Afterloading Equipment Research Articles

Source configuration and dose rates for the selectron afterloading equipment for gynecologic applicators

This paper describes source train configurations of the Selectron LDR-6 that can be used to duplicate commonly used manually afterloadable source configurations for gynecological intracavitary brachytherapy. We demonstrate that the recommended source configuration using 2.5 mm 137Cs spheres is dosimetrically equivalent to its manually afterloaded counterparts using 3M 137Cs sources (20 mm overall length, 14 mm active length). Isodose distributions are in agreement to within 5% for the Fletcher-Suit-Delclos family of tandems, colpostats, and vaginal cylinders. Our data also demonstrate that the isotropic point source model used by most computerized treatment planning systems is a good approximation to source trains of filtered, spherical sources interspersed with solid steel spacers. We conclude that the use of 2.5 mm 137Cs sources in the Selectron remote afterloading system can accurately reproduce the isodose distribution achieved with linear 137Cs manually afterloaded sources.

Cost benefit analysis of radiological protection: a case study of remote after-loading in gynaecological radiotherapy.

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.

Occupational exposure in medicine--a review of radiation doses to hospital staff in north-west England.

The personal monitoring service operated by the Regional Physics Department at the Christie Hospital and Holt Radium Institute, Manchester, monitors staff involved with the uses of ionising radiations at all hospitals and clinics administered by the North Western Region Health Authority in England. Monitoring results relating principally to exposure during 1981 have been collated and examined. The analysis indicates that the doses received by staff are for the most part very low and provide little reason for concern. The only area of work in which worthwhile and cost-effective dose reductions could probably be achieved is that involving the use of pre-loaded applicators in gynaecological intra-cavitary therapy. Some relatively high staff exposures result from the use of this technique, and very significant reductions in these doses are confidently expected from a programme which has now commenced for the increasing use of remotely-controlled after-loading equipment housed in shielded treatment rooms.

The use of Selectron afterloading equipment to simulate and extend the Manchester System for intracavitary therapy of the cervix uteri.

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.