Response of lithium formate EPR dosimeters at photon energies relevant to the dosimetry of brachytherapy

Adolfsson, Emelie; Carlsson, Gudrun Alm; Grindborg, Jan-Erik; Gustafsson, Håkan; Lund, Eva; Tedgren, Åsa Carlsson

doi:10.1118/1.3475938

Cited by 30 publications

(59 citation statements)

References 37 publications

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“…A BRUKER EleXsys E500 was used with a BRUKER standard resonator (4102ST) for all readouts. Details about the dosimeter manufacturing and handling can be found in earlier publications [10][11][12].…”

Section: Dosimeters and Epr Readoutmentioning

confidence: 99%

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A system for remote dosimetry audit of 3D-CRT, IMRT and VMAT based on lithium formate dosimetry

Adolfsson

Gustafsson

Lund

et al. 2014

Radiotherapy and Oncology

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Section: Dosimeters and Epr Readoutmentioning

confidence: 99%

“…Lithium formate has previously been used for verification of IMRT treatments [10] and for measurement around 192 Ir brachytherapy sources [11]. The LET-dependence of response for photon energies < 150 keV relative to 60 Co is known [12] and imply that the lithium formate system is a good candidate for use also in brachytherapy audits.…”

Section: Introductionmentioning

confidence: 99%

A system for remote dosimetry audit of 3D-CRT, IMRT and VMAT based on lithium formate dosimetry

Adolfsson

Gustafsson

Lund

et al. 2014

Radiotherapy and Oncology

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“…Various LiF thermoluminescent dosimeter (TLD) systems have shown a response per unit absorbed dose in the detector that is about 5%-10% higher in 20-50 kV beams than in MV beams (Davis et al 2003, Nunn et al 2008, Carlsson Tedgren et al 2011. On the contrary, the lithium formate electron paramagnetic resonance (EPR) dosimetry system used in this work shows an approximately 6% lower response in kV than in MV beams (Adolfsson et al 2010). The effect of variations of intrinsic efficiency with beam quality is often neglected and has not been investigated for many dosimetry systems including EBT2 radiochromic film in photon beams.…”

Section: Introductionmentioning

confidence: 98%

“…Intrinsic efficiency at brachytherapy beam qualities relative to 60 Co or MV photon beam has been thoroughly investigated for lithium formate EPR dosimeters (Adolfsson et al 2010). No corresponding investigations have to our knowledge been performed for radiochromic film.…”

Section: Relative Intrinsic Efficiencymentioning

confidence: 99%

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Measurement of absorbed dose to water around an electronic brachytherapy source. Comparison of two dosimetry systems: lithium formate EPR dosimeters and radiochromic EBT2 film

et al. 2015

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Interest in high dose rate (HDR) electronic brachytherapy operating at 50 kV is increasing. For quality assurance it is important to identify dosimetry systems that can measure the absorbed doses in absolute terms which is difficult in this energy region. In this work a comparison is made between two dosimetry systems, EPR lithium formate dosimeters and radiochromic EBT2 film. Institute of Physics and Engineering in Medicine7 These authors contributed equally to this work. 8 Author to whom any correspondence should be addressed. Both types of dosimeters were irradiated simultaneously in a PMMA phantom using the Axxent EBS. Absorbed dose to water was determined at distances of 10 mm, 30 mm and 50 mm from the EBS. Results were traceable to different primary standards as regards to absorbed dose to water (EPR) and air kerma (EBT2). Monte Carlo simulations were used in absolute terms as a third estimate of absorbed dose to water.Agreement within the estimated expanded (k = 2) uncertainties (5% (EPR), 7% (EBT2)) was found between the results at 30 mm and 50 mm from the x-ray source. The same result was obtained in 4 repetitions of irradiation, indicating high precision in the measurements with both systems. At all distances, agreement between EPR and Monte Carlo simulations was shown as was also the case for the film measurements at 30mm and 50mm. At 10mm the geometry for the film measurements caused too large uncertainty in measured values depending on the exact position (within sub-mm distances) of the EBS and the 10 mm film results were exculded from comparison.This work has demonstrated good performance of the lithium formate EPR dosimetry system in accordance with earlier experiments at higher photon energies ( 192 Ir HDR brachytherapy). It was also highlighted that there might be issues regarding the energy dependence and intrinsic efficiency of the EBT2 film that need to be considered for measurements using low energy sources.

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Characterization of nanoDot optically stimulated luminescence detectors and high‐sensitivity MCP‐N thermoluminescent detectors in the 40–300 kVp energy range

2017

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Purpose: To investigate empirically the energy dependence of the detector response of two in vivo luminescence detectors, LiF:Mg,Cu,P (MCP-N) high-sensitivity TLDs and Al 2 O 3 :C OSLDs, in the 40-300-kVp energy range in the context of in vivo surface dose measurement. As these detectors become more prevalent in clinical and preclinical in vivo measurements, knowledge of the variation in the empirical dependence of the measured response of these detectors across a wide spectrum of beam qualities is important. Method: We characterized a large range of beam qualities of three different kilovoltage x-ray units: an Xstrahl 300 Orthovoltage unit, a Precision x-Ray X-RAD 320ix biological irradiator, and a Varian On-Board Imaging x-ray unit. The dose to water was measured in air according to the AAPM's Task Group 61 protocol. The OSLDs and TLDs were irradiated under reference conditions on the surface of a water phantom to provide full backscatter conditions.To assess the change in sensitivity in the long term, we separated the in vivo dosimeters of each type into an experimental and a reference group. The experimental dosimeters were irradiated using the kilovoltage x-ray units at each beam quality used in this investigation, while the reference group received a constant 10 cGy irradiation at 6 MV from a Varian clinical linear accelerator. The individual calibration of each detector was verified in cycles where both groups received a 10 cGy irradiation at 6 MV. Results: The nanoDot OSLDs were highly reproducible, with AE1.5% variation in response following >40 measurement cycles. The TLDs lost~20% of their signal sensitivity over the course of the study.The relative light output per unit dose to water of the MCP-N TLDs did not vary with beam quality for beam qualities with effective energies <50 keV (~150 kVp/6 mm Al). At higher energies, they showed a reduced (~75-85%) light output per unit dose relative to 6 MV x rays.The nanoDot OSLDs exhibited a very strong (120-408%) dependency of the light output relative to 6 MV x rays. Variations up to 15% between different x-ray units with equivalent effective energies were also observed. Conclusions: While convenient for clinical use, nanoDot OSLDs exhibit a strong variation in their measured light output per unit dose relative to 6 MV in the 40-300 kV x-ray range. This variability differs unit-to-unit, limiting their effective use for in vivo dosimetry applications in the kilovoltage x-ray energy range. MCP-N TLDs offer a much more stable response, but suffer from variations in sensitivity over time dependent on radiation history, which requires careful experimental handling.

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Response of lithium formate EPR dosimeters at photon energies relevant to the dosimetry of brachytherapy

Cited by 30 publications

References 37 publications

A system for remote dosimetry audit of 3D-CRT, IMRT and VMAT based on lithium formate dosimetry

A system for remote dosimetry audit of 3D-CRT, IMRT and VMAT based on lithium formate dosimetry

Measurement of absorbed dose to water around an electronic brachytherapy source. Comparison of two dosimetry systems: lithium formate EPR dosimeters and radiochromic EBT2 film

Characterization of nanoDot optically stimulated luminescence detectors and high‐sensitivity MCP‐N thermoluminescent detectors in the 40–300 kVp energy range

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