We have investigated the thermoluminescent response and fading characteristics of germanium- and aluminium-doped SiO(2) optical fibres. These optical fibres were placed in a solid phantom and irradiated using 6 and 10 MV photon beams at doses ranging from 0.02 to 0.24 Gy delivered using a linear accelerator. In fading studies, the TL measurements were continued up to 14 days post-irradation. We have investigated the linearity of TL response as a function of dose for Ge-, Al-doped optical fibre and TLD-100 obtained for 6 and 10 MV photon irradiations. We have concentrated on doses that represent a small fraction of that delivered to the tumour to establish sensitivity of measurement for peripheral exposures in external beam radiotherapy.
Ion beams are used in radiotherapy to deliver a more precise dose to the target volume while minimizing dose to the surrounding healthy tissue. For optimum dose monitoring in ion-beam therapy, it is essential to be able to measure the delivered dose with a sensitivity, spatial resolution and dynamic range that is sufficient to meet the demands of the various therapy situations. Optical fibres have been demonstrated by this group to show promising thermoluminescence properties with respect to photon, electron and proton irradiation. In particular, and also given the flexibility and small size of optical fibre cores, for example 125.0+/-0.1 microm for the Al- and Ge-doped fibres used in this study, these fibres have the potential to fulfill the above requirements. This study investigates the thermoluminescence dosimetric characteristics of variously doped SiO(2) optical fibres irradiated with alpha particles from (241)Am. Following subtraction of the gamma contribution from the above source, the thermoluminescence characteristics of variously doped SiO(2) optical fibres have been compared with that of TLD-100 rods. The irradiations were performed in a bell jar. Of related potential significance is the effective atomic number, Z(eff) of the fibre, modifying measured dose from that deposited in tissues; in the present work, a scanning electron microscope and associated energy dispersive X-ray spectroscopy facility have been used to provide evaluation of Z(eff). For Ge-doped fibres, the effective atomic numbers value was 11.4, the equivalent value for Al-doped fibres was 12.3. This paper further presents results on dose response and the glow curves obtained. The results obtained indicate there to be good potential for use of variously doped SiO(2) optical fibres in measuring ion-beam doses in radiotherapeutic applications.
Radiation effects of photon irradiation in pure Photonic Crystal Fibres (PCF) and Flat fibres (FF) are still much less investigated in thermoluminescense dosimetry (TLD). We have reported the TL response of PCF and FF subjected to 6 MV photon irradiation. The proposed dosimeter shows good linearity at doses ranging from 1 to 4 Gy. The small size of these detectors points to its use as a dosimeter at megavoltage energies, where better tissue-equivalence and the Bragg-Gray cavity theory prevails.
This paper describes a preliminary study of the thermoluminescence (TL) response of doped SiO(2) optical fibres subjected to (241)AmBe neutron irradiation. The TL materials, which comprise Al- and Ge-doped silica fibres, were exposed in close contact with the (241)AmBe source to obtain fast neutron interactions through use of measurements obtained with and without a Cd filter (the filter being made to entirely enclose the fibres). The neutron irradiations were performed for exposure times of 1-, 2-, 3-, 5- and 7-days in a neutron tank filled with water. In this study, use was also made of the Monte Carlo N-particle (MCNP) code version 5 (V5) to simulate the neutron irradiations experiment. It was found that the commercially available Ge-doped and Al-doped optical fibres show a linear dose response subjected to fast neutrons from (241)AmBe source up to seven days of irradiations. The simulation performed using MCNP5 also exhibits a similar pattern, albeit differing in sensitivity. The TL response of Ge-doped fibre is markedly greater than that of the Al-doped fibre, the total absorption cross section for Ge in both the fast and thermal neutrons region being some ten times greater than that of Al.
Study has been made of the thermoluminescence (TL) response of silica-based Ge-doped cylindrical, flat and photonic crystal fibres (referred to herein as PCF-collapsed) to electron (6, 12 and 20 MeV) and photon (6, 10 MV) irradiation and 1.25 MeV γ-rays, for doses from 0.1 Gy to 100 Gy. The electron and photon irradiations were delivered through use of a Varian Model 2100C linear accelerator located at the University of Malaya Medical Centre and γ-rays delivered from a 60Co irradiator located at the Secondary Standard Dosimetry Laboratory (SSDL), Malaysian Nuclear Agency. Tailor-made to be of various dimensions and dopant concentrations (6-10% Ge), the fibres were observed to provide TL yield linear with radiation dose, reproducibility being within 1-5%, with insensitivity to energy and angular variation. The sensitivity dependency of both detectors with respect to field size follows the dependency of the output factors. For flat fibres exposed to 6 MV X-rays, the 6% Ge-doped fibre provided the greatest TL yield while PCF-collapsed showed a response 2.4 times greater than that of the 6% Ge-doped flat fibres. The response of cylindrical fibres increased with core size. The fibres offer uniform response, high spatial resolution and sensitivity, providing the basis of promising TL systems for radiotherapy applications.
In regard to thermoluminescence (TL) applied to dosimetry, in recent times a number of researchers have explored the role of optical fibers for radiation detection and measurement. Many of the studies have focused on the specific dopant concentration, the type of dopant and the fiber core diameter, all key dependencies in producing significant increase in the sensitivity of such fibers. At doses of less than 1 Gy none of these investigations have addressed the relationship between dose response and TL glow peak behavior of erbium (Er)-doped silica cylindrical fibers (CF). For x-rays obtained at accelerating potentials from 70 to 130 kVp, delivering doses of between 0.1 and 0.7 Gy, present study explores the issue of dose response, special attention being paid to determination of the kinetic parameters and dosimetric peak properties of Er-doped CF. The effect of dose response on the kinetic parameters of the glow peak has been compared against other fiber types, revealing previously misunderstood connections between kinetic parameters and radiation dose. Within the investigated dose range there was an absence of supralinearity of response of the Er-doped silica CF, instead sub-linear response being observed. Detailed examination of glow peak response and kinetic parameters has thus been shown to shed new light of the rarely acknowledged issue of the limitation of TL kinetic model and sub-linear dose response of Er-doped silica CF.
This study analysed the physical effects of Cichorium Pumilum (CP), as a natural photosensitizer (PS), and Protoporphyrin IX (PpIX), as a synthetic PS, encapsulated with silica nanoparticles (SiNPs) in photodynamic therapy. The optimum concentrations of CP and PpIX, needed to destroy Red Blood Cells (RBC), were determined and the efficacy of encapsulated CP and PpIX were compared with naked CP and PpIX was verified. The results confirmed the applicability of CP and PpIX encapsulated in SiNPs on RBCs, and established a relationship between the encapsulated CP and PpIX concentration and the time required to rupture 50% of the RBCs (t50). The CP and PpIX encapsulated in SiNPs exhibited higher efficacy compared with that of naked CP and PpIX, respectively, and CP had less efficacy compared with PpIX.