1
|
Dosimetric accuracy of a cross-calibration coefficient for plane-parallel ionization chamber obtained in low-energy electron beams using various cylindrical dosimeters. POLISH JOURNAL OF MEDICAL PHYSICS AND ENGINEERING 2021. [DOI: 10.2478/pjmpe-2021-0036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Abstract
Introduction: The accuracy of the cross-calibration procedure depends on ionization chamber type, both used as reference one and under consideration. Also, the beam energy and phantom medium could influence the precision of cross calibration coefficient, resulting in a systematic error in dose estimation and thus could influence the linac beam output checking. This will result in a systematic mismatch between dose calculated in treatment planning system and delivered to the patient.
Material and methods: The usage of FC65-G, CC13 and CC01 thimble reference chambers as well as 6, 9, and 15 MeV electron beams has been analyzed. A plane-parallel PPC05 chamber was calibrated since scarce literature data are available for this dosimeter type. The influence of measurement medium and an effective point of measurement (EPOM) on obtained results are also presented.
Results: Dose reconstruction precision of ~0.1% for PPC05 chamber could be obtained when cross-calibration is based on a thimble CC13 chamber. Nd,w,Qcross obtained in beam ≥ 9MeV gives 0.1 – 0.5% precision of dose reconstruction.
Without beam quality correction, 15 MeV Nd,w,Qcross is 10% lower than Co-60 Nd,w,0. Various EPOM shifts resulted in up to 0.6% discrepancies in Nd,w,Qcross values.
Conclusions: Ionization chamber with small active volume and tissue-equivalent materials supplies more accurate cross-calibration coefficients in the range of 6 – 15 MeV electron beams. In the case of 6 and 9 MeV beams, the exact position of an effective point of measurement is of minor importance. In-water cross-calibration coefficient can be used in a solid medium without loss of dose accuracy.
Collapse
|
2
|
Akino Y, Das IJ, Fujiwara M, Kaneko A, Masutani T, Mizuno H, Isohashi F, Suzuki O, Seo Y, Tamari K, Ogawa K. Characteristics of microSilicon diode detector for electron beam dosimetry. JOURNAL OF RADIATION RESEARCH 2021:rrab085. [PMID: 34559877 DOI: 10.1093/jrr/rrab085] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 05/31/2021] [Indexed: 06/13/2023]
Abstract
A microSilicon™ (PTW type 60023), a new unshielded diode detector succeeding Diode E (model 60017, PTW), was characterized for electron beam dosimetry and compared with other detectors. Electron beams generated from a TrueBeam linear accelerator were measured using the microSilicon, Diode E, and microDiamond synthetic single-crystal diamond detector. Positional accuracy of microSilicon was measured by data collected in air and water. The percent depth dose (PDD), off-center ratio (OCR), dose-response linearity, dose rate dependence, and cone factors were evaluated. The PDDs were compared with data measured using a PPC40 plane-parallel ionization chamber. The maximum variations of depth of 50% and 90% of the maximum dose, and practical depth among all detectors and energies were 0.9 mm. The maximum variations of the bremsstrahlung dose among all detectors and energies were within 0.3%. OCR showed good agreement within 1% for the flat and tail regions. The microSilicon detector showed a penumbra width similar to microDiamond, whereas Diode E showed the steepest penumbra shape. All detectors showed good dose-response linearity and stability against the dose rate; only Diode E demonstrated logarithmic dose rate dependency. The cone factor measured with microSilicon was within ±1% for all energies and cone sizes. We demonstrated that the characteristics of microSilicon is suitable for electron beam dosimetry. The microSilicon detector can be a good alternative for electron beam dosimetry in terms of providing an appropriate PDD curve without corrections, high spatial resolution for OCR measurements and cone factors.
Collapse
Affiliation(s)
- Yuichi Akino
- Department of Radiation Oncology, Osaka University Graduate School of Medicine, Suita, Osaka, 565-0871, Japan
- Department of Radiation Oncology, Suita Tokushukai Hospital, Suita, Osaka, 565-0814, Japan
| | - Indra J Das
- Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Masateru Fujiwara
- Department of Radiation Oncology, Suita Tokushukai Hospital, Suita, Osaka, 565-0814, Japan
| | - Akari Kaneko
- Department of Radiation Oncology, Suita Tokushukai Hospital, Suita, Osaka, 565-0814, Japan
| | - Takashi Masutani
- Department of Radiation Oncology, Suita Tokushukai Hospital, Suita, Osaka, 565-0814, Japan
| | - Hirokazu Mizuno
- Department of Central Radiology, Osaka Rosai Hospital, Sakai, Osaka, 591-8025, Japan
| | - Fumiaki Isohashi
- Department of Radiation Oncology, Osaka University Graduate School of Medicine, Suita, Osaka, 565-0871, Japan
| | - Osamu Suzuki
- Osaka Heavy Ion Therapy Center, Osaka, 540-0008, Japan
| | - Yuji Seo
- Department of Radiation Oncology, Osaka University Graduate School of Medicine, Suita, Osaka, 565-0871, Japan
| | - Keisuke Tamari
- Department of Radiation Oncology, Osaka University Graduate School of Medicine, Suita, Osaka, 565-0871, Japan
| | - Kazuhiko Ogawa
- Department of Radiation Oncology, Osaka University Graduate School of Medicine, Suita, Osaka, 565-0871, Japan
| |
Collapse
|
3
|
Anusionwu PC, Alpuche Aviles JE, Pistorius S. The use of 0.5r cav as an effective point of measurement for cylindrical chambers may result in a systematic shift of electron percentage depth doses. J Appl Clin Med Phys 2020; 21:117-126. [PMID: 31898872 PMCID: PMC6964751 DOI: 10.1002/acm2.12797] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 10/29/2019] [Accepted: 11/22/2019] [Indexed: 11/29/2022] Open
Abstract
Electron dosimetry can be performed using cylindrical chambers, plane‐parallel chambers, and diode detectors. The finite volume of these detectors results in a displacement effect which is taken into account using an effective point of measurement (EPOM). Dosimetry protocols have recommended a shift of 0.5 rcav for cylindrical chambers; however, various studies have shown that the optimal shift may deviate from this recommended value. This study investigated the effect that the selection of EPOM shift for cylindrical chamber has on percentage depth dose (PDD) curves. Depth dose curves were measured in a water phantom for electron beams with energies ranging from 6 to 18 MeV. The detectors investigated were of three different types: diodes (Diode‐E PTW 60017 and SFD IBA), cylindrical (Semiflex PTW 31010, PinPoint PTW 31015, and A12 Exradin), and parallel plate ionization chambers (Advanced Markus PTW 34045 and Markus PTW 23343). Depth dose curves measured with Diode‐E and Advanced Markus agreed within 0.2 mm at R50 except for 18 MeV and extremely large field size. The PDDs measured with the Semiflex chamber and Exradin A12 were about 1.1 mm (with respect to the Advanced Markus chamber) shallower than those measured with the other detectors using a 0.5 rcav shift. The difference between the PDDs decreased when a Pinpoint chamber, with a smaller cavity radius, was used. Agreement improved at lower energies, with the use of previously published EPOM corrections (0.3 rcav). Therefore, the use of 0.5 rcav as an EPOM may result in a systematic shift of the therapeutic portion of the PDD (distances < R90). Our results suggest that a 0.1 rcav shift is more appropriate for one chamber model (Semiflex PTW 31010).
Collapse
Affiliation(s)
- Princess C Anusionwu
- CancerCare Manitoba, Winnipeg, Canada.,Department of Physics & Astronomy, University of Manitoba, Winnipeg, Canada
| | - Jorge E Alpuche Aviles
- CancerCare Manitoba, Winnipeg, Canada.,Department of Physics & Astronomy, University of Manitoba, Winnipeg, Canada.,Department of Radiology, University of Manitoba, Winnipeg, Canada
| | - Stephen Pistorius
- CancerCare Manitoba, Winnipeg, Canada.,Department of Physics & Astronomy, University of Manitoba, Winnipeg, Canada.,Department of Radiology, University of Manitoba, Winnipeg, Canada
| |
Collapse
|
4
|
Evaluation of characteristics of high-energy electron beams using N-isopropyl-acrylamide gel dosimeter. Radiat Phys Chem Oxf Engl 1993 2017. [DOI: 10.1016/j.radphyschem.2017.02.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
5
|
Siebers JV, Ververs JD, Tessier F. Quantitative ionization chamber alignment to a water surface: Theory and simulation. Med Phys 2017; 44:3794-3804. [PMID: 28477370 DOI: 10.1002/mp.12319] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 10/25/2016] [Accepted: 12/08/2016] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To examine the response properties of cylindrical cavity ionization chambers (ICs) in the depth-ionization buildup region so as to obtain a robust chamber-signal - based method for definitive water surface identification, hence absolute ionization chamber depth localization. METHOD & MATERIALS An analytical model with simplistic physics and geometry is developed to explore the theoretical aspects of ionization chamber response near a phantom water surface. Monte Carlo simulations with full physics and ionization chamber geometry are utilized to extend the model's findings to realistic ion chambers in realistic beams and to study the effects of IC design parameters on the entrance dose response. Design parameters studied include full and simplified IC designs with varying central electrode thickness, wall thickness, and outer chamber radius. Piecewise continuous fits to the depth-ionization signal gradient are used to quantify potential deviation of the gradient discontinuity from the chamber outer radius. Exponential, power, and hyperbolic sine functional forms are used to model the gradient for chamber depths of zero to the depth of the gradient discontinuity. RESULTS The depth-ionization gradient as a function of depth is maximized and discontinuous when a submerged IC's outer radius coincides with the water surface. We term this depth the gradient chamber alignment point (gCAP). The maximum deviation between the gCAP location and the chamber outer radius is 0.13 mm for a hypothetical 4 mm thick wall, 6.45 mm outer radius chamber using the power function fit, however, the chamber outer radius is within the 95% confidence interval of the gCAP determined by this fit. gCAP dependence on the chamber wall thickness is possible, but not at a clinically relevant level. CONCLUSIONS The depth-ionization gradient has a discontinuity and is maximized when the outer-radius of a submerged IC coincides with the water surface. This feature can be used to auto-align ICs to the water surface at the time of scanning and/or be applied retrospectively to scan data to quantify absolute IC depth. Utilization of the gCAP should yield accurate and reproducible depth calibration for clinical depth-ionization measurements between setups and between users.
Collapse
Affiliation(s)
- Jeffrey V Siebers
- Department of Radiation Oncology, University of Virginia, Charlottesville, VA, 22908, USA.,Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, 23298-0058, USA
| | - James D Ververs
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, 23298-0058, USA.,Department of Radiation Oncology, Wake Forest University Baptist Medical Center, Winston Salem, NC, 27157, USA
| | - Frédéric Tessier
- Ionizing Radiation Standards, National Research Council of Canada, Ottawa, K1A OR6, Canada
| |
Collapse
|
6
|
Ono T, Araki F, Yoshiyama F. Possibility of using cylindrical ionization chambers for percent depth-dose measurements in clinical electron beams. Med Phys 2011; 38:4647-54. [DOI: 10.1118/1.3608903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
7
|
Experimental determination of the effective point of measurement of cylindrical ionization chambers for high-energy photon and electron beams. Phys Med 2010; 26:126-31. [PMID: 19926506 DOI: 10.1016/j.ejmp.2009.10.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Revised: 07/31/2009] [Accepted: 10/08/2009] [Indexed: 11/20/2022] Open
|
8
|
Ververs JD, Schaefer MJ, Kawrakow I, Siebers JV. A method to improve accuracy and precision of water surface identification for photon depth dose measurements. Med Phys 2009; 36:1410-20. [PMID: 19472648 DOI: 10.1118/1.3098125] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
The objective of this study is to present a method to reduce the setup error inherent in clinical depth dose measurements and, in doing so, to improve entrance dosimetry measurement reliability. Ionization chamber (IC) depth dose measurements are acquired with the depth scan extended into the air above the water surface. An inflection region is obtained in each resulting percent depth ionization (PDI) curve that can be matched against other measurements or to an inflection region obtained from an analogous Monte Carlo (MC) simulation. Measurements are made with various field sizes for the 6 and 18 MV photon beams, with and without a Pb foil in the beam, to determine the sensitivity of the dose inflection region to the beam conditions. The offset between reference and test data set inflection regions is quantified using two separate methods. When comparing sets of measured data, maxima in the second derivative of ionization are compared. When comparing measured data to MC simulation, the offset that minimizes the sum of squared differences between the reference and test curves in the ionization inflection region is found. These methods can be used to quantify the offset between an initial setup (test) position and the true surface (reference) position. The ionization inflection location is found to be insensitive to changes in field size, electron contamination, and beam energy. Data from a single reference condition should be sufficient to identify the surface location. The method of determining IC offsets is general and should be applicable to any IC and other radiation sources. The measurement method could reduce the time and effort required in the initial IC setup at a water surface as setup errors can be corrected offline. Given a reliable set of reference data to compare with, this method could increase the ability of quality assurance (QA) measurements to detect discrepancies in beam output as opposed to discrepancies in IC localization. Application of the measurement method standardizes the procedure for localizing cylindrical ICs at a water surface and thereby improves the reliability of measurements taken with these devices at all depths.
Collapse
Affiliation(s)
- J D Ververs
- Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
| | | | | | | |
Collapse
|
9
|
Das IJ, Cheng CW, Watts RJ, Ahnesjö A, Gibbons J, Li XA, Lowenstein J, Mitra RK, Simon WE, Zhu TC. Accelerator beam data commissioning equipment and procedures: Report of the TG-106 of the Therapy Physics Committee of the AAPM. Med Phys 2008; 35:4186-215. [PMID: 18841871 DOI: 10.1118/1.2969070] [Citation(s) in RCA: 287] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- Indra J Das
- Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Günhan B, Kemikler G, Koca A. Determination of surface dose and the effect of bolus to surface dose in electron beams. Med Dosim 2004; 28:193-8. [PMID: 14563440 DOI: 10.1016/s0958-3947(03)00072-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
When treating tumors from surface to a certain depth (<5 cm), electron beams are preferred in radiotherapy. To increase the surface doses of lower electron beams, tissue-equivalent bolus materials are often used. We observed that the surface doses increased with increasing field sizes and electron energies. At the same time, we also observed that all electron parameters were shifted toward the skin as much as the thickness of the bolus used. The effect of bolus to the surface doses was more significant at low electron energies than at higher electron energies. Rando phantom measurements at 6-, 7.5-, and 9-MeV were slightly lower than the solid phantom measurements, which could only be explained by the inverse square law effect and the Rando phantom contour irregularity.
Collapse
Affiliation(s)
- Basri Günhan
- Istanbul University, Cerrahpaşa Medical Faculty Department of Radiation Oncology, Istanbul, Turkey.
| | | | | |
Collapse
|