Thermoluminescent (TL) dosimeters have become a versatile system of dosimeters for assessment of dose in clinical applications of ionizing radiation. The advantages of TL dosimeters include high sensitivity, miniature size, tissue equivalence, low fading, re-usability and linear dose response. Being a passive device, TL dosimetry by mail provides an easy way for intercomaparison of dose in different institutions. This paper elucidates applications of TLD in some of the conventional and emerging fields of medical applications in radio diagnosis, nuclear medicine and radiotherapy, including neutron.

Use of multileaf collimator (MLC) for shaping the treatment fields in external beam therapy is now a common practice. Tongue and groove arrangement is used in all commercially available multileaf collimators to limit interleaf leakage. The tongue and groove effect (TGE) is an under-dosing effect in the region of overlap between two adjacent leaves of a multileaf collimator. Mean dose reduction (MDR) and its spatial extent (in terms of FWHM) at the field junction defined by Varian Standard 80 leaves MLC for 6 and 18 MV photon beams were measured using radiographic and radiochromic films. Measured values of MDR and mean FWHM are presented for three different field geometries, namely, a narrow field, a medium size rectangular field and an irregular field at the depth of dose maximum (dm) as well as at 10 cm depth. These three fields correspond to the treatment fields used in intensity modulated radiotherapy (IMRT) and conformal/conventional radiotherapy. FWHMs are found to be independent of beam energy, depth of measurement and field geometry. However, MDR depends on beam energy, depth of measurement and field geometry. Maximum dose reduction of 17.6% with spatial extent of 2.8 mm was observed at the dm of 6 MV photon beam for the narrow field.

The mega voltage photons interacting with the patient results in the production of scattered photons, secondary electrons and neutrons. These secondary particles lead in the deterioration of primary beam to a certain extent in terms of radiation flux and energy and it is relevant for radiation protection considerations of the patient during treatment. In this study an experimental method was used to estimate the quantum of flux due to primary and secondary photons, as well as recoil electron from the telecobalt beams by introduction of various intervening materials. The components of the Cobalt-60 output beam at different distances from the source position were studied in detail. At 50 cm distance from the source position, the recoil electron flux contribution is 13.8 %, 5.1 %and 4.7 %for depleted Uranium, tungsten and lead collimators respectively. At 80 cm distance the recoil electron contributes less than 2 % of the total flux. The effect of introduction of 5 mm Perspex plate in the beam will increase the flux of the recoil electron from 5.1 % to 17 %at 50 cm distance from the source and it is insignificant beyond 80cm. The recoil electron contribution is significantly less in tale Caesium beam compared to telecobalt beam. The outcome of this study helps in taking appropriate measures to reduce the less penetrating components In the useful beam.

A HDR 1000 PLUS well type ionization chamber, procured from Standard Imaging, USA, and maintained by Medical Physics & Safety Section (MPSS), Bhabha Atomic Research Centre (BARC), India, as a reference well chamber 1 (RWCHI), was traceably calibrated against the primary standard established by Radiological Standards Laboratory (RSL), BARC for 192lr HDR source, in terms of air korma strength (AKS). An indigenously developed well-type ionization chamber, reference well chamber 2 (RWCH2) and electrometer system, fabricated by CD High Tech (CDHT) instruments Private Ltd., Bangalore, India, was in turn calibrated against RWCH1. The CDHT system (i.e. RWCH2 and CDHT electrometer system) was taken to several hospitals, in different regions of the country, to check the calibration status of lg21r HDR sources. The result of this calibration audit work is reported here.

The 137Cs lntracavitary Kit, supplied by Board of Radiation and lsotope Technology (BRIT), is in clinical use for over two decades. Recently, BRlT has modified the design of the 137Cs sources. This paper gives the dosimetry data for the new type of 137Cs sources. The dose rate constant, which is the dose rate, in tissue, at 1 crn on the transverse axis along the centre of the active source, worked out to be 0.934 Gy.h1.cm2.U-I for the CSA-1 type source of active length 1.5 cm and 1 .012 cGy.h-l.cm2.U-I for CSA-2 type source of active length 1.0 cm. The dose rate constant evaluated using Monte Carlo simulation (MCNP codeversion 3.1) agrees within 1 %. The dose rate constant measured using TLD and perspex phantom yielded a value of 0.927 cGy.k1.cm2. U1 for CSA-1 type source and 1.053 cGy.h-'.cm2.U-I for CSA-2 type source, which are well within the uncertainty of measurement. Dose contributions at points A and B, as defined in the Manchester system of dosimetry, have been worked out for standard loadings.

Internal dosimetry is a branch of medical physics that deals with the measurement of the internally absorbed dose by an organ after applying isotopes. In this study, internal radiation absorbed dose has been calculated for 99mTc and 131I, which are frequently used for functioning tests and therapeutic treatments of thyroid, respectively. In these cases, some amount of isotopes are accumulated in other tissues like brain, which are very soft and cannot be regenerated if they are damaged. Using ionizing radiation inside the body and to ensure the safety of brain, the internal radiation absorbed dose has been calculated applying direct counting measurement. Accumulation of isotopes to target organ has been measured and this target organ is considered as primary target organ; also this organ is considered as source with respect to other organs. These organ counts have been measured by computer-based scintillation system. The amount of exposure in brain has been measured with the help of the data obtained from the special set-up equipment, including Nal detector, radiation survey meter and water phantoms of various sizes. Absorbed dose in brain for each isotope has been calculated by applying time-activity curve analysis. Finally, these results have been compared with the data in ICRP Reports 53 and 71.

Amongst the man made ionising radiations, x- ray diagnostic procedures contribute the highest per capita radiation dose to population over and above the natural background radiation. Although the x- ray diagnostic procedures have revolutionised the medical diagnosis and treatment of many diseases, it is many a times being over-used as a routine diagnostic procedure like blood or urine test. The patient receives radiation dose in excess due to bad practice and bad equipment, and hence every x-ray machine should be subjected to periodic quality assurance (QA) test. Extensive radiation protection surveys and QA tests of 190 x-ray installations in southern Rajasthan was carried out. It was observed that the kVp calibration was within limit in only 43.6 % of the surveyed units. Similarly the mA linearity was within the prescribed limit in 22.9 % of the units. Out of 190 x - ray machines, 97 (51 % ) were more than 10 years old and were never subjected to QA tests after installation. The detailed results of beam alignment test, congruency of optical and radiation field, kVp linearity, timer linearity and availability of radiation protection equipment such as lead barrier and lead apron are discussed.