The meson therapy research program at the Los Alamos Meson Physics Facility (LAMPF) is briefly described. It is stated that tests will start on a magnetic collection channel for pions at LAMPF within one or two months, and the biomedical pion channel is described. The problems encountered in pion dosimetry are briefly discussed. (WDK

Knapp, E.A.

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* <?LA-UH- 73-;/J£< &4J/- 73/t2Z — / TITLE: MESON FACTORIES, PI MESON DELIVERY, AND PI MESON DOSIMETRY FOR CANCER THERAPY AUTHOR(S): E. A. Knapp # SU3MITTEDTO: PROCEEDINGS of the 59th Scientific Assembly and Annual Mtg of the Radiological Society of North America By acceptance of this article for publication, the publisher recognizes the Government's (license) rights in any copyright and the Government and its authorized representatives have unrestricted right to reproduce in whole or ib part said article under any copyright secured by the publisher. The Los Alamos Scientific Laboratory requests that the publisher identify this article as work performed under the auspices of the U. S. Atomic Energy Commission. of the University of California IOS AlAMOS, NEW MEXICO §7544 - N O T I C E -This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employes , nor any of their contractors, subcontractors) or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com-pleteness ot usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately jwned rights. DISTRIBUTION OF. THIS DOCUMENT » UNUMITEQ •MTO No* 830 E.Nev2S29 UNITED STATES ATOMIC ENCHGV COMMISSION CONTRACT W-»4aS-KNO. ! • MASTER 65-« c flftj *v(3 £ - v ify+T'tf'jg *vv t -v* MESON FACTORIES, PI MESON DELIVERY, AND PI MESON DOSIMETRY FOR CANCER THERAPY Within one or two months tests will start on a magnetic collection channel for pi mesons at the Los Alamos Meson Physics Facility. This chan-nel will make available to the medical community for the first time, thera-peutically interesting beams of pions for biomedical research and for the therapy of cancer. Some time in the next few years several other facilities of a similar nature will become operational around the world, and an active world wide program of research in the radiobiology, dosimetry, and therapeutic behavior of pion beams will be carried on. Why this sudden interest in pions for therapy of cancer? It is only now that this application of pions has been possible, due to the advent of a new class of physics research accelerators, the meson factories. These accelerator installations are characterized by the very high current proton beams that they accelerate and the copious quantities of pi and mu mesons that are produced in targets which are intro-duced into these primary beams. In fact, these accelerators are designed to provide secondary beams of pi and mu mesons of such intensity that the nuclear physics studies done with them may approach in accuracy the studies done up to now in the primary beams of accelerators themselves. It should be made clear that it is not necessary to have such a sophisticated accelerator for the production of pi mesons if the only application is to be cancer therapy. It would be possible to reduce the cost of the Los Alamos Facility by a very Rosen, L., "Meson Factories," Physics Today, Vol. 19, no. 12, Dec. 1966. - 2 -large factor if the system were to be optimized for cancer therapy alone. 2 In fact, it can be demonstrated rather convincingly that, if pion therapy is spectacularly successful, it need not be merely a laboratory curiosity. Reasonably priced accelerator systems which would be compatible with tho hospital environment are quite feasible. In the case of the Los Alamos Meson Factory, a beam current which is more than adequate for the therapy job is to be available, and a rather con-ventional magnetic channel for the collection and focusing of the pions has been designed. We strongly felt that for the first trial with pions we should not get too involved with very complex magnetic systems, but that a rather straightforward system would let us concentrate on the formidable problems associated with delivery and dosimetry. However, if the trials are success-ful, it will be necessary to go to very high acceptance channels, using either superconducting technology or pulsed focusing techniques. Figure 1 shows the pion channel designed for the therapy facility at Los Alamos. In principal the system works as follows: pions originate at a production target located in the main proton beam line, where up to 1 ma of 800 MeV protons are focused. The target material will probably be carbon, but other materials are possible. The choice of target and production angle is dictated by a trade-off between meson flux and electron contamination, the latter being lower with lower 2 aaterials in the target. A beam with a rather wide momentum spread (more than _ Knapp, E. A., "Possible Pion Sources for Radiotherapy," to be published in the Proceedings of the 2nd Meeting on Fundamental and Practical Aspects of the Application of Fast Neutrons in Clinical Radiotherapy, The Hague, Netherlands, Oct. 3-5, 1973. Lundy, A., R. Hutson, E. Knapp, L. Rosen, "Status and Plans for the Negative Pion Radiotherapy Facility at the Los Alamos Meson Physics Facility/' Paper presented at the 3rd International Conference on Medical Physics, Goteborg, Sweden, August 1972. - 3 . 16%) is focused upon a wedge degrader, which serves to reduce the energy of the Most energetic particles to that of the lowest energy ones, thus approximately monochromatizing the bean. In our studies of the beam optics aade during the design of this channel we found it almost impossible to tailor the momentum spectrin to achieve the required precision of the dose deposition without a trick of this type. The monochromatized bean is then focused by use of five quadrupole magnets into a line focus about 1 meter from the end of the last magnet. This line focus is adjusted to fall at the end of the range of the pions, and in this line they come to rest and produce the star radiation which is their characteristic. For each star there is about 140 NeV of energy re-leased in the form of heavy fragments, protons and neutrons, with the source at the position of the star. This process can be seen in Pig. 2, where the stopping line of pions is illustrated. Me next will spread the beam of pions out (up/down) over the volume of the tumor by modulating the energy of the entering pion at the entrance to the body. This is accomplished by placing a variable thickness absorber between the last magnet and the patient. By varying the speed with which the absorber changes thickness the intensity of pions stopping as a function of depth can be varied. Alternatively a "ridge filter" can be employed to approximate the action of a varying thickness ab-sorber. The "ridge filter" is a plate with a corrugated surface which pro-vides different thicknesses to particles with different positions in the in-coming beam; the dose distribution is then smoothed by the particle multiple scattering in coming to rest. Problems of tissue inhomogeneity can be minimized by employing no abutting field techniques. The skin to tumor dose ratio is so favorable that probably little additional gain can be obtained using multi-port techniques, unless there is a dose rate gain, which has yet to be established. As can be seen in the graph, the pions show a clear advantage in localizability - 4 -over any other foil of radiation being considered, including protons, which give the best field shape for the heavy ions (even though they don't have a high LET). In conclusion, the problems in delivery, which we will have, involve the production of a converging bean of pions which can be controlled precisely as to energy and focus. These problems appear to be well in hand. In dosimetry, we then determine how the dose should be distributed in order to obtain the best possible distribution of biological effect. This will be one of the most complex dosimetry problems with which medical phys-icists have ever had to deal. The radiation field is extremely mixed, being composed of pions, muons, heavy fragments, alpha particles, protons and x rays and electrons. The mixture of these components strongly varies as a function of position within the star region as well as in the "plateau region." To visualize this, consider the mixing ratio of radiations at the front and at the back of the stopping region, as shown in Fig. 3. This ratio will be drastically different, because all of the incoming pions must pass through the closest edge of the star region, but only the star products themselves contribute at the far edge of the peak. The program in dosimetry will consist of a series of physical and biological experiments which we hope will determine the correct pion stopping distribution which achieves a uniform biological effect throughout the peak region with minimal effects in the surrounding regions, independent of treat-ment volume. As we progress we will determine quantities related to radiation quality, such as LET, as a function of depth and correlate this theoretically to the observed biological results. Some work has already started along these lines with theoretical models developed at Oak Ridge National Laboratory. Experimentally we expect to use ionization and multiplication chambers, Rossi-type proportional counters, solid state detectors, and any other tools which will - s -aid in understanding this very complex radiation field. As the pions cone to rest and then produce stars they emit characteristic radiations. These nay be useful for the purpose of napping the stopping region during irradiation. We will be developing apparatus to view and localize these radiations, with the goal of being able to nap the treatnent volune during an irradiation to observe innediately changes in characteristics of the bean if they occur and to verify the corrections node for tissue inhono-geneities. If possible the intercalibration of our neasurenent of dose with nethods used elsewhere will be achieved by close cooperation with the other centers involved in high-LET radiation research. In addition, calorinetric intercalibrations will be attempted. In conclusion, neson factories have given the radiation therapist his first opportunity to investigate the effects of pi neson radiations on cancer. We have constructed a neson delivery systen which provides therapeutically useful beans of pions in a precisely controlled naimer, and will begin the testing of the systen within the next ttfo nonths. The radiation field pro-vided by this pion bean will give a real challenge to the nodical physicist, in that the dosinetry required to understand the predict the effect of this bean on living systens is fomidable indeed. We feel that we have a good start toward a progran which will provide guidance in the early stages of therapy for the physician, and will lead to basic understanding of this conplex radiation field as well as the effects of radiation in general. 0 - QUADRUPOLE MAGNET T-PWN PRODUCTION TARGET B- BENDING MAGNET S-BEAM STOP 0 - MOMENTUM DISPERSION PLANE W- WEDGE ENERGY DEGRADER V- VARIABLE THICKNESS DEGRADER C- COLLIMATORS M-BEAM MONITOR TRANSVERSE^ PLANE OPTICF 1 METER i i BEND PLANE OPTICS FALSE FLOOR THE LOS ALAMOS MESON PHYSICS FACILITY BIOMEDICAL PION CHANNEL STUBOUT FLOOR &?^&3mm«zmm%*0*&iv. Fan shaped Pion beam (Plane of fan in plane of figure) Collimator Range Shifter Treatment volume outline lovsO>alanios •el>*nMII« l«to»r«t»ffif / \ Patient cross section Cylindrical Pion stopping region Treatment volume shaping with fan beam-a rapid vertical scan of stopping region is accompanied by a slow translation of the patient perpendicular to the plane of the fan. •* DEPTH DOSE DISTRIBUTIONS . 3xK ~ ^ » , 3xl( , 6xK r* F t / - * , . )*Ar/( Is Ne/ r— — * _ *^ V* cm2 _ ""{VxlO7 He/cm2) (4xlO*H/cm2) • - » * ** ^ . ^ -i • - - . * * * » ^ * ^ 1 DER ' * » r 1 1-3 J-J5 1-8 *""i 1. , •3,2-6 \ t \ - i I I i> i i i i i i i i • \ N \ X X \ V \ \ \ X \ X ^ . 8 2 ' UJ or 500 300 200 100 50 30 20 -10 16 20 . . . . 0 4 DEPTH IN TISSUE (cm) 60Coyroys '' 1 OER 2-7 1 /BMVxroys * - » * ^ l > — l i ^ . *-*_ i 1 i i I s J 4 MeV neutrons ' — - . ^ ' — —4~ 6xl0 8»^cm 2 terminating I0-I5CITI | '-'1 S x l o V / c m * terminating l 2 - 5 - ! 5 c m j _ . — . * ' . - - -. ' - „ - *-_ i / i / / • * OER y i \ 1-5 / i i 11 M H M •1 •ii I ' I t l l n • t 1 • i i _ , * * - *« 8 12 16 20 (Fowler, Proc. Phys. Soc. 8 J , 1051 (1965)) (Horst and Conrad, Fortschritte auf dem Gebiete der Rontgenstrahlen u. der Nuklearmedizin, Diagnostik, Physik, Biologie, Therapie IS5, 299(1966)) 

Meson factories, pi meson delivery, and pi meson dosimetry for cancer therapy

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