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more of a feeling for a moving field (rather than a dependence upon an engineering design) than did Wachsman. Quimby (New York) presented her methods for calculating dosage and described the use of various kinds of wedge filters and bolus material in horizontal arc therapy. She seems to faver the use of the term "convergent beam therapy' 'to distinguish it from vertical arc rotational therapy. Dr. Gunther Barth (Erlangen, Germany) described the experiences of 31⁄2 years with Siemen's spiral path convergent beam apparatus. He showed that all of the deep, approximately spherical-shaped tumors could be attacked by this method but not the long-stretched-out tumors. He demonstrated that tumor doses up to 8,000 r. could be applied even at 250 k. v. p. without passing the skin tolerance. He also gave some simple factors that could be used to calculate tumor dose from standard isodose charts. Dr. Sangster (Amsterdam) described a gadget and a method of obtaining 3-dimensional pictures of any distribution of crossfire radiation with 3 or more bundles of primary photons. It was essentially a geometrical method of determining the curves of intersection of surfaces determined by the isodoses of intersecting beams of radiation. He pointed out some of the complications of square or rectangular fields used in multiple-field techniques and, hence, also applicable to moving fields. He described a simple method for arriving at an approximate 3-dimensional picture that did not depend upon the photographic procedures of Howard Flanders at Hammersmith or the point-by-point construction method of Mayneord at the Royal Cancer Hospital. Lokkerbol (Amsterdam) described a combined radium X-ray treatment of cervical cancer. The radium methods were based on the Paris technique. He used a wedge-filtered convergent beam moving field to obtain optional dose distributions in the pelvis. Andreas Siegert (Erlangen) described some systematic measurements using a 70-millimeter3 volume microchamber he had made in a water phantom fitted with a female bony pelvis. With this equipment he investigated the combined use of radium applicators and the convergent beam (Siemen's spiral) method of rotation. He found that it was possible to fill up some of the holes in the three-dimensional radium isodose pattern by using various field-focus diaphragms. He was able to avoid overdosage of rectum, bladder, and skin, and seemed excited about the possibilities of the combination of the two methods.

In discussions of some of the dosage patterns of the Germany machinery, Smithers, of the Royal Cancer Hospital, described a series of his experiments using a sword swallower from a circus and a small measuring device on the end of a long wand. The actual measurements he got in the esophagus using one form of rotational beam were considerably different from those calculated. He pointed out the need for a much more detailed investigation of the dosage picture in rotating beams.

Hare and Trump (Boston) gave their usual excellent presentation of the observations they have made using the 2-million-electron-volt Van de Graff in a simple rotational pattern. This material has previously been presented in American meetings but they are building up a greater patient load that is making their presentation more and more impressive at each meeting.

Peterson (Burlington) was said to have presented a paper on a new apparatus for moving-beam therapy. He discussed the problem of producing a threedimensional isodose pattern whose shape would closely approximate the shape of the tumor under treatment. He described a mechanism that would allow the rotation of a tube about a tumor mass with continuous variation and speed of vertical and horizontal motion and at the same time a rotation of the tube itself. Desaive (Liege, Belgium) gave a theoretical statement on the principles of the application of teletherapy machines with isotope sources to moving fields; and using various kinds of electronic devices to fix the course of motion, he emphasized the idea of automatic adjustment of the beam. Krebs and Anderson (Aarhus, Denmark) presented their results on 300 patients with cancer of the esophagus. They pointed out that the curative effect was only about 2 percent but that the average survival time was doubled after the adoption of rotational therapy and is now about 9 months. They, however, were doing their work on patients who were in poor condition on admission and feel that the results are comparable to that obtained by surgical methods. They were impressed especially by the palliative effects and believe that if they had selected patients early in the course of the disease, as they plan to do, they would have been able to get much better results than they now present.

In all of my discussions with persons doing some sort of moving-field therapy. a number of points became obvious. The Germans seem to be talking only of a particular machine that performed a certain type of motion, and their ideas of rotation were fixed by the engineering of the machine. Many of the others,

especially the Italians, spoke of a pet technique of their own. Very few, and these were the English, Becker in Germany, and Muller in Switzerland, seemed to appreciate that a machine can be made to accomplish any motion and that the primary purpose is to build up shaped fields of radiation within the body. Outstanding among the groups thinking along these lines are Smithers and Lederman at the Royal Cancer Hospital, Green at the Royal Northern Hospital, Taylor at Southampton, and almost all of the English physicists attending the meetings.


One of the problems brought up at the discussions following the faculty of radiologists meeting was the general agreement that radiation therapy of the future would be primarily directed toward the establishment of a shaped field of concentrated radiation and that this could be accomplished in a beam geometry only by the use of moving fields. This general idea was more or less agreed to by most of the therapists and physicists with whom the problem was discussed, but there was also concern over the limiting factors of moving-field therapy. In summarizing the discussions with many people it seems that these limiting factors


(1) The complexity of the routine determination of the three-dimensional isodose patterns resulting from a complex moving field. It seems to me that this is not a true limit to moving-field therapy since the methods for solution are well known. The complexity that makes a problem of moving fields is in the great mass of tedious work necessary with known methods. I believe that the bottleneck in using complicated moving fields is the development of an automatic three-dimensional isodose plotter which will reduce this mass of tedious work, and the concurrent development of a group of technicians who can quickly adapt moving fields to individual patients.

(2) Determining the shape of the required field is a problem in diagnostic radiography and is an absolute limit to any but the simplest moving-field patterns. The development of diagnostic methods, however, is proceeding rapidly in the fields of tomography and various new forms of machinery have been suggested. Mayneord's department, particularly, is now investigating a number or ultrasonic devices that do not depend upon tissue density as does X-ray, but on something similar to tissue elasticity. Various other forms of tumor localization methods with isotopes are under investigation and are discussed more fully later.

(3) The major problem in moving-field therapy seems to be that of integral dose. With the development of more complex moving-field patterns an evident increase in the total radiation absorbed by the body outside of the field of concentrated dose might be the ultimate limiting factor of any moving-field pattern provided Mayneord's megagram roentgen definition of integral dose is used. Some criticisms of the original definition of integral dose, however, are of great importance.

Dr. J. E. Roberts (University of London) began the discussions at the integraldose symposium and I quote his abstract in full since, in my opinion, it was the most important single paper presented at the congress.

"Some Limitations From the Concept of Integral Dose

"Since the concept of integral dose as a measure of total energy absorbed in the body during radiation treatment was introduced some 13 years ago, considerable changes in outlook have occurred in the field of dosage. This is particularly evident in the relation between tissue ionization and true energy absorption. Although the point may be academic, there can be little justification for the retention of the megagram-roentgen as a unit of integral dose in preference to the joule or calorie.

"A disappointing feature has been the absence of conclusive evidence of a close relationship between integral dose and any clearly defined or measurable form of constitutional radiation reaction. Expectation of such a correlation was based largely on assumed production by radiation of a universal toxic substance, presumably common to all or most tissues. The evidence for such a product other than those common to all necrotic processes is not yet conclusive.

"The greatest difficulty in the application of the integral dose concept arises from the variation of sensitivity, with respect to constitutional effects, of different tissues. This can lead to gross differences in limiting integral dose according to the physical technique used. It is suggested that greater atten

tion should be paid to the distribution of energy deposited in the body during treatment with particular reference to the integral dose in known sensitive tissues."

In the discussion that followed the paper, Mayneord stressed the fact that bis introduction of the integral dose concept was a first approximation and was not intended to be the final answer. Throughout all of the discussions both at the Congress and in individual talks a few basic ideas were repeated.

(1) Integral dose is a first approximation concept and the method of calculating it is only a first approximation to the concept. A measurement of the true integral dose is now probably available for the first time with chemical dosimetry and will be a check on these calculations; but since in the phantoms in which chemical dosimetry is carried out the concept is that only of total absorbed energy, the measurement will still be only a first approximation idea.

(2) Integral dose defined as total megagram-roentgens assumes the body to be a uniform water phantom, an assumption that is entirely too simple. The ever increasing work on liver, spleen, marrow, and partial body irradiation shows marked differences in sensitivities of the various parts. Mayneord has already anticipated these criticisms in his articles of the 1940's.

(3) To a certain extent the megagram-roentgen unit is tied to the operating definition of the roentgen. At the Congress a new unit has been proposedthe "rad" which is defined as 100 ergs/gram. How this unit can be applied to the concept of integral dose has not yet been determined but there are immediately visible possibilities on an operational level. With the possibilty of chemcal dosimetry the total volume absorption of energy under any condition is a simple measurement for any one condition but is tediously complicated by the large number of possible combinations of conditions. I can see no way of generalizing it to a single formula. The conversion to "rad" units will necessitate actual measurements of absorption in tissues. On a macroscopic dosimetry scale this, too, is a simple measurement problem and is already being done at ORINS and other centers. It is apparent, however, that even if a true integral dose could be measured under certain simplified ideal conditions the criticisms of Roberts and others might still hold true since the effective pharmacological action does not take place in a macroscopic scale but within areas of a size corresponding to a small multiple of the average range of the secondary electrons. This concept of microdosimetry is an essential element in the future development of therapy with radiation.

Following this discussion Rajewsky (Frankfort, Germany) described a large series of experiments (largely in the field of total and partial body irradiation) which pointed out that the integral dose concept must be changed to take into account the individual sensitivities of various organs. Henry Kohn (San Francisco) pointed out in a detailed discussion the necessity for a biological; as well as a physical dosimetry.


The problem of the supply of clinical physicists (hospital physicists in England) had been chosen for detailed study and recommendations to subcommittee No. 6 of the TEB. Throughout my European trip I made a point of discussing these problems with about 20 or 30 hospital physicists and many therapists and isotope users in all of the countries visited. Dr. Mayneord was especially interested and has a real concern over the adequacy of the system he helped to build many years ago in Great Britain.

Apparently there are an insufficient number of hospital physicists in Great Britain and there is a real problem of recruitment. With many exceptions the system followed is about as follows: Students who have qualified with honors in physics (chemistry or math) in the British university system are apparently on a par with our outstanding students who have taken a B. S. degree with a major in physics. These students are hired to work at the lowest of three grades of hospital physicist. Their salary scale seems to correspond with a $3,000 to $4,000 yearly salary in America. They have had no previous experience in medical problems. As a junior-grade hospital physicists they receive on-the-job training from a higher grade physicist and from the therapist. This introductory on-the-job training is apparently fairly well but informally standardized. The techniques of individual patient dose calculations, equipment maintenance, calibration, dosimetry, and therapy preparation are fairly routine. If the student is interested and has the mental equipment, he continues his

studies and along with his work he is allowed to take what we would consider a master's degree. The university curricular regulations are not as formalized as in America and the diploma does not seem to be as outstanding a milestone as we make it. With sufficient proficiency the physicist is advanced to a middle step corresponding in salary to a $5,000 to $6,000 level in America. At this point he is expected to be well acquainted with the standard procedures and is given considerable responsibility in routine matters. It is expected that he has accepted hospital physics as a lifetime job and he usually stays in the field. During the next few years he acquires a reputation and there is often a shifting of jobs from one center to another. The final step is the development of research ideas and the taking on of greater responsibilities in teaching. It would correspond to the acquisition of a Ph. D. degree in America, although the situation is not nearly so formalized (on the university curricular, residence, examination time schedule) as we are accustomed to. Some of the best hospital physicists in Great Britain do not have a doctorate or receive it very late in life. This is neither a handicap nor an indication of lack of scholastic efficiency as we might consider it. The only formal distinction I can see which marks the next step is a salary increase to the position of senior hospital physicist. This corresponds to our $6,000 to $8,000 level. Many persons get their degrees long after they have become a senior grade physicist. Some have received doctorates at a much lower salary level.

Because of the close association and frequent contact (most top-grade hospital physicists seem to know every other one in Great Britain) the on-the-job training is very standard. A man can shift from one center to another without disturbing his daily pattern of routine activities. The types of research being done and the opportunities for such is an entirely different matter. With a few outstanding exceptions the research opportunities, especially the time, money, and equipment, seem to depend upon the medical doctor in charge. The medical doctor's opportunities in turn seem to depend entirely upon his relationships with the Medical Research Council. One of the outstanding disappointments of my visit to Great Britain was seeing the tremendous patient load on men who had unlimited research ideas. Even men with the reputations of Mitchell, Smithers, and Lederman have patient loads big enough for 2 or 3 men. This patient load along with the centralization of research into a few large centers, without even crumbs for the hinterlands, has caused much discontent among both physicists and therapists.

The relationship of the therapist and the physicist is not generally that of the glorious wedding of two technical specialists working as a team to further the interest of each patient as we have sometimes been led to believe. I heard of many cases in which an omniscient physician treated the physicist as a secondclass citizen. Nothing much of value seems to come out of these centers. I personally visited very few centers, and these were carefully chosen, but here the relationship is more like that of the ideal recognition by each man of both his own limitations and the other man's responsibilities.

It is impossible to generalize but in trying to find out whether there was anything besides personality that made the difference between a good and a mediocre physicist-therapist combination, it seemed that where the M. D. had an excellent understanding of physics he had an active physicist working with him. Also, where the physicist had a good understanding of human physiology, they often were very productive and the M. D.'s associated with them were willing to subordinate their own judgment on nonclinical phases of the problems.

For the most part the clinical physics situation in countries other than England appears to be in much the same position as in America. In the centers where I was able to talk to physicists there was no evidence of formal training. In Becker's Institute there is one physicist who seems to have an excellent understanding of his duties. He took his usual training at the University of Gottingen, then went to work for one of the large X-ray commercial firms for sufficient time to become acquainted with the X-ray machinery. He was then taken over by Drs. Becker and Scheer, who are giving him the clinical part of his training. Most of the routine physics in Heidelberg is done by a large staff of techinicians who are trained in the department at Heidelberg. Dr. Becker was of the opinion that in 4 or 5 other places in Germany there was as much activity as in his department. The rest of the centers, however, had only relatively routine technicians and did little or no investigational work. In France, the Gustave Roussy Institute had a number of well-trained technicians

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and at least one top-rate physicist, but the language difficulty was a barrier to my getting information. It was obvious, however, that the Ph. D. was definitely subordinated and even the younger M. D.'s were without any authority of their own. In Italy this tendency was even more marked. The professor was the bossman and nobody else was allowed to think.

Dr. Mayneord has by far the largest hospital-physicist manufacturing plant in operation, but even his plant cannot turn out a sufficient number to supply the need. He was interested in the plans we are working up for formal training and would be happy to obtain a number of exchange students. His ideas for research projects are without end, and he has one of the few departments where students can receive a complete training. The funds for his department, however, are limited. His interest in any student would be heightened if the student had some research funds attached to him. Dr. Clarkson introduced me to the secretary of the Hospital Physicists Association. They have a few foreign members and would welcome others from the States. If there is to be an active concentration on clinical physics training in the United States, they will offer any help they can give and would welcome the establishment of a sister society or branch of their society in America.

During my talks with many of the English hospital physicists, I outlined some of the conversations with Hoecker, Kerman, and Clark, and the ideas expressed at the TEB executive committee meeting. To my surprise the English hospital physicists were usually of the opinion that a more formal scholastic training was highly desirable, and that a systematic recruitment of new talent is absolutely necessary. The only objections were the concern that a formalized system of attracting students would dry up the present occasional sources of excellent men from the fields of engineering, electronics, and pure physics. There was also some concern that such a course be so specialized as to minimize the importance of the larger field of medical physics. Many of the English hospital physicists were of the opinion that such a scholastic system as the subcommittee No. 6 might propose must almost certainly be organized in Great Britain since they, too, have had troubles with recruitment. The general feeling is that the isotope problems and the diagnostic and therapy problems in X-ray are expanding rapidly and will be capable of supporting a major career for a large number of specialists.

Probably the most interesting and important feeling that I got from the investigation of hospital physics was the persistent mumbling undercurrent of dissatisfaction of the Ph. D. with the tendency for some M. D.'s to adopt an attitude of omniscience. They apparently consider the physicist a high-grade technician rather than a coworker of equal standard. This dissatisfaction was obvious to me even at the highest levels and could easily destroy any program we might develop in America.


A. Scintillation detector, the Royal Cancer Hospital

Dr. Belcher, physicist at the Royal Cancer Hospital, demonstrated a number of his new clinical scintillation dosimeters and detectors. He is using an anthracene crystal in a polished light pipe of dural metal attached to a photomultiplier tube. The amplified impulses are attached to a simple electrometer system. By this method he has been able to record dose rates of the order of 1 r per hour within a sensitive volume of 1 mm3 but displacing a somewhat larger volume of phantom material. Attached to the device is an ingenious shutter mechanism that interrupts the optical path and allows for the direct and immediate calibrations of anomalous results due to radiation striking the photomultiplier tube, to dark currents, and to temperature differences. Clinical probes have been designed with a single- or double-sensitive probe on the same photomultiplier tube. For example, when the double probe is placed over a blood vessel and when the impulses are shown on a recording mechanism, it is possible to accurately measure linear flow rates. This device has been used already in such clinical problems as the measurement of portal blood flow. It could and is being extended to many other flow and circulatory studies. The smallness and maneuverability of the single-probe device make it an ideal instrument for thyroid surgery. Belcher's studies are being published shortly and will be well worth detailed study. This is one of the few instrument ideas I saw in Europe which appear to be worth swiping.

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