Determination of the air w-value in proton beams using ionization chambers with gas flow capability.
The purpose of this work was to determine the w-value of air for protons using the paired gas method. Several plastic- and magnesium-walled chambers were used with air, synthetic air, nitrogen, and argon flowing gases. Using argon as a reference gas, the w-value of air was measured and ranged from 32.7 to 34.5 J/C for protons with energies encountered in radiotherapy. Using nitrogen as a reference gas, the w-value of air ranged from 35.2 to 35.4 J/C over the same range of proton energies. The w-value was found, at a given energy, to be independent of the ion chamber used. The uncertainty in these measurements was estimated at 5.2% at the 2sigma level. This uncertainty was dominated by the 4.4% uncertainty in the w-value of the reference gas.
Moyers
M F
MF
Loma Linda University Medical Center, Department of Radiation Medicine, California 92354, USA.
Vatnitsky
S M
SM
Miller
D W
DW
Slater
J M
JM
D000388:Air; D001128:Argon; D005740:Gases; D006801:Humans; D009584:Nitrogen; D061766:Proton Therapy; D011874:Radiometry / Q000295:instrumentation*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D011882:Radiotherapy, High-Energy / Q000379:methods / Q000706:statistics & numerical data
D005740:Gases; D001128:Argon; D009584:Nitrogen