Energy and angular anisotropy optimisation of a p-type diode for in vivo dosimetry in photon-beam radiotherapy

Photon dosimetry using selective data sampling with Particle Swarm optimization algorithm based on NaI(Tl) scintillation detector

Sodium Iodide doped with Thallium NaI(Tl) scintillation detectors have potential for the development of an active dosimeter for photon radiation. We aim to show that the photon dosimetry response for NaI(Tl) scintillation detector may be optimized by employing the Particle Swarm optimization algorithm, when the selective data sampling is applied for the detector readout. In this work, Sodium Iodide doped with Thallium NaI(Tl) scintillation detector is considered due to being highly sensitive to gamma radiation, and one of the affordable room temperature detectors. In this research, we intend to measure the dosimetry response of the NaI(Tl) detector for various gamma sources, as an example, by measuring the ambient dose equivalent H*(10) for different gamma radioactive sources. Furthermore, we demonstrate that the photon dosimetry response may be well optimized for various energies, especially at lower energies, by increasing the energy interval number in data sampling over the NaI(Tl) scintillation detector readout with the help of an optimization algorithm. The simulation software Geant4 has been used for determining the NaI(Tl) scintillation detector readout. To this end, experimental ambient dose equivalent measurements for gamma radiation sources are compared with the theoretical results. As three and six energy intervals are considered for the selective data sampling along with an optimization algorithm based on NaI(Tl) detector output, the error percentage will be less than 20 and 10%, respectively.

Evaluation of Given Dose Accuracy in Radiation Therapy of Patient with Breast Cancer Using Diode In Vivo Dosimetry

Background: The main goal of radiation therapy is to deliver the highest dose to the tumor and at the same time the lowest dose to the surrounding normal tissue. In vivo dosimetry is a quality control procedure that, instead of controlling the components separately, directly examines the dose reached to the tumor area. Objectives: In this study, the entrance, exit, and middle dose of the breast and supraclavicular area of patients with breast cancer under radiation therapy were measured and compared with calculations. Methods: In this experimental study, the entrance and exit doses of 33 patients with breast tumors treated with 6 MV and 18MV photons were measured simultaneously. The measurement was done, using p-type diodes after calibration and, then, the midpoint dose was calculated, using the transfer method and arithmetic mean method. Also, the entrance dose, exit dose, and midline dose measured with dosimeter were compared with the calculated values in the treatment planning system. Results: There was no significant difference between calculated and measured doses in the entrance, exit, and midline point in breast regions (P > 0.05), but in the supraclavicular region, a challenge was observed. The difference in entrance and midline point between calculation and measurement is not significant based on the transfer method, but there is a significant error based on the arithmetic mean method (P < 0.05). Conclusions: In vivo dosimetry by measured real given dose to the patient can perform a basic role in the quality control of the radiotherapy department. It seems in the entrance dose, the relative error is smaller but due to the smaller value of exit dose, the relative error in small values is more apparent.

Effect of electron contamination of a 6 MV x-ray beam on near surface diode dosimetry

In critical organ in vivo x-ray dosimetry, the relative contaminating electron contribution to the total dose and total detector response outside the field will be different to the corresponding contributions at the central axis detector calibration position, mainly due to the effects of shielding in the linear accelerator head on the electron and x-ray energy spectrum. To investigate these contributions, the electron energy response of a Scanditronix PFD diode was measured using electrons with mean energies from 0.45 to 14.6 MeV, and the Monte Carlo code MCNP-4C was used to calculate the electron energy spectra on the central axis, and at 1 and 10 cm outside the edge of a 4 x 4, 10 x 10 and a 15 x 15 cm(2) 6 MV x-ray field. The electron contribution to the total dose varied from about 8% on the central axis of the smallest field to about 76% at 10 cm outside the edge of the largest field. The electron contribution to the total diode response varied from about 7-8% on the central axis of all three fields to about 58% at 10 cm outside the edge of the smallest field. The results indicated that a near surface x-ray dose measurement with a diode outside the treatment field has to be interpreted with caution and requires knowledge of the relative electron contribution specific to the measurement position and field size.