Thermoluminescence dosimetry materials: Properties and uses

Luminescence properties of tricalcium phosphate doped with dysprosium

Tricalcium phosphate having effective atomic number Z_eff = 15.785, equivalent to that of bones was studied for its thermoluminescence (TL) and photoluminescence (PL) properties. Different samples with varied concentrations of the dopant Dy³⁺ (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mol %) were synthesized by the chemical co-precipitation technique. Phase and compound confirmations were done using X-Ray Diffraction (XRD) and the phosphors' crystallite size was calculated using Scherrer's formula which was found to range between 27 nm and 49 nm. The surface morphological study was done using Field Emission-Scanning Electron Microscopy (FE-SEM). Other characterization techniques used for compound confirmation included Energy Dispersive X-Ray Spectroscopy (EDX) and Fourier Transform Infrared Spectroscopy (FTIR). Samples were further irradiated by gamma rays (emitted from Co-60) with dose varying from 10 Gy to 5 kGy in order to study their TL properties. Concentration optimization of the given phosphor was done in terms of its TL intensity and was found to be 0.5 mol %. The TL dose response of the phosphor was linear over a wide range of dose (10 Gy-3 kGy). Deconvolution was performed on the glow curve for 10 Gy dose, giving six peaks (at 127^o, 153^o, 185^o, 218^o, 313^o and 335^oC) suggesting the presence of six different types of traps. Other characteristics of the TL material i.e. repeatability and fading were also studied. Overall, the phosphor showed promising results for its utility in TL dosimetry. In addition to the TL, PL further confirmed the presence of dopant in the phosphor. Moreover, the dopant concentration was optimized in terms of the nanophosphor's PL intensity. The Commission International de l'Éclairage (CIE) was used to calculate chromaticity coordinates, colour rendering index and colour temperature in order to investigate the phosphor's application in white LEDs.

A dosimetric study of skin toxicity induced by 3-D conventional and intensity-modulated radiotherapy techniques using immobilization mask for treatment of head-and-neck (nasopharyngeal cancer) carcinoma: a prospective study

Background

The purpose of this study was to investigate variations in surface dose, with and without the use of a Klarity® Mask (Orfit Industries America, Wijnegem, Belgium), using intensity-modulated radiotherapy (IMRT) and 3-D conventional radiotherapy (3D-CRT).

Materials and methods

Thermoluminescent dosimeters (TLDs) together with a phantom were used to examine acute skin toxicity during nasopharyngeal cancer treatment. These plans were sequentially delivered to the perspex phantom. Dosimeters were placed in five fixed regions over the skin. A Klarity mask for immobilization was used for covering the head, neck, and shoulder. The phantom was irradiated with and without a Klarity Mask, using IMRT and 3D-CRT, respectively.

Results

The Klarity mask increased the skin doses for IMRT and 3D-CRT approximately 18·6% and 8·6%, respectively, from the prescribed maximum skin dose using treatment planning system (TPS). Additionally, the average percentage dose between IMRT and 3D-CRT received on the surface region was 30·9%, 24·9% with and without Klarity mask respectively. The average percentage dose received on surfaces from the total therapeutic dose 70 Gy, without using the mask was 7·7% and 5·7%, for IMRT and 3D-CRT, respectively. The TPS overestimated the skin dose for IMRT planning by 20%, and for 3D-CRT by 16·6%, compared with TLD measurements.

Conclusions

The results of this study revealed that IMRT significantly increases acute skin toxicity, compared with CRT. Although it is recommended to use Klarity mask as a sparing tool of normal tissue, it increases the risk of skin toxicity. In conclusion, skin dose is an important issue of focus during radiotherapy.