The use of a BF3 remmeter to calibrate neutron activation foils in the medical linear accelerator environment.

A technique has been developed for radiation protection purposes whereby it is possible to measure the dose-equivalent due to neutrons from a dual energy medical linear accelerator using a conventional BF3 neutron remmeter to calibrate gold foils. This technique has been applied to measuring the neutron dose-equivalent from a Philips SL75-20 medical linear accelerator. The tenth value distance for the entrance maze is 3.3 +/- 0.5m compared to a typically quoted value of 5m. This suggests that the use of wood and boron tiles in the construction of the entrance maze can reduce neutron propagation down the maze.

The commissioning and acceptance of a commercially manufactured radiotherapy beam tissue compensating filter system.

The principles of tissue compensation in radiotherapy and the methods for their implementation on the GE RT/Plan computer are briefly described. The HEK Medizintechnik GmbH Medical Systems Tissue Compensator cutting device is described, along with the testing procedure adopted for its commissioning and quality assurance testing of the total system. The HEK machine hardware proved to be well engineered, but there were many deficiencies in the software supplied to interface it to the planning computer. Most errors were fatal to the program producing a compensator but a number of errors allowed the cutter to manufacture shapes which on close inspection turned out to be incorrect. These faults were traced to incorrect algorithms and/or incorrect software implementation. It is stressed that the software errors were entirely the responsibility of HEK and that the GE equipment and software were not deficient in any way. However, the experiences of the Adelaide group suggest that caution should be exercised when purchasing two pieces of interacting equipment from separate suppliers.

The use of high-energy electrons to depilate the breech of sheep.

The use of high-energy electrons for permanently depilating areas of sheep skin was evaluated. The most effective dose of electrons for depilation was 17.5Gy. Histological changes in skin treated at this dose were examined in one sheep over 18 months and in 5 sheep over 89 d. Effects of treatment on bodyweight gains and fleece growth were examined by comparing the productivity of a further 5 sheep treated on the breech with high-energy electrons, with that of conventionally mulesed sheep (n = 5) and untreated controls (n = 5). Electron treatment resulted in immediate death of cells in the germinative region of the wool follicle bulbs. Within 10 d of treatment the treated areas were completely depilated. Wool follicle shafts in the treated areas regressed rapidly towards the epidermis and remained quiescent for the whole trial (89 d). A sheep treated 18 months previously has remained largely depilated, although a few sparse fibres are present. Epidermal acanthosis and orthokeratosis were present at 26 d after treatment. The thickened stratum corneum then sloughed off, but the epidermis remained acanthotic for the entire trial. Sweat glands and most sebaceous glands were destroyed by the treatment and were replaced by fibrotic, avascular tissue in the dermis. In all other respects the external appearance of the electron-treated breech was similar to that of mulesed sheep. There were no apparent side-effects of treatment. Neither mulesing nor electron treatment altered weight gains or fleece growth rates.