An automated system for the measurement of alanine/EPR dosimeters

Sharpe, Peter; Sephton, J.P.

doi:10.1016/s0969-8043(00)00068-3

Cited by 22 publications

(8 citation statements)

References 3 publications

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“…However, no investigations concerning radical yield for high-energy photons and electrons have been reported. Lately, the dose accuracy has been enhanced due to more precise EPR detection schemes, more precise correction factors for influence quantities as well as reporting of statistical uncertainty in EPR alanine dosimetry (Sharpe and Sephton 2000, Hayes et al 2000, Chen et al 2002, Sleptchonok et al 2000, Nagy et al 2000a, Nagy et al 2000b, Nagy et al 2002.…”

Section: Introductionmentioning

confidence: 99%

An investigation of the photon energy dependence of the EPR alanine dosimetry system

et al. 2003

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The electron paramagnetic resonance (EPR) alanine dosimetry system is based on EPR measurements of radicals formed in alanine by ionizing radiation. The system has been studied to determine its energy dependence for photons in the 10-30 MV region relative to those of 60Co and to find out if the system would be suitable for dosimetry comparisons. The irradiations were carried out at the National Research Council, Ottawa, Canada and the doses ranged from 8 to 54 Gy. The EPR measurements were performed at the University of Oslo, Norway. The ratio of the slope of the alanine reading versus dose-to-water curve for a certain linac photon beam quality and the corresponding slope for a reference 60Co gamma-radiation gives an experimental measure of the relative dose-to-water response of the EPR alanine dosimetry system. For calculating the linear regression coefficients of these alanine reading versus dose curves, the method of weighted least squares was used. This method is assumed to produce more accurate regression coefficients when applied to EPR dosimetry than the common method of standard least squares. The overall uncertainty on the ratio of slopes was between 0.5 and 0.6% for all three linac energies. The relative response for all the linac beams compared to cobalt was less than unity: by about 0.5% for the 20 and 30 MV points but by more than 1% for the 10 MV point. The given standard uncertainties negate concluding that there is any significant internal variation in the measured response as a function of beam quality between the three linac energies. Thus, we calculated the average dose response for all three energies and found that the alanine response is 0.8% (+/-0.5%) lower for high energy x-rays than for 60Co gamma-rays. This result indicates a small energy dependence in the alanine response for the high-energy photons relative to 60Co which may be significant. This result is specific to our dosimetry system (alanine with 20% polyethylene binder pressed into a particular shape) including its waterproofing sleeve of PMMA (2 mm thick); however, we expect that this result may apply to other similar detectors.

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Section: Introductionmentioning

confidence: 99%

An investigation of the photon energy dependence of the EPR alanine dosimetry system

et al. 2003

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“…The dosimeters were conditioned at 55% relative humidity for ten weeks prior to use in order to reduce post-irradiation fading. After each irradiation the pellets were shipped to NPL in batches of 40 pellets, where they were evaluated following the standard procedure (Sharpe and Sephton 2000). Unlike ionization chambers, the dose response of solid state detectors like films or alanine depends explicitly on the charge, the fluence and the energy E of the particles which constitute the mixed radiation field.…”

Section: Alanine Electron Paramagnetic Resonance (Epr) Dosimetrymentioning

confidence: 99%

End-to-end tests using alanine dosimetry in scanned proton beams

et al. 2018

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This paper describes end-to-end test procedures as the last fundamental step of medical commissioning before starting clinical operation of the MedAustron synchrotron-based pencil beam scanning (PBS) therapy facility with protons. One in-house homogeneous phantom and two anthropomorphic heterogeneous (head and pelvis) phantoms were used for end-to-end tests at MedAustron. The phantoms were equipped with alanine detectors, radiochromic films and ionization chambers. The correction for the 'quenching' effect of alanine pellets was implemented in the Monte Carlo platform of the evaluation version of RayStation TPS. During the end-to-end tests, the phantoms were transferred through the workflow like real patients to simulate the entire clinical workflow: immobilization, imaging, treatment planning and dose delivery. Different clinical scenarios of increasing complexity were simulated: delivery of a single beam, two oblique beams without and with range shifter. In addition to the dose comparison in the plastic phantoms the dose obtained from alanine pellet readings was compared with the dose determined with the Farmer ionization chamber in water. A consistent systematic deviation of about 2% was found between alanine dosimetry and the ionization chamber dosimetry in water and plastic materials. Acceptable agreement of planned and delivered doses was observed together with consistent and reproducible results of the end-to-end testing performed with different dosimetric techniques (alanine detectors, ionization chambers and EBT3 radiochromic films). The results confirmed the adequate implementation and integration of the new PBS technology at MedAustron. This work demonstrates that alanine pellets are suitable detectors for end-to-end tests in proton beam therapy and the developed procedures with customized anthropomorphic phantoms can be used to support implementation of PBS technology in clinical practice.

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“…All alanine pellets were read out (Sharpe and Sephton 2000) at the NPL and the absolute dose at Point 2 calculated as described earlier.…”

Section: Audit Proceduresmentioning

confidence: 99%

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

et al. 2017

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A UK multicentre audit to evaluate HDR and PDR brachytherapy has been performed using alanine absolute dosimetry. This is the first national UK audit performing an absolute dose measurement at a clinically relevant distance (20 mm) from the source. It was performed in both INTERLACE (a phase III multicentre trial in cervical cancer) and non-INTERLACE brachytherapy centres treating gynaecological tumours. Forty-seven UK centres (including the National Physical Laboratory) were visited. A simulated line source was generated within each centre's treatment planning system and dwell times calculated to deliver 10 Gy at 20 mm from the midpoint of the central dwell (representative of Point A of the Manchester system). The line source was delivered in a water-equivalent plastic phantom (Barts Solid Water) encased in blocks of PMMA (polymethyl methacrylate) and charge measured with an ion chamber at 3 positions (120° apart, 20 mm from the source). Absorbed dose was then measured with alanine at the same positions and averaged to reduce source positional uncertainties. Charge was also measured at 50 mm from the source (representative of Point B of the Manchester system). Source types included 46 HDR and PDR Ir sources, (7 Flexisource, 24 mHDR-v2, 12 GammaMed HDR Plus, 2 GammaMed PDR Plus, 1 VS2000) and 1 HDRCo source, (Co0.A86). Alanine measurements when compared to the centres' calculated dose showed a mean difference (±SD) of +1.1% (±1.4%) at 20 mm. Differences were also observed between source types and dose calculation algorithm. Ion chamber measurements demonstrated significant discrepancies between the three holes mainly due to positional variation of the source within the catheter (0.4%-4.9% maximum difference between two holes). This comprehensive audit of absolute dose to water from a simulated line source showed all centres could deliver the prescribed dose to within 5% maximum difference between measurement and calculation.

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An automated system for the measurement of alanine/EPR dosimeters

Cited by 22 publications

References 3 publications

An investigation of the photon energy dependence of the EPR alanine dosimetry system

An investigation of the photon energy dependence of the EPR alanine dosimetry system

End-to-end tests using alanine dosimetry in scanned proton beams

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

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