Microdosimetric measurements for neutron-absorbed dose determination during proton therapy

Perez‐Andujar, A; DeLuca, P.M.; Thornton, Allan F.; Fitzek, Markus M.; Hecksel, Draik; Farr, J

doi:10.1093/rpd/ncs002

Cited by 7 publications

(6 citation statements)

References 25 publications

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“…TEPCs have been applied to measure single‐event distributions of many types of ionizing radiation, including photons, neutrons, and heavy charged particles. These detectors can and have been used to conduct measurements around proton and carbon therapy beams . The event‐size spectra obtained during measurements can range from around 0.1 keV/μm to > 1000 keV/μm.…”

Section: Measurement Approachesmentioning

confidence: 99%

“…These detectors can and have been used to conduct measurements around proton and carbon therapy beams. 163,241,242 The event-size spectra obtained during measurements can range from around 0.1 keV/lm to > 1000 keV/lm. The absorbed dose contributions from various types of secondary particles can be differentiated via the microdosimetric spectrum because different secondary particles have different lineal energies in the active volume.…”

Section: B2 Fast Neutron Detectorsmentioning

confidence: 99%

“…[243][244][245] TEPC detectors are usually calibrated with an internal alpha particle source, 244 Cm, where the energy deposited in the cavity, expressed in keV/ lm, can be obtained from the stopping power of the alphas and the counter diameter. 242,[246][247][248] This calibration is generally the principal source of uncertainty in this type of measurement, suffering from a poor resolution of the calibration peak as well as uncertainties associated with the stopping power value and mean chord length.…”

Section: B2 Fast Neutron Detectorsmentioning

confidence: 99%

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AAPM TG158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

et al. 2017

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The introduction of advanced techniques and technology in radiotherapy has greatly improved our ability to deliver highly conformal tumor doses while minimizing the dose to adjacent organs at risk. Despite these tremendous improvements, there remains a general concern about doses to normal tissues that are not the target of the radiation treatment; any "nontarget" radiation should be minimized as it offers no therapeutic benefit. As patients live longer after treatment, there is increased opportunity for late effects including second cancers and cardiac toxicity to manifest. Complicating the management of these issues, there are unique challenges with measuring, calculating, reducing, and reporting nontarget doses that many medical physicists may have limited experience with. Treatment planning systems become dramatically inaccurate outside the treatment field, necessitating a measurement or some other means of assessing the dose. However, measurements are challenging because outside the treatment field, the radiation energy spectrum, dose rate, and general shape of the dose distribution (particularly the percent depth dose) are very different and often require special consideration. Neutron dosimetry is also particularly challenging, and common errors in methodology can easily manifest as errors of several orders of magnitude. Task Group 158 was, therefore, formed to provide guidance for physicists in terms of assessing and managing nontarget doses. In particular, the report: (a) highlights major concerns with nontarget radiation; (b) provides a rough estimate of doses associated with different treatment approaches in clinical practice; (c) discusses the uses of dosimeters for measuring photon, electron, and neutron doses; (d) discusses the use of calculation techniques for dosimetric evaluations; (e) highlights techniques that may be considered for reducing nontarget doses; (f) discusses dose reporting; and (g) makes recommendations for both clinical and research practice.

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Section: Measurement Approachesmentioning

confidence: 99%

Section: B2 Fast Neutron Detectorsmentioning

confidence: 99%

Section: B2 Fast Neutron Detectorsmentioning

confidence: 99%

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AAPM TG158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

et al. 2017

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“…Tissue-equivalent proportional counters (TEPC) have also been used to measure microdosimetric neutron spectra from proton therapy. [24][25][26] While TEPC are sensitive over the entire neutron energy range of interest in proton therapy, the published microdosimetric spectra reported frequency distributions as a function of lineal energy rather than neutron fluence as a function of energy. In short, measurements of secondary neutrons from proton therapy either have not included spectral data or spectral results did not provide neutron fluence as a function of energy or were measured using detectors with limited response to neutron energies greater than 20 MeV.…”

Section: Introductionmentioning

confidence: 99%

Secondary neutron spectrum from 250‐MeV passively scattered proton therapy: Measurement with an extended‐range Bonner sphere system

Howell

Burgett

2014

Medical Physics

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Purpose: Secondary neutrons are an unavoidable consequence of proton therapy. While the neutron dose is low compared to the primary proton dose, its presence and contribution to the patient dose is nonetheless important. The most detailed information on neutrons includes an evaluation of the neutron spectrum. However, the vast majority of the literature that has reported secondary neutron spectra in proton therapy is based on computational methods rather than measurements. This is largely due to the inherent limitations in the majority of neutron detectors, which are either not suitable for spectral measurements or have limited response at energies greater than 20 MeV. Therefore, the primary objective of the present study was to measure a secondary neutron spectrum from a proton therapy beam using a spectrometer that is sensitive to neutron energies over the entire neutron energy spectrum. Methods: The authors measured the secondary neutron spectrum from a 250-MeV passively scattered proton beam in air at a distance of 100 cm laterally from isocenter using an extended-range Bonner sphere (ERBS) measurement system. Ambient dose equivalent H*(10) was calculated using measured fluence and fluence-to-ambient dose equivalent conversion coefficients. Results: The neutron fluence spectrum had a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate energy continuum between the thermal and evaporation peaks. The H*(10) was dominated by the neutrons in the evaporation peak because of both their high abundance and the large quality conversion coefficients in that energy interval. The H*(10) 100 cm laterally from isocenter was 1.6 mSv per proton Gy (to isocenter). Approximately 35% of the dose equivalent was from neutrons with energies ≥20 MeV. Conclusions: The authors measured a neutron spectrum for external neutrons generated by a 250-MeV proton beam using an ERBS measurement system that was sensitive to neutrons over the entire energy range being measured, i.e., thermal to 250 MeV. The authors used the neutron fluence spectrum to demonstrate experimentally the contribution of neutrons with different energies to the total dose equivalent and in particular the contribution of high-energy neutrons (≥20 MeV). These are valuable reference data that can be directly compared with Monte Carlo and experimental data in the literature. © 2014 Author(s)

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“…Thus, regardless of the delivery method, neutron exposures are a potential concern. 4 In general, passive delivery systems confer somewhat higher neutron dose exposures than dynamic systems, although a comparison of recent studies [4][5][6][7] and earlier studies 8,9 suggests that neutron exposures are decreasing over time as beam delivery techniques are improved. The study of stray external neutron exposures from passive systems is of paramount importance, as the overwhelming majority of patients receive passive treatments.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo and analytical model predictions of leakage neutron exposures from passively scattered proton therapy

2013

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Microdosimetric measurements for neutron-absorbed dose determination during proton therapy

Cited by 7 publications

References 25 publications

AAPM TG158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

AAPM TG158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

Secondary neutron spectrum from 250‐MeV passively scattered proton therapy: Measurement with an extended‐range Bonner sphere system

Monte Carlo and analytical model predictions of leakage neutron exposures from passively scattered proton therapy

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