A Magic Bullet for Cancer (Physics and Medicine Combine to Forge a New Weapon)

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NOTE TO EDITORS: being forged a t the front fer s of medlclne and physics. Thls story outllnes the posslbilitlct that radiotherapbsts may soon be able t o dellver a tumordestroying dose of radfation preclsely a t the t-r site, affecttng little of the healthy tissue around It. A potentially powerful weapon against some cancers i s PHYSICS AND MEDICINE CW6INE TO FOREA NEY YEAPON In theory It should work. If I t dat, a tiny particle that In nrtun is the glue that holds the nuclrl of atom together can be forged into a powerful weapon against the debrls ofa =shed atun. It lasts only 2.5 hundredarlllionths ofa second. But l n that time I t can be funnelled clown a channel a t controlled rnetgy so that It penetrates a target t o a predetannlned depth. A t that depth It I t captured hy and explodes the nucleus o f another 8tm, de'llvrrlng 140 a ill lon electron volts of energy witha space the

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If.the target is within a human body, and the given depth 1s the site of cancer, the result can be a cancer-killing dose o f r8dfatfon delivered precisely t o ths itiseared area, with little or no effect on fntervenlng healthy tissue. I t it almost literally a "mglc bullet," and 8 radlothrraplst's dream. If I t works f t can add imneasurably t o the tools a t his dltposal Slgnlficant progress hat been mde In radiation therapy during the last twenty ytsrt. Radiation therapy cures a large number of patients with cancer but ttl11, from figures developed by the Itntrlcan Cancer Soclety, over 330,003 people will be expected t o die from cancer this year. The use o f highly ionlring particles such as the! pi meson (as we11 as protons, helium lons, heavy ions and neutrons( may have a tremendous Impact on the control of those tumor cases that are frqurntly not controlled locally by existing treatment trchntquts. So far the use of the p i meson i s an unrealftad dream. Nevertheless the possibillty that plons will work i n hospitals the w a y they work In nature i s considemd SO great that some physics 'Irboratorics are now adding experimental meson treatment facll ities to the buslncss ends of the powerful accelerators with wh kh thty do hng the rift top hls tka ted of these is a facility now under construction a t Stanford University i n California under a grant fm

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the Reseirrch Applied to National Nkds (RANN) directorate of the National Science Foundation. There Professors H. Alan Schwettman hlcolm Bagshaw, Yilliw Fairbanksand Henry bplan, am rrwmying the technologies o f superconductivity and high rnerOy physics t o produce the prototype o f a device that could ultimately be installed as 1 hospital treatment facility. Fairbank and Schwetlmn 8re u#mg the first physicists t o apply t o the design o f an atom smasher the (superconducting) ability of conductors to carry electric current wfthout resistance a t temperatures approaching absolute zero- 273 degrees below zero kntrigradc. Kaplan I s the radlo- therapist who pioneered the origlnal use o f electron accelerators i n cancer therapy. "Physicists have known how t o produce pions for years," Schwettman notes. "But up t o now the intensities of the pion beams have been too low to be useful." 'So far," he notes, *the value of pions is still unproven He and hit colleagues expect t o be set up t o do prelinfnary tissue and animal tests u l t h i n the next year to I8 months, and be rea@ t o go into full-scale operation some the later. A similar experiment Ina non-superconducting facility of earlier design a t be reaching the animal test stage i n the next year.

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Thetplon was first discovered f n 1947 among particles caused by collisions betueen cosmic radiation and atoms I n the earth's atmosphere. It a n now be routinely produced for experimental purposes by the high energy accelerators with which physicists examine the particles and forces that make up the nuclei o f atoms, but not yet i n beams of i Intensity hfgh enough for medical purposes. i What Kaplm wants and Schwettman f s bullding under the NSF grant 1s hstrunmt capable o f collecting and delivering toa cancer site between a billion and 10 billion pions per second. The advantage of pions over tradftional sources o f radiation therapy such as the X-rays with which cancers are now routinely treated i s that they deliver thclr energy t o the core o f the disease. X-rays deliver the bulk of their energy t o the outside o f the body, often causing severe skin damage as therapists seek to get useful mounts of energy t o the site of a detp cancer. I t 1s fn the effort to iaka radlothcrapy more effective thatthls experimental pion focussing instrument is king built. The pion i s about 280 times as massive as the more cQmy)n "They am nally very csoterlc prrtlcler," Schwetmn observes. "If Ir)nn they were discovered anytody hac! suggested that they might

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Plops, once they are produced, last only some 2.5 hundred-mlllionths ofa second 0- mugh time to travel about 30 feet. They penetrate matter t o depths which can be determined precisely by their energy and the drnslty o f the target. And they hold on t o mst o f their energy until they cane to rest. A t that pofnt, Schmttmrn explains,thq y find tam atonic nucleus -0 utwlty o f an aton o f oxygm -- and go Into orbft around it, fomlng what I s called a PI-nesfc atan. Bcing so wch heavier thrn electrons, they orbit the nucleus much closer l n , close enough to be captured by it. fhy excite the nucleus they enter to 8nemrg~1of 140 mtlllon electron volts, and the nucleus rllaort lltrrrlly explodes into tragamts.. 6y cm ful ty contro'lllng the Input energy, Schmttman notes, rutlotharapists and phytlclsts can regulateto within 10 percent 'fderlly,' Schwettuwn notest "we would like to deliver betuecn bllllon and t t n bllllon plant per second to r;mcer area.* Abwt 20 parcent of the released energy would be dellvered i n are8 of the exploded nucleus, destroying the diseased cells around The rest would leave the patient's body, having considerably reduced' effect on it, either as neutrons or as g u m rays -- a klnd o f high

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of exactly what i s happening a t the s ttc of the pion decay. been treated with plon beams.” But he and hls colleagues are convinced that plons n t l l hold inmcasurable advantages over conventional rrdiatlon therapy. And I with RANN support, they are getting8 chance to prove lt.