Search

Developments in a new system of brachytherapy for tumours of the eye are reported. This involves the use of 125I sources with special screens and filters to avoid irradiation of vital structures and to produce a homogeneous radiation field. Methods for the treatment of tumours of the lids, conjunctiva, retina, choroid and lachrymal gland have been developed. Sixteen out of 20 treatments appear to have been successful. This system would seem to be a material advance on those previously reported.

It has long been suspected that the depth-dose characteristics of modern 60Co teletherapy units are no longer well represented by the traditional data of The British Journal of Radiology Supplement 11. Extensive measurements have been undertaken on three modern 60Co units in an attempt to clarify this position. Three different values of source-toskin distance were studied, namely 50, 80 and 100 cm. Systematic deviations from the traditional data are unambiguous, amounting to up to 3% at 80 cm SSD and as much as 7% at 50 cm SSD. Comparison with calibration results at a large number of institutions lends confidence that the present results are representative of modern treatment units.

Three Philips 250/15, 250 kV X-ray units are in use in the Radiotherapy Department at Groote Schuur Hospital, operating at 15 mA and 50 cm FSD. The beam is filtered by 1 mm of tin, 0·25 mm of copper and 1 mm of aluminium, giving a half value layer of 3·5 mm copper. Checks of skin dosage by means of thermoluminescent dosimetry (TLD) revealed unexpectedly low doses towards the edge of a wide field (25 × 8 cm) on the long axis. In order to investigate this further, isodose curves were plotted using a Toshiba MRA-301 automatic isodose curve plotter on each of the three X-ray units. With each unit, a marked asymmetry of the radiation beam was found, the beam being more intense on the anode side than the cathode side. This effect is illustrated in Fig. 1 for a 25 × 10 cm field. The dotted lines on the cathode side are the curves from the anode side reflected about the central axis to facilitate comparison. An isodose curve plotted without an applicator exhibited the same asymmetry, eliminating the applicator as...

One of the features which detract from the advantages of insertion or implantation of radioactive sources in the treatment of tumours is the difficulty in screening sensitive structures within the treatment volume. In addition, where very large doses are administered with electro-magnetic radiation, for instance in the treatment of intra-ocular tumours with radioactive plaques, the doses administered to surrounding structures may be considerable. It seems that these difficulties might be largely overcome by the use of low-energy isotope sources and suitable integral shielding. For example, the use of 125I seeds has been considered, which were first described by Henschke and Lawrence (1965). The isotope emits 27 to 35 keV X rays which permit highly effective screening by thin lead foil (0·25 mm of lead reduces primary radiation from 125I by 99·9 per cent, and absorbs scattered radiation and secondary electrons almost entirely). Suitable seeds for this purpose, consisting of radioactive sodium iodide absorb...

A tissue-equivalent phantom containing thermoluminescent dosimeters was mailed in succession to Mount Vernon Hospital, Northwood, Middlesex, England, to Groote Schuur Hospital, Capetown, South Africa, and to Winnipeg General Hospital, Winnipeg, Canada, to determine the accuracy and consistency in treatment for carcinoma of the cervix under hyperbaric oxygen conditions. (Protocol of the Medical Research Council's Working Party on Radiotherapy and Hyperbaric Oxygen.) The data were analysed by the Radiological Physics Center, Houston, Texas, and substantiate uniformity at and between the participating institutions.

Seeds containing iodine 125 as supplied by Lawrence Soft Ray Corporation have now been used at this hospital to treat a variety of patients with tumours which would have been treated with applicators or moulds loaded with 182Ta or 226Ra if the seeds had not been available. Iodine seeds have also been extensively used at other hospitals, e.g. Kim and Hilaris (1975), Hilaris (1976), and Charyulu et al. (1976). The advantages of 125I over 182Ta have already been outlined earlier (Sealy et al., 1976; Hering et al., 1977). However, whereas the radiobiological effectiveness (RBE) of the 182Ta radiation relative to 250 kV X rays is well known, there is at present no such information available for 125I. By considering the LET spectrum of the X rays of 125I, Kim and Hilaris (1975) have predicted an RBE of the seeds for human tumours higher than one and less than 1.5. Some radiobiological studies are needed to test this prediction and this has led to some preliminary investigations on vicia faba as outlined below.