Advances in Radiation Dosimetry

Nath, Ravinder; Huq, M. Saiful

doi:10.1007/978-3-662-03107-0_17

Cited by 3 publications

(1 citation statement)

References 270 publications

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“…The differences observed will then reflect how different users apply the protocols as written. This review will not focus on discussions of the details of various N K based protocols or comparisons among them because results of extensive comparisons have been reported in the literature (namely, see the review by Nath and Huq (1995), Huq and Nath (1991) and references therein). It is also beyond the scope of this work to review the development of standards of absorbed dose to water, which would require on its own a separate review, and only a summary will be presented.…”

Section: Introductionmentioning

confidence: 99%

Advances in the determination of absorbed dose to water in clinical high-energy photon and electron beams using ionization chambers

Huq

Andreo

2004

Phys. Med. Biol.

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During the last two decades, absorbed dose to water in clinical photon and electron beams was determined using dosimetry protocols and codes of practice based on radiation metrology standards of air kerma. It is now recommended that clinical reference dosimetry be based on standards of absorbed dose to water. Newer protocols for the dosimetry of radiotherapy beams, based on the use of an ionization chamber calibrated in terms of absorbed dose to water, N(D,w), in a standards laboratory's reference quality beam, have been published by several national or regional scientific societies and international organizations. Since the publication of these protocols multiple theoretical and experimental dosimetry comparisons between the various N(D,w) based recommendations, and between the N(D,w) and the former air kerma (NK) based protocols, have been published. This paper provides a comprehensive review of the dosimetry protocols based on these standards and of the intercomparisons of the different protocols published in the literature, discussing the reasons for the observed discrepancies between them. A summary of the various types of standards of absorbed dose to water, together with an analysis of the uncertainties along the various steps of the dosimetry chain for the two types of formalism, is also included. It is emphasized that the NK-N(D,air) and N(D,w) formalisms have very similar uncertainty when the same criteria are used for both procedures. Arguments are provided in support of the recommendation for a change in reference dosimetry based on standards of absorbed dose to water.

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Section: Introductionmentioning

confidence: 99%

Advances in the determination of absorbed dose to water in clinical high-energy photon and electron beams using ionization chambers

Huq

Andreo

2004

Phys. Med. Biol.

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Principles and requirements of external beam dosimetry

Chen

D’Errico

Nath

2006

Radiation Measurements

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

1997

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Recently, it has been recommended that electron beam calibrations be performed at a new reference depth [Burns et al., Med. Phys. 23, 383 (1996)] given by dref = 0.6R50-0.1 cm, where R50 is the depth of 50% depth dose. In order to calibrate electron beams at dref with a Farmer type cylindrical ionization chamber, the values of the perturbation correction factors Pwall and Pfl at dref are required. Using a parallel plate Holt chamber as a reference chamber, the product PwallPfl has been determined for a 6.1-mm-diameter PTW cylindrical ionization chamber at dref as a function of R50 of clinical electron beams (6 < or = nominal energy E < or = 22 MeV). Assuming that Pwall for the PTW chamber is unity in electron beams, the measured Pfl values ranged from 0.96 to 0.98 as the energy is increased. These results are in close agreement with recently reported calculated values. Determination of dref requires the knowledge of R50. A relation between I50 and R50 is given in the IAEA Protocol [TRS No. 277 (IAEA, Vieńna, 1987), pp. 1-98] for broad beams at SSD = 100 cm. It has been shown experimentally that the equation R50 = 1.029 x I50-0.063 cm, derived by Ding et al. [Med. Phys. 22, 489 (1995)] from Monte Carlo simulations of realistic clinical electron beams, can be used satisfactorily to obtain R50 from I50, where I50 is the depth of 50% ionization. The largest difference between the measured value of R50 and that calculated by using the above equation has been found to be about 1 mm at 22 MeV.

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Advances in Radiation Dosimetry

Cited by 3 publications

References 270 publications

Advances in the determination of absorbed dose to water in clinical high-energy photon and electron beams using ionization chambers

Advances in the determination of absorbed dose to water in clinical high-energy photon and electron beams using ionization chambers

Principles and requirements of external beam dosimetry

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

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