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The British Journal of Radiology, Vol 70, Issue 837 946-949, Copyright © 1997 by British Institute of Radiology

ARTICLES

Low energy X-ray depth dose data for use in radiotherapy--comments on the review of BJR Supplement 17

RM Harrison
Regional Medical Physics Department, Newcastle General Hospital, Newcastle-upon-Tyne, UK.

Percentage depth dose data acquired during the revision of BJR Supplement 17: Central Axis Depth Dose Data for Use in Radiotherapy have been reviewed. Coverage of the half value layer (HVL) and field diameter rang was broad, although gaps were apparent at HVLs of 3-5 and 6-7 mm A1 and field diameters > 14 cm. Comparisons of submitted data with that in Supplement 17 indicate a generally even spread of data about the existing PDD values. Most data agreed to within +/- 5% at 2 cm and +/- 15% at 10 cm depth. Systematic discrepancies may be due to the use of different phantom materials. There is evidence that the spread of data is at least partially due to the problems of beam quality specification. The inadequacy of the first HVL as a specifier of beam quality is a well known and a more realistic specifier might be defined in terms of a broad beam dose ratio at defined depths, for a given beam geometry.




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