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A retrospective study has been undertaken in an attempt to identify physical parameters that could confidently be used to predict an enhanced risk of bladder morbidity following intracavitary brachytherapy. 366 women received brachytherapy as all, or part, of their treatment for cervical cancer at the Christie Hospital in 1990 and 1991, and of these, 60 patients developed identifiable bladder morbidity (graded on a scale of 1-4 using the Franco-Italian glossary). These were age and stage matched with 60 asymptomatic women who were also treated for cervical cancer by brachytherapy during the same time period. The sizes of applicators used in the two groups were noted and compared. The two groups were also compared with respect to the heights of the applicator set above the symphysis pubis, the degree of anteversion or retroversion of the applicator sets and where possible, the doses at the International Commission on Radiation Units and Measurements (ICRU) bladder reference point. Where CT scans of the applications were available, these were reviewed to see if any differences in the size, shape or location of the bladder were apparent. No significant difference was found between the two groups of patients for any of the parameters investigated. The physical factors investigated in this study cannot be used to reliably predict bladder complications. There was a significant correlation between bladder morbidity and morbidity in other pelvic sites.

A technique, originally developed for calibrating small low activity caesium sources, which uses a Farmer-type ionization chamber, has been further developed for use with iridium wires. Correction factors have been generated to account for the finite source and detector sizes, and attenuation in the source carriers. The air kerma calibration factor for heavily filtered 280 kV X-rays was used for reference back to the National Standard. The results of this calibration method have been compared with the calibration figures given by the manufacturers over a 5 year period for the emissions from 50 batches of wires of varying strengths. Agreement to within +/- 3.2% was achieved in all cases, establishing that the method is satisfactory for acceptance testing purposes. The mean agreement was good to within 0.2%, but the possibility of a systematic error of between 1% and 3% existing both in this method and in the method used by the manufacturer is discussed.

Intracavitary radiotherapy is conceptually an attractive method of boosting dose to nasopharynx cancer whilst sparing sensitive normal tissues. A high dose rate (HDR) microselectron can be used to deliver a brachytherapy boost conveniently, safely, comfortably and effectively. Following external radiotherapy a single outpatient treatment has been given to patients using the remote afterloading system of sources placed in modified paediatric endotracheal tubes. This has been associated with good primary control and no evidence of serious morbidity in eight patients. The main limitation of this method is restriction of its utilization to small volume primary disease.

A technique for deriving the reference air kerma rate for low activity brachytherapy sources that is traceable to the therapy level standard at the National Physical Laboratory is presented. Correction factors have been generated to account for the finite source and detector size. The air kerma rate calibration of the secondary standard for caesium quality has been derived by polynomial curve fitting. The reference air kerma rates for several caesium tubes and needles have been determined and the results compared with the manufacturers' source test reports. For all the source types used the agreement between methods was within 2%.

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 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.

The decision to endorse and implement the BCRU recommendation has been taken after careful consideration and discussion amongst those currently active in brachytherapy treatment at the Christie Hospital, Manchester. We believe it to be both logical and scientifically sound. The practical measures discussed here outline how the Manchester System will operate with the new method of source specification, and we urge other users of the Manchester System throughout the world to adopt similar measures and accept the BCRU recommendations also.

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.