Effects of inaccurate small field dose measurements on calculated treatment doses

Kairn, Tanya, Charles, Paul, Crowe, Scott, & Trapp, Jamie (2016) Effects of inaccurate small field dose measurements on calculated treatment doses. Australasian Physical & Engineering Sciences in Medicine. (In Press)

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Abstract

Given the difficulty and potential time- or financial-costs associated with accurate small field dosimetry, this study aimed to establish the clinical necessity of obtaining accurate small field output factor measurements and to evaluate the effects on planned doses that could arise if accurate measurements are not used in treatment planning dose calculations.

Isocentre doses, in heterogeneous patient anatomy, were calculated and compared for 571 beams from 48 clinical radiotherapy treatments, using a clinical radiotherapy treatment planning system, with reference to two different sets of beam configuration data. One set of beam configuration data included field output factors (total scatter factors) from precisely positioned and response-corrected diode measurements and the other included field output factors measured using a conventional technique that would have been better suited to larger field measurements. Differences between the field output factor measurements made with the two different techniques equated to 14.2% for the 6×6 mm2 22 field, 1.8% for the 12×12 mm2 23 field, and less than 0.5% for the larger fields. This led to isocentre dose differences of up to 3.3% in routine clinical fields smaller than 9 mm across and up to 11% in convoluted fields smaller than 15 mm across.

If field widths smaller than 15 mm are used clinically, then accurate measurement (or-remeasurement) of small field output factors in the treatment planning system’s beam data is required in order to achieve dose calculation accuracy within 3%. If such measurements are not completed, then errors in excess of 10% may occur if very small, narrow, concave or convoluted treatment fields are used.

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ID Code: 96709
Item Type: Journal Article
Refereed: Yes
Keywords: Stereotactic radiosurgery, Treatment planning, Radiation therapy
DOI: 10.1007/s13246-016-0461-y
ISSN: 1879-5447
Subjects: Australian and New Zealand Standard Research Classification > PHYSICAL SCIENCES (020000) > OTHER PHYSICAL SCIENCES (029900) > Medical Physics (029903)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Funding:
Copyright Owner: Copyright 2016 Springer
Deposited On: 07 Jul 2016 22:22
Last Modified: 28 Jul 2016 16:40

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