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 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.
Chofor
N
N
Working Group Medical Radiation Physics, Carl von Ossietzky University Oldenburg, 26111 Oldenburg, Germany.
Looe
H K
HK
Kapsch
R P
RP
Harder
D
D
Willborn
K C
KC
Rühmann
A
A
Poppe
B
B
D000388:Air; D003037:Cobalt Radioisotopes / Q000627:therapeutic use*; D003198:Computer Simulation; D004867:Equipment Design; D006801:Humans; D015233:Models, Statistical; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012542:Scattering, Radiation
D003037:Cobalt Radioisotopes