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POTENTIAL USE OF SUPERCONDUCTING MAGNETS FOR NEUTRON THERAPY
R. Duthil, F. Kircher, J. Lottin, S. Palanque, J. Aucouturier, P. Fache
To cite this version:
R. Duthil, F. Kircher, J. Lottin, S. Palanque, J. Aucouturier, et al.. POTENTIAL USE OF SUPER-
CONDUCTING MAGNETS FOR NEUTRON THERAPY. Journal de Physique Colloques, 1984, 45
(C1), pp.C1-697-C1-701. �10.1051/jphyscol:19841142�. �jpa-00223614�
Colloque C I , suppl6ment a u n o 1, Tome 45, janvier 1984 page Cl-697
POTENTIAL USE OF SUPERCONDUCTING MAGNETS FOR NEUTRON THERAPY
R. Duthil, F. Kircher, J.C. Lottin, S. Palanque, J. Aucouturier* and P.
ache*
CEA/SacZay, DPh/PE-STPE, 91191 Gif-sup-Yvette Cedex, France
*DT, CGR MeV, 78530 Buc, F r a m e
Resume
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On donne l e s r e s u l t a t s d ' u n e etude de f a i s a b i l i t e s u r l ' u t i l i s a - I t i o n - d ' a i m a n t s supraconducteurs en n e u t r o n o t h e r a p i e . Deux p o s s i b i l i t e speuvent S t r e envisagees :
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aimants supraconducteurs u t i l i s e s dans l a l i g n e i s o c e n t r i q u e du t r a n s p o r t d e f a i s c e a u p r i m a i r e . On p e u t a i n s i t r a n s p o r t e r des p a r t i c u l e s p l u s Gnergetiques ( j u s q u ' a 70 MeV P r o t o n s ) qu'avec l e s systemes a c t u e l s , avec une r e d u c t i o n de p o i d s . C e t t e s o l u t i o n p o u r r a i t O t r e mise en oeuvre t r e s r a p i dement.-
un c y c l o t r o n supraconducteur i s o c e n t r i q u e , t r a v a i l l a n t 8 un champ moyen de 4,7 T, c a p a b l e d ' a c c 6 l e r e r des deutons j u s q u l & 3 0 rleV. La f a i s a b i l i t e d ' u n e t e l l e machine e s t & peu p r e s e t a b l i e mais des developpements t e c h n i q u e s s o n t n e c e s s a i r e s , e s s e n t i e l l e m e n t cause de l a r o t a t i o n e t de l a m i n i a t u r i s a t i o n du c y c l o t r o n .A b s t r a c t
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The r e s u l t s o f a f e a s i b i l i t y s t u d y on t h e use o f s u p e r c o n d u c t i n g magnets f o r n e u t r o n t h e r a p y d e v i c e s w i l l be r e p o r t e d . Two l j o s s i b i l i t i e s can be f o r e s e e n :-
SC magnets used i n t h e i s o c e n t r i c p r i m a r y beam t r a n s p o r t l i n e . The advan- t a g e i s t o i n c r e a s e t h e energy o f t h e p a r t i c l e s which can be t r a n s p o r t e d ( u p t o 70 FleV f o r p r o t o n s ) , compared t o e x i s t i n g systems, w i t h a l o w e r w e i g h t . T h i s s o l u t i o n c o u l d be used v e r y q u i c k l y .-
a SC i s o c e n t r i c c y c l o t r o n , w o r k i n g a t on average f i e l d o f 4.7 T f o r acce- l e r a t i n g d e u t e r o n s up t o 30 MeV. The f e a s i b i l i t y o f such a machine i s f a i r l y e s t a b l i s h e d b u t t e c h n i c a l developments a r e needed, m a i n l y i n view of t h e r o t a t i o n and o f t h e m i n i a t u r i s a t i o n o f t h e c y c l o t r o n .INTRODUCTION
About a dozen c e n t e r s a r e now t r e a t i n g cancers w o r l d w i d e w i t h n e u t r o n t h e r a p y . Most of them a r e w o r k i n g w i t h c y c l o t r o n s a c c e l e r a t i n g p r o t o n s o r deuterons up t o s e v e r a l t e n s o f FleV, t h e n bombarding a t a r g e t t o produce n e u t r o n s . However, most o f t h e s e i n s t a l - l a t i o n s d o n o t f u l f i l l a1 l t h e u s e r ' s r e q u i r e m e n t s , a v a i l a b l e w i t h ' c o n v e n t i o n a l i n s t a l l a t i o n s : h o s p i t a l s u r r o u n d i n g , f u l l a v a i l a b i l i t y o f t h e machine, complete r o t a t i o n o f t h e n e u t r o n s o u r c e around t h e p a t i e n t , beam p e n e t r a t i o n ( d e p t h dose c u r v e ) . P a r t i c u l a r l y , t h e u s e r s would l i k e t o have t h e p o s s i b i l i t y o f t r e a t i n g deep tumors, r a d i o r e s i s t i v e up t o now, which needs more e n e r g e t i c beams. T y p i c a l e n e r g i e s r e - q u i r e d a r e 30 FleV f o r d e u t e r o n beams o r 70 HeV f o r p r o t o n beams, w i t h a c u r r e n t around 30 PA.
T h i s energy i n c r e a s e m a i n l y r a n k s w i t h a w e i g h t i n c r e a s e o f t h e magnetic r o t a t i n g system, l e a d i n g t o more and more d i f f i c u l t mechanical problems. The use o f supercon- d u c t i n g magnets can push away t h e p r e s e n t l i m i t a t i o n s , m a i n l y t h r o u n h t h e m a g n e t i c f i e l d i n c r e a s e t h e y a1 l o w . Two ways have been i n v e s t i g a t e d , s u p e r c o n d u c t i v i t y b e i n p use e i t h e r f o r t h e maonets of t h e beam h a n d l i n g system o r f o r t h e c y c l o t r o n i t s e l f i n a i s o c e n t r i c r o t a t i n o system.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841142
Cl-698 JOURNAL DE PHYSIQUE I
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SUPERCONDUCTING BEAM HP$NDLINP SYSTEHThe use o f SC magnets r a t h e r t h a n copper ones i n t h e beam h a n d l i n g system, r o t a t i n p around t h e p a t i e n t , w i l l enable t o i n c r e a s e b y a f a c t o r l a r q e r t h a n 2 t h e energy o f t h e p r i m a r y beam, i n a s i m i l a r space.
1.1
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Beam l i n e parametersWe assume t h e f o l l o w i n ! beam c h a r a c t e r i s t i c s :
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70 NeV p r o t o n s , - ( ~ / n ) ~ = 50 mm-mrad-
( € 1 ~ ) ~ = 30 mm-mrad-
ap/p = 0.3 %A s o l u t i o n which f u l f i l l s t h e o p t i c s and t h e r a p e u t i c needs i s shown on f i a . 1. Two superconducting d i p o l e s (A1 and A2) and two c o n v e n t i o n a l quadrupoles ( Q 1 and Q2) a r e needed. The r e q u e s t e d space i s s i m i l a r t o t h e one used f o r a 25 FeV p r o t o n h a n d l i n g system u s i n g o n l y c o n v e n t i o n a l maflnets.
1.2
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The superconducting d i p b l e sT h e i r main c h a r a c t e r i s t i c i s t o be curved-ones. As n o e x p e r i e n c e i s a v a i l a b l e t o o u r knowledge on such SC magnets, t h e f o l l o w i n g o p t i o n s have been t a k e n :
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t h e maximum c e n t r a l f i e l d i s l o w : 4 T- t h e nominal c u r r e n t i s choosen around 50 % o f i t s c r i t i c a l value,
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t h e c o i l shape i s simple, e n a b l i n g random w i n d i n g .Some o t h e r c h a r a c t e r i s t i c s o f t h e s e d i p o l e s a r e g i v e n i n t a b l e I .
I I I
I
U s e f u l a p e r t u r e d i a m e t e r (mm) I n n e r c o i l d i a m e t e r (mm) I O u t e r c o i l d i a m e t e r (mm)
Outer c o l l a r d i a m e t e r (mm) O v e r a l l i r o n dimension (mm) C e n t r a l f i e l d (T)
Nominal c u r r e n t (A)
O v e r a l l c u r r e n t d e n s i t y ( ~ / c m ~ )
T a b l e I : F a i n c h a r a c t e r i s t i c s o f t h e SC d i p o l e s
The w e i g h t o f such d i p o l e s compared t o c o n v e n t i o n a l ones, f o r t h e same beam eneroy :
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d i p o l e A1 : 0.4 t o n f o r t h e SC v e r s i o n , v e r s u s 2.5 t o n s f o r t h e c o n v e n t i o n a l one.-
d i p o l e A2 : 1 t o n f o r t h e SC v e r s i o n , v e r s u s 7 t o n s f o r t h e c o n v e n t i o n a l one.1.3
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Cyrogenic a s p e c tThe m a i n problem i s t o assume a good c o o l i n g of t h e d i p o l e s and o f t h e e l e c t r i c a l c o n n e c t i o n s whatever t h e p o s i t i o n o f t h e r o t a t i n g system i s . The f o l l o w i n g c h o i c e have been made :
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use o f b o i l i n g h e l i u m a t 4.2 K and atmospheric pressure,-
h o r i z o n t a l c u r r e n t l e a d s w i t h an e v a p o r a t o r assuming a permanent c o o l i n g d u r i n g t h e r o t a t i o n ,-
thermal s h i e l d s u s i n g h e l i u m gas.-
a l l t h e c o o l i n g c i r c u i t s a r e i n s e r i e s .The c a l c u l a t e d h e l i u m consumption i s around 1.5 l / h .
A n e n e r a l v i e w o f t h e i m p l a n t a t i o n i s shown on f i g . 2. A l l t h e maqnetic elements a r e f i x e d on a g e n e r a l support. A 50 1 h e l i u m Dewar i s used t o f e e d t h e system. A coun- t e r w e i g h t i s use t o balance t h e system: The t o t a l w e i g h t o f t h e SC system has been e s t i m a t e d t o 4 t o n s , t o be compared t o 30 t o n s f o r a c o n v e n t i o n a l s o l u t i o n . I 1
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SUPERCONDUCTING CYCLOTRON11.1
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I n t e r e s t o f u s i n q s u p e r c o n d u c t i n g c o i l sThe use o f superconducting c o i l s i n a c y c l o t r o n enables t o reduce t h e e x t r a c t i o n r a d i u s by a f a c t o r o f a b o u t 3, f o r a q i v e n energy. The same f a c t o r can be g o t on t h e o v e r a l l dimensions, which means a tremendous r e d u c t i o n o f t h e t o t a l weight, and thus, t h e p o s s i b i l i t y t o p u t d i r e c t l y t h e c y c l o t r o n i n t h e r o t a t i n g system.
Among many a p p l i c a t i o n s , superconducting c o i l s a r e now used f o r l a r g e c y c l o t r o n s f o r n u c l e a r p h y s i c s : t h e f i r s t machine i s now i n o p e r a t i o n a t Flichigan S t a t e U n i v e r s i t y
( 1 ) and s e v e r a l o t h e r s a r e under c o n s t r u c t i o n i n Canada, I t a l y , t h e US
...
F o r n e u t r o n t h e r a p y , a p r o p o s a l was made few y e a r s ago b y Hepburn and a1 ( 2 ) . A s m a l l SC c y c l o t r o n i s under development i n Japan ( 3 ) .
11.2
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RequirementsThe f i r s t r e q u i r e m e n t i s t o reduce t h e t o t a l w e i g h t o f t h e system t o a b o u t 15 t o n s t o e n a b l e t h e r o t a t i o n . To f u l f i l l t h i s r e q u i r e m e n t an average f i e l d around 5 T i s necessary. The second p o i n t i s t h e c h o i c e between a p r o t o n machine o r a d e u t e r o n one, t h e beam bombarding a b e r y l l i u m t a r g e t . T h i s i s m a i n l y a t h e r a p e u t i i t ' s problem.
11.3.
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The m a g n e t i c s t r u c t u r eA magnetic s t r u c t u r e which f u l f i l l s t h e r e q u e s t e d f i e l d v a r i a t i o n s can be determined w i t h e x i s t i n g programs f o r t h e c y l i n d r i c a l system a n d f o r t h e p o l e t i p geometry.
The main parameters of t h e magnetic c o n f i g u r a t i o n which has been chosen a r e l i s t e d i n t a b l e 11.
C o i l s :
- - I n n e r d i a m e t e r (mm)
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O u t e r d i a m e t e r (mm)-
H e i g h t (mm)-
Gap between c o i l s (mm)-
C e n t r a l f i e l d ( T )-
Plaximum f i e l d on t h e c o n d u c t o r ( T )-
Ampereturns ( p e r c o i l )-
O v e r a l l c u r r e n t d e n s i t y (A/cm2)-
S t o r e d energy (HJ) I r o n :-
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I n n e r d i a m e t e r (mm) - Outer d i a m e t e r (mm) - H e i g h t (mm)-
Weight ( t ) Pole t i p s :-
Number-
Diameter (mm)T a b l e I 1
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R a i n parameters o f t h e m a g n e t i c c o n f i g u r a t i o nC1-700 JOURNAL DE PHYSIQUE 11.4
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The superconducting c o i l sThe SC c o i l s use Nb T i conductor. The nominal c u r r e n t i s 400 A, about 90 % o f t h e c r i t i c a l c u r r e n t . No s p e c i a l problem has been seen f o r t h e c o i l c o n s t r u c t i o n . The i n n e r p a r t o f t h e h e l i u m t a n k can be used as a mandrel ; t h e c o i l i s impregnated t h e n c o n s t r a i n e d a t room temperature w i t h a r i n g , a c t i n q as t h e o u t e r p a r t of t h e he1 ium t a n k .
The c o i l d e f o r m a t i o n due t o t h e magnetic f o r c e s can be l i m i t e d t o few t e n t h s o f mm.
I n case o f quench, t h e c a l c u l a t e d maximum t e m p e r a t u r e i n t h e c o i l i s around 170°K.
11.5
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CryogenicsHere again, t h e m o s t d i f f i c u l t problem i s t o g e t a sood c o o l i n g o f t h e c o i l s and o f a l l t h e e l e c t r i c a l j u n c t i o n s whatever t h e p o s i t i o n o f t h e c y c l o t r o n i s . S o l u t i o n s s ' i m i l a r t o those chosen f o r t h e r o t a t i n g beam h a n d l i n g system a r e recommended. The e s t i m a t e d h e l i u m consumption i s 5 l / h .
11.6
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O t h e r p a r t s o f t h e c y c l o t r o nA schematic v i e w o f t h e c y c l o t r o n i s shown on f i g . 3. The s t u d y has p o i n t e d o u t t h e f o l l o w i n g remarks : t h e t a r q e t must be s e p a r a t e d from t h e m a g n e t i c p l a n , o t h e r w i s e t h e p a r t i c l e s cannot g e t o u t o f i t . Even so, d e u t e r o n s a r e e a s i e r t o i n j e c t t h a n p r o t o n s . The RF system i s made w i t h one dee w o r k i n g a t 35 MHz and 50 kV. A d i f f i c u l t problem t o s o l v e i s due t o t h e r o t a t i o n o f some p a r t s o f t h e RF, some o t h e r s b e i n g f i x e d . A model w i l l be necessary t o t e s t t h i s system, w h i c h m u s t a l s o be connected.
The i n t e r n a l t a r q e t and t h e c o l l i m a t o r can be deduced f r o m p r e s e n t r e a l i s a t i o n s . 11.7
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Therapy c o n f i a u r a t i o nA t h e r a p y c o n f i g u r a t i o n i s suggested on f i g . 4 showing t h e c y c l o t r o n , t h e c o l l i m a t o r , t h e s u p p o r t and t h e c o u n t e r w e i g h t ; t h e r o t a t i o n a n g l e i s 185". One has t o n o t i c e t h e compacity o f t h e system, needing a t o t a l h e i g h t l e s s t h a n $ 3 m ; t h e e s t i m a t e d w e i g h t i s around 16 t o n s .
CONCLUSIONS
The c o n c l u s i o n s w h i c h can be drawn a r e n o t i c e a b l y d i f f e r e n t f o r each system :
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t h e s u p e r c o n d u c t i n g beam h a n d l i n g system does n o t r e q u i r e l a r g e development ; a model o f curved d i p o l e i s t h e o n l y t e c h n i c a l development t o be done. T h i s s o l u t i o n c o u l d be o p e r a t e d r a t h e r q u i c k l y on e x i s t i n g c y c l o t r o n s , e n a b l i n g p r o t o n beam t r a n s p o r t up t o 70 VeV.-
i f no fundamental problems has been seen which would show t h e non f e a s i b i l i t y o f an i s o c e n t r i c c y c l o t r o n , s e v e r a l developments a r e f o r e s e e n ; t h e y a r e m a i n l y due t o t h e cornpacity and t h e n e c e s s i t y o f r o t a t i o n .I n e v e r y case, t h e use o f s u p e r c o n d u c t i n g magnets would e n a b l e t o e x t e n d t h e p r e s e n t p o s s i b i 1 i t i e s o f n e u t r o n t h e r a p y .
ACKNOWLEDGHENTS
T h i s s t u d y was p a r t l y s u p p o r t e d by t h e "D616gationGGni.raleti 1 a R e c h e r c h e S c i e n t i f i q u e e t Technique". We thank P l r BRONCA, H r DESPORTES, Flr PRUGNE (CEA), P l r AZAM and Mr MILCAMPS (CGR MeV) f o r t h e i r c o n s t a n t s u p p o r t .
REFERENCES
( I ) HALLOR i.1.
,
P a r t i c l e A c c e l e r a t o r Conference (1983), I n i t i a l o p e r a t i o n o f t h e HISU s u p e r c o n d u c t i n g c y c l o t r o n .( 2 ) HEPBURN J.D., BIGHAP4 C.D., SCHNEIDER M.R., J. R a d i a t i o n Oncoloqy B i o l . Phys.
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(1977) 387-391, Superconduction c y c l o t r o n n e u t r o n source f o r therapy.
( 3 ) TAKEKOSHI H. & a l . B u l . o f t h e I n s t i t u t e of Chemical Research; Kyoto U n i v e r s i t y 59 (1981), s t a t u s o f t h e c o n s t r u c t i o n o f a small s u p e r c o n d u c t i o n c y c l o t r o n .
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F i g . 1 : beam l i n e
F i g . 3 : SC c y c l o t r o n
F i g . 4 : i m p l a n t a t i o n
