Head-scatter factors in blocked photon fields.

The behavior of the head-scatter factor in shielded 6 and 25 MV X-ray beams from a Philips SL25 linear accelerator was investigated by measuring incident fluences by direct (in-air) and indirect (in-phantom) methods. It was found that perturbations in head-scatter produced by shielding blocks arranged to define a slit-shaped field are considerably less than 1% in unwedged beams, even when 80% of a 20 x 20 cm2 field is shielded. The results are independent of beam energy and orientation of the slit with respect to the collimator jaws.

Equivalent squares of irregular photon fields.

The tables of equivalent fields published by the British Journal of Radiology (BJR) are intended for calculation of depth-dose functions in rectangular photon fields. We have investigated the validity of the equivalent-field concept for fields of arbitrary shape over a range of photon energies, field sizes and depths. We show that the empirical scatter-radius function (Day function) used to generate the equivalent-field tables is a good approximation to the average over energy of normalized scatter-air ratios extracted from BJR beam data for depths up to 10 cm.

Total skin electron irradiation: efficacy in early mycosis fungoides.

The rare, indolent, but lethal malignancy, mycosis fungoides (MF), is amenable to durable remissions if treated topically at an early stage with nitrogen mustard, PUVA, or radiotherapy. A modification of conventional therapeutic irradiation which utilizes electron beams rather than photons, has been in use since 1951. This method, termed total skin electron irradiation (TSEI), has achieved consistently good CR rates (95-100%) at a variety of centres in the U.

Head-scatter factors in rectangular photon fields.

Head-scatter factors were measured for a range of field sizes of rectangular shape from a linear accelerator that provides 6 and 25 MV photon beams. For a given field length and width, exchange of the inner and outer collimator pairs produces differences in the head-scatter factor of up to about 2% and 3% in open and wedged fields, respectively. Dependence on elongation deviates by up to 2% from that given by the equivalent squares.