Focus-skin Distance Research Articles

Clinical Evaluation of Supervoltage Roentgentherapy

The the0 retical advantages of supervoltage roentgentherapy can only be assessed by results obtained from clinical use. Although the first supervoltage units were first used clinically more than 25 years ago, there is a scarcity of quantitative clinical data that demonstrates the superiority of supervoltage roentgentherapy in any group of cancer patients (2, 3, 4, 5, 13, 14, 23, 24, 25, 26, 27). The term supervoltage must be clearly defined. Teleradium units that contain 5 to 10 grams of radium are not considered supervoltage equipment. The wave length o f the rays emitted must be augmented by other physical factors that include a long source-skin distance (SSD) to produce beams similar to those of the million volt X-ray generators which, in comparison with orthovoltage radiation, are characterized by : 1. Skin-sparing. This is a result of the phenomenon of electronic build-up below the surface of the skin. 2. An increase in depth dose. 3. Enhancement of systemic and organ tolerance. Tolerance is enhanced because less energy is absorbed, for the same tumor dose, by the surrounding structures and the body. 4. A decrease in bone absorption. This is advantageous when bone must be traversed because the tissue doses are the same values obtained form depth dose tables, whereas with 3-1 mm. Cu HVL beam, tissue doses may be 10 to 20 per cent less than the values of the depth dose tables. The million volt X-ray generators, linear accelerators, betatrons and kilocurie cobalt-60 units produce beams which fulfill these four criteria. The hectocurie cobalt60 units and, less so, the cesium-137 units are not comparable to supervoltage equipment in all respects. The depth doses are comparable to those of 3-5 mm. Cu half-value layer (HVL) beams with focal-skin distance (FSD) of 50 to 70 centimeters.

The dependence of depth dose on focal skin distance.

The dependence of depth dose on focal skin distance has been the subject of a number of investigations. Mayneord and Lamerton (1941) reduced the then available depth dose data from a variety of centres for a variety of focal skin distances to one reference focal skin distance using a suitable conversion factor. The basis for their conversion factor is the inverse square law factor which is given by Mayneord and Lamerton used combinations of F and (F + 1)/2 to reduce the published data to a standard focal skin distance. In the depth dose determinations by the group in Saskatoon (Johns, Fedoruk, Kornelsen, Epp and Darby, 1952; Supplement No. 5), careful measurements were made of the variation with focal skin distance. Their measurements showed that the conversion factor usually lay between (1 + F)/2 and F and varied from F to (1 + F)/2 as the area of the field increased from zero area to a large field. The factor was also shown to be a complicated function of the quality of the radiation. In calculations of tumour dose in rotation therapy, use has been made of the concept of tumour air ratio (Johns, Morrison and Whitmore, 1956; Johns, Whitmore, Watson and Umberg, 1953). This has been defined as the ratio of the dose at the point in tissue to the dose at the same point in space “in air”.

Patient exposure to ionizing radiation in dental radiography.

The use of ionizing radiations and exposure of the individual are increasing. As larger segments of the population are being exposed, two important requirements become apparent. The first is that exposures to various radiations be accurately evaluated; the second, that all possible means be taken to reduce exposures in necessary medical and dental procedures. In dental radiography, patient exposure may be reduced by the use of faster films, increased focal skin distance, and more penetrating radiation. The effects of these factors have been considered by various authors. Trout, Kelley and Cathey (1) and Seeman and Cleare (2) have shown that with increased filtration substantial reduction in the dosage to the skin and the first few millimeters of underlying tissue is possible without affecting the diagnostic value of the resulting roentgenograms. The use of such filtration results in a roentgen beam having greater penetration and thereby reduces the ratio of skin to bone dosage. This reduction in skin dose is due to the increase in the ratio of radiation incident upon the skin to that which is useful in producing the x-ray image. The quality of the beam may be further improved by raising the operating potential from the usual 60 or 65 kvp to the range between 85 and 100 kvp. Increase of the focal skin distance from 8 to 16 inches will further favorably increase the ratio of radiation incident on the skin to that which is useful in producing a radiographic image. For example, if the film is so placed that the beam has traversed 4 cm. before striking it, the increase in radiation reaching it will be 19 per cent. The employment of ultra-speed film in those cases which will allow its use can further reduce exposure of all tissues irradiated by a factor of four (3). The object of the investigation to be reported here was to determine the dose delivered to the apical areas during dental radiography, under certain operating conditions. The conditions chosen were the usual operating voltages, i.e., 60 and 65 kvp, added filtration of 0 and 1.0 mm. aluminum, and an 8-inch focal skin distance. The inherent filtration of the machine which was used is 1.2 mm. aluminum (including tube wall, oil, and cone). Method In order to simulate actual anatomical and geometrical conditions as closely as possible, a phantom head was constructed of Lucite, in sections projected from those given in Eycleshymer and Schoemaker (4). This was done so that all air cavities in the head and neck would be preserved in their relationship to each other and to solid tissue. This phantom, in a typical experimental set-up, is shown in Figure 1. To accommodate the ionization chamber, six holes were drilled in one side of the head and two holes in the neck. These holes were so cut and shaped that, when the ionization chamber was inserted, essentially no air cavity was present.

Stimulation of hair growth in rabbits by ionizing radiations.

IN the course of experiments on tracing the location of radioactive phosphorus injected intradermally1, observations were made concerning the growth of hair. A series of rabbits was given a dose of 1,000 r. or 1,500 r. (100 kV., 7 m.amp., 2 mm. aluminium filter; half-value layer, 0.11 mm. copper; focus–skin distance, 15.5 cm.) through a ‘new moon and sixpence’ pattern in a lead shield backed with ‘Perspex’ (a circular area of 3 cm. diameter separated by a strip of skin 1 cm. in width, from a crescent-shaped exposed area of skin also 1 cm. in width surrounding half its circumference), and a solution containing 0.4 mc. of radioactive phosphorus was injected within the circle immediately after exposure.

The treatment of lung cancer with radiation and radiomimetic drugs.

The encouraging results obtained by Roswit and his associates (4) by combining roentgen irradiation with nitrogen mustard in the treatment of pulmonary carcinoma prompted the writers to undertake this form of therapy between 1950 and 1954. Although the response of pulmonary carcinoma to nitrogen mustard is limited, it is sufficient to suggest that if it were combined with radiation better palliation might then be achieved. Results from irradiation alone are only fair. With the addition of nitrogen mustard, an increase in mean survival from 9.4 months to 12.8 months from onset of symptoms has been reported. In experiments on mice, Karnofsky et al. (2) found that the toxicity of mustard, as measured by its lethal effect, was reduced by preliminary irradiation. In view of this apparent decrease in the effectiveness of the drug, it was decided to give the irradiation following rather than preceding the administration of the mustard, a procedure which had also been tried by others. It gradually became apparent, however, that the magnitude of the systemic reaction, particularly the hernocytic depression, limited the amount of radiation which could be given. Several ways of avoiding this were possible: The dose of mustard could be reduced, there could be a delay between the administration of mustard and irradiation to allow recovery, or the irradiation could be spread over a much longer period of time. None of these seemed desirable, so that in our later patients, the x-ray therapy was given first, followed at once by nitrogen mustard while the tissues were undergoing their fullest radiation reaction. The lower systemic toxicity which could be expected seemed an advantage and Klopp's work (3) indicated that there would be no impairment of effectiveness of the mustard. Material and Methods Our pulmonary cancer series numbered 38 patients, 32 males and 6 females, and included 20 squamous-cell, 8 undifferentiated, and 3 anaplastic carcinomas and 2 adenocarcinomas. The diagnosis in the remaining 5 was based on the finding of neoplastic cells in sputum. In all except 12 obviously inoperable patients exploratory thoracotomy was done, with partial resection of the tumor (19 cases) or pneumonectomy (7 cases). Patients with evidence of generalized carcinoma were not accepted for treatment. No patient with a recorded white blood count under 5,000 received chemotherapy. The radiation was given at 250 kvp, h.v.1, 1.5 mm, Cu, and focal-skin distance 50 cm. The treatment was directed to both the primary tumor and the mediastinum. A tissue dose rate of about 1,000 r per week was maintained. Six patients received intravenous nitrogen mustard initially and 6 following irradiation. The dose was 0.2 mg. per kilogram of body weight on each of four successive nights.

On the specification of moving beam therapy techniques.

In radiotherapy there has been a tendency for unsuitable terms to be used and to persist, in spite of the fact that they cannot stand up to logical analysis. For instance such terms as contact therapy, and even superficial and deep therapy are all some-what anomalous. In contact therapy it is only the applicator which is in contact with the patient, and the description is really applied to techniques using a short focus-skin distance with low tube kilovoltage. Similarly, inherent in the present use of the terms superficial and deep therapy is the kilovoltage used, rather than the depth of treatment in the patient's body. Thus a superficial set may be used at 140 kV to treat lesions at a depth of 2 to 4 cm, whilst, in a glancing field technique for breast cases, a deep therapy tube is used to treat only the superficial layers of the chest wall. In the same way it seems that confusing terms may develop in connection with the new techniques of moving beam therapy. For instance converging beam therapy is a term already used to describe a technique in which the axis of the beam traverses the volume of a cone, first converging towards the axis and then diverging from the axis to the surface of the cone. A beam whose axis follows the surface of a cone is also converging in a somewhat different sense.

Modification of electron filter to improve light localization of a cobalt-60 beam.

The distribution of ionization in the first few millimeters of tissue-like material was studied with a cobalt-60 teletherapy unit (1, 2). It was found that for short cone-to-skin distance (C.S.D.) the effect of electrons from the collimating system could be reduced appreciably by thin filters which did not noticeably affect the gamma-ray dosage pattern. Optimum results were obtained with the filter mounted over the lower end of the treatment cone. With this arrangement, however, the filter obscured the beam of light from the light localizer unless it was removed with each use. The interference of a filter with light localization is not encountered with x-ray generators in which the filter employed to harden the beam is located above the mirror of the localizer. Below the collimating system of an x-ray generator, filters to reduce electron contamination are generally not needed, for several reasons. For units operating below the supervoltage region, the average energy of secondary electrons is low, and they are removed from the beam through air scatter even for short diaphragm-skin distances. Further, the focal spot of an x-ray generator is usually small in comparison with the size of a teletherapy source. Therefore, for a given focal skin distance, long diaphragm-skin distances can be used without resulting in wide penumbras. Filters to reduce electron contamination are not needed when the diaphragm-skin distance is large. The low-activity sources employed in some teletherapy units necessitate treatment with short source-to-skin distances (S.S.D.) if the treatment time is to be kept within reasonable limits. If the penumbra width is to be kept small, this requires treatment at a short cone-to-skin distance, for which the electron contamination is appreciable. To minimize the skin dose, it was felt advisable to use an electron filter for treatment dose to the cone. It was also considered desirable to retain the light localizer without having to remove and replaces the filter with each use. Since the purpose of a light localizer is to mark the outer extremities of the field, it was found possible to leave the filter attached to the cone without hindering this function of the localizer. In fact, the method developed is believed to have improved light localization. Method of Mounting Filters and Results A Lucite cap, with bottom and walls of 1.5 mm. thickness, was constructed to fit over the end of the cone (Fig. 1). A sheet of cadmium, 0.25 mm, thick, was then attached to the Lucite so as to cover the opening of the cone except for a narrow slit (about 1 mm.) around the edges. With this arrangement, the filter can easily be removed if desired. The light pattern from the localizer is shown in Figure 2. This pattern was made with the light from the bulb of the light localizer collimated so that its image in the mirror reproduced the source in both shape and position.

Technical note: wedge filters.

In 1950, Ellis, Shanks, Kemp and Oliver published details of the construction of a set of brass wedge filters and gave isodose curves for each. These wedges were used close to the skin and at a focus-skin distance of 30 cm. In Adelaide these filters were proportionally diminished, sited at the top diaphragm of a treatment cone, and used at F.S.D.50 cm.

Simple distance-measuring and centering device for x-ray therapy machine.

I wish to describe an extremely simple method for accurately spacing and centering the tube head of the Profexray skin therapy machine. Although the apparatus which I have devised is not available commercially, it is easily constructed at a cost of less than $1. The device is used with the detachable narrow treatment cone of 15 cm. focus-skin distance, supplied with the machine, and enables one to treat an open field at any chosen longer distance. For illustration, I shall choose a focus-skin distance of 20 cm. The device consists of a cylindrical block of wood measuring 5 cm. longer than the cone and of such diameter that it just fits inside the cone. A circular piece of tin is nailed to its upper end, serving as a flange to prevent the cylinder from dropping through the cone (Figure 1). 1, cylindrical block of wood with circular piece of tin

Radiological demonstration of the zygomatic arch.

One of the usually more difficult radiological technical problems is adequate demonstration of the zygomatic arch. This prominent facial structure is important to the plastic surgeon because of traumatic external deformities; to the ophthalmologist because trauma changes the orbital shape and eye levels, with resulting diplopia of serious nature; to the rhinologist because of injuries to the maxillary antrum; to the dentist because depression can interfere with the mandibular articulations and movement of the coronoid process and muscles of the jaw, producing bite deformities. The projections used by most technicians fail to produce views at these levels sufficiently measurable and comparable to give the radiologist and clinician a clear idea of the scope of the problem. The zygomatic arch is composed of several bony parts. The main structure is the malar bone, which is a roughly rectangular plate. This is attached anteriorly to a projection from the maxillary bone, superiorly to a projection from the combined frontal and sphenoid bones, and posteriorly to a projection from the temporal bone. The relatively free malar borders between the bone attachments of the maxillary process and the frontosphenoid process form the lateral border and a portion of the inferior border of the orbit. Unfortunately, injury of the zygomatic arch usually involves several of the bony parts and is quite often compounded into the maxillary sinus. The number of fractures and their location, the magnitude of the depressions in the arch, and the shifts of bone mass have to be shown by various technical positions, with the uninjured side serving as a model for the injured side. These views are preferably taken at right angles to each other to present the maximum deviations in the various planes. Three routine views, all of which show the opposite side for comparison, will demonstrate the arch in its entirety and will give measurable evidence of the amount of deformity involved. The first view is obtained in the usual nose-chin position for the maxillary sinus study. The nose and chin rest on the table top over the mid-line of the table and cassette, with the mid-line sagittal section of the head vertical to the table top. The tube is placed with the central ray perpendicular to the table top and projecting through the floor of the orbits to pick up the inferior orbital ridges. This view is taken with a Bucky, with the average factors, for an average patient thickness of 23 cm., of 74 kv.p., 50 ma. sec., 40 in. focal skin distance. The film thus obtained outlines the inferior orbital ridge and will outline fractures in this area of the maxilla, demonstrating measurably any downward depression of the inferior orbital ridge, in addition to showing maxillary antral changes. The arch itself is not demonstrated, and both sides are shown for comparison in a single view.

II. Beam Definition, Beam Direction, and Protection Problems

The target of the X-ray tube is enclosed in a massive lead cone at the open end of which are placed two sets of 2-inch thick blocks mounted at right angles (Fig. 2). These blocks form the usual type of adjustable diaphragm device for square and rectangular fields. The original ones were of lead which transmitted approximately 7 per cent. of the primary beam, and even more in places where they had brass inserts. They were replaced by blocks of G.E.C. heavy alloy (95 per cent. tungsten), and the method of mounting was modified to avoid brass inserts. The radiation escaping the outside edges of the blocks was lessened by reducing the maximum aperture, limiting the field to 22 × 18 cm. at 100 cm. focus-skin distance. A steel holder was added in which heavy alloy inserts could be fitted for defining circular fields (Fig. 3A) and grid fields (Fig. 3B). Thin perspex plates incorporated in these inserts removed the electrons produced by the X-ray beam glancing on their tapered apertures. These fields are used at two focus-skin distances (67 cm. and 100 cm.) in order to increase the number of available field sizes. In practice the diaphragms for defining square and oblong fields are closed until they just obscure parts of the circle and are then opened slightly. This stops radiation escaping around the outside of the circular insert. For grid fields the adjustable diaphragm is used to define the superficial field size.

Depth dose data, 75 kVp to 140 kVp.

Depth dose data for the range of energies from 75 kVp to 140 kVp are not as useful from a clinical point of view as those in the standard therapy region—150–400 kVp. Occasionally, however, depth dose data for this region are required. Since facilities for the rapid measurement of depth dose are now available in this laboratory, a careful investigation of depth dose for this energy range has been carried out. The results presented in this paper are for a selection of areas from 0 to 100 cm.2, for focal-skin distances from 15 to 30 cm., and for qualities of radiation with half-value layers of 1·0, 2·0, 3·0 and 4·0 mm. Al. A comparison is made of these results with those of Braestrup (1944). Measurements were made in a water phantom with a flat-type ionization chamber similar to that described previously (Johns, Fedoruk, Kornelsen, Epp and Darby, 1952). The cylindrical chamber was 1 mm. deep and 7 mm. in diameter, giving a volume of 150 mm.3 The front wall was polystyrene, 0·25 mm. thick, coated on the inside with aquadag, while the collecting electrode consisted of “air wall” material. The chamber was made to have the same quality dependence as a Victoreen chamber for qualities with half-value layers from 1·0 to 4·0 mm. Al. This ionization chamber was moved by remote control in the phantom, and measurements were carried out to a depth of 10 cm.

Depth dose data, 150 kVp to 400 kVp.

Depth dose measurements have been made in a water phantom with a small ionization chamber connected to an automatic recording system. Results are reproducible to within 0·5 per cent. Measurements were made for areas from 0 to 400 cm.2, focal-skin distances from 40 to 100 cm., half-value layers from 0·5 to 5 mm. Cu, and depths from 0 to 20 cm. The data obtained will be included in a collection of Central Axis Depth Dose Data to be published as Supplement No. 5 to The British Journal of Radiology.

Roentgen doses during diagnostic procedures.

The ever-increasing exposure of man to ionizing radiations in medicine, industry, and warfare presents the problem of determining, with practical accuracy, the doses to which an individual may be subjected. Skin, depth, and volume doses used in therapy can be determined from tables on these subjects formulated by Quimby (11), Mayneord (21), and others. Formulae for dosages delivered by radioactive isotopes also have been described in the literature (25, 26). This report is devoted to describing a method by which skin, depth, and integral doses resulting from diagnostic radiologic procedures can be estimated. Leonard (1), in 1898, was the first to describe an “x-ray burn” in the American literature. Leddy and his associates (2–5) published a series of articles in 1935 and 1937 warning of the dangers associated with fluoroscopy. Braestrup (6), in 1942, calculated the average radiation doses that a patient would receive during several types of diagnostic radiologic examination. Smedal (7), also in 1942, published tables of roentgen outputs with several different filters, target-film distances, kilovoltages, and milliampere-seconds used in some of the diagnostic procedures. Martin (8), in 1947, showed by means of graphs the effects of various filters and focal-skin distances on the radiation dose received per second per milliampere at 70 kv.p. for several common diagnostic examinations. The above-mentioned reports and the experimental data recorded in the next section of this study demonstrate large variations in dose rates from different types of roentgenographic and fluoroscopic machines under supposedly identical conditions. The graphic and tabular information presented in this paper was formulated primarily for use in the Department of Radiology of the Hospital of the University of Pennsylvania, in which the measurements were made, and it should not be assumed that they are applicable elsewhere. However, it is believed that anyone wishing to use these values can do so by making ionization chamber readings on his own machine, using 1 mm. Al added filter, 26.4 inches target-chamber distance, and any convenient milliampere-seconds and kilovoltage, and comparing his result with the values given herein. If such values check fairly closely with those shown in Figure 3, these curves can be used for that machine. If there is a great difference, the ratio of the measured value to the value from Figure 3 will be a correction factor which will enable practical estimates to be made. Experimental Data The basic data described herein are air-dose rates measured at focal spot-chamber distances of from 30 to 100 cm. in the central beams of x-rays produced by 12 fourvalve rectified, 1 mechanically rectified, and 1 self-rectified roentgenographic and fluoroscopic units. Measurements of air-dose rates were made by means of a Victoreen condenser r-meter.

Measuring and centering device for use on x-ray machine.

The accompanying picture is of a device to be used on the tube head of the profexray® lowvoltage therapy x-ray apparatus. It is intended as a simplified device for centering the x-ray beam and measuring the focus-skin distance. As may be noted in the picture, the filter carrier is employed to hold the centering and measuring rod. The filter carrier is a nonconductive material, such as plastic. It fits snugly in a slot provided for it in the tube head. With the filter carrier in place, the lucite® disk, about the size of a quarter in diameter, is in the center of the x-ray beam. The measuring rod, bent at its lower end at an angle of 90 degrees, is inserted into the side of the disk so that the rod tip is seen at the exact center. The rod slips easily up and down through its

Penumbra effect in therapy cones.

Most deep x-ray therapy cones currently in use or commercially available are so-called “false” cones, i.e., they contain a collimating lead diaphragm at or near the tube-end which is designed to restrict the x-ray beam to the size of the desired treatment portal. The side walls consist of light, thin, moderately radio-translucent sheet metal, the sole function of which is structural support. Sometimes these side walls contain observation windows. In occasional instances they may serve to absorb scattered radiation from the patient. The field delimited by such a collimating lead diaphragm is not of uniform intensity, due to the fact that the focal spot from which the rays originate is not a single point, but an area of considerable magnitude. As a result, the skin portal consists of a central zone of full intensity surrounded by a penumbra zone of partial intensity. The penumbra effect, although well known, has apparently not been taken into full consideration by all manufacturers. The size of the central zone of full intensity in the skin portal produced by this type of cone-diaphragm is given by Formula 1: The width ofthe penumbra zone on each side of the portal is given by Formula 2: Within this zone, the intensity of the primary beam falls from 100 per cent at the inner margin to zero at the outer margin. As the beam passes deeper into the tissues, the penumbra zone becomes wider, creating an area of uncertainty in attempted iso-dose calculations (1, 4). The width of the penumbra zone at any depth can be calculated by Formula 2 if the distance from the skin to the depth in question is added to the value of d″. The experience of the authors is cited with such a cone, made by a well known manufacturer for use with a popular 200-kv.p. x-ray therapy generator, and represented as furnishing a 10 × 10-cm. skin portal and an 80-cm. focus-skin distance. It contained a square lead diaphragm at its tube-end, its aperture measuring 3.7 × 3.7 cm. and located about 29 cm. from the target. The actual field produced by this cone is shown in Figure 1A, where a photographic film was placed in the position of the patient, and in Figure 2A, where iso-dose curves for the area covered by the cone are given. (All measurements were made with a Victoreen condenser r-meter.) The useful projection of the focal spot in this equipment was measured by a modification of the pinhole camera method of Hodges (2). It was found to be a rough trapezoid (Fig. 3) measuring 2.48 × 0.61 cm. This tube was of recent purchase, a General Electric type XPT tube, which we understand enjoys fairly wide use. The skin portal calculated by Formula 1 for this focal spot and cone measured 5.8 × 9.1 cm. and had a penumbra zone 4.4 cm. in width on the long side and 1.1 cm. on the short.

A 2 Me V X-ray generator for therapy.

A brief description is given of a 2 MeV electrostatic generator for X-ray therapy, together with some details of its behaviour during some months of routine clinical use. The servicing problems involved in the use of such an equipment are discussed. Physical measurements preliminary to clinical work are briefly described, details being given of the protection achieved around the set and of dose distributions in a water phantom. Experimental measurements on the variation of dose in the first few millimetres of the phantom, and the effect on this of changes of field size and focus skin distance are discussed.

Studies of the Effect of Roentgen Rays on Healing of Wounds

THE EFFECT OF roentgen rays on the healing of skin incisions in rats has been the subject of previous experimental studies by Pohle and Ritchie (6, 7, 8). In spite of the importance of the clinical aspects, the subsequent literature contains only scanty, conflicting evidence concerning the effect of irradiation upon the healing of surgical wounds. This is particularly true with regard to the use of small doses of roentgen rays; a better understanding of this question should lead to a more satisfactory combined surgical and radiation procedure in the therapy of malignant disease. While Pohle, Ritchie, and Wright (6) demonstrated that wound healing in rats is retarded by irradiation of the skin with 1,000 r, especially when given twenty-four hours after the incision, there is not complete agreement in the literature as to the effect when smaller doses are used. Fukase (4) found that following doses of about 400 r in rabbits the wounds contained less exudate than in the controls. Businco and Cardia (2) believed that 150 r had a stimulating effect on the healing process in dogs, although only four animals were used in their experiments. Nathanson (5), using gamma radiation, found that small doses accelerated the healing of incisions made in the abdominal skin in dogs. Dobbs (3) conducted a series of experiments on rats, in which various amounts of radiation were given to skin wounds. On each of his animals he made two 4 cm. wounds, one of which he exposed to roentgen rays while the other served as a control. The tensile strength of the scars was tested after varying intervals, and in some cases histologic sections were obtained. The results showed that doses of 300 r given immediately after the wound was inflicted caused an increase in the tensile strength of the scar. Doses of about 1,000 r caused a decrease if given prior to the incision and no change if given afterward. The present investigation has been undertaken in order to study the effect of roentgen rays applied in doses of 10, 25, 150, 300, 350, and 700 r upon the healing of wounds in rats. The technical factors were 100 kv., 5 ma., 2 mm. Al, 30 cm. focal skin distance, 2 × 2 cm. field, 45 r/min. (half-value layer in Al, 3.5 mm.). Method and Experiments The method employed was substantially the same as described in our earlier publications. Albino rats of the Sprague-Dawley strain, approximately 200 gm. in weight, were used. Under ether anesthesia a midline incision 4 cm. long was made on the back and a Michel clip applied at the midpoint of the wound. No further closure was attempted. The experimental work was divided into three groups as described below. Group 1: Eighteen rats were used. In each of these one-half of the wound was irradiated immediately after the incision was made, and the other half was used as a control.

Anti-Histamine Ointments for Skin Protection in Radiation Therapy

Every radiotherapist knows, first, that if he is to cure a malignant tumor he must see that it receives an adequate dose of radiation and, second, that the amount that can be delivered to the tumor is limited by the normal organs and overlying skin which must be traversed by the x-ray beam. The methods of obtaining larger tumor doses without excessive damage to normal structures are of two main types, mechanical and biological. The mechanical means of increasing the amount of radiation reaching a tumor are well known. Increasing the focal-skin distance increases the depth dose in relation to the skin dose. Increasing the filtration up to a certain point improves the quality of the beam, which results in a more favorable depth- to skin-dose ratio. A greater focal-skin distance and increased filtration, however, require much longer treatments, which are not always feasible in a busy clinic. Where supervoltage machines with their greater output of highly filtered rays are available, treatments with radiation of excellent quality can be given in a shorter time, without serious skin damage. Another mechanical means of increasing the tumor dose consists in cross-firing. Thus the tumor may be irradiated daily, while the intervening skin receives radiation only every second to fourth day, depending upon the number of portals used. This allows the skin a recovery period between exposures. Of biologic methods of increasing total radiation, fractionation is well known. With proper fractionation and the use of multiple portals, tumor doses can be built up to a relatively high point and the overlying skin still be spared an irreversible reaction. Another biologic means of increasing the tumor dose is the protection of the intervening skin against severe reactions by the use of various powders, lotions, and ointments. The number of such protective applications is legion. It is quite generally agreed that with tissue damage, histamine or histamine-like substances are released from the cells. Working on this premise, Lofstrom and Nurnberger (1) advocated the use of the new anti-histamine drugs, orally or even intravenously, when the occasion demands, to combat the systemic reaction to the product or products of cell destruction. Following a similar procedure, we have been using Benadryl and Pyribenzamine by mouth. With the routine use of 25 mg. of either drug before each meal, we have noted no adverse side effects in over 300 patients except for mild drowsiness in an occasional case. Further studies are planned to determine just what increase there is in the blood histamine during a course of intensive irradiation. It is hoped that this will suggest some explanation for the beneficial effect of these drugs in reducing radiation sickness. We do know that blood histamine values rise following a burn, and Kisima reported an increase in the histamine content of all tissues, as well as that of the blood, following cutaneous burns in dogs.

Beam Localization and Depth Dose Determination

THE RANGE OF THE lethal tumor dose for various malignant neoplasms has been roughly defined, and the practice of delivering this dose within an optimum period of time has also become established. This is evident in the radiation treatment of epidermoid carcinoma of the skin, larynx, and cervix, so that one might assume that similar results should be possible with epidermoid carcinomas of the esophagus and lung. Heavier filtration, increase in the focal skin distance, and higher kilovoltage have made possible a greater depth dose, but radiation sickness from too large a volume dose and local skin reaction have proved to be limiting factors in the delivery of the required amount within the optimum period of time. Volume dose depends chiefly on the field area, treatment site, thickness of the tissue traversed by the radiant energy, and homogeneity of dosingly less important as one increases the number of ports and the quality of radiation. In treatment of deep-seated lesions it becomes imperative to think in terms of tumor dose if one is to avoid over-irradiation of a thin patient or under-irradiation of a stout one. The practice of cross-firing through four large ports to skin tolerance is inefficient, especially if the size, site, and depth of the tumor are not precisely known. A bladder tumor may be 6 cm. from the ventral surface and 15 cm. from the dorsal surface, whereas with a rectal or a cervical tumor this situation may be reversed. The percentage depth dose to a tumor 15 cm. below the skin is small, being 24 per cent of the air dose at 200 kv.p. with 0.5 mm. Cu plus 1 mm. AI, 10 × 10 cm. port, and 50 cm. focal skin distance. Since this results in a poor yield of tumor dose even when skin tolerance is approached (480 r for 2,000 r in air and 2,720 r on the skin), we avoid such distant ports whenever possible. At 6 cm., the depth dose is 72 per cent of the air dose. If isodose curves be made of a tumor treated through four ports 6 and 15 cm. from the tumor, and with the above factors, it will be seen that there is a great difference between the value of the tumor dose from the beam through the distant port and that from the beam through the near port. The ratio of the minimum tumor dose to the difference between the maximum and minimum is known as the “economy quotient” and IS an indication of therapeutic efficiency (1, 2). When the difference between the maximum and minimum tumor dose is small, homogeneous irradiation occurs and the volume dose is also small. (Fig. 1.) If the number of ports be made great enough and the size of each port held to the smallest possible area, irradiation of a tumor is accomplished with the least skin reaction and least volume dose. One should be reluctant to irradiate a tumorbearing volume through a large port at the expense of back-scatter from normal tissue. Moreover, the variation in the intensity within the field of irradiation may be as great as 20 per cent at the periphery of a 15×15 cm. port (6).