THE NEUTRON DOSE CONVERSION COEFFICIENTS CALCULATION IN HUMAN TOOTH ENAMEL IN AN ANTHROPOMORPHIC PHANTOM

Paper

THE NEUTRON DOSE CONVERSION COEFFICIENTSCALCULATION IN HUMAN TOOTH ENAMEL IN AN

ANTHROPOMORPHIC PHANTOM

A. M. Khailov,* A. I. Ivannikov,* V. G. Skvortsov,* V. F. Stepanenko,* A. F. Tsyb,*F. Trompier,† and M. Hoshi‡

Abstract—In the present study, MCNP4B simulation code isused to simulate neutron and photon transport. It gives theconversion coefficients that relate neutron fluence to the dosein tooth enamel (molars and pre-molars only) for 20 energygroups of monoenergetic neutrons with energies from 10�9 to20 MeV for five different irradiation geometries. The datapresented are intended to provide the basis for connectionbetween EPR dose values and standard protection quantitiesdefined in ICRP Publication 74. The results of the calculationsfor critical organs were found to be consistent with ICRP data,with discrepancies generally less than 10% for the fast neu-trons. The absorbed dose in enamel was found to dependstrongly on the incident neutron energy for neutrons over 10keV. The dependence of the data on the irradiation geometryis also shown. Lower bound estimates of enamel radiationsensitivity to neutrons were made using obtained coefficientsfor the secondary photons. Depending on neutron energy,tooth enamel was shown to register 10–120% of the totalneutron dose in the human body in the case of pure neutronexposure and AP irradiation geometry.Health Phys. 98(2):000–000; 2010

Key words: dose reconstruction; dosimetry; Monte Carlo;neutron dosimetry

INTRODUCTION

EPR (ELECTRON paramagnetic resonance)-based dosimetryof human tooth enamel along with cytometry representsa reliable and accurate tool for individual photon doseassessment in cases of unavailable physical dosimetry. In

practice, there are some accidents involving the substan-tial neutron component of the field that are bringing thesubject of the potential of EPR dosimetry to provide theestimation of doses in mixed radiation fields into focus.However, the introduction of EPR dosimetry to a rela-tively new sector, where doses are complex and dependon particle energy, and the processes of energy absorp-tion are complicated, poses some problems and remainsan area for further research.

The first two stages of the EPR dose-reconstructionprocess are determination of the intensity of theradiation-induced EPR signal and a calibration factor toassess the absorbed dose in the enamel. As pointed out byseveral authors (Zdravkova et al. 2002; Fattibene et al.2003; Khan et al. 2003), the neutron and any high-LET(linear energy transfer) radiation produces the sameEPR signal as gamma radiation, so no special treat-ment of samples or spectra processing techniques areneeded. But to reach the final goal of any dosimetry–toprovide a dose reconstruction in body tissues– priorknowledge of the relationship between the dose insamples measured by EPR spectrometry and organabsorbed doses or other protection quantities isneeded. For use in radiological protection, ICRPPublication 74 (ICRP 1997) provides reference con-version coefficients from neutron fluence to bothprotection and operational quantities for irradiation byincident monoenergetic neutrons. Most frequentlyused are the dose-conversion coefficients (DCC),which are defined as absorbed dose in a target object,D(E0), per source particle fluence, �(E0):

Cf�E0� �D�E0�

��E0�(1)

Such coefficients, although being produced for idealizedirradiation geometries and monoenergetic neutrons, maybe helpful in determining the desired dosimetric quanti-ties in actual conditions of exposure. The absorbed dose

* Medical Radiological Research Center, Korolyov str., 4,Obninsk 249036, Russia; † Institute of Radiation Protection andNuclear Safety (IRSN), BP 17, F-92262, Fontenay-aux-Roses,Cedex, France; ‡ Institute of Radiation Biology and Medicine ofHiroshima University (IRBM), 1-2-3 Kasumi, Minami-ku, Hiro-shima, 734-8553, Japan.

For correspondence contact: A. I. Ivannikov, Medical Radiolog-ical Research Center, Korolyov str., 4, Obninsk 249036, Russia;† Institute of Radiation Protection and Nuclear Safety (IRSN), BP 17,F-92262, Fontenay-aux-Roses, Cedex, France, or email [email protected].

(Manuscript accepted 2 April 2009)0017-9078/10/0Copyright © 2009 Health Physics Society

DOI: 10.1097/HP.0b013e3181a86610

1

balt5/zhl-hp/zhl-hp/zhl00210/zhl5398-09a angnes S�3 11/18/09 1:43 Art: 200020 Input-9000

Fn1

AQ: A

in an organ of the human body, DG, given an arbitraryenergy distribution of fluence, is expressed as

DG � �Cf,G�E��E��dE� (2)

Thus, provided such DCC for the dose absorbed inenamel, one could connect EPR data with any dosequantities defined in ICRP 74 (for example organ ab-sorbed dose), making it possible to quickly estimate thedose distribution in a case of accidental overexposure.

Tooth enamel is exposed to ionizing radiation as a partof human body. Neutrons undergo many interactions withina body. These include elastic and inelastic scattering,radiation capture, and other nuclear reactions. Neutrons candeposit energy and create the paramagnetic centers in toothenamel both due to the recoil nuclei and by formation of thesecondary photons produced in enamel and in biologicaltissues surrounding teeth. Therefore, radiation yield ofparamagnetic centers in tooth enamel (and radiation sensi-tivity as well) should also be determined by secondaryphotons produced mainly in reaction of radiationcapture 1H (n, �)2H (E� � 2.23 MeV), which is themost important one contributing significantly to dosein the soft tissue and the only one in the thermal andnear-thermal energy region.

To characterize the response of the EPR signal inenamel to radiation, the amplitude of the signal is related tounits of tissue-absorbed dose according to calibration usinga 60Co photon source and the tissue-equivalent dosimeter,which is called here EPR dose, Depr (Gy):

Depr � I/�ICo-60/DCo-60t �, (3)

where I � radiation-induced EPR signal intensity normal-ized by sample mass in enamel (expressed in arbitraryunits); ICo-60 � EPR signal intensity at exposure to photonsfrom the 60Co source (expressed in the same arbitrary units);Dt

Co-60 (Gy) � is the dose of 60Co photons measured bytissue equivalent dosimeter.

As long as tooth enamel is known to register photonsalmost in corpore, the secondary photons are of particularimportance for the EPR dosimetry of neutrons. Therefore,in case of neutron irradiation, EPR dose in enamel, Depr, canbe expressed through the sum of two separate components:absorbed doses in soft tissue of neutrons and secondaryphotons at the position of the teeth in a phantom, Dt

n and Dt�

(Gy), or doses transferred to enamel by the neutrons andsecondary photons, De

n and De� (Gy), respectively, by the

equations:

Depr � htD�t � ktDn

t , (4)

Depr � heD�e � keDn

e, (5)

where ht and kt � relative EPR sensitivities of enamelto photons and neutrons, respectively, relative to dosein tissue; he and ke � EPR sensitivities of enamel tophotons and neutrons, respectively, relative to dose inenamel.

As can be seen from eqns (4) and (5), to determinedose distribution based on the measured absorbed dosein the enamel, separate Monte Carlo (MC) calculationsof neutron and secondary photon components of thetotal neutron dose in enamel are needed. The resultsobtained by Ivannikov et al. (2004) showed theradiation-induced EPR signal (i.e., EPR dose re-sponse) to be directly proportional to that calculatedby the MC method (MCNP4B code), absorbed dose inenamel in the photon energy range of 13 keV–1.25MeV within the limits, which is determined by errorsof the experiment and calculations. The equality ofenamel EPR dose response and calculated absorbeddose in enamel is expected for photons of all energies.Therefore, for the calculations of photon doses inenamel using MCNP4B code, radiation sensitivity oftooth enamel to photons, h can be put equal to one andomitted with high level of certainty.

The main purpose of this paper is to present DCC datafor the mean absorbed doses of neutrons Cf,n and secondaryphotons Cf,� and for the total neutron dose Cf,T in the lateralenamel region used for the means of EPR applications:

Cf,n�E0� �Dn

e�E0�

��E0�; Cf,��E0� �

D�e �E0�

��E0�; Cf,T�E0� �

DTe �E0�

��E0�,

(6)

where, DeT(E0) is the total neutron absorbed dose in

enamel [sum of Den(E0) and De

�(E0)].Using this DCC, Depr can be expressed as follows:

Depr � ��Cf,n�E��ke � Cf,��E��E��dE� (7)

Providing the energy spectrum of incident neutrons�(E), one may assess the ratio of EPR dose in enamel(Depr) and mean absorbed neutron dose in selected organor tissue (DG):

Depr

DG�

��Cf,n�E��ke � Cf,��E��E��dE�

�Cf�E��E��dE�

(8)

In this work, the role of secondary photons to doseformation at neutron irradiation is also investigated.With regard to such low relative sensitivity to the


2 Health Physics February 2010, Volume 98, Number 2

AQ: B

neutron component of the total neutron dose, accord-ing to eqn (8) the calculated ratio of DCC for thephoton dose in tooth enamel and total absorbed dosefor an organ or tissue can be considered a lower boundestimate of total neutron dose share registered bymeans of EPR dosimetry.

If the human body is exposed to high-energy neu-tron irradiation, the resulting radiation field inside thebody can comprise not only the dose contribution by theincident radiation, but also a large dose fraction attribut-able to scattered neutrons. The present paper also pro-vides an overview of the type of scattered (build-up)photon and neutron spectra to be expected in enamelexposed to monoenergetic neutrons.

In the present paper, the DCC are presented for“pure” neutron irradiation. It is worth noting that, inpractice, neutron fields are always accompanied byphoton fields, and virtually in all radiological acci-dents where neutron exposure was involved, primaryphoton dose component should be considered. There-fore, in order to correctly determine the protectionquantities using EPR measurements data, it is neces-sary to consider a separate contribution of photon andneutron components into the dose-absorbed in toothenamel. The DCC for the case of photon irradiation to

date are thoroughly calculated and may be found inUlanovsky (2005).

MATERIALS AND METHODS

Computational model and Monte Carlo simulationThe hermaphrodite adult mathematical model de-

signed by Cristy and Eckerman (1980) was used tomodel the human body. A geometric model of the humandental region was developed and inserted in the MCNPcode. The geometry parameters of dental region weredefined on the basis of average statistical data fromTolstykh et al. (2000). Element composition of toothmaterials used in MC calculations based on ICRP (1975)data was taken from Ivannikov et al. (2004). The dentalregion for talling was described by cylindrical surfaces ofelliptical section. The thickness of lateral and masticatoryenamel was 0.636 mm and 1.5 mm, respectively. Thespace between the two enamel layers was filled withdentin. The phantom was assumed to be surrounded byvacuum. The geometry is shown in more detail in Fig. 1.Since only tooth enamel of masticatory teeth is used formeans of EPR dosimetry, the dental region of thephantom was split into three parts, and calculations were

Fig. 1. Problem geometry for the calculations (a) and a view of the phantom (b). Tooth enamel cells are separated intothree locations: (1) Right, (2) Left, and (3) Front. Also designated are (4) Soft tissue, (5) Spinal, and (6) Facial bones.


3Neutron dose conversion coefficients calculation ● A. M. KHAILOV ET AL.

F1

made for enamel of two lateral regions (marked as 1 and2 in Fig. 1).

Calculations were performed for uniform whole-body exposure with mono-energetic neutrons with ener-gies from 10�9 to 20 MeV for AP (antero-posterior), PA(postero-anterior), LLAT (left-lateral), RLAT (right-lateral), and ISO (isotropic) irradiation geometries (ICRP1997).

From Fig. 1 it can be seen that left (2) and right (1)tooth lateral parts representing premolars and molars aresymmetrically located in the head. So, in AP, PA, andISO irradiation geometries, the data for left and rightlateral regions are identical. For LLAT and RLATgeometries, the data are given for the left lateral region(marked as 2 in Fig. 1).

MCNP4B (Monte Carlo N-Particle Version 4B)(Briemeister 1997) code was used to simulate the neutronand photon transport. Calculations were performed instandard NP (neutron-photon) mode, which allows forneutron interactions in the creation of secondary photonsthat are banked for later transport. For the calculation ofenergy absorption in the regions of interest, a heating andenergy deposition tally (F6) was used. It assumes thekerma approximation: i.e., the energy transferred torecoil protons and other nuclear emissions is deposited atthe interaction points, and particles are not pursuedfurther. The transport of secondary electrons was nottaken into account either.

ICRP Publication 74 (1997) states kerma approxi-mation to be valid for photons with energies up to about3 MeV and for neutrons up to about 20 MeV, at tissuedepths of 10 mm. Since enamel in vivo is shielded by the

soft tissue of the cheek and saliva of 10–20 mmthickness, one may assume the charged-particle equilib-rium to exist at enamel location. Accordingly, the use ofF6 tally and kerma approximation is considered to give agood estimate for calculation of enamel-absorbed dosesup to neutron energies of about 20 MeV.

The cut-off energies for neutrons and photons were0 and 1 keV, respectively. Molecular binding of hydro-gen for thermal neutrons up to 1 eV was considered byusing the proper MT material card. The time of calcula-tions was set depending on the fractional standard devi-ation of the absorbed dose to the tooth enamel, which didnot exceed 5% for neutrons (except for low energies inPA, RLAT geometries) and around 5–10% for secondaryphotons, respectively.

RESULTS AND DISCUSSION

MCNP4B is a reliable and effective general-purposecode which is commonly used to perform radiationtransport calculations. The authors have already used thesame method of calculation in previous articles (Ivanni-kov et al. 2004; Khailov et al. 2007), where it wasverified by an experiment. But to provide the extravalidation of the data and prove the reliability of thecalculational model used, absorbed dose values per unitneutron fluence in several critical organs were calculatedand compared to the results given in ICRP Publication 74(1997). Fig. 2a and b show selected comparisons of thecalculated organ-dose data. The differences between thecalculations are greatest for deep-lying organs and atneutron energies below 0.01 MeV when the dose values

Fig. 2. Percent differences in critical organ-absorbed dose conversion coefficients between the values presented here andICRP 74 values for monoenergetic neutrons and AP (a) and PA (b) irradiation geometries.



F2

are small and the relative error of calculations is high.For some organs (e.g., the colon under PA irradiation),the results are somewhat higher or lower than that ofICRP in the broad neutron energy range. This can beexplained by averaging of ICRP data or slight geometri-cal differences in organ definitions. The peak at 1 MeVis probably due to rapid change in coefficient values. Forneutrons with energies above 4 MeV, the discrepancybetween the results is not considerable with almost noexceptions. Generally, the data presented indicates thatwith a few exceptions there is a good agreement. Thisdemonstrates that the calculated data for tooth enamel aretrustworthy and could be reliably used for the purposes ofEPR dosimetry.

Calculated conversion coefficients from neutronfluence to absorbed doses in lateral enamel are presentedin Table 1 and graphically in Fig. 3a and b. Thecoefficients are separately given both for the neutron andsecondary photon components of the total neutron dosein enamel. Due to the good agreement of this data andICRP74 data, the doses for different organs are notpresented here because they can be borrowed from thisreference.

The coefficients for PA and RLAT and, especially,for AP and LLAT geometries are very much alike, whichis not surprising given the symmetric placement ofenamel and averaging over lateral teeth used. The rise ofneutron data with incident energy increases can be

readily seen, most rapid in the energy range 0.01–4MeV. The differences between the neutron coefficientsfor various geometries become less expressed with therise in energy since more high-energy neutrons areknown to penetrate tissue easier. The values for photonstend to depend less on energy, since the variations withina factor of 3 are most likely to be caused by thermalneutron build-up in head tissue. The dependence on thegeometry of irradiation is most significant for neutronsup to 1 MeV.

Thus, the results demonstrate that tooth enamel-absorbed dose is strongly dependent on both the incidentneutron energy and irradiation geometry, and this depen-dence is quite complex. They also indicate that secondaryphotons contribute more than 10% to the total dose inenamel for neutrons up to 10 MeV and should always beconsidered in analysis of EPR data in the given energyrange.

The calculation of the neutron-absorbed dose inenamel was complemented by calculations of neutron-and secondary-photon-spectral fluence distributionswith a resolution of 50 –100 keV averaged over thelateral tooth enamel using the track length tally (F4).Although it has been calculated for the whole energyrange mentioned before, for the sake of space the datais presented here for the two most significantenergies—1 and 20 MeV. The spectra in Fig. 4 are

Table 1. Dose conversion coefficients in tooth enamel (absorbed dose per unit neutron fluence), Cf � D ��1, in unitsof pGy cm2 for monoenergetic neutrons incident in various geometries on an adult anthropomorphic computationalmodel. Notations: Cf,n, Cf,y, Cf,T-dose conversion coefficients for neutron, secondary photon and total neutron doserespectively, according to eqn (6). These data and the geometry notation are also presented graphically in Fig. 3.

Energy(MeV)

Geometries of irradiation

AP PA LLAT RLAT ISO

Cf,n Cf,� Cf,T Cf,n Cf,� Cf,T Cf,n Cf,� Cf,T Cf,n Cf,� Cf,T Cf,n Cf,� Cf,T

1.0 � 10�9 0.01 1.04 1.05 0.00 0.22 0.22 0.01 1.08 1.08 0.00 0.25 0.25 0.00 0.53 0.531.0 � 10�8 0.01 1.48 1.49 0.00 0.30 0.30 0.01 1.46 1.47 0.00 0.36 0.36 0.00 0.69 0.701.0 � 10�7 0.01 2.20 2.22 0.00 0.34 0.34 0.02 2.23 2.25 0.00 0.50 0.50 0.01 0.92 0.921.0 � 10�6 0.02 2.49 2.51 0.00 0.61 0.61 0.02 2.91 2.93 0.00 0.57 0.57 0.01 1.15 1.161.0 � 10�5 0.02 2.45 2.47 0.00 0.71 0.71 0.02 2.11 2.13 0.00 0.77 0.77 0.01 1.07 1.081.0 � 10�4 0.02 2.02 2.04 0.00 0.68 0.68 0.02 1.91 1.93 0.00 0.67 0.67 0.01 1.00 1.001.0 � 10�3 0.02 1.87 1.88 0.00 0.55 0.55 0.02 1.75 1.77 0.00 0.63 0.63 0.01 0.90 0.911.0 � 10�2 0.03 1.83 1.85 0.00 0.63 0.63 0.03 1.34 1.37 0.00 0.76 0.76 0.01 0.82 0.831.0 � 10�1 0.15 1.77 1.92 0.00 0.74 0.74 0.19 1.63 1.82 0.00 0.86 0.87 0.05 0.83 0.881.0 � 10�1 0.97 1.48 2.45 0.01 0.79 0.80 1.06 1.47 2.53 0.05 0.91 0.96 0.35 0.87 1.211.0 � 100 2.11 1.22 3.33 0.03 0.78 0.82 2.26 1.21 3.47 0.13 0.75 0.88 0.75 0.81 1.562.0 � 100 2.51 1.21 3.72 0.33 0.95 1.28 2.62 1.06 3.68 0.71 1.05 1.76 1.14 0.87 2.004.0 � 100 5.78 1.10 6.88 1.13 0.81 1.95 5.99 0.95 6.94 2.13 0.85 2.98 2.85 0.70 3.566.0 � 100 9.37 1.08 10.5 3.04 0.85 3.88 9.25 0.87 10.1 4.26 0.88 5.14 5.02 0.75 5.778.0 � 100 10.9 1.70 12.6 4.52 1.36 5.88 10.9 1.53 12.5 6.14 1.38 7.53 6.44 1.24 7.681.0 � 101 14.6 2.32 17.0 6.44 1.60 8.04 14.3 2.08 16.4 8.08 1.66 9.74 8.70 1.66 10.41.2 � 101 17.0 2.65 19.7 7.89 1.49 9.38 17.1 2.24 19.4 10.0 1.78 11.8 10.5 1.81 12.31.4 � 101 19.6 2.31 21.9 9.85 1.95 11.8 19.6 2.47 22.1 11.9 1.93 13.9 12.4 1.78 14.11.6 � 101 21.4 2.24 23.6 11.0 1.67 12.7 21.0 1.94 23.0 13.4 1.72 15.2 13.6 1.68 15.31.8 � 101 22.4 1.69 24.1 13.0 1.45 14.5 22.5 1.70 24.2 15.0 1.42 16.4 14.9 1.45 16.32.0 � 101 25.0 1.42 26.4 15.0 1.30 16.3 25.0 1.55 26.6 17.2 1.25 18.4 17.2 1.24 18.4



T1,F3

F4

shown as fluence in a “bin” divided by the bin width.The area of each spectrum is normalized to 1.

The neutron radiation field inside the enamel is seenas a mixture mainly comprising thermal and incidentneutron energies. The thermal neutron component can beignored, since it is impossible to create ionization inenamel and contributes nothing to the neutron-absorbeddose. As an example, Fig. 4b shows the spectrum inenamel for 20 MeV incident neutrons. The spectrum ofneutrons at the left- and right-hand side are roughly thesame, probably because of the low scattering cross-sections in this region and the small depth of tissuecovering the enamel. Fig. 4a shows the scattering forprimary neutrons of 1 MeV to be more significantespecially in geometries when enamel is heavily shieldedby tissue and facial bones. It can be concluded that onlyin RLAT and PA irradiation cases there can be consid-erable dose contributions by scattered neutrons withstrongly reduced energies.

Since the values of neutron range in a medium areincreasing with its energy, the total neutron spectrumat the enamel location inside the body is shifted moretoward lower energies for small incident energies.Therefore, since that enamel response to the neutronsis dependent on energy, the correct measure of dose byEPR in the future in RLAT and PA geometries will notbe perfectly true without taking this factor into ac-count.

Fig. 4c and d show the secondary photon spectrain enamel to be almost a peak at one energy. It isapparently due to the reaction radiation capture on

hydrogen 1H (n, �)2H, which emits photons with anenergy of 2.2 MeV.

The gamma dose-response of tooth enamel re-ferred to 60Co is known to increase for photons withenergies below 300 keV, having a maximum at 50keV, where it reaches the value of 10. As mentionedpreviously, the MC calculations allow the enamelgamma dose-response alterations to be accounted for.But, in practice, experimental dosimetry is conductedusing photon detectors calibrated in tissue, making theanalysis of the secondary photon component of theradiation field of some importance. The build-up ofenergy-degraded (Compton scattered) photons in thetooth enamel exposed in vivo to an external field isobserved to be somewhat higher for 20 MeV neutrons(Fig. 4d). The component of photons with energieslower than 300 keV for both incident neutron energieswas evaluated to be less than 1% of the total photonfluence for AP and LLAT irradiation geometries.Assuming a dose response of 9 referred to 60Co(Ivannikov et al. 2004) for these photons, the wholephoton-absorbed dose component would be overesti-mated by 5–10% at worst. Thus, one may concludethat gamma dose-response dependence of toothenamel should only be accounted for in cases ofenamel irradiations in tissue- or head-equivalent phan-toms.

If both the spectrum and the radiation character-istics of a radiation field are known, using eqn (8), thecalculated data (Table 1) and the response data (Table2) can be folded with the field data to obtain a ratio of

Fig. 3. Absorbed doses transferred to enamel by neutrons (a) and secondary photons (b) per unit neutron fluence, D ��1,in units of pGy cm2 for monoenergetic neutrons incident in various geometries on an adult anthropomorphiccomputational model. The geometries are AP (antero-posterior), PA (postero-anterior), LLAT (left-lateral), RLAT(right-lateral), and ISO (isotropic).



T2

EPR dose in enamel and mean absorbed neutron dosein selected organs. As for the kt and ke values,significant research effort has already been put into itscharacterization. Some of the results are shown inTable 2. The response of tooth enamel has been foundto be dependent on various experimental conditions,especially neutron energy. However, the experimentaldata on the energy dependence of enamel responseremains limited, rather inconsistent and sometimeseven conflicting. For example, experimental irradia-tions carried out on a Silene reactor (Tikunov et al.2005) showed that tooth enamel for neutron energiesup to 1 MeV provides a sufficiently accurate determi-nation of secondary gamma dose but registers only1–2% of neutron component, whereas in other works

(Khan et al. 2003, 2004) the value obtained forneutrons below 0.45 MeV was several times higher.To date, the experiments carried out proved the toothenamel sensitivity in vitro to neutrons to be weak, atleast for neutron energies up to several MeV, mostprobably due to the small hydrogenous content ofenamel and also its significant increase with incidentneutron energy (Fattibene et al. 2003; Zdravkova et al.2002).

So, the present work used the coefficients for thesecondary photons to assess the lower bound estimateof total neutron dose share registered by means of EPRdosimetry (assuming ke equal to zero). This was madeusing the DCC calculated for total absorbed neutrondose in the human body (the total neutron energy

Fig. 4. Neutron (a, b) and secondary photon (c, d) spectral fluence distribution in lateral tooth enamel for 1 and 20 MeVincident neutrons in left (LLAT) and right (RLAT) lateral irradiation geometries.



absorbed by the phantom, divided by its total mass),which was also calculated but not presented here forthe sake of space, and DCC for the thyroid (chosen forits close location to enamel) taken directly from ICRPPublication 74.

The percent of secondary photon dose in enameland the total neutron dose in the human body is shownin Fig. 5a. There, for up to 0.1 MeV neutrons, theenamel due to photons is guaranteed to register over50% of the dose in tissue (with the exception of PAgeometry). But for energies above about 4 MeV, theunderestimation of total dose by EPR would amount toa factor of 10 to 20. From Fig. 5b, where the results forthyroid are shown, it is seen that enamel registers overhalf of the total dose up to 0.1 MeV neutrons, while forhigh-energy neutrons the secondary photons also be-come insignificant. Except for PA geometries, there isa similarity between the situation with respect towhole-body and thyroid doses.

CONCLUSION

The coefficients calculated can serve as the basisfor correcting retrospective doses in tooth enamel forexposures involving mixed radiation fields. The neu-tron radiation fields are complex and include greatranges of radiation types and energies.Therefore, inte-gration over the neutron spectrum and consideration ofthe contribution from primary incident photons shouldbe carried out.

Still, there are a number of scientific issues thatneed further development to ensure that EPR resultsare correctly treated. It is a matter of time for theenergy and build-up dependence of tooth enamelsensitivity to neutrons to be carefully studied. Subjectto the provision of such dependence and informationon the radiation field, the presented data may be usedfor the direct determination of the various dose quan-tities needed.

Table 2. The summary of experimental conditions and results obtained for the experiments on relative neutronsensitivity of enamel. Notations: kt and ke-EPR sensitivities of enamel to neutrons relatively to dose in tissue and to dosein enamel respectively defined in eqns (4, 5).

Irradiation condition-positionof tooth enamel Neutron source Enamel samples

Relative sensitivity toneutrons, %

kt ke

Bochvar et al. 1997 Theoretical estimate based onexperimentally evaluatedsensitivity to alpha radiation

Energy range1 keV−1 MeV

— 3 � 0.3

Kapchigashev et al.1997

In air, wrapped in teflon andpolyethylene films

In paraffine phantom (diam.20 cm, height 18 cm)

Reactor BR-10,Emean � 0.85MeV, Emax � 10.5MeV

Powder, 0.1 mm 1−1.2 � 2

Fattibene et al. 2003 In PMMA mini-phantom, onesample in air

D-D reaction source,Emean � 2.8 MeV

Powder, 0.5−1 mm 33 � 8

In PMMA phantom (diam. 15cm, height 16 cm)

Tooth halves

In air D-T reaction source,Emean � 14 MeV

Tooth halves 60 � 3

Zdravkova et al. 2002 Under a 2 cm polystyreneplate

Cyclotron p-Bereaction, Emean �30 MeV

Whole tooth 11−13 � 3

Under a 2 cm polystyreneplate

Fission spectrumEmax � 10 MeV

Whole tooth Assessed as0−20

Khan et al. 2003, 2004 In air (polypropylene vials),below a 4 mm wax layer

7Li(p, n)7Be reactionsource, Emean �280 keV

Powder, 0.5mm, 4 mm

10 � 5

In air 7Li(p, n)7Be reactionsource, Emean �167−450 keV

Tooth halves 8 � 4

Tikunov et al. 2005 Rectangular plexiglassmini-phantoms

Reactor Silene,Emean � 0.8 MeV,Emax � 15 MeV

Powder, wrappedin Al foil

0.7 � 0.6

Powder 1.2−2.9 � 0.7Khailov et al. 2007 In air Neutron generator

HIRRAC, Emean �0.3 MeV, Emax �0.8 MeV

Powder 2 � 2



F5

REFERENCES

Bochvar IA, Kleshchenko ED, Kushnereva KK, LevochkinFK. Sensitivity of human tooth enamel to � irradiation andneutrons. Atomnaya Energia 83:845–847; 1997 (in Rus-sian).

Briemeister JF. MCNP—A general Monte-Carlo n-particletransport code. Los Alamos, NM: ; LA-12625-M, version4B, Manual; 2000.

Cristy M, Eckerman F. Description of the mathematical phan-tom. Specific absorbed fraction of energy at various agesfrom internal photon sources. Health and Safety ResearchDivision; ORNL/TM-8381/V1, Appendix A; 1980.

Fattibene P, Anglone M, Pillon M, De Coste V. Tooth enameldosimetric response to 2.8 MeV neutrons. Nucl Instr MethB 201:480–490; 2003.

International Commission on Radiological Protection. Conver-sion coefficients for use in radiological protection againstexternal irradiation. Oxford: Elsevier Science; ICRP Publi-cation 74; Ann. ICRP 26:(3–4); 1997.

International Commission on Radiological Protection. Reportof Task Group on Reference Man. Oxford: Pergamon Press;ICRP Publication 23; 1975.

Ivannikov AI, Tikunov DD, Borysheva NB, Trompier F,Skvortsov VG, Stepanenko VF, Hoshi M. Energy depen-dence of EPR dose response of tooth enamel to photons:experiment and Monte Carlo simulation. Radiat ProtectDosim 108:303–315; 2004.

Kapchigashev SP, Tikunov DD, Ivannikov AI, Potetnya VI.Radiation yield of paramagnetic centers in tooth enamel

irradiated by fast neutrons. Yadernaya Energetica 6:15–23;1997 (in Russian).

Khailov AM, Tikunov DD, Ivannikov AI, Skvortsov VG,Stepanenko VF, Zhumadilov K, Tanaka K, Endo S, HoshiM. EPR dosimetry of neutrons: Enhancement of the appar-ent sensitivity at irradiation in the human head phantom.Radiat Meas 42:1171–1177; 2007.

Khan RFH, Aslam, Rink WJ, Boreham DR. Electron paramag-netic resonance dose response studies for neutron irradiatedhuman teeth. Nucl Instr Meth 225:528–534; 2004.

Khan RFH, Rink WJ, Boreham DR. Dosimetric responseevaluation of tooth enamel for accelerator-based neutronirradiation. Radiat Meas 37:355–363; 2003.

Tikunov DD, Ivannikov AI, Trompier F, Herve M, KhailovAM, Skvortsov VG. Relative sensitivity of tooth enamel tofission neutrons: effect of secondary protons. Radiat Meas39:509–514; 2005.

Tolstykh EI, Degteva MO, Kozheurov VP, Shishkina EA,Romanyukha AA, Wieser A, Jacob P. Strontium metabo-lism in teeth and enamel dose assessment: analysis of theTecha river data. Radiat Environ Bioph 39:161–171; 2000.

Ulanovsky A, Wieser A, Zankl M, Jacob P. Photon doseconversion coefficients for human teeth in standard irradi-ation geometries. Health Phys 89:645–659; 2005.

Zdravkova M, Denis JM, Gallez B, Debuyst R. Sensitivity ofwhole human teeth to fast neutrons and gamma-rays esti-mated by L-band EPR spectroscopy. Radiat Meas 35:603–608; 2002.

f f

Fig. 5. Ratios of secondary photon absorbed dose in tooth enamel to total neutron absorbed dose in human body (a) andthyroid (b) for various geometries.



AQ: C

AQ: D

AQ: E

AQ: F

JOBNAME: AUTHOR QUERIES PAGE: 1 SESS: 3 OUTPUT: Mon Nov 16 05:41:26 2009/balt5/zhl�hp/zhl�hp/zhl00210/zhl5398�09z

A—Is this change OK?

B—Please clarify. To what does the word “one” refer in this sentence?

C—Cite Bochvar et al. (1997) in text.

D—Add publisher for Briemeister 2000.

E—Add city of publication for Christy and Eckerman 1980.

F—Cite Kapchigashev et al. (1997) in text.

AUTHOR QUERIES

AUTHOR PLEASE ANSWER ALL QUERIES 1

Documents

THE NEUTRON DOSE CONVERSION COEFFICIENTS CALCULATION IN HUMAN TOOTH ENAMEL IN AN ANTHROPOMORPHIC PHANTOM