. Dose uncertainty in radiotherapy of patients with head and neck cancer measured byin vivoESR/alanine dosimetry using a mouthpiece. Phys Med Biol 2011; 56:1373-83. [DOI: 10.1088/0031-9155/56/5/010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
|
25
|
Chiu-Tsao ST, Chan MF. Evaluation of two-dimensional bolus effect of immobilization/support devices on skin doses: a radiochromic EBT film dosimetry study in phantom. Med Phys 2010; 37:3611-20. [PMID: 20831069 DOI: 10.1118/1.3439586] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
PURPOSE In this study, the authors have quantified the two-dimensional (2D) perspective of skin dose increase using EBT film dosimetry in phantom in the presence of patient immobilization devices during conventional and IMRT treatments. METHODS For 6 MV conventional photon field, the authors evaluated and quantified the 2D bolus effect on skin doses for six different common patient immobilization/support devices, including carbon fiber grid with Mylar sheet, Orfit carbon fiber base plate, balsa wood board, Styrofoam, perforated AquaPlast sheet, and alpha-cradle. For 6 and 15 MV IMRT fields, a stack of two film layers positioned above a solid phantom was exposed at the air interface or in the presence of a patient alpha-cradle. All the films were scanned and the pixel values were converted to doses based on an established calibration curve. The authors determined the 2D skin dose distributions, isodose curves, and cross-sectional profiles at the surface layers with or without the immobilization/support device. The authors also generated and compared the dose area histograms (DAHs) and dose area products from the 2D skin dose distributions. RESULTS In contrast with 20% relative dose [(RD) dose relative to dmax on central axis] at 0.0153 cm in the film layer for 6 MV 10 x 10 cm2 open field, the average RDs at the same depth in the film layer were 71%, 69%, 55%, and 57% for Orfit, balsa wood, Styrofoam, and alpha-cradle, respectively. At the same depth, the RDs were 54% under a strut and 26% between neighboring struts of a carbon fiber grid with Mylar sheet, and between 34% and 56% for stretched perforated AquaPlast sheet. In the presence of the alpha-cradle for the 6 MV (15 MV) IMRT fields, the hot spot doses at the effective measurement depths of 0.0153 and 0.0459 cm were 140% and 150%, (83% and 89%), respectively, of the isocenter dose. The enhancement factor was defined as the ratio of a given DAH parameter (minimum dose received in a given area) with and without the support device. For 6 MV conventional 10 x 10 cm2 field, the enhancement factor was the highest (3.4) for the Orfit carbon fiber plate. As for the IMRT field, the enhancement factors varied with the size of the area of interest and were as high as 3.8 (4.3) at the hot spot of 5 cm2 area in the top film layer (0.0153 cm) for 6 MV (15 MV) beams. CONCLUSIONS Significant 2D bolus effect on skin dose in the presence of patient support and immobilization devices was confirmed and quantified with EBT film dosimetry. Furthermore, the EBT film has potential application for in vivo monitoring of the 2D skin dose distributions during patient treatments.
Collapse
|
26
|
Chofor N, Harder D, Rühmann A, Willborn KC, Wiezorek T, Poppe B. Experimental study on photon-beam peripheral doses, their components and some possibilities for their reduction. Phys Med Biol 2010; 55:4011-27. [DOI: 10.1088/0031-9155/55/14/005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
27
|
Mapping radiation quality inside photon-irradiated absorbers by means of a twin-chamber method. Z Med Phys 2009; 19:252-63. [DOI: 10.1016/j.zemedi.2009.05.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2009] [Revised: 05/28/2009] [Accepted: 05/30/2009] [Indexed: 11/22/2022]
|
28
|
Use of new radiochromic devices for peripheral dose measurement: potential in-vivo dosimetry application. Biomed Imaging Interv J 2009; 5:e16. [PMID: 21610987 PMCID: PMC3097720 DOI: 10.2349/biij.5.4.e16] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Revised: 06/23/2009] [Accepted: 06/23/2009] [Indexed: 11/17/2022] Open
Abstract
The authors have studied the feasibility of using three new high-sensitivity radiochromic devices in measuring the doses to peripheral points outside the primary megavoltage photon beams. The three devices were GAFCHROMIC® EBT film, prototype Low Dose (LD) Film, and prototype LD Card. The authors performed point dosimetry using these three devices in water-equivalent solid phantoms at x = 3,5,8,10, and 15 cm from the edge of 6 MV and 15 MV photon beams of 10x10 cm(2), and at depths of 0, 0.5 cm, and depth of maximum dose. A full sheet of EBT film was exposed with 5000 MU. The prototype LD film pieces were 1.5x2 cm(2) in size. Some LD films were provided in the form of a card in 1.8x5 cm(2) holding an active film in 1.8x2 cm(2). These are referred to as "LD dosimeter cards". The small LD films and cards were exposed with 500 MU. For each scanned film, a 6 mm circular area centered at the measurement point was sampled and the mean pixel value was obtained. The calibration curves were established from the calibration data for each combination of film/cards and densitometer/scanner. The doses at the peripheral points determined from the films were compared with those obtained using ion chamber at respective locations in a water phantom and general agreements were found. It is feasible to accurately measure peripheral doses of megavoltage photon beams using the new high-sensitivity radiochromic devices. This near real-time and inexpensive method can be applied in a clinical setting for dose measurements to critical organs and sensitive patient implant devices.
Collapse
|
29
|
Abstract
The recent discussion and debate about the use of in vivo dosimetry as a routine component of the radiotherapy treatment process has not included the limitations introduced by the physical characteristics of the detectors. Although a robust calibration procedure will ensure acceptable uncertainties in the measurements of tumour dose, further work is required to confirm the accuracy of critical organ measurements with a diode or a thermoluminescent dosemeter outside the main field owing to limitations caused by a non-uniform X-ray energy response of the detector, differences between the X-ray energy spectrum inside and outside the main field, and contaminating electrons.
Collapse
|
30
|
Chiu-Tsao ST, Chan MF. Photon beam dosimetry in the superficial buildup region using radiochromic EBT film stack. Med Phys 2009; 36:2074-83. [PMID: 19610296 DOI: 10.1118/1.3125134] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
It has been a challenge to perform accurate 2D or 3D dosimetry in the surface region with steep dose gradient for megavoltage photon beams. We developed a dosimetry method in the superficial buildup region for the 6 and 15 MV photon beams using a radiochromic EBT film stack. Eight radiochromic EBT film strips (3 x 20 x 0.024 cm3) stacked together formed a 3D dosimeter. The film stack was positioned above a polystyrene phantom and surrounded by Solid Water slabs (0.2 cm) with the top film layer at 100 cm SSD. A 10 x 10 cm2 open field was used to irradiate the film stack with 1000 MU. All films were scanned using Epson 4870 flatbed scanner with transmission mode, 48 bit color, and 150 dpi (0.017 cm pixel resolution). The pixel values were converted to doses using an established calibration curve. This method allowed dose measurement for depths from 0.012 to 0.18 cm with fine spatial resolution (0.017 cm horizontally and 0.024 cm vertically). For each energy modality, we obtained both the central axis percent depth doses and the beam profiles along the central line covering the primary field and peripheral region at each depth. The primary field doses varied steeply with depth, while those in the peripheral region were weakly dependent on depth. For the 6 MV and 15 MV photon beams, (1) the central axis percent depth doses in the eight film layers ranged from 22% to 66% and from 15% to 44%, respectively; (2) the extrapolated percent depth doses at d = 0 were 15% and 14%, respectively. Agreement with the previously reported central axis percent depth doses in this region using parallel plate thin window ion chamber and ultrathin TLD was observed. The percent depth doses and beam profiles data can be incorporated in the treatment planning system for more accurate assessment of the doses to skin and shallow tumors to accomplish more accurate calculation results in the clinical usage.
Collapse
|
31
|
Edwards CR, Hamer E, Mountford PJ, Moloney AJ. An update survey of UK in vivo radiotherapy dosimetry practice. Br J Radiol 2007; 80:1011-4. [PMID: 17967849 DOI: 10.1259/bjr/14945156] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
A questionnaire was distributed in 2004 to 59 radiotherapy physics departments in the UK to determine whether in vivo dosimetry practice had changed since a similar survey conducted 10 years earlier. The number of centres carrying out central axis dosimetry had increased slightly from 17 centres in 1994 to 22 centres in 2004, with a diode alone being the most commonly used detector. Twice as many centres (43) carried out critical organ dosimetry compared with those carrying out central axis measurements, and this number had also increased slightly above the 1994 value (38). A diode was used by most centres carrying out central axis dosimetry and by about 50% of centres carrying out critical organ dosimetry. The action level adopted by each centre for central axis measurements varied from >+/-3% to >+/-10% difference between the measured and the prescribed dose, with >+/-5% being the most frequent value. It was concluded that there had been little change in in vivo dosimetry practice during the time between the two surveys, and that guidance on the method and applications for in vivo dosimetry is required before recent recommendations for its widespread adoption for routine use can be satisfied.
Collapse
Affiliation(s)
- C R Edwards
- Department of Radiotherapy Physics, University Hospital of North Staffordshire, Princes Road, Hartshill, Stoke-on-Trent, Staffordshire ST4 7LN, UK.
| | | | | | | |
Collapse
|
32
|
Jang SY, Liu HH, Mohan R, Siebers JV. Variations in energy spectra and water-to-material stopping-power ratios in three-dimensional conformal and intensity-modulated photon fields. Med Phys 2007; 34:1388-97. [PMID: 17500470 DOI: 10.1118/1.2710550] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Because of complex dose distributions and dose gradients that are created in three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiation therapy (IMRT), photon- and electron-energy spectra might change significantly with spatial locations and doses. This study examined variations in photon- and electron-energy spectra in 3D-CRT and IMRT photon fields. The effects of spectral variations on water-to-material stopping-power ratios used in Monte Carlo treatment planning systems and the responses of energy-dependent dosimeters, such as thermoluminescent dosimeters (TLDs) and radiographic films were further studied. The EGSnrc Monte Carlo code was used to simulate megavoltage 3D-CRT and IMRT photon fields. The photon- and electron-energy spectra were calculated in 3D water phantoms and anthropomorphic phantoms based on the fluence scored in voxel grids. We then obtained the water-to-material stopping-power ratios in the local voxels using the Spencer-Attix cavity theory. Changes in the responses of films and TLDs were estimated based on the calculated local energy spectra and published data on the dosimeter energy dependency. Results showed that the photon-energy spectra strongly depended on spatial positions and doses in both the 3D-CRT and IMRT fields. The relative fraction of low-energy photons (< 100 keV) increased inversely with the photon dose in low-dose regions of the fields. A similar but smaller effect was observed for electrons in the phantoms. The maximum variation of the water-to-material stopping-power ratio over the range of calculated dose for both 3D-CRT and IMRT was negligible (< 1.0%) for ICRU tissue, cortical bone, and soft bone and less than 3.6% for dry air and lung. Because of spectral softening at low doses, radiographic films in the phantoms could over-respond to dose by more than 30%, whereas the over-response of TLDs was less than 10%. Thus, spatial variations of the photon- and electron-energy spectra should be considered as important factors in 3D-CRT and IMRT dosimetry.
Collapse
Affiliation(s)
- Si Young Jang
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030, USA
| | | | | | | |
Collapse
|
33
|
Edwards CR, Mountford PJ, Moloney AJ. Effect of electron contamination of a 6 MV x-ray beam on near surface diode dosimetry. Phys Med Biol 2006; 51:6471-82. [PMID: 17148830 DOI: 10.1088/0031-9155/51/24/013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In critical organ in vivo x-ray dosimetry, the relative contaminating electron contribution to the total dose and total detector response outside the field will be different to the corresponding contributions at the central axis detector calibration position, mainly due to the effects of shielding in the linear accelerator head on the electron and x-ray energy spectrum. To investigate these contributions, the electron energy response of a Scanditronix PFD diode was measured using electrons with mean energies from 0.45 to 14.6 MeV, and the Monte Carlo code MCNP-4C was used to calculate the electron energy spectra on the central axis, and at 1 and 10 cm outside the edge of a 4 x 4, 10 x 10 and a 15 x 15 cm(2) 6 MV x-ray field. The electron contribution to the total dose varied from about 8% on the central axis of the smallest field to about 76% at 10 cm outside the edge of the largest field. The electron contribution to the total diode response varied from about 7-8% on the central axis of all three fields to about 58% at 10 cm outside the edge of the smallest field. The results indicated that a near surface x-ray dose measurement with a diode outside the treatment field has to be interpreted with caution and requires knowledge of the relative electron contribution specific to the measurement position and field size.
Collapse
Affiliation(s)
- C R Edwards
- Medical Physics Directorate, University Hospital of North Staffordshire, Princes Road, Hartshill, Stoke-on-Trent, Staffordshire, ST4 7LN, UK.
| | | | | |
Collapse
|
34
|
Mazonakis M, Tzedakis A, Damilakis J, Varveris H, Kachris S, Gourtsoyiannis N. Scattered dose to thyroid from prophylactic cranial irradiation during childhood: a Monte Carlo study. Phys Med Biol 2006; 51:N139-45. [PMID: 16585835 DOI: 10.1088/0031-9155/51/8/n01] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The purpose of this study was to estimate the scattered dose to thyroid from prophylactic cranial irradiation during childhood. The MCNP transport code and mathematical phantoms representing the average individual at ages 3, 5, 10, 15 and 18 years old were employed to simulate cranial radiotherapy using two lateral opposed fields. The mean radiation dose received by the thyroid gland was calculated. A 10 cm thick lead block placed on the patient's couch to shield the thyroid was simulated by MCNP code. The Monte Carlo model was validated by measuring the scattered dose to the unshielded and shielded thyroid using three different humanoid phantoms and thermoluminescense dosimetry. For a cranial dose of 18 Gy, the thyroid dose obtained by Monte Carlo calculations varied from 47 to 79 cGy depending upon the age of the child. Appropriate placement of the couch block resulted in a thyroid dose reduction by 39 to 54%. Thyroid dose values at all possible positions of the radiosensitive gland with respect to the inferior field edge at five different patient ages were found. The mean difference between Monte Carlo results and thyroid dose measurements was 9.6%.
Collapse
Affiliation(s)
- Michalis Mazonakis
- Department of Medical Physics, University Hospital of Iraklion, 71110 Iraklion, Crete, Greece.
| | | | | | | | | | | |
Collapse
|
35
|
Edwards CR, Mountford PJ, Green S, Palethorpe JE, Moloney AJ. The low energy X-ray response of the LiF:Mg:Cu:P thermoluminescent dosemeter: a comparison with LiF:Mg:Ti. Br J Radiol 2005; 78:543-7. [PMID: 15900061 DOI: 10.1259/bjr/73133162] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
LiF:Mg:Cu:P thermoluminescent dosemeters (TLD) can be used for the same X-ray dosimetry applications as LiF:Mg:Ti, with each type having the disadvantage of a response dependent on energy, particularly at low energies. Measurements were made of the response per unit air kerma of LiF:Mg:Cu:P and LiF:Mg:Ti to nine quasi-monoenergetic X-ray beams with mean energies from 12 keV to 208 keV. Each measurement was normalized to the value produced by 6 MV X-rays. LiF:Mg:Cu:P was found to under-respond to a majority of these radiations whereas LiF:Mg:Ti over-responded to a majority. Their smallest relative measured response was produced by the lowest energy beam, and the maximum measured relative response of 1.15+/-0.07 and 1.21+/-0.07 for LiF:Mg:Cu:P and LiF:Mg:Ti, respectively, occurred at 33 keV. Energy response coefficients were derived from these measurements to estimate the error introduced by using either type of TLD to measure the dose from an X-ray spectrum different to that used for its absolute response calibration. It was calculated that if the response of either type of TLD was calibrated at 100 kVp, then an error of no more than +/-2% would be introduced into measurements of tube output at potentials of 50-130 kVp. LiF:Mg:Cu:P was found to introduce a larger error (up to 30%) into the measurement of body exit dose than LiF:Mg:Ti at tube potentials of 40-150 kVp, if its absolute response was calibrated using the corresponding body entrance beam. The method should allow this type of error to be estimated in other dosimetry applications for either type of TLD.
Collapse
Affiliation(s)
- C R Edwards
- Medical Physics Directorate, University Hospital of North Staffordshire, Princes Road, Hartshill, Stoke-on-Trent, Staffordshire ST4 7LN, UK
| | | | | | | | | |
Collapse
|