Sophisticated radiotherapy techniques lead to more conformal dose distributions but increase treatment complexity.
Image guidance allows for varying degrees of accuracy in patient
set-up. However, the consequences of inaccurate set-up
and/or patient motion during treatment become more serious when treatment doses are increased and treatment margins
are decreased. Thus, the need to know if the dose has been delivered as planned has driven the development of plastic
scintillation detector systems for accurate measurements in real time with high spatial resolution. We have developed a
clinical prototype comprising 29 scintillating fiber detectors 1 mm in diameter and 2 mm in length. The detectors are
coupled to clear optical fibers that collect the scintillation photons and transport them to a CCD for detection. Open field
profiles and depth-dose profiles in water-equivalent phantoms were compared to ionization chamber measurements in
water. The maximum relative in-field difference was 1.6%. With a standard deviation for in-field measurements smaller
than 1%, this prototype array was found to be accurate, precise and practical. Monte Carlo simulations were also used to
evaluate the response of the scintillation detector to proton beams and to optimize the light collection efficiency. The
Monte Carlo code Geant4 was used to simulate dose deposition, the production of scintillation photons and the
propagation of those photons inside the scintillation detector. Further development of the system will allow thousands of
measurement points distributed in a three-dimensional volume per single irradiation, therefore producing a rapid
evaluation of complex dose distributions emanating from these new complex treatment modalities.
The utilization of scintillation light as a measure of radiation dose has many attractive features for medical applications. When high doses of ionizing radiation are being administered to cancer patients, precise and accurate dosimetry in terms of absolute dose and its location are essential. Fiber Optic Dosimeters [FOD] are unique in this pplication, since compared to other medical radiation dosimeters, they are smaller, more reliable and most significantly, they are human tissue equivalent. The principal limitation of the FOD is its signal to noise ratio, a feature that we discuss in terms of materials science and physical optics. The aim of this study is to outline a theoretical approach to dosimeter design based on geometrical optics that has the potential to increase the signal and decrease the noise.