Measurement of dosimetric parameters for the Alpha-Omega high-dose-rate Iridium-192 source.

Thermoluminescent (TLD) measurements of dose-rate constant, anisotropy function, and radial dose function are reported for the Alpha-Omega high dose rate (HDR) Iridium-192 ((192)Ir) source, which has been available since 1998 for use in the MicroSelectron HDR afterloader manufactured by the Nucletron Corporation. Measurement results are compared with published or available Monte Carlo calculations for both sources. They are found in good agreement, and, within experimental accuracy, no difference is seen in the dosimetric parameters of both sources.

Changing face and different countenances of prostate cancer: racial and geographic differences in prostate-specific antigen (PSA), stage, and grade trends in the PSA era.

The purpose of this investigation was to examine changes in pretreatment prostate-specific antigen (PSA), stage, and grade over the past decade as a function of race and geographic region. A multiinstitutional database representing 6,790 patients (1,417 African-American, 5,373 white) diagnosed with nonmetastatic prostate cancer between 1988 and 1997 was constructed. PSA, stage, and grade data were tabulated by calendar year and region, and time trend analyses based on race and region were performed.

Determination of the tissue attenuation factor along two major axes of a high dose rate (HDR) 192Ir source.

Quantitative information on photon scattering around brachytherapy sources is needed to develop dose calculation formalisms capable of predicting dosimetric parameters with minimal empiricism. Photon absorption and scatter around brachytherapy sources can be characterized using the tissue attenuation factor, defined as the ratio of dose in water to water kerma in free space. In this study, the tissue attenuation factor along two major axes of a high dose rate (HDR) 192Ir source was determined by TLD measurements and MCNP Monte Carlo calculations.

Validity of the interval method for the determination of the anisotropy factor of high dose rate 192Ir sources.

Purpose: This study investigates the validity of the interval method to determine the anisotropy factors of high dose rate (HDR) 192Ir sources.

Methods And Materials: A calculation method, which is one of the various numerical implementations of the Sievert integral and known as the interval method, is applied to determine the anisotropy factors of a HDR 192Ir source. Calculated results from r = 1 cm to 10 cm are compared to published data.

Evaluation of a commercial three-dimensional electron pencil beam algorithm.

Results from beta testing of a commercially available three-dimensional electron pencil beam algorithm (CMS FOCUS, Computerized Medical Systems, Inc. St. Louis, MO) are reported.

Effect of anisotropy corrections on the dynamic dose calculations in high dose rate (HDR) brachytherapy.

An analytic formalism utilizing a convolution technique is presented for the incorporation of anisotropy corrections into the dynamic (or transit) dose calculations in high dose rate (HDR) brachytherapy. A simple numerical implementation of the suggested formalism is also presented. Two calculational examples are provided in order to show some effects of anisotropy corrections on the dynamic dose calculations.

Anisotropy measurements of a high dose rate Ir-192 source in air and in polystyrene.

Anisotropy measurements in air and in polystyrene were performed for a Nucletron microSelectron 10 Ci Ir-192 source. TLD rods of similar sensitivity (+/- 3%) were placed on a semicircle around the source center which had been precisely localized by either radiographic means or direct measurement. The anisotropy, expressed as a ratio of TLD reading at a given angle relative to the longitudinal source axis, over the reading at 90 degrees, was measured for distances between 1 and 10 cm from the source center.

Method for reducing scatter radiation dose to the contralateral breast during tangential breast irradiation therapy.

Purpose: To reduce scatter dose to the contralateral breast during tangential breast irradiation therapy.

Materials And Methods: The authors used a 4-mm-thick commercially available vinyl-coated flexible lead shield that contains a compound of vinyl resin and lead powder of 1-mm-equivalent lead density. Contralateral scatter dose was measured at 5 cm outside the geometric field edge and along the field axis, with and without use of block trays and different wedges.

Craniospinal axis irradiation: an improved electron technique for irradiation of the spinal axis.

In this work we review the dosimetric features of craniospinal axis irradiation in the areas of matching cranial and spinal fields, with reference to the normal structures within the spinal field. The implications of the use of photon or electron modalities for the spinal port were evaluated. A novel method of matching the cranial photon and the spinal electron fields involving a computer-aided junction design is presented.

Fractionated total body irradiation: some radiobiological considerations.

Fractionated total body irradiation (TBI), as conditioning regimen for bone marrow transplantation in the treatment of non-lymphocytic leukaemia, has proved to be less toxic than single fraction TBI. However, higher relapse rates are reported. The linear quadratic (LQ) model has been applied to calculate equivalent total therapeutic doses as well as equivalent tolerance doses for fractionated TBI.

Therapeutic gain with hyperfractionation in prophylactic cranial irradiation of children with acute lymphoblastic leukemia.

IQ deterioration after prophylactic cranial irradiation is a dreaded complication for children with acute lymphoblastic leukemia. Alternate treatment schemes are needed that achieve comparable tumor control, but avoid such long-term complication. To this end, a hyperfractionated treatment scheme is proposed.

Hyperfractionated, twice-a-day, radiotherapy may decrease IQ deterioration due to prophylactic cranial irradiation in childhood acute lymphoblastic leukemia: a radiobiological analysis.

High cure rates in childhood acute lymphoblastic leukemia (ALL) are being achieved with aggressive systemic chemotherapy and treatment to sanctuary sites including prophylactic cranial irradiation. However, IQ deterioration is a dreaded complication of prophylactic cranial irradiation. IQ deterioration is a late sequela.

Dosimetry of shaped electron fields using a radial integration method.

The feasibility of an analytical approach to calculate monitor units for shaped electron fields is investigated. A radial integration method is used to calculate the dose at prescription depth from an average output factor and an average depth dose. This concept, as implemented in a commercial planning system, has been tested on various arbitrary fields, and 66 shaped electron fields clinically used for head and neck, chestwall, internal mammary, breast boost, and skin lesions.

Equivalent total doses for different fractionation schemes, based on the linear quadratic model.

A majority of patients receiving radical radiation therapy are treated with 1.8-2.0-Gy fractions, a dose that has evolved from clinical experience.

Introducing a computerized record and verify system: its impact on the reduction of treatment errors.

A survey of treatment errors has been conducted over a period of several months before and after the introduction of a CMS computerized record and verify system for radiation treatments administered on a Varian CL-1800 accelerator. It was found that treatment errors could be reduced considerably. However, some errors were also caused by wrong data entry into the system.

Exacerbation of psoriasis after megavoltage irradiation. The Koebner phenomenon.

This is a case report of a patient with a known history of psoriasis who experienced an exacerbation after palliative treatment with high-energy irradiation. A discussion of the radiobiology is presented.

Monitoring the radiation dose to a multiprogrammable pacemaker during radical radiation therapy: a case report.

Multiprogrammable pacemakers, using complimentary metaloxide semiconductor (CMOS) circuitry, may fail during radiation therapy. We report about a patient who received 6,400 cGy for unresectable carcinoma of the left lung. In supine treatment position, arms raised above the head, the pacemaker was outside the treated area by a margin of at least 1 cm, shielded by cerrobend blocking mounted on a tray.

Scatter dose from tangential breast irradiation to the uninvolved breast.

Thermoluminescent dosimeters (TLDs) were used to measure scatter radiation to the uninvolved breast in 30 patients who received tangential breast or chest-wall radiation with a technique in which the deep edges of the tangential fields were aligned. In most patients, measurements were made during the 1st week of radiation therapy, after port radiographs were obtained to ensure proper field position and accurate alignment of the posterior tangential field edges. Phantom measurements were made simultaneously with TLD measurements to systematically assess the scatter dose as a function of the wedging, number of fields, type of accelerator, beam energy, and bolus used in each treatment.

Using different sets of wedges: clinical applications, dosimetry and safety interlocks.

Each accelerator is customarily supplied with one set of wedges, typically for a maximum field width of 15 cm across the wedge slope. Clinically, however, the need arises at times for larger wedged fields. Independent jaws may require wedges which are mounted at 90 degrees from a standard set, and some half-field treatment techniques may benefit from half-field wedges.

Impact of CT information on the treatment planning for lung tumors.

With CT information available today, the prevailing, though strong, argument for not applying lung corrections is that all clinical experience gathered so far applies to doses that were prescribed for uniform density throughout the treated volume. To ease the transition from not correcting, to the state of accounting for increased lung transmission, we have planned 10 patients: (a) in the conventional way with a wire contour obtained at simulation; target volume and critical structures were drawn in by the physician utilizing information gathered from diagnostic CT scans and X-ray films; no lung correction was applied for treatment planning. (b) For the same patients, a CT scan was obtained in treatment position and the target volume was outlined on the CT film utilizing the same information as in (a); a relative lung density of 0.

Brachytherapy implants with differently spaced Ir-192 seeds: a dosimetric study.

Brachytherapy implantations traditionally have been carried out with continuous line sources of radium. With the popularity of afterloading implantations, iridium-192 seeds in plastic ribbons have replaced radium in the United States, although continuous sources, such as iridium wires, are widely used in Europe. The authors analyzed the impact of the use of noncontinuous sources in brachytherapy implants.

The neutron dose and energy spectrum outside a 20-MV accelerator treatment room.

A maze design is discussed for a Therac 20 linear accelerator (manufactured by Atomic Energy of Canada, Ltd.) which reduces the flux of neutrons at the door to permissible levels in controlled areas. The L-shaped design allows for a relatively light door at the end of the maze, consisting of 5.

Spinal axis irradiation with electrons: measurements of attenuation by the spinal processes.

Electrons may be used beneficially for spinal axis irradiation in medulloblastoma children to avoid some of the long-term sequelae induced by megavoltage photons. However, the attenuation by the intervening bone ought to be considered. Three-dimensional computer treatment planning with inhomogeneity correction for electron beams is not yet generally available, and alternate methods are needed to evaluate the attenuation by the complex bony structure of the spine.

Irradiation of the thoracic esophagus. Prone versus supine treatment positions.

A vast majority of patients with esophageal cancer receive radiation therapy for cure or palliation. Because of the close anatomic proximity of the esophagus to the spinal cord, and unusually long fields used in the irradiation of esophageal cancer, staying within the spinal cord tolerance is crucial. The present investigation shows how this can be achieved by delivering the radiation in prone position.