A rapid method for electron beam energy check.

Assessment of electron beam energy and its long term stability is part of standard quality assurance practice in radiation oncology. Conventional depth-ionization or depth-film density measurements are time consuming both in terms of data acquisition and analysis. A procedure is described utilizing ionization measurements at two energy specific depths. It is based on a linear relationship between electron beam energy and its practical range. Energy shifts within the range covered by the two measurement depths are easily resolved. Within a range of +/- 0.50 MeV (+/- 1.30 MeV) around the established mean incident energy of 5.48 MeV (20.39 MeV), the method accuracy is better than 0.10 MeV.

Small-field stereotactic external-beam radiation therapy of intracranial lesions: fractionated treatment with a fixed-halo immobilization device.

Current techniques of stereotactic, small-field, external-beam irradiation with linear accelerators require treatment with a single fraction or only a few fractions of radiation with large single doses per fraction. Using a radiolucent halo that remained affixed to the cranium with skin-piercing screws, the authors treated 24 patients with a multifraction technique for benign and malignant brain lesions. The objective of this study was to ascertain the feasibility of maintaining the halo in place for a prolonged, multifraction course of treatment, not to assess treatment efficacy. The halo was affixed for multifraction treatments lasting 19-58 days (mean, 38.7 days; median, 40.0 days) and delivered in 16-31 fractions (mean, 24.9 fractions; median, 25.5 fractions). Two of 24 patients experienced superficial skin infection at the site of fixation, but no other significant acute or chronic toxicity attributable to the stereotactic halo was observed. The authors conclude that stereotactic, small-field, precision irradiation can be accomplished with multiple fractions as well as with a single fraction.

A comparison of calculated and measured data for total body irradiation by 10 MV x-rays.

This paper describes the rationale for using computed rather than measured data as a reference in the dosimetry of total body irradiation. The proof of this statement rests on a comparison of measured dosimetric values for large fields at extended distances with those derived by simple recalculation from the data measured at the isocentre. The depth doses and dose rates were experimentally obtained for 10 MV x-rays at distances of 100, 200 and 300 cm for collimated square fields with sides ranging from 5 to 30 cm. Phantoms of different volumes and shapes, including a RANDO phantom, and a large (50 cm x 50 cm x 50 cm), intermediate (25 cm x 25 cm x 25 cm), and 'mini-phantom' (build-up cap, 4.6 cm diameter) were used. Comparison of the measured and computed data for the largest collimated field shows that (i) calculated dose rates do not differ by more than +1% from the measured data, phantom size and shape having no effect on the results, (ii) depth doses measured in a patient-like RANDO phantom are a maximum of 2% higher than the calculated data but are also 2% lower than the depth doses measured in a standard water tank. For the radiation fields and treatment distances commonly employed in total body irradiation, we conclude that the calculated data can serve as reference values for dosimetry because they have the same inherent uncertainty as the data measured in non-patient-like phantoms.