General characteristics of the use of silicon diode detectors for clinical dosimetry in proton beams

Abstract

The properties of silicon diode detectors, used for dosimetry in clinical proton beams, were investigated with special regard to the measurement of relative dose distributions in water. Different types of silicon diode detector were studied, and the resulting distributions of detector signal versus depth in the water phantom were compared with the corresponding distributions obtained with a plane-parallel NACP ionization chamber. The measurements were performed in a proton beam with an initial energy of 173 MeV.It is shown that the Hi-p silicon detector gives a signal which is proportional to the ionization density in the silicon crystal in all parts of the Bragg curve, and for all levels of accumulated dose to the detector. This is in contrast to detectors based on n-type silicon, or on low resistivity p-type silicon. After pre-irradiation, these latter detectors show a stopping-power dependent recombination, yielding an increase in the detector signal per unit dose with increasing LET. This effect leads to an over-response in the Bragg peak, which increases gradually with the accumulated detector dose.Using the Hi-p silicon diode detector, the depth ionization distribution was found to be equal to the distribution obtained with the plane-parallel NACP ionization chamber at all pre-irradiation levels, within the experimental accuracy. This implies that the quotient between the ionization in the detector and the absorbed dose to the surrounding water is equal for these detectors.

Evaluation of the dosimetric properties of a diode detector for small field proton radiosurgery

“…In addition, the diode exhibited a linear decrease in response with accumulated dose of $\sim 1\%$ per 100 Gy. This loss of sensitivity is a well‐known result of radiation damage typical in silicon diodes (29) where Si nuclei are displaced by particle collisions (11) . Since such displacements occur more often in proton irradiation, loss of sensitivity is greater than is seen with photon radiation (11) .…”

“…This loss of sensitivity is a well‐known result of radiation damage typical in silicon diodes (29) where Si nuclei are displaced by particle collisions (11) . Since such displacements occur more often in proton irradiation, loss of sensitivity is greater than is seen with photon radiation (11) . Because sensitivity tends to decrease following initial radiation exposure, the detector, as is common, comes preirradiated from the manufacture to minimize effect.…”

“…However, Grusell and Medin (11) showed that a highly doped p‐type Si detector designed for use with protons had a response consistent with ionization chambers, which are considered the gold standard for dose measurements. In the present study, we present results from an evaluation of the commercially available PTW PR60020 p‐type diode detector specifically indicated by the manufacturer for proton dose measurements.…”

Dosimetric characterization of a synthetic single crystal diamond detector in a clinical 62 MeV ocular therapy proton beam

“…The dosimetric properties in clinical low energy proton beams of PFD diode and EBT2 films are well documented [12,27].…”

“…Thanks to the high sensitivity per unit volume, small dimensions and high spatial resolution, solid state detectors such as silicon diodes and natural or first prototype synthetic diamond detectors have been reported as promising devices for relative proton dosimetry [9,[11][12][13][14][15][16][17]. The attractive physical and dosimetric properties of diamond make it the material of choice for dosimetric applications.…”