Experimental determination of fluence correction factors at depths beyond  for a Farmer type cylindrical ionization chamber in clinical electron beams

Huq, M. Saiful; Yue, Ning J.; Suntharalingam, N.

doi:10.1118/1.597978

Cited by 11 publications

(8 citation statements)

References 13 publications

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“…This means that the mean electron energy at depth, Ē z , is a good beam quality specifier for P fl . These results demonstrate that, consistent with experimental findings, 15 TG-51's adoption of P fl values at d max with the same mean electron energy for use at d ref is reasonable, although there is a clear discrepancy compared to the values actually used. In Fig.…”

Section: Iiic Beam Quality Dependence Of P Replsupporting

confidence: 83%

Replacement correction factors for cylindrical ion chambers in electron beams

Wang

Rogers

2009

Medical Physics

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Section: Iiic Beam Quality Dependence Of P Replsupporting

confidence: 83%

Replacement correction factors for cylindrical ion chambers in electron beams

Wang

Rogers

2009

Medical Physics

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“…͑16͒ and ͑17͒ in TG-51. 2,5,6 The above procedure is for the determination of R 50 only and does not describe a procedure for the determination of the entire central-axis percentage depth-dose curve in water. Otherwise, the percentage depth-ionization curve measured using an ionization chamber can be converted to a percentage depth-dose curve and R 50 obtained from those data.…”

Section: Iiib Electron Beam Quality Specificationmentioning

confidence: 99%

Recommendations for clinical electron beam dosimetry: Supplement to the recommendations of Task Group 25

et al. 2009

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The goal of Task Group 25 (TG-25) of the Radiation Therapy Committee of the American Association of.Physicists in Medicine (AAPM) was to provide a methodology and set of procedures for a medical physicist performing clinical electron beam dosimetry in the nominal energy range of 5-25 MeV. Specifically, the task group recommended procedures for acquiring basic information required for acceptance testing and treatment planning of new accelerators with therapeutic electron beams. Since the publication of the TG-25 report, significant advances have taken place in the field of electron beam dosimetry, the most significant being that primary standards laboratories around the world have shifted from calibration standards based on exposure or air kerma to standards based on absorbed dose to water. The AAPM has published a new calibration protocol, TG-51, for the calibration of high-energy photon and electron beams. The formalism and dosimetry procedures recommended in this protocol are based on the absorbed dose to water calibration coefficient of an ionization chamber at 60Co energy, N60Co(D,w), together with the theoretical beam quality conversion coefficient k(Q) for the determination of absorbed dose to water in high-energy photon and electron beams. Task Group 70 was charged to reassess and update the recommendations in TG-25 to bring them into alignment with report TG-51 and to recommend new methodologies and procedures that would allow the practicing medical physicist to initiate and continue a high quality program in clinical electron beam dosimetry. This TG-70 report is a supplement to the TG-25 report and enhances the TG-25 report by including new topics and topics that were not covered in depth in the TG-25 report. These topics include procedures for obtaining data to commission a treatment planning computer, determining dose in irregularly shaped electron fields, and commissioning of sophisticated special procedures using high-energy electron beams. The use of radiochromic film for electrons is addressed, and radiographic film that is no longer available has been replaced by film that is available. Realistic stopping-power data are incorporated when appropriate along with enhanced tables of electron fluence data. A larger list of clinical applications of electron beams is included in the full TG-70 report available at http://www.aapm.org/pubs/reports. Descriptions of the techniques in the clinical sections are not exhaustive but do describe key elements of the procedures and how to initiate these programs in the clinic. There have been no major changes since the TG-25 report relating to flatness and symmetry, surface dose, use of thermoluminescent dosimeters or diodes, virtual source position designation, air gap corrections, oblique incidence, or corrections for inhomogeneities. Thus these topics are not addressed in the TG-70 report.

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“…For cylindrical chambers, values of P f l are given in the TG-21 protocol as a function of chamber radius and the mean energy at the point of measurement. One assumes that the values at d max in TG-21 still apply for d ref away from d max ͑further measurements to confirm this, such as those by Huq et al 18 are needed͒. For low-energy beams the TG-21 values apply because d ref is still at d max .…”

Section: Appendix: Calculation Of K Q and K R 50mentioning

confidence: 89%

“…The IAEA Code of Practice also makes this assumption when it uses reference depths away from d max . 2 Huq et al 18 Tables I and II. surements indicate good agreement with the values of P f l used here for cylindrical chambers in electron beams with initial energies from 5 to 20 MeV. 18 It must be emphasized that the procedure outlined here is not as complex as the equations might suggest.…”

Section: Discussionmentioning

confidence: 99%

A new approach to electron‐beam reference dosimetry

Rogers

1998

Medical Physics

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A new approach is proposed for electron-beam dosimetry under reference conditions and data necessary to use this approach are presented. The approach has the following features; it uses ion chambers and starts from an absorbed-dose calibration factor for 60Co to be consistent with the present proposal for the new AAPM photon-beam protocol; it uses R50 to specify the beam quality and the reference depth, dref = 0.6R50 - 0.1 (all quantities in cm), recommended by Burns et al. [Med. Phys. 23, 383-388 (1996)]; it has a formalism which is parallel to the kQ formalism for photon-beam dosimetry; it fully accounts for the impact on stopping-power ratios of realistic electron beams; it allows an easy transition to using primary standards for absorbed dose to water in electron beams when these are available. The equation for dose to water under reference conditions is; DWQ = MPionPgrQk'R50kecalND,w60Co. The term PgrQ is not needed with plane-parallel chambers but corrects for gradient effects with cylindrical chambers and is measured in the user's beam. The parameter kecal is associated with converting the 60Co absorbed-dose calibration factor into one for an electron beam of quality Qe and contains most of the chamber to chamber variation. Calculated values of kecal are presented as well as Monte Carlo calculated Pwall values for plane-parallel chambers in a water phantom irradiated by a 60Co beam since these are needed to calculate kecal. The factor k'R50 is a function of R50 and converts the absorbed-dose calibration factor to that for the electron-beam quality of interest. Two analytical expressions are presented which are close to universal expressions for all cylindrical Farmer-like chambers and for well-guarded plane-parallel chambers respectively. Calculated values are presented graphically for electron beams with energies between 5 and 50 MeV.

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Experimental determination of fluence correction factors at depths beyond for a Farmer type cylindrical ionization chamber in clinical electron beams

Cited by 11 publications

References 13 publications

Replacement correction factors for cylindrical ion chambers in electron beams

Replacement correction factors for cylindrical ion chambers in electron beams

Recommendations for clinical electron beam dosimetry: Supplement to the recommendations of Task Group 25

A new approach to electron‐beam reference dosimetry

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