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Issues involved in the quantitative 3D imaging of proton doses using optical CT and chemical dosimeters


Doran, S and Gorjiara, T and Kacperek, A and Adamovics, J and Kuncic, Z and Baldock, C, Issues involved in the quantitative 3D imaging of proton doses using optical CT and chemical dosimeters, Physics in Medicine and Biology, 60, (2) pp. 709-726. ISSN 0031-9155 (2015) [Refereed Article]

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Copyright 2015 Institute of Physics and Engineering in Medicine Licenced under Creative Commons Attribution 3.0 Unported (CC BY 3.0)

DOI: doi:10.1088/0031-9155/60/2/709


Dosimetry of proton beams using 3D imaging of chemical dosimeters is complicated by a variation with proton linear energy transfer (LET) of the dose–response (the so-called 'quenching effect'). Simple theoretical arguments lead to the conclusion that the total absorbed dose from multiple irradiations with different LETs cannot be uniquely determined from post-irradiation imaging measurements on the dosimeter. Thus, a direct inversion of the imaging data is not possible and the proposition is made to use a forward model based on appropriate output from a planning system to predict the 3D response of the dosimeter.

In addition to the quenching effect, it is well known that chemical dosimeters have a non-linear response at high doses. To the best of our knowledge it has not yet been determined how this phenomenon is affected by LET. The implications for dosimetry of a number of potential scenarios are examined.

Dosimeter response as a function of depth (and hence LET) was measured for four samples of the radiochromic plastic PRESAGE®, using an optical computed tomography readout and entrance doses of 2.0 Gy, 4.0 Gy, 7.8 Gy and 14.7 Gy, respectively. The dosimeter response was separated into two components, a single-exponential low-LET response and a LET-dependent quenching. For the particular formulation of PRESAGE® used, deviations from linearity of the dosimeter response became significant for doses above approximately 16 Gy.

In a second experiment, three samples were each irradiated with two separate beams of 4 Gy in various different configurations. On the basis of the previous characterizations, two different models were tested for the calculation of the combined quenching effect from two contributions with different LETs. It was concluded that a linear superposition model with separate calculation of the quenching for each irradiation did not match the measured result where two beams overlapped. A second model, which used the concept of an 'effective dose' matched the experimental results more closely. An attempt was made to measure directly the quench function for two proton beams as a function of all four variables of interest (two physical doses and two LET values). However, this approach was not successful because of limitations in the response of the scanner.

Item Details

Item Type:Refereed Article
Keywords:optical CT, proton therapy, PRESAGE
Research Division:Physical Sciences
Research Group:Medical and biological physics
Research Field:Medical physics
Objective Division:Health
Objective Group:Clinical health
Objective Field:Clinical health not elsewhere classified
UTAS Author:Baldock, C (Professor Clive Baldock)
ID Code:97724
Year Published:2015
Web of Science® Times Cited:15
Deposited By:Office of the School of Engineering
Deposited On:2015-01-11
Last Modified:2017-11-01
Downloads:361 View Download Statistics

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