Measurement of neutron ambient dose equivalent in passive carbon‐ion and proton radiotherapies

Yonai, Shunsuke; Matsufuji, Naruhiro; Kanai, Tatsuaki; Matsui, Yoshihiko; Matsushita, Kaoru; Yamashita, Haruo; Numano, Masumi; Sakae, Takeji; Terunuma, Toshiyuki; Nishio, Teiji; Kohno, Ryosuke; Akagi, Takashi

doi:10.1118/1.2989019

Cited by 88 publications

(77 citation statements)

References 25 publications

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“…Both experimental methods and Monte Carlo (MC) simulations were used in these studies Zacharatou Jarlskog et al, 2008;Jiang et al, 2005;Polf et al, 2005;Agosteo et al, 1998). For ions heavier than protons, measurements of neutron contamination in therapeutic ion beams are scarce and dedicated mainly to 12 C ion beams (Iwase et al, 2007;Gunzert-Marx et al, 2008;Yonai et al, 2008). Using MC calculations, different types of secondary radiation have been evaluated for a variety of ion beams (Porta et al, 2008;Iwase et al, 2007;Gunzert-Marx et al, 2008;Pshenichnov et al, 2005;Gudowska et al, 2007;Hultqvist and Gudowska, 2009).…”

Section: Introductionmentioning

confidence: 99%

Secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with proton and carbon ion beams

Hultqvist

Gudowska

2010

Radiation Measurements

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Section: Introductionmentioning

confidence: 99%

Secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with proton and carbon ion beams

Hultqvist

Gudowska

2010

Radiation Measurements

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“…2͑a͒ at 20 cm from the field edge. Yonai et al, 37 using a WENDI-II detector, showed that the ambient dose equivalent among different facilities differs by up to a factor of 3. Their results for the dose equivalent at 50 cm from the isocenter are larger than Fig.…”

Section: Ivc Equivalent Dosementioning

confidence: 99%

Assessment of out‐of‐field absorbed dose and equivalent dose in proton fields

et al. 2009

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Purpose:In proton therapy, as in other forms of radiation therapy, scattered and secondary particles produce undesired dose outside the target volume that may increase the risk of radiation-induced secondary cancer and interact with electronic devices in the treatment room. The authors implement a Monte Carlo model of this dose deposited outside passively scattered fields and compare it to measurements, determine the out-of-field equivalent dose, and estimate the change in the dose if the same target volumes were treated with an active beam scanning technique. Methods: Measurements are done with a thimble ionization chamber and the Wellhofer MatriXX detector inside a Lucite phantom with field configurations based on the treatment of prostate cancer and medulloblastoma. The authors use a GEANT4 Monte Carlo simulation, demonstrated to agree well with measurements inside the primary field, to simulate fields delivered in the measurements. The partial contributions to the dose are separated in the simulation by particle type and origin. Results: The agreement between experiment and simulation in the out-of-field absorbed dose is within 30% at 10-20 cm from the field edge and 90% of the data agrees within 2 standard deviations. In passive scattering, the neutron contribution to the total dose dominates in the region downstream of the Bragg peak ͑65%-80% due to internally produced neutrons͒ and inside the phantom at distances more than 10-15 cm from the field edge. The equivalent doses using 10 for the neutron weighting factor at the entrance to the phantom and at 20 cm from the field edge are 2.2 and 2.6 mSv/Gy for the prostate cancer and cranial medulloblastoma fields, respectively. The equivalent dose at 15-20 cm from the field edge decreases with depth in passive scattering and increases with depth in active scanning. Therefore, active scanning has smaller out-of-field equivalent dose by factors of 30-45 in the entrance region and this factor decreases with depth. Conclusions: The dose deposited immediately downstream of the primary field, in these cases, is dominated by internally produced neutrons; therefore, scattered and scanned fields may have similar risk of second cancer in this region. The authors confirm that there is a reduction in the out-of-field dose in active scanning but the effect decreases with depth. GEANT4 is suitable for simulating the dose deposited outside the primary field. The agreement with measurements is comparable to or better than the agreement reported for other implementations of Monte Carlo models. Depending on the position, the absorbed dose outside the primary field is dominated by contributions from primary protons that may or may not have scattered in the brass collimating devices. This is noteworthy as the quality factor of the low LET protons is well known and the relative dose risk in this region can thus be assessed accurately.

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“…1,[9][10][11][12][13][14] There are a few reports of neutron doseequivalent measurements made in proton therapy centers with either the wide-energy neutron detection instrument (WENDI) or smart WENDI (SWENDI), a type of Rem-meter that is sensitive over an energy range adequate for measuring neutrons from proton therapy. [14][15][16][17] Like standard Remmeters, however, these detectors provide only a single doseequivalent value and do not provide the neutron spectrum. There are also several reports of measurements with detectors such as track etch detectors 14,18 or thermoluminescent detectors 19 that have limited or no response to neutrons with energies greater than 10 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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Measurement of neutron ambient dose equivalent in passive carbon‐ion and proton radiotherapies

Cited by 88 publications

References 25 publications

Secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with proton and carbon ion beams

Secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with proton and carbon ion beams

Assessment of out‐of‐field absorbed dose and equivalent dose in proton fields

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

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