The characteristics of the epithermal neutron beam at BMRR were measured, calculated, and reported. This beam has already been used for animal irradiations. We anticipate that it will be used for clinical trials. Thermal and epithermal neutron flux densities distributions, and dose rate distributions, as a function of depth were measured in a lucite dog-head phantom. Monte Carlo calculations were performed and compared with the measured values. 2 refs., 4 figs., 1 tab

Benary, V.

Fairchild, R. G.

Fiarman, S.

Greenberg, D.

Kalef-Ezra, J.

Kamen, Y.

Wielopolski, L.

UNT Digital Library

DISCLAIMERThis report was prepared as an account of work sponsored by an agency of (he United StatesGovernment, Neither the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsi-bility for the accuracy, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-ence herein to any specific commercial product, process, or service by trade same, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof. The viewsand opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or any agency thereof.BNL—45930! DE91 011028DOSE MEASUREMENTS AND CALCULATIONS IN THE EPITHERMAL NEUTRONBEAM AT THE BROOKHAVEN MEDICAL RESEARCH REACTOR (BMRR)V.Benaryw( R.G. Fairchiid1, J. Kalef-Ezra1-3, D. Greenberg\Y. Kamen1, S. Fiannan1,and L. WielopolskiM'Medical Dept, Brookhaven National Laboratory, Upton, NY, USA*Tel Aviv University, Tel-Aviv, Israel^University of loannina, Ioannina, Greece'Radiation Oncology DepL, SUNY-SB, Stony Brook, NY, USAINTRODUCTIONThe characteristics of the epitbennal neutron beam at BMRR were measured, calculated, andreported by R. G. Fairchiid (1). This beam has already beea used for animal irradiations. We anticipatethat it will be used for clinics! trials. Thermal and epithennal neutron flux densit:es distributions, anddose rate distributions, as a function of depth were measured in a ludte dog-head phantom. MonteCarlo calculations were performed and compared with the measured values.MEASUREMENTS AND CALCULATIONSPop-Head phantom. A lucitc dog-head phantom similar is size and shape to that of a Labradorretriever (Fig. 1) was constructed in our* laboratory. The central part was cored to a rectangular well4W in depth, 3J4" in length, and 3VV in width. This was filled with different sett of horizontal luciteplates. Each set of plates had precfeely machined grooves, to accommodate either foils, cadmiumcapsules with foils, TLD's, or silicon diodes (Fig. 2). This arrangement allowed for measurements atprecise depths on the central axis. The composition and the density of ludte is, for our purposes, verysimilar to tissue. The phantom was irradiated with its central axis (center of the plates) aligned with thecentral axis of the port. A series of irradiations were conducted with the phantom touching the bare 10*x 10" port. Another series had the phantom placed against a 2*-thick IiOH collimator, with an apertureof about 4" x 4', inserted in the port The experiments were A t- To check the dosimetry in an asymmetric geometricalconfiguration;• To obtain dosimetric data for animal irradiations;• To assess the influence of beam delimiters (collimator;);• To compare the measured values with the Monte Carlocalculations.Calculations. The Monte Carlo computer program MCNPwas used to generate neutron lluence rates and dose rates in adog phantom. The neutron source used in the calculations hada pancake geometry of 10* x 10" and was situated directly infront of the phantom or the collimator, when one was used.The energy spectrum of the source was the calculated spectrumreported by Wheeler et al.(2). The calculated values werecompared to the measured results. The main discrepancy wasobserved in the calculations of the 7 dose.F i g . 1«•• • MASTER eDISTRIBUTION OF THIS DOCUMENT IS UNLIMJTB?Thermal and enithermal neutron fluenee rates. Bare and cadmium-encapsulated gold foils wereused to measure tbe thermal and epithennal neutron flux. The epithermal neutron fluence rate wascalculated by the cadmium ratio method. Tbe measured values of the neutron fluence rates with andwithout a collimator are shown in Fig. 3, and the calculated (MCNP) values are given in Fig. 4. Whenwe compared the ratio: thermal neutron fluence rate (bare port)/thermal neutron fluence rate(collimator) at the peak and at the surface of the phantom, a skin-sparing effect was suggested whena coUimator was used. The magnitude of this effect will be influenced by the combined geometry of thecollimator and the phantom. The measured and the calculated values are in good agreement; however,the calculated epithennal neutron fluence rate drops faster with depth in phantom.Effective Dose Rate. The effective dose rates for phantom irradiations on the bare port and witha collimator are given in Figs. 5 aw) 6 at a power of 1MW. For the 14N(n,p)14C reaction, a N contentof 1.84% by weight and an RBE of 1.6 were used. The same RBE was used for tbe fast neutroneffective dose. The RBE used for tbe 10B(n^)7U reaction was 23. Tbe shape of tbe curves in Fig. 6was influenced by the irregular shape of the phantom.THERMAL AND EP1THERMA1. FtUENCE RATE IN LUCfTE DOG PHANTOMMEASURED•Thermolflux•Epfthermol flux•Thermal flux (col)»Epithermal flux (col)UCHP CALCULATIONS•Thermal flux•Eptthermoi flux•Thermal flux (eel)•Epithennal flux (col)2 4 6 8Depth in Phantom (cm)Re, 32 4 6 8Depth in Phantom (cm)FT* 4MEASURED OOSE DISTRIBUTIONS IN DOG PHANTOM-1MWNO COLUMATOR ? WfTH COLUMATOR2 4 6Depth In phantom (cm)14N(n.p)14C- • Total gamma- • Fast neutron- • Z ppm 1 0BRe, 52 4 6Oepth in phantom (cm)• 3 0 p p m 1 0 B• Total bckg. (no TOB)* Total bckg. -I- 3 ppm B• Total bckg. + 30 ppm 1 0BFig. 6225.193-2-10-117.7-ltr117.53113447.161253JM0-"7.7-l<Tu3355X1520352.03Z793-10-"---_0.850.8433-W 1 1---The caJculated (MCNP) dose distributions were in good agreement with the measured values withthe exception of the calculated ^ doses. As can be seen in Table 1, the -y doses were much lower,probably due mainly to the cross sections used.Table 1. Beam Parameters in Dog Phantom.Measured MCNPBare Coll Bare CollFast neutron dose rateat 0 depth rad-rbe/MW-minPeak total y dote raterad-rbe/MW-minFast neutron dose/to, neutronat peak rad-rbe/n-cmPeak 7 dose/th. neutronat peak rad-rbe/n-cmPeak bckgr (no l 0B) dose raterad-rbe/MW-minPeak bckgr 3 ppm 10B dose ratend-rbe/MW-minPeak bckgr 30 ppm 10B dose raterad-rbe/MW-minINTERCAUBRATION OF EPITHERMAL NEUTRON BEAMSMeasurements and/or calculations of beam parameters in air are not enough to characterize aneutron beam. Dose components must be measured and calculated in a phantom. The compositions,shapes, and sizes of the phantoms, as well as She geometry of the bean, make k difficult to comparethe performance of the different neutron beams. We suggest standardizing the phantom and thereported measured or calculated parameters in a manner similar to that which follows.Phantom. A simple, inexpensive, and easily machined lucite right circular cylinder, 16.5 cm indiameter, 25 cm high, was built. A thin lucite tube was inserted along its central axis. Ludte rods wereinserted in the tube. Each set of rods had indentations to allow the insertion of detectors (foils, TLDs,or solid state silicon diodes) at well-defined depths in the phantom. A provision is made for theinsertion of a lucite tube off axis, in which measurements can be made for calculation benchmarking.Beam Parameters in Air. It is our opinion that the parameters, measured and/or calculated at theirradiation port face, which must be reported in order to characterize the eptthermal beam are:Neutron spectrum;Epithermal neutron Dux density;Absorbed dose rate from gammas and fast neutrons free in air;Gamma dose and fast neutron dose per epithermal neutron.Beam Parameters in Standard Phantom. Graphic representations of the thermal neutron fluxdensity and dose rate distributions as a function of depth in phantom must be reported.A beam aperture of 10 by 10 cm is suggested. In any case, the irradiation geometry must be welldefined. The advantage depth and the therapeutic gain will complete the data necessary for an effectiveintercalat ion of epithermal neutron beams.REFERENCES1. R.G. Fairchild et al. Installation and testing of an optimized neutron beam at the BMRR. NeutronBeam Design, Development and Performance for Neutron Capture Therapy. O.K. Karling, J.A.Bernard and R.G. Zamenhof, Eds. Basic Life. Sciences, VoL 54, 185, Plenum Press, New York(1990).2. FJ. Wheeler et al. Physics design for the BMRR epithermal neutron source. Neutron Beam Design,Development and Performance for Neutron Capture Therapy. O.K. Karling, J-A. Bernard and R.G.Zamenhof, eds. Basic Life Science, Vol. 54, 83, Plenum Press, New York (1990).(Research supported by US DOE contract DE-AC02-76CH00016)

Dose measurements and calculations in the epithermal neutron beam at the Brookhaven Medical Research Reactor (BMRR)

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Dose measurements and calculations in the epithermal neutron beam at the Brookhaven Medical Research Reactor (BMRR)

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