Characterization of the radiation quality of 60Co therapy units by the fraction of air kerma attributable to scattered photons

In this work we present a new parameter for characterizing the emitted photon spectra of (60)Co radiotherapy units. It is intended to propose this parameter for the revised DIN standard 6809-1. In the previous DIN regulation, it had been sufficient to state the nature of the radioactive material wit...

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Bibliographic Details
Published in:Physics in medicine & biology 2007-04, Vol.52 (7), p.N137-N147
Main Authors: Chofor, N, Looe, H K, Kapsch, R P, Harder, D, Willborn, K C, Rühmann, A, Poppe, B
Format: Article
Language:English
Subjects:
Air
Cobalt Radioisotopes - therapeutic use
Computer Simulation
Equipment Design
Humans
Models, Statistical
Models, Theoretical
Monte Carlo Method
Phantoms, Imaging
Photons
Radiosurgery - instrumentation
Radiosurgery - methods
Radiotherapy - methods
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted - methods
Scattering, Radiation
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Summary:In this work we present a new parameter for characterizing the emitted photon spectra of (60)Co radiotherapy units. It is intended to propose this parameter for the revised DIN standard 6809-1. In the previous DIN regulation, it had been sufficient to state the nature of the radioactive material within the source. However, scatter processes within the radioactive material as well as the source housing and the collimator system influence the shape of the photon spectrum, with a noticeable contribution in the low-energy portion. The fraction of the air kerma for a given distance from the source, position and beam size in air comprising all contributions by scattered photons up to an upper energy limit for the emitted spectrum from (60)Co decay, will be proposed as a typical parameter. The new quantity, which is termed the 'fraction of air kerma attributable to scattered photons', P(E)(Scatter), has been calculated for E = 1.17 MeV and compared for four different Monte Carlo-simulated spectra of used (60)Co devices. Not included in this new formalism is the air kerma contribution by scattered photons in between the two lines of the (60)Co spectrum. A simple measurement procedure based on the signal ratio of two Farmer chamber detectors with different wall materials is discussed and its feasibility shown.
ISSN:0031-9155
1361-6560
DOI:10.1088/0031-9155/52/7/N03