A method of determining the effective electron density of hip prostheses using a scanning liquid ionization chamber (SLIC) electronic portal imaging device (EPID) is described. The method involves establishing an empirical relationship between the pixel intensity values (extracted from a portal image) and the corresponding equivalent thickness of an inhomogeneity such as a hip prosthesis. This is done using a composite phantom made of polystyrrene with embedded inhomogeneities of Aluminum, Copper and Lead. Results for 6 and 10 MV photons show that the relationship depends on the characteristics of the imaging device and on the photon energy, provided the atomic number (Z) of the inhomogeneity is sufficiently low such that the Compton effect remains the dominant photon interaction. The portal images of a pelvic phantom with prosthesis were then used to provide X-ray attenuation information, which allowed the determination of the equivalent path length containin9 the inhomogeneity and, therefore, its effective electron density.

Electrons are widely used for the treatment of superficial malignant tumours. Radiation field is modified by placing the lead or Cerrobend cutouts on the application. For electrons, variation in output is not systematic with the increase or decrease in field size. In this paper, we have evaluated the variation in electron output, percentage depth dose and dmax for smaller fields with lead cutouts. It is observed that the relations give by various authors for predicting outputs for irregular fields did not agree with our data and variation of more than + 10% was found. So, we conclude that it is prudent to measure individualised output for irregularly shaped electron fields for calculating the tumour dose.

To ensure accurate dose delivery to target site in external beam therapy and brachytherapy, various authors have conducted tests to assess the process of manual dose calculations. In-vivo dosimetric measurement is one of these methods to verify these calculations. In this study, an attempt has been made to compare the manually calculated dose to dose estimated using a chemical dosimeter (FBX) solution (In-vivo method, using polypropylene vials), on 12 patients of carcinoma of uterirne cervix in external beam therapy. Dose measured by FBX vial varies in the range oft 2 to 6.75%, as compared with manual calculations. These variations seen may be attributed to the location of the vial position in the vagina, with reference 111 the beam axis (may not be horizontal), off axis position, manual calculation variations and reproducibility of the FBX system etc. FBX dosimetry offers itself as an in-vivo method to estimate the dose delivered to the target site in external beam therapy.

A diamond detector was used to measure dose distributions around a Nucletron microSelectron 192lr HDR source. Relative 2D dose distributions along the source axis (0-7 cm) at distances ranging from 0.5 to 7 cm from the source center were measured in a water phantom. Relative dose rates transverse to the source axis were also measured at distances of 0.5-7 cm from the source center. The measured data was normalized to 1.115-cGy h-1U-1 along the source transverse axis at 1 cm. Excellent agreement between measured, two-dimensional dose distributions and corresponding published TLD/diode measurements and Monte Carlo calculations was observed.

Restenosis following balloon angioplasty occurs within six months in 30 - 50% of the cases. It is a major limiting factor in long term effectiveness of this procedure. Implantation of suitable intracoronary stent following balloon angioplasty reduces the rate of restenosis to about 20%. lntracoronary irradiation following balloon angioplasty is a recent development in the fields of interventional cardiology and radiation oncology for the management of benign diseases. Experience in the use of low doses of ionising radiation in other non-malignant diseases such as pterygia of the eye, keloids and heterotopic bone formation form the basis of this new application of radiation in human health care programme. A protocol has been developed at Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai, to scrutinise the proposals for the clinical trials involving intracoronary irradiation and to regulate the procedure from radiation safety standpoint. The regulatory requirements for clearance of clinical trials are: Catheterisation Laboratory with proper shielding: source container and storage facilities; availability of an RSO; ethical committee approval; facility for source calibration: and dosimetry; availability of protection level instruments; established procedure for the safe disposal of decayed source and waste; documentation of emergency procedures and patient informed consent form. This paper presents safety aspects associated with intracoronary brachytherapy techniques currently being tried out in some cardiology centres to inhibit restenosis.

View-box is the last and important but often neglected link in the imaging Process. The quality assurance programme for view-boxes includes the measurement of the intensity of light-output (luminance) in Candella/m2 and the extent of variation in luminance (inhomogeneity) over the front surface of the view-box. An expensive instrument, photometer, is required to conduct both of these tests. Instead, an inexpensive Light Dependent Resistor (LDR) in combination with Ohm-meter may be used. The importance of quality assurance checks is indicated by the fact that majority of view-boxes (37.5%, 36 out of 49) had luminance less than 800 cd/m2, while the recommended level is about 1000 cd/m2 or more. Again, 55% view-boxes (27 out of 49) were found with inhomogeneity in luminance more than 10% while the permissible limit is up to 10%.

Bangladesh requires 200 radiotherapy facilities, 4 are in use; 400 medical physicists are needed, 3 are employed. On a private basis, a DGMP working group started in 1996, annual workshops on 'Medical physics in cancer diagnosis and treatment', joined by many working physicists interested to become medical physicists. Basic topics were the principles, applications, acceptance, dosimetry and planning of 6 0 Co radiotherapy. In 1996, the Bangladesh Association of Physicists in Medicine (BMPA) was founded, a young scientific society requiring international co-operation. The long experience in Medical Physics in India, its neighbouring country, could be verfy helpful in providing excellent medical physics courses. To absorb new technology and science, it is necessary to change the education policy: creativity and innovativeness must be valued more than the old knowledge, being replaced quickly by new knowledge and new technologies.