Nucl ear I nst rument s and Methods in Physi cs Resear ch A330 ( 1993) 296- 305 Nort h-Hol l and Magnet i c scanni ng syst em f or heavy i on t her apy Th . Haber er , W . Becher , D . Schar dt and G . Kr af t Gesel l schaf t f ür Schwer i onenf or schung mbH, Pl anckst r . 1, 6100 Darmst adt , Ger many Recei ved 11 Januar y 1993 Beams of heavy i ons have f avour abl e physi cal and bi ol ogi cal pr oper t i es f or t he use in r adi ot her apy . These advant ages ar e mos t pr onounced if t he beam is del i ver ed ma t umor - conf or m way by act i ve beam scanni ng . A magnet i c scanni ng t echni que is used to spr ead t he beam l at er al l y . The r ange of t he par t i cl es in t i ssue is cont r ol l ed by t he var i at i on of t he beam ener gy in t he accel er at or . Comput er si mul at i ons wer e used to compar e a di scr et e scan mode ( pi xel scan) with a cont i nous scan mode ( r ast er scan) . It was f ound t hat bot h methods l ead t o near l y i dent i cal r esul t s . The desi gn and t echni cal r eal i zat i on of t he magnet i c scanni ng syst em at GSI combi nes f eat ur es of bot h scan t echni ques . Fi r st r esul t s usi ng t he l at er al beam scanni ng method as wel l as t he combi nat i on of t he act i ve ener gy var i at i on with t he magnet i c beam scanni ng ar e pr esent ed . 1 . I nt r oduct i on It is t he f i nal goal of any r adi ot her apy to shape t he t reat ment vol ume as exact l y as possi bl e to t he t umor as t he t ar get vol ume . In s ome cases a sof t but cont r ol l ed decay of t he dose f r om t he cent er to t he out er par t is want ed . But most l y a shar p cut of f of t he dose is needed in or der to spar e t he sur r oundi ng heal t hy t i ssue or cr i t i cal st r uct ur es to a max i mumext ent . Nowadays, it is possi bl e to del i neat e t he cont our s of a t umor with an ext reme pr eci si on usi ng t he new di agnost i c met hods of comput er t omography or MRI t omography . Because a bet t er dose l ocal i zat i on was al ways an i mpr ovement in r adi ot her apy, l ar ge ef f or t is made to i mprove t he pr eci - si on of convent i onal t her apy whi ch is lim i t ed mai nl y by t he physi cal nat ur e of t he i oni si ng r adi at i on . Heavy i ons exhi bi t a di f f er ent i nt er act i on mecha- ni sm with mat t er compar ed to t he convent i onal l y used el ect romagnet i c r adi at i on . They have an i nver sed dept h- dose- pr of i l e with a l ow dose at t he ent r ance channel and a hi gh dose at t he end of t hei r r ange in t he t umor . The smal l r ange st r aggl i ng and l at er al scat - t er i ng enabl es to fill compl ex t ar get vol umes with hi gh accur acy . For heavy i ons bet ween car bon and neon t he el evat ed dose at t he end of t he r ange is connect ed to an i ncr eased r el at i ve bi ol ogi cal ef f i ci ency - cor r e- spondi ng to enhanced cel l ki l l i ng, whi l e in t he ent r ance channel bef or e t he t umor, t he i oni sat i on densi t y and bi ol ogi cal ef f i ci ency ar e l ower [ 1] . Fi nal l y beams of heavy i ons pr oduce a t r ace of posi t r on em i t t i ng i so- t opes whi ch can be moni t ored f r om out si de and can be 0168- 9002/ 93/ $06. 00 C 1993 - El sevi er Sci ence Publ i sher s B.V. Al l r i ght s r eser ved NUCLEAR I NSTRUMENTS &METHODS IN PHYSI CS RESEARCH Sect i on A used to cont r ol t he posi t i on of t he t her apy beam and t he del i ver ed dose [ 2] . Heavy i on t her apy whi ch so f ar was onl y per f or med at LBL Ber kel ey conf i rmed t he super i or i t y compar ed to convent i onal t her apy . For t he beam del i ver y syst em pr esent l y in use at t he LBL Ber kel ey and desi gned f or t he heavy i on t reat ment at HI MAC in Chi ba [ 3] passi ve beam shapi ng t echni ques ar e pr ef er r ed because of t hei r si mpl i ci t y . However , usi ng passi ve beam shapi ng it is not possi bl e to achi eve a compl et e t umor conf or m t reat ment and t he t umor dose is wi del y det er m i ned by t he t ol er ance of t he t umor bed and t he sur r oundi ng heal t hy t i ssue . The max i mum success of heavy i on t her apy can be expect ed onl y when t he i r r adi at i on will be mos t conf or m to t he shape of t he t umor and t he dose out si de t he t umor is m i ni m i zed [ 4, 5] . In par t i cul ar it has to be avoi ded t hat t he hi ghl y ef f i ci ent par t of t he par t i cl e beam, i .e. t he Br agg peak i ons, hi t s t he heal t hy t i ssue ar ound t he t umor . For a t umor conf or m t reat ment , act i ve beam del i v- er y syst ems usi ng magnet i c scanni ng t echni ques l i ke r ast er scanni ng i ncl udi ng act i ve ener gy var i at i on by t he accel er at or ar e pr esent l y devel oped [ 6- 8] . These novel t echni ques imply s ome i mport ant advant ages . The di s- t r i but i on of t he st oppi ng par t i cl es can be shaped ex- act l y to t he t umor vol ume in or der to pr event par t i cl es f r om deposi t i ng t hei r bi ol ogi cal l y ver y ef f ect i ve dose out si de t he t ar get vol ume . The use of r i dge f i l t er s or wat er col umns to adj ust t he r ange can be avoi ded whi ch consi der abl y r educes t he beam cont am i nat i on caused by nucl ear f ragment at i on . Col l i mat ors or bol i