Composition of A‐150 tissue‐equivalent plastic

Smathers, James B.; Otte, Victor A.; Smith, Alfred R.; Almond, Peter R.; Attix, F.H.; Spokas, J. J.; Quam, William M.; Goodman, L.J.

doi:10.1118/1.594380

Cited by 80 publications

(24 citation statements)

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“…Volume changes could also be due to the hygroscopic nature of some ion chamber walls such as A-150 plastic. [10][11][12][13][14][15] The hygroscopic property of an ionization chamber wall is a slow process and affects the signal over a long period of time, when left in uncontrolled environment. This is the reason that ion chambers were traditionally kept in a desiccator to maintain proper humidity level.…”

Section: Introductionmentioning

confidence: 99%

Thermal and temporal response of ionization chambers in radiation dosimetry

Das

Zhu

2004

Med. Phys.

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The temporal and thermal response of various commonly used ion chambers (NEL, Exradin, PTW) with different wall and electrode materials is studied in a water phantom. Measurements were taken in heating water bath having an automatic temperature control mechanism. All chambers were submersed at 3 cm depth in water phantom and connected to separate electrometers for simultaneous readings for a given dose from a 6 MV beam. The temporal response was studied at approximately +/- 10 degrees C from room temperature, i.e., 10 degrees C and 30 degrees C. Temporal results show that all chambers reach quick equilibrium response within < 2 minutes of submersion in water. The steady-state thermal response was dependent upon the water temperature and wall and electrode compositions. The temperature and pressure corrected response of the NEL chamber was least affected by the changes in water temperature, where as the Exradin chamber has positive and PTW has negative slope with water temperature. The response varied within +/-1.5% between 10 degrees C-50 degrees C temperature and is mainly dependent on volume changes rather than the humidity. A correction factor based on thermal coefficients is derived for each chamber. It is concluded that ion chamber correction factors can be divided into first order; temperature and pressure connection, second order; volume correction for thermal expansion, and third order; humidity correction. To eliminate dosimetric error, the temporal and thermal response should be known for a chamber or water phantom temperature should be maintained close to room temperature.

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Section: Introductionmentioning

confidence: 99%

Thermal and temporal response of ionization chambers in radiation dosimetry

Das

Zhu

2004

Med. Phys.

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“…The TE chamber was constructed with the outer shell, the inner electrode, and the guard ring composed of A-150 TE plastic. 40 Methane-based TE gas 38 flows through the chamber's active volume. For the nonhydrogenous chamber, magnesium, and argon were the wall material and gas of choice, respectively, due to their relatively low neutron interaction cross-sections.…”

Section: Methodsmentioning

confidence: 99%

Comparison of secondary neutron dose in proton therapy resulting from the use of a tungsten alloy MLC or a brass collimator system

et al. 2011

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The dual ionization chamber method is suitable for measuring secondary neutron doses resulting from proton irradiation. The results of measurements downstream from a closed tungsten alloy MLC and a brass block indicate that, even in an overly pessimistic worst-case scenario, secondary neutron production in a tungsten alloy MLC leads to absorbed doses that are nearly equivalent to those seen from brass collimators. Therefore, the choice of tungsten alloy in constructing the leaves of a proton MLC is appropriate, and does not lead to a substantial increase in the secondary neutron dose to the patient compared to that generated in a brass collimator.

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“…Figure 5 illustrates the chamber's design, including a wall and a central electrode that are made of A-150 tissuesubstitute plastic. 35 A special jig, shown in Fig. 6, precisely positions a Lucite phantom in the reference beam.…”

Section: B Absorbed Dose Measurements With An Ionization Chambermentioning

confidence: 99%

Dosimetry for ocular proton beam therapy at the Harvard Cyclotron Laboratory based on the ICRU Report 59

Newhauser

Burns²,

Smith

2002

Medical Physics

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The Massachusetts General Hospital, the Harvard Cyclotron Laboratory (HCL), and the Massachusetts Eye and Ear Infirmary have treated almost 3000 patients with ocular disease using high-energy external-beam proton radiation therapy since 1975. The absorbed dose standard for ocular proton therapy beams at HCL was based on a fluence measurement with a Faraday cup (FC). A majority of proton therapy centers worldwide, however, use an absorbed dose standard that is based on an ionization chamber (IC) technique. The ion chamber calibration is deduced from a measurement in a reference 60Co photon field together with a calculated correction factor that takes into account differences in a chamber's response in 60Co and proton fields. In this work, we implemented an ionization chamber-based absolute dosimetry system for the HCL ocular beamline based on the recommendations given in Report 59 by the International Commission on Radiation Units and Measurements. Comparative measurements revealed that the FC system yields an absorbed dose to water value that is 1.1% higher than was obtained with the IC system. That difference is small compared with the experimental uncertainties and is clinically insignificant. In June of 1998, we adopted the IC-based method as our standard practice for the ocular beam.

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Composition of A‐150 tissue‐equivalent plastic

Cited by 80 publications

References 0 publications

Thermal and temporal response of ionization chambers in radiation dosimetry

Thermal and temporal response of ionization chambers in radiation dosimetry

Comparison of secondary neutron dose in proton therapy resulting from the use of a tungsten alloy MLC or a brass collimator system

Dosimetry for ocular proton beam therapy at the Harvard Cyclotron Laboratory based on the ICRU Report 59

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