当前位置： SCI文献检索 > AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE期刊下所有文献 > Field size consistency of nominally matched linacs.

Field size consistency of nominally matched linacs.

Abstract：

:Given that there is increasing recognition of the effect that sub-millimetre changes in collimator position can have on radiotherapy beam dosimetry, this study aimed to evaluate the potential variability in small field collimation that may exist between otherwise matched linacs. Field sizes and field output factors were measured using radiochromic film and an electron diode, for jaw- and MLC-collimated fields produced by eight dosimetrically matched Varian iX linacs (Varian Medical Systems, Palo Alto, USA). This study used nominal sizes from 0.6 × 0.6 to 10 × 10 cm(2), for jaw-collimated fields, and from 1 × 1 to 10 × 10 cm(2) for MLC-collimated fields, delivered from a zero (head up, beam directed vertically downward) gantry angle. Differences between the field sizes measured for the eight linacs exceeded the uncertainty of the film measurements and the repositioning uncertainty of the jaws and MLCs on one linac. The dimensions of fields defined by MLC leaves were more consistent between linacs, while also differing more from their nominal values than fields defined by orthogonal jaws. The field output factors measured for the different linacs generally increased with increasing measured field size for the nominal 0.6 × 0.6 to 1 × 1 cm(2) fields, and became consistent between linacs for nominal field sizes of 2 × 2 cm(2) and larger. The inclusion in radiotherapy treatment planning system beam data of small field output factors acquired in fields collimated by jaws (rather than the more-reproducible MLCs), associated with either the nominal or the measured field sizes, should be viewed with caution. The size and reproducibility of the fields (especially the small fields) used to acquire treatment planning data should be investigated thoroughly as part of the linac or planning system commissioning process. Further investigation of these issues, using different linac models, collimation systems and beam orientations, is recommended.

journal_name

Australas Phys Eng Sci Med

journal_title

Australasian physical & engineering sciences in medicine

authors

Kairn T,Asena A,Charles PH,Hill B,Langton CM,Middlebrook ND,Moylan R,Trapp JV

doi

10.1007/s13246-015-0349-2

subject

Has Abstract

pub_date

2015-06-01 00:00:00

pages

289-97

issue

eissn

0158-9938

issn

1879-5447

journal_volume

pub_type

杂志文章

在线工具

Field size consistency of nominally matched linacs.