Radiological Laboratory, University of California School of Medicine, San Francisco, Semiannual Report for December 31, 1954, Atomic Energy Commission Contract No. at-11-1-Gen-10, Project No. 2

Page 1

UnclassVied Health and Biology University of CalFfornia School of Medicine, San Frsncisco Department of Radiology for period ending December 31, 195L Atomic Energy Commission Contract No. BT-Il-1-GEN-10, Project No. 2

Page 2

I. Synchrotran Magnet and Related Equip at II. Synchrotron Camponents Activities Relating t o the Use of Radiation C. Ionization Chamber Improvement IV. Activities by Person I. Effect of Cell Concentration and Ckygen Tension on 11. Reaction of the Mouse Spleen t o X-Rays Measured the Sensitivity of Selected Microorganisms t o X-Rays by Changes i n Organ Weight I. Cancer of the Thyroid 11. Current Status of Patients Treated for HyperthyIt should be noted t h a t the semiannual progress reports of the Radiological Laboratoq do not attempt t o describe progess inall of the research programs, but only in those in uhich same significant results have been achieved but which are not sufficiently camplete -to be written as final reports.

Page 3

Whereas the expected activity of the Physics Section relates t o the deliverance of radiation doses with t h e 70 Hev synchrotron t o biological specimens and human cancer patients and t o the physical interpretation of the doses delivered, nevertheless, before these ends can be accanplishrd the synchrotron must be capable of reproducible and essentially continuous operation. To achieve this conciition, a development program has been in operation f o r nearly three years and, although apparently nearly completed, the program is still in progress at this writing. I. Synchrotron Magnet and Related Equipment A. Field ComDensation. The x-ray beam which is produced naturally by the synchrotron is sharply peaked and requires a specially shaped cmpensating filter in order t o obtain a substantially uniform field of absorbed dose-rate under quasi-clinical conditions. WWul changes of a p propriate components have been s h m t o change the shape of the natural x-ray beam appreciably and consequently t o require a different contour on the C(PPpensating filter. Satisfactory filters have been shaped for beams available i n the past. The present filter, although not quite satisfactory, is adequate for testing purposes and only m e or two days will be requFred t o foma final. contour uhen desired. A more difficult problem relates to maintaining coaxial alignment between this filter and the x-ray beam, particularly for va riot ~ar~guhtions of the magnet and x-ray beam. An aut mati c mechanism t o sense lack of alignment and t o provide a correcting motion has been designed, built, amplifisr. The problem lies i n minimizing zero drift, and several mplifier designs have been investigated for suitability. Excepting perhaps the present design, none have been good enough. We are currently testing a somewhat unorthodox amplifier which features high gain, high negative fee& back, and u n i t output gain with the output signal taken frcm the feedback t o 100 microvolts per day appears t o have been achieved. is adequate tor research in physics and biology but would be inadequate f o r clinical use. A new system has been designed and built, using motor-driven piston valves and roller-bearing O-ring seals. Assembly of t h e functioning unit has been completed and the initial, long-term p u m p d m nm is in PWP3Ss. The synchrotron magnet superstructure has been modified t o pr+ vide the necessary space for future installation of this unit. The controls (not yet assembled) will be kept simple since this unit i s expected t o be a stopgap measure betneen the present condition and the ultimate mmr -s e ales off vacuum tubes. All parts operated as predicted excepting only a special d.c. A t this writing, the desired condition of maJdmum drift-rate equal B. Vacuum System. The vacuum system supplied with the synchrotron

Page 4

II. mc hro tro q Dmw onenta A. Vacuum Tube (Donut) Manufacture. The donut originally supplied Kith the synchrotron cracked and was patched several times with thermofinally delivered i n November, 19%. rently under investigation. Francisco Operations Office assisted in securing the loan of a donut awned by the U.S. Navy for our use while awaiting arrival of the above mentioned nical advances in donut &sign have led this Laboratory to institute pilot production of donuts. (bly designs permitting frequency modulation and not abrogating sealing-off in principle were considered. Che design has been made i n two modifications and each of these was tested briefly i n the synchrotron. Each was successful i n producing multimillion volt x-rays and the second produced greater x-ray intensity (output) than the first. Although the output naa not as high in either case as with t h e General Electric donuts, the radiofrequency power supply system was not designed for proper operation uith the donuts developed by us. Since a simper pmer oscillator will be needed anyway for the frequency modulation, this unit has been designed t o f i t the characteristics of our donut8 and parts have been ordered. It is also fair t o note that most of the repair and main te - nance time during this report periodhas been spent on the existing radicb frequency power system. has been used almost exclusively for more than two years. 1954, an improper suspension of the &nut from the poles of the magnet caused a vibration failure of the filament in this injector. had operated 1,428 hours and gave no indication that it would not last However, during the long operating life of t h i s injector, one definite change in its characteristics has been noted, the reasan for uMch can only be inferred. chrotron w a s directly related t o injector positioning. The parameter of greatest iniportance appeared t o be angulation of the injected electrons with respect toa tangent drawn t o the equilibrium orbit radtus at the injector azimuth. The emission pattern of the injected elect rm uas measured at t h e University of California Radiation Laboratory, Berkeley, under the supervision of Mr, Wesley A. Rutz. A most remarkable correlation between emission pattern and tray output was found and typical examples are shown in Figs. 1 and 2. Fig. 1 shows t h e emission and output patterns for a tungsten filament injector, both patterns being recorded in Novmuber, 1952. Fig. 2 shows a capo site of three patterns: (1)emissian 88 i n November, 1952, (2) output a8 i n January, 1953, and (3) output as in S a p tember, 195L, which is clearly U f e r e n t from (2). The inference is that the emission pattern had changed. These patterns are typical of those Another donut, ordered as a spare in March, 1953, w a s The adequacy of this donut is curIt should be noted t h a t the U.S. AEC San The practical unavailability o f spare donuts and the need f o r techB. Injectors. m e injector (with a lanthanum hexaboride cathode) In 1952 ue found t h a t the x-ray output frm the qn-

Page 6

which have been taken f o r a variety of injectors and in four donuts. This stuw indicated that, in order t o be accelerated and ultimately t o contribute t o x-ray output, electrons must initially be projected i n a particular direction within very narrou angular limits. ferred angle of projection i s not well h m but i s in the neighborhood of bo inward with respect t o the orbit circle passing through the inIt is also worth noting that the output fr m the widened emission An-pattern in Fig. 2 is somewhat less than from the n mu u er pattern. other injector which had an emission and output pattern similarly Wide also gave relatively low output. Presuming thata conclusion can be &am from only two observations, it would be well t o consider in any future injector development program that a highly peaked emission pattern should be tested. It might even be that a cathode-ray spot would be useful. III. Activities Relating tothe Use of Radiation A. Calorimeter. A vacuum calorimeter has been built to measure x-ray beam intensity and ultimately tissue absorption in absolute energy units. Although preliminary measurements with this unit have been made using 250 lm x-rays, it has been neither possible nor desirable t o make corresponding measurements using the x-rap frau the synchrotron while that unit was under development. A reconstructim of the calorimeter has been i n progress which is aimed a t minimizing the quantity of material having appreciable vapor pressure in the evacuable space. Also, one of the four thermistors in the temperature-sensing bridge had been broken and no satisfactory replacement was found in t h e existing stock. A neu supply of thermistors wan obtained and the detailed characteristics of each were determined. Two bridges were selected by t e s t fran many apparent possibilities. LCuy reasonable selection can be balanced a t a fixed temperature. criterion involved an unchanged balance point in spite of willful temperature changes of one o r more degrees. Both bridges are mounted in the abindividual thermistors can be used t o indicate t h e absolute temperature of the bridge not in active use a t any time is a spare and the B. Isodose Plotter. Following the general method used Laugblin (l), the construction of a device which will. automatically plot isodose charts has been started. charts necessary t o plan treatments and, f o r US, trades synchrotron operating time for shop time. sumably indicate only current resulting frm ionization in the cavity. Actually, there i s also a spurious current through the insulator separating the two electrodes of interest. Many obsemations hawe been recorded in the. literature of co nhc t iv it y changes following irradiation but few of Such changes durinq irradiation. In this Laboratory t h e problem of measuring conductivity changes during irradiatim has beem examined t o the This device Wiy save much time in preparing the C. Jonization Chamber Improvement. Cavity ionization chambers pre-

Page 7

point of identification of the techniques necessary. system has been used which prevents any conduction path f r m the high voltage t o the collector electrode without first crossing the guard elecThe guard electrode was grounded, as is the customary practice. The system j u s t described was not good enough, apparently, in that appreciable conduction occurred between collector and guard electrodes. The apparent collector potentials were all Vithin one v o l t of ground p+ tential although B contact potential through the insulator could haye supplied an additional. potential difference. For t h i a application rmd f o r proper use of very small volume cavity chambers, it would appear that means should be found t o maintain automatically t h e guard electrode at the same potential as the collecting electrode. We have designed two such units which operate on different principles but either one achieves in principle the desired gain of plus one from input, t o output. A small ride investigation is about to start that will examine just how nearly balanced the collector and guard potentials must be for a situation we shall t o use for very small ionization chambers. IV. Activities b~ Person Personnel of WSsection ordinarily have specific areas of responsibi lit y and only occasionally does a group work on a ccompon problem. David L. Dye, Ph.D., has had the prime responsibility f o r developnent and operation of the compensating filter servamechanism system. Mrs. Helen E. Jones, B.S., has taken the responsibility f o r operation and develop ment of both counter techniques and t h e calorimeter. John L. Radsliif, B.S., has been associated with t h e donut development program, including instmmentation and reduction t o practice. circuit developrjent has been carried by S. Winston. The mechanical skills of Hew D. Steier have been invaluable in the shop. In addition t o these Laboratory personnel, t h e X-Ray Department of the General Electric Comparu. i s maintaining at this Laboratory a field ates satisfactorily as a medical device. The presence of Mr. DuChama haa been invaluable as a liaison person with that Company as well as a hand helping t o develop the synchrotron to a state of clinical usability. Operation and maintenance of the synchrotron and smne electronic 1. J. S. Laughlin, Memorial Center, New Yorkr Private cctxauuicatlon,

Page 8

d major interest of this section has been the critical waluation of tests for the determination of the REE (relative biological effectiveness) of various kinds of ionizing radiation. Publications thus far have dealt with the tests based on the reaction of the testes of the mouse, rat, and hamster (publ. no. Z), the bday old chick embryo (publ. no. l), the moue thymus (publ. no. 5 and UCSF'-9), and the haploid s t r a i n of SaccharoIlrpces certhe mouse spleen i s presented below. Another report in this series based on the reaction ofAmong the objectives of t h e microbiological studies has been the stan& ardization of technique so t h a t canparable experiments can be carried out with different kinds of bacteria end unicellular yeasts. fects of c e l l concentration and olygen tension at the time of irradiatitm upon the IDSO of sir different strains of microorganisms is reported below. q o of the mouse, rat, and hamster. The experiments compare single doses w i t h two fractions. ( 2 ) The effect of single doses of x-rays upon the grcnrth of the bones in the tail of the rat. (3) The life-span and tumor i n c i b n c e of the CAFl mouse and the FAC(1)Fl rat, the two hybrid strains used as standard experimental stock animals in this Laboratory. A study of the efWork in progress that is not yet rea@ f o r reporting includes the fol- (1)The effect of fractionating whole-bow irradiation upon the EFFECT OF CFLL CONCEWEiATION AND CXYGEN TENSION ON THE SENSITIVITP aF The relation between t h e radiation s6nSitirLty of a suapeneian of microorganisms and the concentration of the Cells in t h e suspension has received relatively little attention in the p&, although it is of impoz ~ tance from both theoretical and practical &andpoints. In the caae of enzymes, viruses, and organic cmpounds, an increase resistance t o x-rays u i t h an increase in the concentration of the test material has beea obsemd. Dale (1) concluded that this was a result of their inactivation by radicals produced i n the surrounding madim, i.e. by an indirect mechanism. Studies of this type with microorganims, however, are complicated by t h e changes in in the suspending medium at the time of irradiation that result from t h e metabolic activities of the cella. Such changes are marked when relatively concentrated cell suspensions are employed. relations, the effect of cell cancentration upon the sensitivity to x-rap of S i x Strains of …