Our results showed the dosimetric properties of the RGD, including the energy dependence of the dose response, reproducibly, variation, and angular dependence in low-energy photons and suggest that the accuracy of the absorbed dose in low-energy photons is affected by the readout method and the distribution of radiophotoluminescence centers in the RGD.
We have developed a practical dose verification method for radiotherapy treatment planning systems by using only a Farmer ionization chamber in inhomogeneous phantoms. In particular, we compared experimental dose verifications of multi-layer phantom geometries and laterally inhomogeneous phantom geometries for homogeneous and inhomogenous dose calculations by using the fast-Fourier-transform convolution, fast-superposition, and superposition in the XiO radiotherapy treatment-planning system. We applied the dose verification method to three kernel-based algorithms in various phantom geometries with water-, lung- and bone-equivalent media of different field sizes. These calculations were then compared with experimental measurements by use of the Farmer ionization chamber. The fast-Fourier-transform convolution algorithm overestimated the dose by about 8% in the lung phantom geometry. The superposition algorithm and the fast-superposition algorithm were both accurate to better than 2% when compared to the measurements even for complex geometries. Our dose verification method was able to clarify the differences and equivalences of the three kernel-based algorithms and measurements with use only of commonly available apparatus. This will be generally useful in commissioning of inhomogeneity-correction algorithms in the clinical practice of treatment planning.
In order to evaluate the usefulness of a metal oxide-silicon field-effect transistor (MOSFET) detector as a in vivo dosimeter, we performed in vivo dosimetry using the MOSFET detector with an anthropomorphic phantom. We used the RANDO phantom as an anthropomorphic phantom, and dose measurements were carried out in the abdominal, thoracic, and head and neck regions for simple square field sizes of 10 x 10, 5 x 5, and 3 x 3 cm(2) with a 6-MV photon beam. The dose measured by the MOSFET detector was verified by the dose calculations of the superposition (SP) algorithm in the XiO radiotherapy treatment-planning system. In most cases, the measured doses agreed with the results of the SP algorithm within +/-3%. Our results demonstrated the utility of the MOSFET detector for in vivo dosimetry even in the presence of clinical tissue inhomogeneities.
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