Method of calculating the isodose shift in correcting for oblique incidence in radiotherapy

Journal Article · Thu Nov 01 04:00:00 EST 1973 · Brit. J. Radiol., v. 46, no. 551, pp. 978-982

DOI:https://doi.org/10.1259/0007-1285-46-551-978· OSTI ID:4333768

Giessen, P H.V.D.

A theoretical basis is put forward for the isodose shift'' method of correcting for beam obliquity in radiotherapy. A formula is deduced for the shift factor, i.e. the fraction of the gap t along a given nay by which the isodose curve must be moved. When t is small compared with the SSD, the shift factor is independent of t, but does depend on the radiation energy, SSD, field area and depth in the absorbing medium. For depths below about 7 cm, the factor for a given beam is sensibly constant. It is further shown that a single value of the factor may be used for all fields and depths (for a given radiation and SSD) with an error of up to 1 per cent for depths below 7 cm and up to about 2 per cent for smaller depths. The recommended average shift factor for 100 cm SSD is 0.7 for x rays from 1 to 5 MV (including /sup 60/Co gamma nays) and 0.6 for x rays from 5 to 15 MV. The calculated values agreed well with empirical values found in the literature. (auth)

• Research Organization: Radio-Therapeutisch Instituut, Tilburg, Netherlands
• NSA Number: NSA-29-025879
• OSTI ID: 4333768
• Journal Information: Brit. J. Radiol., v. 46, no. 551, pp. 978-982, Journal Name: Brit. J. Radiol., v. 46, no. 551, pp. 978-982; ISSN BJRAA
• Country of Publication: United Kingdom
• Language: English

Related Subjects

*RADIOTHERAPY-- ISODOSE CURVES
ALIGNMENT
BEAM OPTICS
MATHEMATICAL MODELS
N72100* --Physics (Radiation & Shielding)--Radiation Physics
SPATIAL DOSE DISTRIBUTIONS