Dosimetric scintillating screen detector for charged particle radiotherapy quality assurance

An apparatus for determining the spatial distribution and intensity of a penetrating radiation beam characterized generally by a propagation direction inside a body, the apparatus comprising:

• a tissue phantom disposed between a radiation source and a radiation detector;
• a scintillating screen disposed behind the tissue phantom for emitting light in response to the radiation received by the scintillating screen, the scintillating screen comprising a mixture of at least two scintillators wherein each scintillator has a different characteristic response and a different spectral output;
• a means of optical communication between the output of the scintillating screen and at least one imaging sensor, wherein the means of optical communication has a nonuniform spectral transmission;
• and
• at least one imaging sensor in optical communication with the scintillating screen for providing a high resolution imaging sensor output indicative of the spatial distribution and intensity of the radiation beam, wherein the imaging sensor has a nonuniform spectral sensitivity;
• wherein the composition of the scintillating screen, the means of optical communication, and the at least one imaging sensor form a system wherein the relative contribution of the at least two scintillators of the mixture produce an imaging sensor output which is proportional to a characteristic of the radiation beam incident on the scintillating screen at each measurement position accessible with the tissue phantom;
• wherein each scintillator of the mixture contributes a detection signal per deposited energy Dn(LET,F)=∫dλρnSn(λ)En(LET,F)An(λ)Q(λ)T(λ) to the total imaging sensor output and a fractional contribution
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• to the total imaging sensor output;
• wherein n is the index of the nth scintillator in the mixture, Dn(LET,F) is the detection signal per deposited energy for the nth scintillator as a function of the linear energy transfer (LET) and fluence (F), ρn is the areal density of the nth scintillator, Sn(λ) is the characteristic spectrum of the nth scintillator, En(LET,F) is the luminous efficiency of the nth scintillator as a function of the linear energy transfer (LET) and fluence (F), An(λ) is the attenuation factor for the nth scintillator due to self-absorption and scattering by the scintillation layer, Q(λ) is the spectral sensitivity of the imaging sensor, and T(λ) is the spectral transmission of the means of optical communication;
• and wherein the fractional contribution, fn, of at least one scintillator of the mixture to the sensor output varies by at least 3% from what it would be with a means of optical communication having uniform spectral transmission T(λ)=1 and with the at least one imaging sensor having uniform spectral sensitivity Q(λ)=1 for a beam with LET and fluence that is clinically relevant.