ML20073E101

Feasibility Study for Epithermal Neutro-Beam Facility at Washington State Univ Radiation Ctr

ML20073E101
Person / Time
Site:	Washington State University
Issue date:	07/31/1994
From:	Nigg D, Wheeler F EG&G IDAHO, INC., IDAHO NATIONAL ENGINEERING & ENVIRONMENTAL LABORATORY
To:
Shared Package
ML20073E091	List: ML20073E088 ML20073E094 ML20073E101
References
EGG-NRE-11296, NUDOCS 9409280236
Download: ML20073E101 (26)

Text

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t EGG-NRE-11296 L

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i Feasibility Study for an Epithermal tjeutron-Beam Facility at the Washington State University Radiation Center F. J. Wheeler D. W. Nigg l

Published July 1994 Idaho National Engineering Laboratory EG&G Idaho, Inc.

Idaho Falls, Idaho 83415 Prepared for the U.S. Department of Energy office of Energy Research Under DOE idaho operations office Contract DE-AC07-76lD01570 D [

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l ABSTRACT A feasibility study has been performed to investigate modifications of the Washington State University Research Reactor facility to provide an epithermal-neutron beam for Neutron Captura Cancer Therapy. This facility, originally a General Electric concept, nas since been converted to utilize TRIGA-type fuel elements.

Results of calcJlations using the two-dimensional DORT discrete-ordinates computer code show that, assuming availability of appropriate materials, it will be possible to modify the facilities and obtain an epithermal beam of sufficient intensity with low contaminant and favorable directional properties. Two concepts were investigated, both requiring utilization of a reconfigured thermal column. These were: (1) a beam exit port interior to the existing thermal column cavity, and (2) a beam exit port exterior to the thermal column, or brought out flush with the outer shield wall for better access. With the interior beam, a high intensity (2-5x10' n/cm's) beam with excellent purity can be achieved with an AIF,/Al composite material and, using AI,O,, a beam comparable to the epithermal-neutron beam at the Brookhaven Medical Research Reactor (presently the best epithermal beam in the world) can be achieved. With the exterior beam, an intensity adequate for therapy (6x10' to 10' n/cm's) and excellent purity can be achieved using the AIF /Al material. Facility modifications would consist of removing the graphite, lead shielding and H O tank prese,ntly located in the thermal column and installing new materials to provide the epithermal beam, in addition to the neutron filtering material, bismuth and lead gamma shields and collimators would be required as well as >

lithiated polyethylene or equivaient materials. Shield walls about the thermal-column opening would also be required to restrict access and minimize radiation dose to occupied areas around the thermal column. This study did not consider the use of fission plates to enhance the beam. Studies underway at another institution indicate a beam with superici characteristics to the results herein quoted can be obtained with fission plates or perhaps other convertor concepts. Additicnal regulatory and operational concerns would have to be addressed if the convertor concept is used.

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CONTENTS ABSTRACT. . . . . iii ACRONYMS .

. vii

1. INTRODUCTION. .

.1

2. WSU FACILITY DESCRIPTION .5 2.1 Reactor . . .5 2.2 Thermal Column . . .8

3. ANALYSIS . . . . . . . . .

12 3.1 Calculations for Standard Core Layout (Interior Beam) . . , 12 3.2 Calculations for BNCT Core Layout (Interior Beam) . . . 15 3.3 Calculations for BNCT Core Layout (Exterior Beam). 16 3.4 Beam Tailor. . . .

18 3.5 Bean, Shutter .

19 3.6 Patient Treatment Room . 19

4. CONCLUSIONS . .

. . . . . . 20 1

5. REFERENCES . . .

. . . 21 FIGURES l

1. Comparison of epithermal-neutron beams . . . . . . . . . . . . .4

2. Elevation plan sketch . . . . . . . . . . .5

3. A view into the reactor pool below the bridge . . . . . . . . . .6

4. Reactor operator moving the core and bridge. . . . . . . . . . . . . . .6

5. Plan view of WSU reactor beam port facilities . . . . . . . . .7

6. View into the evacuated thermal column. . . . . . . . . . . . .B 7a. View of the room just outside the present thermal column. . . .9 i 7b. View of the front of the enclosed thermal column . . . . .9 l 1

Ba. Mockup of the core adjacent to the protruding core of the thermal column  !

. 10 8b. View of beam ports and thermal column core . . 10

9. Core 33x layout, January 13,1993. . 13

10. Thermal column assembly (evacuated). .

13

11. Thermal cole,an asserably for interior beam-port stuJies. 14 V

12. WSU TRIGA: performante versus filter thickness . . 14

13. Core 34 BNCT. . . . . . . . 15

14. Thermal column assembly with AIF,/A1 filter . 17

15. Thermal column assembly with A1F /A1 and A1 O filter . . . 17 3 2 3

16. Calculated neutron flux spectrum for BNCT Case E4 . . 18

. i TABLES '

1. Characteristics of actual epithermal beams . . .2

2. Calculated characteristics of proposed epithermal-beam concepts . . .3

3. DORT cases with current fuelloading pattern . . . . . . 12

4. Calculated increase in beam performance with BNCT core layout . . . . . 15

5. Beam churacteristics for exterior beam port with BNCT core layout. . . . . . . 16 i

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ACRONYMS BMRR Brookhaven Medical Research Reactor BNCT Boron Neutron Capture Therapy eV Electron volts -

GTR?. Georgia institute of Technology Research Reactor HFR High Flux Reactor KERMA Kinetic Energy Released in Matter i kev Kilo-e!ectron volts K, Fast-neutron KERMA factor K, Gamrna KERMA factor MITR-fl Massachusettes institute of Technology Research Reactor NCT Neutron Capture Therapy i PBF Power Burst Facility '

RBE Relative biological effectiveness R, Ratio of neutron current to neutron flux TRIGA Transient Reactor Irradiator-General Atomics WSU Washington State University i I

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Feasibility Study for an Epithermal Neutron-Beam Facility at the Washington State University (WSU) Radiation Center

1. INTRODUCTION '

Neutron Capture Therapy (NCT) is experiencing renewed interest as a treatment modality for brain (and other) cancer patients. Required for NCT are both an effective drug and an appropriate neutron beam. The only NCT now being performed is in Japan using thermal neutron beams and the borocaptate sodium  ;

compound. It is the thermal-neutron flux that is most effective in generating therapeutic dose to tissue. With an incident thermal neutron beam however, it is necessary to surgically displace the scalp and skull during therapeutic radiation to avoid surface tissue damage and to be able to deliver dose to the cancer cells that ,

are deep inside the brain. In the United States as well as in Europe, researchers are concentrating on neutron beams with incident neutron energies predominantly in the epithermal 10.5 electron volts (ev) to 10 kilo-electron volts (kev)J energy range. Epithermal neutrons are surface sparing, they penetrate a few centimeters into tissue before producing the peak thermal-neutron flux. With epithermal neutrons it is hoped to avoid surgery during radiation therapy, thus providing a much safer and more acceptable procedure. i The characteristics of an epithermal beam important for therapy are: '

1) Intensity: Dose delivery rate is directly proportional to the intensity of the neutron current in the beam.

Also, as the beam is shaped and otherwise tailored to an individual irradiation, intensity is lessened so ,

it is advantageous to start with an inherent, high intensity. For a well-designed epithermal beam having incident flux intensity 10'(n/cm's), a single-fraction relative biological effectiveness (RBE) dose rate of about 20 cGy/ min to healthy tissue (with 50 ppm "B) at peak depth will be achieved, if a '

tolerance dose of 14 Gy (Eq) for peak healthy-tissue dose is targeted, then total irradiation time would '

be about 70 minutes. If fractionation is used, total treatment time may be somewhat more, but time per fraction would then be about 20 30 minutes.

2) Contaminant: Neutrons with energies above 10 kev are very damaging to healthy tissue due to the recoil protons produced when neutrons undergo elastic scatter reactions with hydrogen. Therefore,  ;

it is important to design the neutron beam such that the relative intensity of above-10 kev neutrons j is low. It is possible to design a beam where this component is negligible. Also/ there are incident  ;

gamma rays in any neutron beam due to neutron capture events in structure and it is necessary to l minimize this component. Finally, the thermal-neutron flux in the free beam should be minimized to '

reduce surface-tissue damage. The magnitudes of the fast-neutron and gamma components are often expressed as Kinetic Energy Released in Matter (KERMA) factors. For a therapeutic beam, the gamma KERMA factor (K ) should be reduced to order 10 ", and the fast-neutron KERMA factor (K,) should be reduced to a few times 10" 3)

Collimation: A well-collimated beam is desirable, although not entirely necessary for effective therapy.

A perfectly-collimated (forward directed) beam will have a ratio of neutron current to neutron of 1.0 since current is the forward component of flux. A 2rr isotropic beam has neutrons emanating randomly in the forward direction and has an R equal to 0.5. The collimated beam is more efficient at generating thermal flux in tissue and as a re'sult, reduces K and K relative to peak thermal flux.

Also, an isotropic beam diverges rapidly with distance and pos tioning" error becomes large.

)

There are currently three facilities in the world that have epithermal beams. These are the Brookhaven Medical Research Reactor (BMRR), the Massachusetts institute of Technology Research Reactca (MITR-il), and the High Flux Reactor (HFR) at Petten, The Netherlands. Some characteristics of these beams. are shown in Table 1.

I Table 1. Characteristics of Actual Epithermal Beams' Reactor Epithermal-Flux Fast-Neutron Gamma Collimation R Intensity '

KERMA K KERMA K (Neutron (10' n!cm# s) (10 " cGy/n-cm') (10 " cGy/n-Em') Current / Flux)

HFR 0.33 10.4 8.40 0.95 (45 MW)

MITR-il 0.20 13.0 14.0 -

t5 MW)

BMRR 1.80 4.3 1.30 -0.60 (3 MW)

Note: ' Except for R,, these data are taken from Reference 1.

Human clinical trials are proposed for the HFR (Glioma Multiforme), for the MITR-II (Metastatic Melanoma of the extremities) and for the BMRR (Glioma Multiforme and Ocular Melanoma). It is believed by some that the existing epithermal beams are good enough for early studies but researchers almost unanimously agree that better beams must be developed for clinical applications. The predicted (calculated) characteristics of selected beam concepts now being proposed are shown in Table 2.

The proposed reactor concepts offer significant advantage in beam intensity and quality compared to .

existing beams. The accelerator concepts require further development, particularly in target cooling and beam '

current. There are other concepts and reactor upgrades proposed that are not listed in Table 2.

! Figure 1 presents a comparison of existing and conceptual epithermal-neutron sources. Here intensity and purity are compared with purity defined as:

R' BeamPuri ty=

(4Kf +Ky)

Here; R is a measure of the beam collimation, K, is the fast neutron component (here weighted by 4 to l

accoun. for RBE) and K is the incident gamma component. Others may have a different quantification formula for beam purity t$ut this definition is certainly adequate for comparison.

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Table 2. Calculated Characteristics of Proposed Epithermal Beam Concepts.

Reactor Epithermal-Flux Fast. Neutron Gamma Collimation R Intensity KERMA K KERMA K (Neutron

) (10' n/cm' s) (10'" cGy/n-cm') (10 " cGy/n-dm')

l Current / Flux)

Power Burst 10.0 2.0 1.0 0.95 Facility (20 MW)

Georgia Institute 2.5 1.5 1.0 0.85 of Technology l Research Reactor (5 MW)

FIR l' 3.5 2.6 1.0 0.60 (TRIGA)

(0.25 MW)

RFQ Accelerator' 1.1 4.7 -

0.61 (10 mA)

TC Accelerator' O.16 . .

~ 0.6 (4 mA)

WSU Facility' O.6-5.0 1.5-4.0 0.6-0.9

- 1.0 (1 MW)

Notes: ' Reference 2, page 5.

• Reference 3.

• Referenes 4.

• WSU - Results indicated that beam characteristics in the listed ranges can be obtained, however, there are trade-offs in design goals.

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Figure 1. Comparison of Epithermal-Neutron Beams.

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2. WSU FACILITY DESCRIPTION 2.1 Reactor The Radiation Center at WSU houses a 1 MW convectively-cooled reactor. The reactor building sits on a hill and is isolated from the WSU campus and any residential areas. The reactor facility was originally a General Electric concept but was later modified to utilize Transient Reactor Irradiator-General Atomics (TRIGA) fuel elements and is recently referred to as a TRIGA facility. The reactor core resides in a large pool of ordinary water and is presently licensed to operate at 1 MW. A bridge over the poolis used to configure the core, insert experiments etc. and a reactor operator can safely occupy the bridge while the react 7r is in operation. Figure 2 shows a sketch of an elevation plan showing the relationship of the pool, core and bridge, thermal column, and beam room. Figure 3 shows a view into the pool helow the reactor bridge looking toward the core at the bottom of the pool. Figure 4 shows a reactor operator atop the bridge (moving the core). The TRIGA fuel in the core consists of standard elements and FLIP fuel. The reactor is inherently safe since the fuel elernents contain a large amount of zirconium hydride which, when heated, decreases core reactivity, preventing reactor runaway. Figure 5 shows a sketch of the thermal column and reactor core. The core is mounted on tracks and can easily be moved when in shutdown mode. The core can be positioned immediately adjacent to the thermal-column wall providing a large leakage flux into the thermal column.

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! 2.2 Thermal Column Figure 6 shows the evacuated cavity of the thermal column and hgme 7a shows the room outside the pool  ;

as presently configured. There is a large-vehicle door opposite the thermal column and there is ample room outside the thermal column for shielding, patient manipulation and eqmpment associated with the irradiations.

There is a 10-inch ordinary concrete ceiling above the room. The thermal column contains many stringers of graphite, then lead shielding bricks, and a final light-water tank which is recessed about 6 inches into the heavy-concrete wall. Figure 7b shows the outer portion of the water tank as viewed from the room.

Essentially, the thermal column consists of a column of graphite in a scaled container which will withstand

, the pressure of the water. The container is made up of an aluminum transition section near the core and steel sections in the shielding wall. This aluminum section is tapered on the sides so as to not interfere with the beam ports (Figures 8a and 8b). The front plate (f acing the reactor) is 1/2" thick 2S aluminum which is reinforced with eight 1" x 8" aluminum ribs. These ribs are welded together to form a grid designed to  :

withstand the water head with minimum deflection. The tapered walls of the transition transfer this load to '

, aluminum walls of the column. The aluminum walls extend outward to a point opposite the actual pool wall.

The aluminum section of the container rests on a concrete pad on the pool floor and is encased by about 1 foot of reinforced concrete which restrains the forces at this depth tending to coilapse the column. Sections of aluminum I-beam have been welded to the aluminum walls and imbedded in the reinforced concrete. This 1-beam will withstand the forces tending to push the entire column out of the pool. Circuiting the entire aluminum transition is a seepage collector. Any seepage into this collector will be collected in the common q drain. The plate on the water side of the column is separated from the core by 3/8" to 1/2" of water. The ,

support angles protruding from the grid plate provide this clearance. Water convection currents in this space  ;

will provide cooling for heat produced in the thermal shield when the reactor is operated at high power levels. '

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The thermal shield consists of 2.75" of lead brick. This also assists in shielding the column during shutdown and removes a large percent of the low-energy core gammas during operation. Around the outer perimeter of the aluminum section there is welded a small angle. The steel section of the column is bolted to this angle. This joint is not sealed but merely serves to align the two sections of the column. At this point '

the column is 2" wider in each direction. This extra space is occupied by 1" of shielding lead on all walls.

There is another similar step 18" f arther out. Here the addit ional space is occupied by 2" of lead. The outer end of the column is 6' x 6' and is occupied by lead brick and a final water tank. The inner walls of the column are lined with 1/4" sheets of Boral. These sheets are mounted on the walls with flush fasteners.

They are mounted so that no abrupt steps exist on the column's inner surf ace to interfere with placing of the graphite fogs. These sheets of high neutron absorbing material are placed on the walls to reduce activation of the concrete and the column container. Also by providing a surf ace which is black to thermal neutrons, the desired cosine flux distribution can be more nearly approached. Although cadmium would be a much cheaper neutron absorber, Boral has been used because of its shorter half life and because access to the pool is desired. Fast neutrons escaping the column will be slowed down and captured in the concrete. This effect wdl only be significant for radiation dose near the inner end of the column and substantially decays out within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. .

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3. ANALYSIS The two dimensional DORT* deterministic (Sn) code was used to determine estimated beam parameters.

The locally extended BUGLE 80* cross section library was used in the DORT model. The reactor core and filter were represented as horizontal, cylindrical regions in the calculational model. This cylinder model will not be good for fluyes in and near the core but past studies for the BMRR and GTRR ign show that it provides quite good results for the beam predictions. Future calculations will employ three-dimensional calculations and independent physics data for verification of results.  ;

3.1 Calculations fOr Standard Core Layout (Interior Beam)

Figuro 9 shows a non Boron Neutron Capture Therapy (BNCT) core layout for core 33X (Jan.1993) provided by WSU personnel. DORT calculations were performed to estimate beam performance with this core placed at the O' 0" location (next to the thermal column).

Figure 10 shows a sketch of the evacuated thermal column. Calculations were performed for both AIF (70/30) and Al,0, as a primary neutron spectrum shaping material. The AIF /Al materialis ped b by investigators in Helsinki Finland neutron facility. Figure 11 shows etch of ana s,k,.

assumed Theconfiguration Al,0, material for the is presently calculations. empf,oyed Here the beam for the exit port is located 1-1.2 meters from the core side of the thermal cclumn. Table 3 lists the thicknesses of the components assumed inside the thermal column.

Table 3. DORT Cases With Current Fuel Loading Pattern.

Case Filter Material Filter Thickness Bismuth Gamma 'Li/ poly (cm) Shield Thickness

• Thickness (cm)

(cm) 11 A1 F,/A1' (70/30) 85.0 10.0 6.0 12 A1F3 /A1 (70/30) 70.9 11.4 6.3 >

13 A1 F,/A1 (70/30) 62.2 11.0 6.8 14 A 1,O, 70.9 11.4 6.3 Note: 1. assumes 100% theoretical density for the A1F with a matnx consisting of 70% A1F and 30% A1.

2. vanes because of available mesh spacing in mo' del.

• Figure 12 shows the predicted performance for intensity and fast-neutron KERMA for these four cases.

The one case for Al O demonstrates the superior performance of the AIF /Al composite. For this thickness (71 cm), the A1F,/*Af beam intensity is five times that with Al,0, and th'e fast KERMA is nearly a factor of two less.

It must be pointed out that this model willlikely underestimate the fast-neutron KERMA, probably by about .

20% Therefore, a calculated K of 2x10 " will likely increase to 2.4x10 " for the actual beam. Also, no '

optimization was done for the incident gamma dose nor the thermal flux.

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Coro 33X layout (non BNCT) h 6---e AIF/Al epi flux (10' n/cm's)

E y

4.0 5--5 AIF/Al fast KERM,A (10[ cGy / epi flux)

+ AL,0 3epi flux (10 n/cm s)

A AL,0 fast 3 KERMA (10" cGy / epi flux)

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, 90.0 l

Filter thickness (cm)

Figure 12. WSU TRIGA: per1:ninance versus filter thickness.

14

l 3.2 Calculations for BNCT Core Layout (Interior Beam) i Figure 13 shows a layout provided by WSU personnel for BNCT. This layout (core 34 BNCT) is designed to enhance leakaDe from the core to the thermal column. One calculation was performed for the interior beam using this layout and the filter configuration of case 12 (71 cm AIF,/AI). Table 4 shows the change in beam performance when the new core layout is chosen.

Calculations were also pe formed with FLIP (high enriched) fuel placed in the row nearest the thermal column. For this core loading, beam intensity increased very significantly (-10' ) but results are not reported here because loadin0 FLIP fuel at the core edge is not allowed in the reactor technical specifications.

Table 4.

(70/30). Calculated increase in Beam Performance with BNCT Core Layout; interior Beam, 71-cm AIF,/Al Quantity Core Layout 33X Core Layout 34  % Change J

(January 1993) Case 12 (BNCT) Case 15 l

Epithermal Neutron Flux 1.99 x 10' 2.84 x 10'

+ 43%

intensity (n/cm's) at 1 MW Fast-Neutron KERMA 1.55 x 10 " 1.56 x 10'"

(cGy/ Epithermal Flux)

-0 1

I 2 3 4 ) h 7 N 4 i + +++++++

^-

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Figure 13. Core 34 BNCT 15

3.3 Calculations fOr BNCT Core Layout (Exterior Beam)

The DORT calculations indicate that an excellent beam can be obtained interior to the thermal column.

There are two significant disadvantages however to the interior beam: (1) positioning capability, and (2) higher background-dose exposure to patient and therapist.

Therefore, a model was constructed to investigate beam characteristics obta nable when the beam exit port is brought out to the end of the thermal column where access is excellent (Figure 7). A sketch of this concept is shown in Figure 14 and an alternate concept is shown in Figure 15. Fnr this model, 65-cm of AIF,/Al(70/30) was assumed as the primary filter material. Variations in materials in regions interior to the thermal column wc e made to investigate the effect on beam characteristics.

Calculated results for these cases are shown in Table 5.

Table 5. Beam Characteristics for Exterior Beam Port with BNCT Core Layout; 65 -cm AIF,/Al (70/30) as Primary Filter Material.

Case Filter Collimator Side Reflector Flux Intensity"' Fast Neutron Gamma

• Perimeter (n/cm2 x) @ 1 MW KERMA KERMA (cGy/ flux) (cGy/ flux)

El AIF3 /Al Bismuth Borax 8.16 x 10 8 2.65 x 10" 8.7 x 10 r E2 AIF,/Al Bismuth Al,0, 1.00 x 10' 2.43 x 10'" 8.1 x 10

E3 AIF3 /Al Al O Al O 8.00 x 10' 2.17 x 10~" 8.9 x 10 "

2 3 2 3 E4 Al,0, Bismuth Al,0, 8.46 x 10' 2.24 x 10'" 1.2 x 10 "

E5 AIF,/Al Lead Borax 8.42 x 10' 2.46 x 10~" 1.04 x 10'"

Note: 1. an alternate core representation of core layout 34 gave intensitites about 20% less than listed here.

2. not including gammas from thermal-flux suppression mechanism Of any)

3. Na,840,10H,0 ,

The gamma KERMAs listed in Table 5 mean little in these cases because there is nothing yet in the design to remove thermal flux. There are three ways the thermal flux can be suppressed and the way this is done wi!' affect the collimator design and perhaps the filter thickness. One way would be to place a cadmium sheet

(-30 mils) at the end of the filter. This would eliminate the thermal neutrons without diminishing the epithermal flux but would cause the generation of hard gammas which might affect the shield /collimator designs. Another way would be to incorporate lithium (~1%) into the AIF /Al composite. This would diminish epithermal flux somewhat but would beneficially suppress gamma proc}uction and might reduce the thickness of bismuth (or lead) shielding required. A third way could be to use lithium sheeting built into the flux tailor (described later) re0 i on. The first two methods would produce a good epithermal beam but would reduce the thermal-flux intensity if one wants the capability to convert to a thermal beam for cell / murine experiments. The third method would produce a good epithermal beam and a much stronger thermal beam should it be desirable to convert.

Materials used at the filter perimeter should be further investigated. For example, the use of a very common (incxpensive) material (Al O ) at the sides of the collimator instead of a flux suppressor (borax) '

increases beam intensity by 20% ar$d' decreases the f ast KERMA by 10%. This would be a no cost option to improve the beam. Figure 16 shows the calculated neutron spectrum for a typical run (case E4).

16

Case E4: 65-cm AIF/Al, exterior beam Al,03 at penmeters

- 10, B 10' 5

To 7

'E 10' Y

b E s y 10 t

5 m

o.

.5 10' tot epi flux = 8.5x10' fast KERMA = 2.24E-11 10' #

10" 10 10' 10 10" 10' 10' 10' 10' Energy (eV)

Figure 16. Calculated neutron flux spectrum for BNCT Case E4.

Case E3 shows that no gain is achieved by replacing the collimator with Al.0, and, as might be expected, the gamma KERMA is dramatically increased. Case E4 was run to deterrr,ine if isss AIF,/Al could be used by placing Al O at the outer perimeter of the filter. For this case the outer 25 cm of-the cylindrical representatior$ was assumed to be the oxide. The effect (compare with case E1) is to reduce the intensity by about 15%. This configuration should be investigated further since it reduces the AIF /Al requirements by more than one half (saves ~20K). For a configuration with the same fast KERMA, the Intensity may not ,

be that much different. This result needs verification however since it is not clear why the f ast KERMA is less i with this configuration. '

Case E5 is also a cost saving configuration since there is already an existing supply of lead and bismuth is more expensive. The beam is actually a little better with lead except for the gamma KERMA which may not be a problem anyway. .

3.4 Beam Tailor The team tailor, alluded to previously, could be removable sections defining the last portion of the beam-tailoring system. Potentially, several beam tailors could be constructed and the beam could rapidly be changed from a large field to a small field or perhaps from an epithermal beam to a thermal beam for cell / murine research or as a prompt gamma facility.

18

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Figure 14. Thermal column assembly with A1F /A1 filter (not to scale).

3 d_ NM=dr.r.

,. m heavy cuncrete

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.d.r) .

3.5 Beam Shutter 1

There is no beam shutter in the present facility and it would be a major campaign 4 o construct a large WSU concept since the reactor can be scrammed to a er for the The reactor core then can be manually retracted several teet back a er of seconds.

into the cent the thermal column in just a few seconds to reduce the gamma field even more and away from would be possible to incorporate an external shutter for further protection. a moves This collimator opening for further protection.up to position the beam tailor and e mo 3.6 Patient Treatment Room it will be necessary to construct a room around the beam facility to isolat radiation to an acceptable level in all other areas of the facility. e the radiation field and reduce polyethylene. A heavy door at the entrance would e oralso boratedbe r I

i t

19

4. CONCLUSIONS The results of these studies indicate that a useful epithermal beam can be obtained with a modified reactor f acility. The exterior concept has lower intensity than the interior concept; however, it is more desirable because of excellent access to the beam port. Except for changing the fuel loading pattern, no core or control-system modifications are required. A treatment room with thick concrete (or equivalent) walls and ceiling would have to be constructed to keep the radiation dose to staff at an acceptable level. A prelsminary study based on non seismic issues has concluded that the present structure could accommodate the weight of the walls and ceiling. Design studies for the treatment room are now underway at WSU.

.?0

n

5. REFERENCES I

1. B. H. Liu et al., " Enhancement of the Epithermal Neutron Beam Used for Boron Neutron Capture Therapy,"

Int. J. Radiation Oncology Biol. Phys., 28, 1994, 1149-1156.

2. R. L. Moss,

• Review of Reactor. Based Neutron Beam Development for BNCT Applications," Advances in Neutron Capture Therapy, edited by A. H. Soloway, et al., Plenum Press,1993.

3. J. W. Blue et al., "A Study of Low Energy Proton Accelerators for Neutron Capture Therapy," Proceedings of the Second International Symposium on Neutron Capture Therapy, edited by H. Hatanaka, Nishimura Co. Ltd.,1985,147.

4. J. C. Yanch and X-L. Zhou, " Accelerator-Based Epithermal Neutron Beam Design for Neutron Capture Therapy," Med. Phys.,19, 3, May/ June 1992, 709-721.

5. W. A. Rhoades and R. L. Chulds, Updated Version of the DOT 4 One- and Two-Dimensional Neutron / Photon Transport Code, ORNL-5851, Oak Ridge National Laboratory,1982.

6. R. W. Roussin, BUGLE-80, Coupled 47-Neutron, 20-Gamma Ray, P, Cross-Section Library for LWR Shielding Calculations, DLC-75, Oak Ridge National Laboratory,1980.

l 1

l l

23

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