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Fast 2D phantom dosimetry for scanning proton beams
Author(s) -
Boon S. N.,
van Luijk P.,
Schippers J. M.,
Meertens H.,
Denis J. M.,
Vynckier S.,
Medin J.,
Grusell E.
Publication year - 1998
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.598221
Subject(s) - dosimetry , imaging phantom , proton , medical imaging , medical physics , proton therapy , optics , physics , nuclear medicine , materials science , nuclear physics , medicine , radiology
A quality control system especially designed for dosimetry in scanning proton beams has been designed and tested. The system consists of a scintillating screen ( Gd 2O 2S : Tb ) , mounted at the beam‐exit side of a phantom, and observed by a low noise CCD camera with a long integration time. The purpose of the instrument is to make a fast and accurate two‐dimensional image of the dose distribution at the screen position in the phantom. The linearity of the signal with the dose, the noise in the signal, the influence of the ionization density on the signal, and the influence of the field size on the signal have been investigated. The spatial resolution is 1.3 mm (1 s.d.), which is sufficiently smaller than typical penumbras in dose distributions. The measured yield depends linearly on the dose and agrees within 5% with the calculations. In the images a signal to noise ration (signal/1 s.d.) of 10 2has been found, which is in the same order of magnitude as expected from the calculations. At locations in the dose distribution possessing a strong contribution of high ionization densities (i.e., in the Bragg peak), we found some quenching of the light output, which can be described well by existing models if the beam characteristics are known. For clinically used beam characteristics such as a Spread Out Bragg peak, there is at most 8% deviation from the NACP ionization chamber measurements. The conclusion is that this instrument is a useful tool for quick and reliable quality control of proton beams. The long integration‐time capabilities of the system make it worthwhile to investigate its applicability in scanning proton beams and other dynamic treatment modalities.