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Rad 8 is a small, in-house computer system for calculating radiotherapy dose distributions, both for multiple field and rotational external beam techniques and for interstitial and intracavitary radium treatments. Implementing the system has its difficulties, particularly in obtaining the necessary beam profile information. Several approaches have been tried and finally a separate profile generator program was written. Other difficulties encountered with beam data storage were overcome by making minor changes to the system programs. The various calculation techniques have been evaluated, and in general found to be satisfactory, and suitable factors to be used in the inhomogeneity correction for 4 MV X rays have been calculated based on previously published measured data. An option to change beam weightings exists and this can be used to renormalize dose distributions to give percentage isodose curves relative to the prescribed tumour dose. If this procedure is followed dose homogeneity over the target volume can readily be assessed, and the exposure times may easily be calculated from the new weightings. Certain shortcomings in the rotating beam program and the radium program may easily lead to error if extreme care is not exercised.

Cost–benefit analysis, in which a monetary value is assigned to radiation-induced health detriment, is used to establish whether a proposed course of action to reduce the dose rate in a particular environment is reasonable in the “as low as reasonably achievable” context. The instantaneous dose rate is used in conjunction with a use factor and a man-occupancy factor to establish a dose accumulation rate. This, in turn, is used to calculate what capital expenditure on radiation protection measures is reasonable. Such an approach provides an objective method of assessing and comparing radiation protection problems and leads to better consistency in allocating available resources.

The ICRP system of dose limitation requires radiation exposures to be kept “as low as reasonably achievable” (ALARA). The International Commission on Radiological Protection (ICRP) advocates a form of cost benefit analysis for this purpose, in which a comparison is made between the costs of protective measures and the benefits of reduced radiation exposure. In the UK, the National Radiological Protection Board (NRPB) has been developing a framework for the practical application of cost benefit techniques to aid the evaluation of investments in radiological protection. One such investment, being undertaken at a number of radiotherapy centres, concerns remote after-loading equipment to replace the use of radium in the treatment of gynaecological cancers. The introduction of such equipment can offer a complete solution to the radiological protection problems associated with manual radium insertions but involves large capital expenditures on equipment and shielded treatment rooms.This paper describes a cost benefit analysis of introducing remote after-loading equipment at the Christie Hospital and Holt Radium Institute in Manchester. In accordance with the NRPB framework, it is shown that the introduction of after-loading equipment, when housed in appropriately protected rooms, should result in a substantial net benefit and would therefore be justified on radiological protection grounds according to the ALARA principle.

An investigation has been made into the changes in total dose required as a consequence of proposed increases in dose-rate in low-dose-rate treatments of cancer of the uterine cervix. The relationship between total irradiation time and dose-rate has been measured using an assay based on mouse-tail radionecrosis, with irradiation schedules similar to existing and proposed human cervix treatments. This relationship, which is similar to that observed in other biological systems, predicts that the total dose for epithelial tolerance should be reduced by about one third when the dose-rate is increased from 1.0 to 3.5 Gy per hour. The clinical implications of this finding are discussed.

The recommendations of the International Commission on Radiation Units and Measurements for reporting intracavitary therapy have been considered with particular regard to the Manchester method of treating cancer of the cervix uteri. The total reference air kerma is calculated and tabulated as a function of prescription for the standard Manchester applicator arrangements. Furthermore, it is shown that the volume contained within a particular isodose surface may be determined, with very acceptable accuracy, from the total reference air kerma by the use of a simple empirical expression.

When Selectron afterloading machines were introduced in the Christie Hospital the first aim was to reproduce, as closely as possible, the isodose distributions achieved with the traditional Manchester Radium System. This resulted in the establishment of standard pellet loading patterns, and standard treatment times, for programming the Selectron channels. However, the availability of whole-body CT scanning facilities provides a method of accurately locating the source positions with respect to the local anatomy and hence the possibility of dosage control based on doses to specific pelvic structures. Various computer programs have been written to extract source position data from the CT images, to allow the operator to propose pellet loading patterns and treatment times, and ultimately to display the resultant isodose distribution superposed on the cross-sectional scans. The effects on the dose distribution arising from changing the number of pellets, the pellet positions within the applicators, and the treatment times, are briefly discussed.

This book has been published as the twenty-first volume in a series entitled Frontiers in Radiation Therapy and Oncology. It contains the proceedings of the twenty-first Annual San Francisco Cancer Symposium which was held at the end of February and beginning of March 1986, and consists of 21 papers plus three pages of verbatim discussion. Somewhat surprisingly, the discussion section appears in the middle of the book and refers only to the first ten chapters, perhaps because the programme on the first day ran ahead of schedule! For review purposes however, the discussion section conveniently divides the book into two halves, pre-discussion papers being generally of a more technical nature whereas the later ones have a more clinical bias.The quality of the papers in the first half is variable, and sadly in two or three cases the editors must be criticised for accepting inadequate contributions. The first chapter on fractionation and daily dose, for example, is extremely short and without references. The anecdotal style is not without a certain charm, but it will be a disappointment to those looking for scientific content.