Focus-skin Distance Research Articles

The Standardisation of Radiological Apparatus

In radiotherapy it seems to me that all the factors leading up to the provision of a standard X-ray beam could, with advantage, be considered from the point of view of standardisation. It would obviously be advantageous if the high-tension units could be so designed and constructed that certain minimum standards of performance are reached, and if the parts of such units could be interchangeable. Especially does this apply to shockproof cables, rectifying valves, and X-ray tubes. If these could be changed without difficulty the work of the radiologist would be made easier and his choice of apparatus wider. Given a beam of a certain penetrating power, the radiotherapist wishes to know the isodose curves for a given field size and focus-skin distance. It is quite certain that, for reasons which will be discussed later by Dr. Read, the isodose distributions from various types of applicator and various types of X-ray tubes are not the same. This diversity of beams results in difficulties in reproducing techniq...

On the Energy Absorbed by a Patient During X-ray Treatment

The integral dose delivered during therapeutic treatment, with X rays of half-value layer between 2 and 4 mm. of Cu, can be estimated rapidly, and with reasonable accuracy, from the curves which have been shown. The absorption depends principally upon the area and site of the field, and to a much smaller extent upon focal-skin distance, linear dimensions of the patient, and half-value layer of the radiation.

ReviewSupervoltage X-ray Therapy, PhillipsRalph.

This book is a report on the work of the millionvolt apparatus installed at St. Bartholomew's Hospital in 1936 as a result of the generosity of Mrs. Meyer Sassoon and the vision of the Cancer Committee of the Hospital. The choice of apparatus was made following discussions with Metropolita-Vickers after Finzi, Donaldson, Canti, Hopwood, Paterson, and Levitt had inspected the first continuously-evacuated apparatus for 200 kV at the Sheffield Radium Centre. The report emphasises the wisdom of the decisions made to obtain a million-volt constant potential apparatus capable of easy and safe use in the treatment of cancer, with a short focal-skin distance.

Physical, Biochemical, and Therapeutic Aspects of Volume Dose

Some four years ago experimental and theoretical investigations on the absorption of energy during X-ray and radium treatments were published (Mayneord, 1940). It was then emphasised that the total energy absorbed throughout the body is a quantity of great physical and clinical importance, and this conclusion has since been developed in much other published work. The unit of “integral dose” then suggested was the gramme-rontgen, which is the energy conversion when 1 r is delivered to 1 gramme of air and is approximately equal to 85 ergs. A megagrammerontgen (one million gramme-rontgens) is approximately equivalent to 2 calories. For experimental investigation of the energy absorbed when the whole body is irradiated, a model patient of elliptical cross-section and divided into slabs has been constructed. In some of these slabs condenser ionization chambers can be placed. With a focal-skin distance of 250 cm., so that the beam or radiation was large enough to cover the whole model, measurements have been ma...

The Calculation of Dosage Rate in Rectangular Fields

The dosage rate at any point irradiated by an X-ray field may be regarded as made up of two parts, one due to the primary radiation, and the other due to the secondary radiation produced by this. Clarkson (1941) has shown how the dosage rate due to secondary radiation in a field of any shape can be determined by dividing the field into a number of sectors, measuring these, and adding together their individual contributions. In the case of rectangular fields it is possible, using the principle of his method, to construct a single set of curves from which, given the central depth dose data tabulated by Mayneord and Lamerton (1941), the secondary radiation at nearly all points in a field of any size, and for any quality of radiation and focal skin distance, can be determined without the necessity of measuring sectors. This saves time if a number of points have to be calculated as is the case when an isodose diagram is to be drawn. If O (Fig. 1*), is any point in a rectangular field ABCD, at a cm. from BC, and b cm. from AB, and OQ is a small sector of radius r cm. and angle dθ, lying in the triangle EOB, then the dosage rate at a point deep to O, due to secondary radiation from the sector OQ, is, (Clarkson), where F(r) is the amount of secondary radiation which the point would receive from a circular field of radius r cm. centred at O.

Some Data Concerning the Use of X-ray Beams in Direct (Cross-Firing) Opposition

A Technique widely used in deep X-ray therapy (e.g., for irradiation of the axilla, pelvis, whole limbs, neck, etc.) is that which utilises two identical beams cross-firing through opposite fields or portals. One of the chief reasons for this wide use is that the technique represents one of the simplest methods of achieving (a) a large dose at the centre point between the fields1 relative to that received by the skin surface—it is in this region that the disease is usually situated and (b) a high degree of dosagė homogeneity between the two fields. The latter is of the utmost importance in the treatment of many cases where the disease is extensive. It is of value to the radiologist using such a technique to know how the dosage conditions provided by it depend upon the various physical factors, radiation quality, focus-skin distance, field size and separation of the opposing fields. The last of these is usually equal to the maximum thickness of the part to be irradiated. A few specific cases of this method...

A Study of Roentgen-Ray Distribution at 60-140 Kv.P.

Studies of the distribution of radiation about an x-ray tube are not new. Kaye (1) wrote about it in 1909. Coolidge and Kearsley (2) reported on it in 1922, and Bouwers (3) discussed it in 1928. More recently its significance and practical application have been reported by Ginsberg and Landauer (4). The subject has an important application in superficial therapy, where common practice calls for the use of large fields at a short focal skin distance. The distribution problem is especially important because the use of shock-proof tubes and equipment has made it more difficult to change from one type of tube to another. With non-shock-proof tubes it was a simple matter to remove the diagnostic tube from the lead glass bowl and substitute the therapy tube. A study of distribution and field coverage may have a useful application in the planning of protection and the design of equipment, especially in fluoroscopy. Also, to a lesser degree, it may be of value in diagnostic applications, although the distances us...

Quality, Area, and Distance Relationship for D5, D10, and D15. II

In the preceding article the authors have presented curves and tables showing the relationship between depth intensities and the three other factors, quality of radiation, treatment area, and focal skin distance, and have demonstrated a method of transposing a known depth dose for one set of conditions to any other desired set of conditions providing both are within the following range: 0.9 to 9.0 mm. copper H.V.L., 25 to 400 sq. cm. treatment area, 50 to 100 cm. focal skin distance. It is intended here to consider depth doses associated with the lower voltages, including the qualities from 2 to 12 mm. aluminum H.V.L., areas from 10 to 200 sq. cm., and distances from 20 to 60 cm. Thus the quality range considered here is an extension of that considered in the preceding paper, where the lower limit of quality was 0.9 mm. copper H.V.L., which, expressed in terms of aluminum, is 12.1 mm. aluminum H.V.L. The data necessary to make this extension were obtained during the last several years by measurements with...

A Survey of Depth Dose Data

A survey has been made of published depth dose and backscatter data. The influence of (1) focal-skin distance, (2) quality of radiation expressed as half-value layer in copper, and (3) area of field on percentage depth dose has been investigated. In the light of this analysis published data have been corrected to standard radiation conditions, and mean values obtained. Tables have been drawn up giving the percentage depth dose for qualities of radiation from 1·0 to 5·0 mm. copper half-value layer at depths to 20 cm. for field areas up to 400 cm.2 and focal-skin distances from 40 to 100 cm. A less comprehensive survey has been made of radiations up to 17 mm. copper half-value layer, the results of which are embodied in curves and tables. Mean values of percentage surface backscatter have been derived from the literature for field areas up to 400 cm.2 for qualities up to 14 mm. copper half-value layer. Information is also given whereby one may derive half-value layers in copper from the radiation conditions.

The Evolution of Dosimeters in Roentgen Ray Therapy

The First Roentgen Ray Dosimeter The first estimates of quality and quantity of roentgen rays were made by observations of the density of the shadows cast by the bones and flesh of the operator's hand upon fluoroscopic screens and photographic plates (1896). The injuries which resulted from this procedure led to the use of the bones of skeleton hands imbedded in wax as a substitute for living hands. This contraption was called the “;osteoscope.” It was the first roentgen dosimeter. Arithmetic Computation of Roentgen Ray Dose Radiologists soon learned that the roentgen ray skin dose depended principally upon four technical factors: Voltage at the tube which was measured by inches of spark gap, current through the tube measured in milliamperes, focal skin distance in inches, and time of application. These factors then were arranged in formulae to calculate skin dosage with unfiltered and later with filtered roentgen rays for different treatment conditions (1, 2, 3). The pattern of a formula in general use w...

The construction of a continuously evacuated experimental X-ray tube with a transmission target

The description is given of a demountable, continuously evacuated experimental X-ray tube with a transmission target, in which modifications in design of anode, filament, and filament hood can be made. The pumping plant, vacuum technique and electrical circuits are described. Operating at 35 kV to 40 kV and 12 mA with a focal skin distance of 5 cms and a circular field of 5 cm diameter, the tube has an output of 200 r. per minute. It is held in an earthed insulator, a photograph of which is given.

Calculation of Energy Absorbed in Irradiated Tissue

IN a previous letter1, a method was outlined for the volume integration of dosage for X- and gamma-ray beams of radiation. The result of the calculations for a beam of X-rays passing through a ‘water phantom’ from a 200 kv. Metropolitan-Vickers X-ray tube filtered through 1 mm. copper and 1 mm. aluminium at a focal skin distance of 40 cm. showed the integrated dosage R, to be where A is the area of the applicator at the skin surface and r the maximum skin dose for a large applicator (20 cm. × 15 cm.).

A Physical Investigation of the Radiation from a Low-voltage X-ray Tube (Cautery Technique)

A study has been made of the physical properties of the radiation produced at 44 kV by the “Metalix” therapy apparatus. Absorption measurements in aluminium, water, and certain other solutions are described. The first half-value layer of the unfiltered radiation is found to be 0·30 mm. Al, corresponding to an equivalent wavelength of 840 X.U. Central axis depth-dose curves for the unfiltered and filtered radiation at various focal-skin distances are given, together with some complete isodose curves. A condenser chamber for the measurement of the dosage-rate in air which may be used with standard Victoreen condenser dosemeter is described. A surface dosage rate of 7,610 r/min. is obtained with the unfiltered radiation at the shortest focal-skin distance (2·0 cm.), but the penetration is very small, 4 mm. of water being sufficient to reduce the dosage-rate to one half of its surface value. Owing to the heavy absorption of the water the amount of scattered radiation outside the geometrical edge of the beam is small. Measurements of the stray radiation around the tube are described. The results of other workers are discussed, and, finally, a description is given of an attempt to determine the energy distribution in the spectrum of the radiation by an analysis of the absorption curve in aluminium.

Clinical Aspects of Supervoltage Roentgen Therapy in Cancer

THE supervoltage apparatus used by our group since 1933 has been described on several previous occasions. Essentially, the tube is a copy of one built by Professor C. C. Lauritsen at the California Institute of Technology. The valve tube transformer circuit is of the Villard type. The voltage used is 525 to 550 kv. The focal skin distance is 52 cm. and the filtration equivalent to 0.8 mm. lead (half value layer 0.56 mm. lead and 2.8 cm. aluminum). The current through the tube is approximately 3.2 ma., the output being 15 r per minute. The effective wave length is 0.044 Ångstrom (Fig. 1). In the treatment of deep-seated malignancies, it has been shown in the past that, as voltages have been increased, the five-year cures have been increased. Changing from 130 to 140 kv. to 200 kv. was a definite advance. With the advent of supervoltages, in the realm of 500 kv. or more, it was hoped that results would be markedly improved, as absorption of greater intensities in the depths might be expected. It was thought that larger total dosages might be administered, as there would be less skin injury with the supervoltages, due to a decrease in back-scatter and an increase in forward-scatter. A comparison between patients treated in the past with 200 kv. and those treated with supervoltage in more recent years, is almost impossible because other factors beside voltage have been variable. The mode of application of roentgen therapy, fractionation of dosage, time factor of individual applications, and total elapsed time of the entire series have all been altered. These are all very important factors and each may be just as important as the factor of voltage. A description of some of the various lesions treated by means of supervoltage will be given. Carcinoma of the Inner Surface of the Cheek.—This is usually of low grade malignancy and quite resistant to irradiation. We selected a few specimen cases of these conditions for treatment by fractionated supervoltage alone. As these lesions were rather near the surface, adequate dosage could have been secured by lower voltages. The tumor in these cases received about 80 per cent of the surface dosage (as measured by the Lauritsen chamber). Table I shows the method of treatment in these cases, with dosage and results. We realize that fractionated dosage with the ordinary 200 kv. might have accomplished the same result with proper filtration and prolongation of dosage (although, personally, we have never been able to secure similar regressions with 200 kv.). The total dosage of supervoltage in these patients was not large. The majority received a total of about 3,000 r (air), given at the rate of 150 r daily. In some cases the treatment was completed without definite erythema. In none of these cases have there been any late skin changes, telangiectasia or fibrosis, and, in all, the texture of the skin at the present time appears perfectly normal. Carcinoma of the Esophagus.

Further Experiments with X-ray Tubes for High Voltages up to One Million Volts

An improved, sealed-off, one million-volt “Metalix” X-ray tube is described. With a wall thickness of 2·5 mm. Cu, the output of this tube at 800 kV constant potential, in a direction perpendicular to the beam of electrons, has been found to be approximately 14 r/min. for 1 metre focal-skin distance and 1 mA tube current. Half-value layers up to 10·3 mm. Cu and 4·2 mm. Pb were measured. The amount of back scatter, the percentage depth dose at 10 cm. below the surface and the exit dose at 20 cm., have been measured under various conditions with a waterphantom. At one million volts and 1 mA approximately 90 mm. lead is required in order to reduce the primary radiation, at a focus skin distance of 1 metre, to the so-called tolerance dose (10−5 r/sec.). The scattered radiation, however, emerging from a paraffin block struck by the unfiltered primary beam, can readily be absorbed by a few mm. lead. Finally, the output, in the direction of the beam of primary electrons, was measured. At 800 kV pulsating tension,...

An Optical Device for the Accurate Alignment of an X-ray Beam

In the treatment of patients by X rays it is desirable to know the precise location of the beam at the exit, as well as at the incident surface. This knowledge enables much more exact positioning of the patient to be made and allows of the use of either natural or artifical surface markings in the alignment. As an example, we may quote the necessity for accurate direction and position of the beam if strip fields are to be used effectively in the treatment of an œsophagus. The construction of any mechanical apparatus for defining the position of the beam in space is not easy owing to the large focal skin distances employed in high-voltage therapy, and the consequent difficulty in designing a light and rigid structure. We have recently designed and made use of the following simple device which has been found to be eminently practical and to increase considerably the ease and accuracy of setting up the patient. A brass tube (Fig. 1), 16 in. long, is fitted with a stop A at one end, having a ¼ in. diameter ce...

Measurements of Low-Voltage X Rays (Chaoul Technique)

An account is given of measurements of X rays produced at 60 K.V. and used at small (5 cm. and 3 cm.) focal skin distances. A new type of distribution dosage-rate meter is described, suitable for such work. Spectroscopic and absorption measurements of “quality” give an average wavelength of about 0·32 A. The X-ray output of such apparatus is such that at 5 cm. f.s.d. the dosage rate is about 25 r/min. ma. Investigations are described of back-scatter, percentage depth dose and complete distribution of radiation. The results of measurements of stray radiations are also recorded. Some theoretical possibilities of mathematical study of the dosage distribution problem are indicated.

Observations on the Use of 800,000-volt Roentgen Rays in Radiation Therapy

IN the beginning of 1933, an 800,000-volt peak transformer and a cascaded Coolidge tube, were added to the equipment of radium and 200,000 volt-transformers and oil-cooled, shockproof Coolidge tubes in the department of radiation therapy at the Mercy Hospital, Chicago. I take the liberty to record the observations made with the ultra-short wave roentgen ray in the treatment of malignant tumors. A thorough efficiency in the operation of the new installation was soon acquired, the greatest difficulty being in the operation of the two-section tube. However, a new and improved tube was installed about Sept. 1, 1933. Since then, there has not occurred a single breakdown due to puncture or leakage, though the tube, at the present writing, has registered more than 2,000 hours at a 10-ma. load. The transformer and cascaded tube with water-cooling and oil vacuum pumps are as easily operated as a 200,000-volt transformer and oil-cooled gas-free tubes. The observations may be divided into those of a physical nature and biologic reactions, observed clinically in the tumors and in the patients. The physical factors should designate the quality of the radiation, the relative distribution of the radiation intensities in the tissues, and the quantity or radiation dose absorbed in the body. The biologic factors comprise the palliative effects—relief from pain, bleeding, and infection, the state of the blood, and the arrest in growth and resorption of the tumor tissue. The radiation dose is the product of quality or intensity and the time duration of application. It may be expressed in a biologic or physical magnitude. The former may be denoted as the erythema skin dose, the threshold skin dose of Failla and Quimby, or the tolerance skin dose of Schmitz. The ratio between these biologic doses is as 150 : 100 : 200. The physical unit of the radiation dose is the international r, which should be determined by standardized dose meters. In denoting the dose in either the biologic or physical measurements, the following factors should always be stated: the voltage or wave length; the half value layer; the type of current and transformer: the type of tube, whether water- or oil-cooled, or whether made of thin glass or pyrex glass walls; the filter, and its position within the radiation beam; the focus-skin distance; the size, location, and number of fields; the milli-ampere load, and the number of r applied to each field. Thus, one may be able to duplicate the technic either for experimental or therapeutic purposes. It is necessary also to describe the diameters of the body portion which contains the growth and the size of the growth, with its relation to the body surfaces on which the fields are placed. In this way the topographical relations are obtained which should facilitate the planning of a correct technic of treatment.

Irradiation and Electrosurgery in the Management of Carcinoma of The Urinary Bladder

Introduction THE treatment of carcinoma of the urinary bladder with radium, roentgen rays, and electrosurgery is not new. Considerable experience along these lines during the past 17 years has taught me that it is generally best to begin treatment with thorough external roentgen irradiation, followed promptly with the indicated surgical procedure and irradiation within the bladder with radium element. Treatment is completed with active post-operative external roentgen irradiation. Preliminary or Pre-operative Roentgen Therapy.—Regardless of the type or location of the carcinoma within the bladder, treatment almost always begins with thorough roentgen irradiation. These treatments are so planned that they will be completed within two weeks' time, with not more than eight to ten days actually consumed in the treatments. The number of ports of entry varies from four to seven according to the size of the patient's pelvis. They are taken from the lower abdominal region, the sacro-gluteal region, from the lateral aspects of the pelvis, and from the perineum. Generally in this two weeks of preliminary roentgen treatment each port is treated twice with rays generated by valve tube machines with condensers and constant potential at 190,000 volts, the focus-skin distance being 50 cm., the filter 0.75 mm. Cu plus 3 mm. Al, 37 per cent of such rays reaching a depth of 10 centimeters. The number of ports of entry, taken together with the time duration of the treatment over each, is so planned that not less than 750 r units dosage will actually be delivered to the diseased bladder by the total irradiation from all ports. The second series of pre-operative roentgen-ray treatments is given in exactly the same way, thus bringing the total dosage up to 1,500 r units. Clinical Results of Pre-operative Irradiation.—Frequently following preliminary roentgen irradiation there is marked improvement in the patient's general condition, especially in cases suffering with severe hemorrhage and secondary infection. Bleeding is controlled, often within 24 hours after treatment is begun. Aside from the benefit that the patient experiences from this alone, is the fact that further cystoscopic studies can be made much more valuable because the vision of the examiner is not clouded with blood, and he is, therefore, able better to define the extent of the involvement. Urinary sediment, pus cells, and débris, i.e., products of a chronic infection, lessen and in some cases entirely disappear. Because of this the temperature is lowered and will sometimes reach normal within a few days or before preliminary treatment is completed. In a considerable percentage of cases there will appear multiple implantations in the wall of the bladder following operation.

Cancers Produced in Rabbits by the Action of X Rays Upon Inflammatory Lesions

Several rabbits were allowed to survive from the groups in which we had produced abscesses by subcutaneous injection of streptobacillus caviae and which were subsequently treated with X rays. After a period of about a year had elapsed, sarcomas were found to have developed in these rabbits in those parts which had previously undergone treatment. The conditions of the experiments, undertaken in collaboration with Vinzent, have been reported in two communications with summaries of observations on three sarcomas of the thigh (rabbits Nos. D46, D43, and D45). Since then two new cases have occurred. Rabbit No. D83. October 10, 1927: injection of culture beneath skin of thigh. October 22: irradiation of inoculated region; focal-skin distance 30 cm., filter 31 mm. of aluminium; tension 160 KV; intensity 6 milliamperes; time 12 minutes; dose 915 r. March 22, 1928: persistence of deep-seated abscess; second irradiation under same conditions; time 6 minutes; dose 455 r. March 19, 1929: third irradiation following ap...