Publikation: Adapting a practical EPR dosimetry protocol to measure output factors in small fields with alanine
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Purpose
Modern radiotherapy techniques often deliver small radiation fields. In this work, a practical Electron Paramagnetic Resonance (EPR) dosimetry protocol is adapted and applied to measure output factors (OF) in small fields of a 6 MV radiotherapy system. Correction factors and uncertainties are presented and OFs are compared to the values obtained by following TRS-483 using an ionization chamber (IC).
Methods
Irradiations were performed at 10 cm depth inside a water phantom positioned at 90 cm source to surface distance with a 6 MV flattening filter free photon beam of a Halcyon radiotherapy system. OFs for different nominal field sizes (1 × 1, 2 × 2, 3 × 3, 4 × 4, normalized to 10 × 10 cm2) were determined with a PinPoint 3D (PTW 31022) IC following TRS-483 as well as with alanine pellets with a diameter of 4 mm and a height of 2.4 mm. EPR readout was performed with a benchtop X-band spectrometer. Correction factors due to volume averaging and due to positional uncertainties were derived from 2D film measurements.
Results
OFs obtained from both dosimeter types agreed within 0.7% after applying corrections for the volume averaging effect. For the used alanine pellets, volume averaging correction factors of 1.030(2) for the 1 × 1 cm2 field and <1.002 for the larger field sizes were determined. The correction factor for positional uncertainties of 1 mm was in the order of 1.018 for the 1 × 1 cm2 field. Combined relative standard uncertainties uc for the OFs resulting from alanine measurements were estimated to be below 1.5% for all field sizes. For IC measurements, uc was estimated to be below 1.0%.
Conclusions
A practical EPR dosimetry protocol is adaptable for precisely measuring OFs in small fields down to 1 × 1 cm2. It is recommended to consider the effect of positional uncertainties for field sizes <2 × 2 cm2.
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HÖFEL, Sebastian, Pauline LIEBIG, Michael K. FIX, Malte DRESCHER, Felix ZWICKER, 2023. Adapting a practical EPR dosimetry protocol to measure output factors in small fields with alanine. In: Journal of Applied Clinical Medical Physics. Wiley. 2023, 24(12), e14191. eISSN 1526-9914. Available under: doi: 10.1002/acm2.14191BibTex
@article{Hofel2023Adapt-68650, year={2023}, doi={10.1002/acm2.14191}, title={Adapting a practical EPR dosimetry protocol to measure output factors in small fields with alanine}, number={12}, volume={24}, journal={Journal of Applied Clinical Medical Physics}, author={Höfel, Sebastian and Liebig, Pauline and Fix, Michael K. and Drescher, Malte and Zwicker, Felix}, note={Article Number: e14191} }
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<rdf:RDF xmlns:dcterms="http://purl.org/dc/terms/" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:bibo="http://purl.org/ontology/bibo/" xmlns:dspace="http://digital-repositories.org/ontologies/dspace/0.1.0#" xmlns:foaf="http://xmlns.com/foaf/0.1/" xmlns:void="http://rdfs.org/ns/void#" xmlns:xsd="http://www.w3.org/2001/XMLSchema#" > <rdf:Description rdf:about="https://kops.uni-konstanz.de/server/rdf/resource/123456789/68650"> <dc:creator>Liebig, Pauline</dc:creator> <dc:contributor>Drescher, Malte</dc:contributor> <dc:contributor>Zwicker, Felix</dc:contributor> <dcterms:isPartOf rdf:resource="https://kops.uni-konstanz.de/server/rdf/resource/123456789/29"/> <dc:contributor>Höfel, Sebastian</dc:contributor> <dcterms:title>Adapting a practical EPR dosimetry protocol to measure output factors in small fields with alanine</dcterms:title> <dc:creator>Drescher, Malte</dc:creator> <dc:date rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">2023-12-08T10:00:55Z</dc:date> <dc:rights>Attribution 4.0 International</dc:rights> <void:sparqlEndpoint rdf:resource="http://localhost/fuseki/dspace/sparql"/> <bibo:uri rdf:resource="https://kops.uni-konstanz.de/handle/123456789/68650"/> <dc:creator>Fix, Michael K.</dc:creator> <dc:creator>Zwicker, Felix</dc:creator> <dcterms:available rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">2023-12-08T10:00:55Z</dcterms:available> <dcterms:issued>2023</dcterms:issued> <dspace:hasBitstream rdf:resource="https://kops.uni-konstanz.de/bitstream/123456789/68650/1/Hoefel_2-q683bwykqyp71.pdf"/> <dc:contributor>Liebig, Pauline</dc:contributor> <dc:language>eng</dc:language> <dcterms:abstract>Purpose<br />Modern radiotherapy techniques often deliver small radiation fields. In this work, a practical Electron Paramagnetic Resonance (EPR) dosimetry protocol is adapted and applied to measure output factors (OF) in small fields of a 6 MV radiotherapy system. Correction factors and uncertainties are presented and OFs are compared to the values obtained by following TRS-483 using an ionization chamber (IC).<br /><br />Methods<br />Irradiations were performed at 10 cm depth inside a water phantom positioned at 90 cm source to surface distance with a 6 MV flattening filter free photon beam of a Halcyon radiotherapy system. OFs for different nominal field sizes (1 × 1, 2 × 2, 3 × 3, 4 × 4, normalized to 10 × 10 cm<sup>2</sup>) were determined with a PinPoint 3D (PTW 31022) IC following TRS-483 as well as with alanine pellets with a diameter of 4 mm and a height of 2.4 mm. EPR readout was performed with a benchtop X-band spectrometer. Correction factors due to volume averaging and due to positional uncertainties were derived from 2D film measurements.<br /><br />Results<br />OFs obtained from both dosimeter types agreed within 0.7% after applying corrections for the volume averaging effect. For the used alanine pellets, volume averaging correction factors of 1.030(2) for the 1 × 1 cm<sup>2</sup> field and <1.002 for the larger field sizes were determined. The correction factor for positional uncertainties of 1 mm was in the order of 1.018 for the 1 × 1 cm<sup>2</sup> field. Combined relative standard uncertainties u<sub>c</sub> for the OFs resulting from alanine measurements were estimated to be below 1.5% for all field sizes. For IC measurements, uc was estimated to be below 1.0%.<br /><br />Conclusions<br />A practical EPR dosimetry protocol is adaptable for precisely measuring OFs in small fields down to 1 × 1 cm<sup>2</sup>. It is recommended to consider the effect of positional uncertainties for field sizes <2 × 2 cm<sup>2</sup>.</dcterms:abstract> <dc:creator>Höfel, Sebastian</dc:creator> <dspace:isPartOfCollection rdf:resource="https://kops.uni-konstanz.de/server/rdf/resource/123456789/29"/> <foaf:homepage rdf:resource="http://localhost:8080/"/> <dcterms:hasPart rdf:resource="https://kops.uni-konstanz.de/bitstream/123456789/68650/1/Hoefel_2-q683bwykqyp71.pdf"/> <dc:contributor>Fix, Michael K.</dc:contributor> <dcterms:rights rdf:resource="http://creativecommons.org/licenses/by/4.0/"/> </rdf:Description> </rdf:RDF>