About 57% of the total number of cancer cases occur in low and middle income countries. Radiotherapy is one of the main components of cancer treatment and requires substantial initial investment in infrastructure and training. Many departments continue to have basic facilities and to use simple techniques, while modern technologies have only been installed in big cities in upper-middle income countries. More than 50% of cancer patients requiring radiotherapy in low and middle income countries lack access to treatment. The situation is dramatic in low income countries, where the proportion is higher than 90%. The overall number of additional teletherapy units needed corresponds to about twice the installed capacity in Europe. The figures for different income level groups clearly show the correlation between gross national income per capita and the availability of services. The range of radiotherapy needs currently covered varies from 0% and 3-4% in low income countries in Latin America and Africa up to 59-79% in upper-middle income countries in Europe and Central Asia. The number of additional radiation oncologists, medical physicist, dosimetrists and radiation therapists (RTTs) required to operate additional radiotherapy departments needed is 43 200 professionals. Training and education programmes are not available in every developing country and in many cases the only option is sending trainees abroad, which is not a cost-effective solution. The implementation of adequate local training should be the following step after establishing the first radiotherapy facility in any country. Joint efforts should be made to establish at least one radiotherapy facility in countries where they do not exist, in order to create radiotherapy communities that could be the base for future expansion.

Polymer gel dosimeters offer a wide range of potential applications in the three-dimensional verification of complex dose distribution such as in intensity-modulated radiotherapy (IMRT). Until now, however, polymer gel dosimeters have not been widely used in the clinic. One of the reasons is that they are difficult to manufacture. As the polymerization in polymer gels is inhibited by oxygen, all free oxygen has to be removed from the gels. For several years this was achieved by bubbling nitrogen through the gel solutions and by filling the phantoms in a glove box that is perfused with nitrogen. Recently another gel formulation was proposed in which oxygen is bound in a metallo-organic complex thus removing the problem of oxygen inhibition. The proposed gel consists of methacrylic acid, gelatin, ascorbic acid, hydroquinone and copper(II)sulphate and is given the acronym MAGIC gel dosimeter. These gels are fabricated under normal atmospheric conditions and are therefore called 'normoxic' gel dosimeters. In this study, a chemical analysis on the MAGIC gel was performed. The composition of the gel was varied and its radiation response was evaluated. The role of different chemicals and the reaction kinetics are discussed. It was found that ascorbic acid alone was able to bind the oxygen and can thus be used as an anti-oxidant in a polymer gel dosimeter. It was also found that the anti-oxidants N-acetyl-cysteine and tetrakis(hydroxymethyl)phosphonium were effective in scavenging the oxygen. However, the rate of oxygen scavenging is dependent on the anti-oxidant and its concentration with tetrakis(hydroxymethyl)phosphonium being the most reactive anti-oxidants. Potentiometric oxygen measurements in solution provide an easy way to get a first impression on the rate of oxygen scavenging. It is shown that cupper(II)sulphate operates as a catalyst in the oxidation of ascorbic acid. We, therefore, propose some new normoxic gel formulations that have a less complicated chemical formulation than the MAGIC gel.

This topical review provides an up-to-date overview of the theoretical and practical aspects of therapeutic kilovoltage x-ray beam dosimetry. Kilovoltage x-ray beams have the property that the maximum dose occurs very close to the surface and thus, they are predominantly used in the treatment of skin cancers but also have applications for the treatment of other cancers. In addition, kilovoltage x-ray beams are used in intra operative units, within animal irradiators and in on-board imagers on linear accelerators and kilovoltage dosimetry is important in these applications as well. This review covers both reference and relative dosimetry of kilovoltage x-ray beams and provides recommendations for clinical measurements based on the literature to date. In particular, practical aspects for the selection of dosimeter and phantom material are reviewed to provide suitable advice for medical physicists. An overview is also presented of dosimeters other than ionization chambers which can be used for both relative and in vivo dosimetry. Finally, issues related to the treatment planning and the use of Monte Carlo codes for solving radiation transport problems in kilovoltage x-ray beams are presented.

Investigation of the normoxic PAGAT polymer gel dosimeter has been undertaken. The concentrations of the chemical components of the gel were varied and its response to ionizing radiation evaluated. Using MRI, the formulation to give the maximum change in the transverse relaxation rate R2 was determined to be 4.5% N, N'-methylene-bis-acrylamide (bis), 4.5% acrylamide (AA), 5% gelatine, 5 mM tetrakis (hydroxymethyl) phosphonium chloride (THPC), 0.01 mM hydroquinone (HQ) and 86% H2O. The optimal post-manufacture irradiation and post-irradiation imaging times were both determined to be 12 h. The R2-dose response was linear up to 7 Gy with R2-dose sensitivities of (0.183 +/- 0.005) s(-1) Gy(-1), (0.182 +/- 0.005) s(-1) Gy(-1) and (0.192 +/- 0.005) s(-1) Gy(-1) when imaged at 12 h, 7 days and 24 days post-irradiation, respectively. The R2-dose sensitivities were within the range of previously published values for the hypoxic PAG formulations. For the imaging parameters used in this study the optimum dose resolution was achieved for low doses. The normalized R2 edge response showed a high degree of spatial stability over a 24 day period. This study has shown that the normoxic PAGAT polymer gel has the properties of a dosimetric tool, which can be used in clinical radiotherapy. The PAGAT polymer gel has been shown to have similar qualities to the PAG polymer gel, while offering the significant advantage of simplification of the manufacturing procedure.

In this study the stability of different polymer gel dosimeters is investigated. Further to a previous chemical stability study on a (6%T, 50%C) PAG gel, the change in slope and intercept of the linear part of the R2-dose plot is recorded with time for different gel formulations. In addition to this R2-dose-response stability study, the dose edge of a half-blocked field was recorded with time. Three different PAG type polymer gels, a hydroxyethyl acrylate (HEA) gel and two different normoxic polymer gels were investigated. In the PAG type polymer gels, the relative concentration of gelatin and comonomers was varied in order to study the influence of the different components, that constitute the dosimeter, on the stability. It is shown that the R2-dose-response stability is largely determined by the chemical composition of the gel dosimeters. All the PAG gel dosimeters and the normoxic gel dosimeters are found to preserve the integrity of the dose distribution up to 22 days after irradiation. The half-life of the change in dose sensitivity of a MAGIC gel is found to be 18 h compared to 5.7 h for a (6%T, 50%C) PAG gel. A maximum relative decrease in dose sensitivity of 21% was noted for the MAGIC gel compared to an increase of 50% for a (6%T, 50%C) PAG gel. A loss of integrity of the dose distribution was found in the HEA gel.

A novel two-dimensional finite element method for modelling the diffusion which occurs in Fricke or ferrous sulphate type radiation dosimetry gels is presented. In most of the previous work, the diffusion coefficient has been estimated using simple one-dimensional models. This work presents a two-dimensional model which enables the diffusion coefficient to be determined in a much wider range of experimental situations. The model includes the provision for the determination of a drift parameter. To demonstrate the technique comparative diffusion measurements between ferrous sulphate radiation dosimetry gels, with and without xylenol orange chelating agent and carbohydrate additives have been undertaken. Diffusion coefficients of 9.7 +/- 0.4, 13.3 +/- 0.6 and 9.5 +/- 0.8 10(-3) cm2h-1 were determined for ferrous sulphate radiation dosimetry gels with and without xylenol orange and with xylenol orange and sucrose additives respectively.

The luminescence spectroscopy of atomic cadmium isolated in the solid rare gases is recorded using pulsed synchrotron radiation excitation of the 5p 1 P 1 ←5s 1 S 0 resonance transition. Steady-state and time-resolved analysis of the ultraviolet ͑UV͒ emission bands recorded in the Cd/Ne, Cd/Ar, and Cd/Kr systems allows identification of the associated 227.3, 233.4, and the 241/262 nm bands to the singlet fluorescence of atomic cadmium. The origin of the pair of singlet emission bands at 241 and 262 nm in the Cd/Kr system is ascribed to the coexistence of two nondegenerate minima on the 5p 1 T 1u surface. The weak band present in the Cd/Kr system at 326 nm and the intense pair at 324.4 and 329.6 nm in Cd/Xe all have decay times longer than 1 s and are associated with the triplet transitions of atomic cadmium. Line shape analysis of the near-UV emission pair in Cd/Xe allows a tentative assignment of the narrow 329.6 nm band to the 5p 3 P 0 →5s 1 S 0 transition. The intensity of the triplet state emission was observed to be enhanced in the heavier rare gases, being completely absent in Ne and Ar, weak in Kr, and the only emission observed in Xe. The efficiency of intersystem crossing in the Cd/RG systems is very similar to that exhibited by the Zn/RG matrix systems. However, the presence of the 5p 3 P 0 →5s 1 S 0 emission in Cd/Xe resembles the Hg/RG matrix systems, a reflection of the larger spin-orbit splitting in atomic cadmium compared with zinc.

The report concludes with nine general recommendations: (1) Radiotherapy should be applied as accurately as reasonably achievable, technical and biological factors being taken into account. (2) For consistency in prescribing, reporting and recording, recommendations of the International Commission on Radiation Units and Measurements should be implemented. (3) Each institution should determine uncertainties for their treatment procedures. Sample data are tabulated for typical clinical scenarios with estimates of the levels of accuracy that are practically achievable and suggested action levels. (4) Independent dosimetry audits should be performed regularly. (5) Comprehensive quality assurance programs should be in place. (6) Professional staff should be appropriately educated and adequate staffing levels should be maintained. (7) For reporting purposes, uncertainties should be presented. (8) Manufacturers should provide training on all equipment. (9) Research should aid in improving the accuracy of radiotherapy. Some example research projects are suggested.