John P. Kelley

Influence of Cable Length on Dose Rate and Half-Value Layer in Diagnostic X-Ray Prooedures

Interest in the patient dose incurred in diagnostic fluoroscopy and radiography, together with a tendency toward certain changes in technic and equipment, led to the belief that some investigation into the effect of these changes on the patient dose was justified. The changes in mind are the tendency toward reduced tube current and higher voltages in fluoroscopy and the use of tube-supporting structures requiring longer shock-proof cables between the x-ray tube and the high-voltage generator. The assumption is often made that a reduction in tube current will bring about a directly proportional reduction in patient dose. This assumption may not be valid at the low currents used in fluoroscopic procedures, since the electrical capacity of shock-proof cables acts as a filter, having a tendency to alter the waveform to the x-ray tube in the direction of constant potential, an effect which is related to the length of the cable, the tube current, and the kilovoltage used. Even before the use of shock-proof cabl...

Broad Beam Attenuation in Concrete for 50 to 300-Kvp X-Rays and in Lead for 300-Kvp X-Rays

Broad Beam Attenuation Data in Concrete, 50 to 300 kvp For x-ray installations up to 400 kvp it has been the general practice to use lead as the shielding material; at the lower voltages lead is a very effective barrier, since attenuation is largely due to photoelectric absorption. With the increased use of concrete for structural purposes in walls, floors, and ceilings of new buildings, it may be desirable to use concrete rather than lead as the barrier material. In existing structures, concrete may provide all or part of the necessary protection. Attenuation data for lead have been generally available. For concrete, attenuation data have been available for the higher voltages but not generally for low voltages. The reason for this lack of information in the lower voltage range lies in the fact that the data must be obtained with large fields (at least 3 feet in diameter) at the barrier. Large sheets of concrete of thin section are not easily made and do not lend themselves to the repeated handling requi...Broad Beam Attenuation Data in Concrete, 50 to 300 kvp For x-ray installations up to 400 kvp it has been the general practice to use lead as the shielding material; at the lower voltages lead is a very effective barrier, since attenuation is largely due to photoelectric absorption. With the increased use of concrete for structural purposes in walls, floors, and ceilings of new buildings, it may be desirable to use concrete rather than lead as the barrier material. In existing structures, concrete may provide all or part of the necessary protection. Attenuation data for lead have been generally available. For concrete, attenuation data have been available for the higher voltages but not generally for low voltages. The reason for this lack of information in the lower voltage range lies in the fact that the data must be obtained with large fields (at least 3 feet in diameter) at the barrier. Large sheets of concrete of thin section are not easily made and do not lend themselves to the repeated handling requi...

Conventional Building Materials as Protective Radiation Barriers

The assumtion is often made in x-ray protection planning that conventional building materials provide no shielding. The exception is concrete which, due to wide use, is accepted by everyone as a satisfactory shield. It is not at all unusual to encounter instances where any material other than lead or concrete is considered unacceptable for wall construction without the addition of a very thin sheet of lead. All materials provide some protection, however, and it would seem advisable to take this fact into consideration in shielding calculations. Some types of construction involve materials of a heterogeneous nature and the problem of calculating shielding data under such circumstances does not seem to be a simple one. The only solution apparent to us was actually to construct some typical wall sections and make transmission measurements. The x-ray source used in these investigations consisted of a resonant transformer operating at a nominal frequency of 1,200 cycles, and a grounded anode, beryllium window ...The assumtion is often made in x-ray protection planning that conventional building materials provide no shielding. The exception is concrete which, due to wide use, is accepted by everyone as a satisfactory shield. It is not at all unusual to encounter instances where any material other than lead or concrete is considered unacceptable for wall construction without the addition of a very thin sheet of lead. All materials provide some protection, however, and it would seem advisable to take this fact into consideration in shielding calculations. Some types of construction involve materials of a heterogeneous nature and the problem of calculating shielding data under such circumstances does not seem to be a simple one. The only solution apparent to us was actually to construct some typical wall sections and make transmission measurements. The x-ray source used in these investigations consisted of a resonant transformer operating at a nominal frequency of 1,200 cycles, and a grounded anode, beryllium window ...

Physical Characteristics of the Radiations From 2-Pulse, 12-Pulse, and 1,000-Pulse X-Ray Equipment

Exposure data, attenuation data, basic depth dose data, and radiographs obtained using single-phase, three-phase, and battery-powered systems are presented. The information presented is typical of a single three-phase system. It is presumed that such a study performed on other three-phase, twelve-pulse systems would lead to different numbers, but the basic concepts presented here would probably be of a comparable nature. This study presents the areas of interest that should be considered in any similar work on other systems.

Scattered Radiation in a Phantom from Diagnostic Quality Radiation

INFORMATION on the x-ray dose outside the defined field has long been of interest to the radiation therapist and to the hospital physicist working with him; this was provided in therapy isodose curves usually to a level of 5 per cent of the surface dose. As the patient dose in diagnostic radilogy came under observation, the dose to tissue outside the irradiated field was of interest. Therapy isodose charts were not of much help, since the scattered radiation had been measured at higher energies and only in the areas immediately adjacent to the irradiated field. The measurement of exposure rates outside and remote from the diagnostic field is difficult because of the low exposure rates. In the literature there are many reports on the dose to specific tissues under a stated set of conditions. For evaluation of equipment and technical procedures, we had need for information that would enable us to arrive at some reasonable assessment of the exposure outside the defined field over a wide range of conditions. ...

Determination of Half-Value Layer

In the determination of half-value layer, the geometry involved is usually described as “good” geometry or “poor” geometry. In general, these terms have reference to measurements made under narrow-beam and broad-beam conditions. Such conditions have not been too well explored. Narrow-beam determinations can always be made under laboratory conditions, but such conditions may not lend themselves to measurement technics in a working therapy installation, where restrictions may be imposed by equipment limitations on filters and diaphragms. The object of our investigation is the derivation of information that might be used to correct a half-value layer determination made under generally available conditions to some common denominator that could be described as narrow-beam conditions. We are presenting here the first phase of a study, the full report of which will cover the variables involved and their influence on the resulting determination. It has been found, as had been expected, that the irradiated area of...

Isodose Curves for Superficial Therapy

Isodose curves for the low voltages and small fields used in superficial x-ray therapy have been the subject of few publications. Excellent central-axis depth-dose data are available as a result of work by Andrews and Braestrup, by Braestrup, and by Johns, Epp, and Fedoruk. In 1941, Lamerton published isodose curves for four widely used fields at a single half-value layer, and in 1943 Mayneord made available additional material at two lower voltages. Having recently completed work on isodose curves for the small fields used in intracavitary therapy, the authors considered it worthwhile to explore the fields and radiation qualities usually associated with superficial therapy. It was thought that some significant information might be developed regarding the radiation at the edges of such fields and that this might be of value in correlating the size of the lesion and the size of field required for an adequate dose. Instruments and Equipment In the study covering intracavitary fields, a modified Royal Cancer...

The deterioration of x-ray fluoroscopic screens. Final report.

The results of a five-year study on the deterioration of x-ray fluoroscopic screens are presented. Findings indicate that x-ray exposure did not significantly deteriorate the screens and that fluorescent and ultraviolet light did cause serious deterioration. Screens should be covered when not in use.

LEAKAGE RADIATION THROUGH LEAD GLASS IN FLUOROSCOPIC SCREEN ASSEMBLIES.

As increased kilovoltages came into use for fluoroscopic examinations, the National Committee on Radiation Protection and Measurements (NCRPM) found it necessary to increase the recommended lead equivalent of lead glass over fluoroscopic screens. More recently, the International Commission on Radiological Protection (ICRP) has been reviewing maximum permissible doses to the lens of the eye. NCRPM Handbook 59 issued in 1954 recommended a basic permissible dose of 300 mr per week to the lens and an assumed average depth of 3 mm. for purposes of calculation. In early 1957, the NCRPM issued an addendum to Handbook 59 in which it was stated that the accumulated dose to the lens of the eye “shall not be limited by the dose to the head and trunk.” The dose to the head and trunk was covered under the clause on doses to external organs which were listed as whole-body, head and trunk, active blood-forming organs or gonads. The maximum permissible dose to these organs accumulated to any age “shall not exceed 5 Rem t...As increased kilovoltages came into use for fluoroscopic examinations, the National Committee on Radiation Protection and Measurements (NCRPM) found it necessary to increase the recommended lead equivalent of lead glass over fluoroscopic screens. More recently, the International Commission on Radiological Protection (ICRP) has been reviewing maximum permissible doses to the lens of the eye. NCRPM Handbook 59 issued in 1954 recommended a basic permissible dose of 300 mr per week to the lens and an assumed average depth of 3 mm. for purposes of calculation. In early 1957, the NCRPM issued an addendum to Handbook 59 in which it was stated that the accumulated dose to the lens of the eye “shall not be limited by the dose to the head and trunk.” The dose to the head and trunk was covered under the clause on doses to external organs which were listed as whole-body, head and trunk, active blood-forming organs or gonads. The maximum permissible dose to these organs accumulated to any age “shall not exceed 5 Rem t...