Head-scatter factors in blocked photon fields.

The behavior of the head-scatter factor in shielded 6 and 25 MV X-ray beams from a Philips SL25 linear accelerator was investigated by measuring incident fluences by direct (in-air) and indirect (in-phantom) methods. It was found that perturbations in head-scatter produced by shielding blocks arranged to define a slit-shaped field are considerably less than 1% in unwedged beams, even when 80% of a 20 x 20 cm2 field is shielded. The results are independent of beam energy and orientation of the slit with respect to the collimator jaws.

Equivalent squares of irregular photon fields.

The tables of equivalent fields published by the British Journal of Radiology (BJR) are intended for calculation of depth-dose functions in rectangular photon fields. We have investigated the validity of the equivalent-field concept for fields of arbitrary shape over a range of photon energies, field sizes and depths. We show that the empirical scatter-radius function (Day function) used to generate the equivalent-field tables is a good approximation to the average over energy of normalized scatter-air ratios extracted from BJR beam data for depths up to 10 cm.

Total skin electron irradiation: efficacy in early mycosis fungoides.

The rare, indolent, but lethal malignancy, mycosis fungoides (MF), is amenable to durable remissions if treated topically at an early stage with nitrogen mustard, PUVA, or radiotherapy. A modification of conventional therapeutic irradiation which utilizes electron beams rather than photons, has been in use since 1951. This method, termed total skin electron irradiation (TSEI), has achieved consistently good CR rates (95-100%) at a variety of centres in the U.

Head-scatter factors in rectangular photon fields.

Head-scatter factors were measured for a range of field sizes of rectangular shape from a linear accelerator that provides 6 and 25 MV photon beams. For a given field length and width, exchange of the inner and outer collimator pairs produces differences in the head-scatter factor of up to about 2% and 3% in open and wedged fields, respectively. Dependence on elongation deviates by up to 2% from that given by the equivalent squares.

Head-scatter factors and effective x-ray source positions in a 25-MV linear accelerator.

The behavior of the effective source position and the correction factor associated with the collimator opening (head-scatter factor) were investigated for the 6- and 25-MV x-ray beams of a linear accelerator. The primary photon fluence was measured in air for square field sizes from 5 x 5 cm to 40 x 40 cm at distances from the nominal source of 80 to 140 cm, for open and wedged fields (wedge angle 60 deg). An inverse-square analysis shows that, for open fields, the effective source position of the accelerator is about the same (approximately 1 cm downstream) at 6 and 25 MV, for all field sizes.

Total-skin electron irradiation for cutaneous T-cell lymphoma: the Northern Israel Oncology Center experience.

Total-skin electron irradiation (TSEI) is effective and frequently used in the treatment of cutaneous T-cell lymphoma. A treatment technique has been developed at our center, using the Philips SL 75/10 linear accelerator. In our method, the patient is irradiated in a recumbent position by five pairs of uncollimated electron beams at a source to skin distance of 150 cm.

Radiation qualities of x-ray beams in cooperative clinical trials.

X-ray beams are usually described by "MV" numbers which represent accelerating potentials (AP) and approximations to the maximum energies in the photon spectra. However, these numbers do not uniquely specify the properties of the beams. Current high energy photon dosimetry protocols specify radiation quality in terms of a measured ionization ratio which is equivalent to the ratio of the tissue-maximum ratios at depths 10 cm and 20 cm, for field size 10 cm X 10 cm [TMR)20(10].

Field matching considerations in craniospinal irradiation.

Radiotherapy of the craniospinal axis in leukemia and medulloblastoma patients usually involves parallel-opposed lateral cranial fields adjacent and orthogonal to a posterior spinal field. Most current treatment protocols require rotation of the cranial fields to compensate for the divergence of the spinal field such that the adjacent field edges abut along the match line in the mid-saggital plane. Some departments introduce gaps up to 1-2 cm wide between the matched fields out of concern for overdosing the spinal cord.

Experience in the treatment of localized carcinoma of the prostate by definitive external irradiation.

One hundred and sixteen patients with stages A2, B, and C histologically proven adenocarcinoma of the prostate were treated by definitive radiation. They received first whole pelvic irradiation, 46 Gy in 23 treatments, followed by a prostatic "boost" of 20 Gy in 10 fractions. Five-year survival rates varied between 39 and 84%.

The Clatterbridge high-energy neutron facility: dosimetry intercomparisons.

Dosimetry intercomparisons have been performed between the Clatterbridge high-energy neutron facility and the following institutions, all employing beams with similar neutron energies: Université Catholique de Louvain, Belgium; University of Washington, Seattle, USA; MD Anderson Hospital, Houston, USA; and Fermi National Accelerator Laboratory, Batavia, USA. The purpose of the intercomparison was to provide a basis for the exchange of dose-response data and to facilitate the involvement of Clatterbridge in collaborative clinical trials. Tissue-equivalent ionization chambers were used by the participants in each intercomparison to compare measurements of total (neutron plus gamma) absorbed dose in the host institution's neutron beam, following calibration of the chambers in a reference photon beam.

A comparison of commercial treatment planning systems when calculating dose under shielding blocks.

Several commercial computerized treatment planning systems were compared when calculating dose under shielding blocks in soft tissue and lung tissue. A test case was studied in which a water-equivalent phantom containing a removable cork insert was exposed to 60Co radiation with and without a lead block in the beam. For simplicity, all cross sections were square and only central axis doses were considered.

Correlations of dose and time-dose-fractionation factors (TDF) with treatment results and side effects in cancer of the uterine cervix.

Treatment results and side effects were analyzed for 57 patients with stage IB-IIIA cancer of the uterine cervix who received external beam radiotherapy combined with intracavitary insertion of cesium-137 sources. The total dosage and time-dose-fractionation (TDF) factors were calculated at point A and at points of maximum exposure in the rectum and bladder. The overall 5-year survival was 62%, and 78% of the complete responders were free of disease at 5 years.

Perturbation of cobalt 60 radiation doses by metal objects implanted during oral and maxillofacial surgery.

The influence on cobalt 60 dose distributions of typical metal parts used in oral and maxillofacial surgery was studied. Relative doses were determined by exposing x-ray films in a polystyrene phantom set-up containing samples of Vitallium, titanium, and stainless steel. Optical densities were converted to doses with the aid of sensitometric curves.

The effect of single-dose radiation on cell survival and growth hormone secretion by rat anterior pituitary cells.

Cranial irradiation has been shown to impair growth hormone secretion in children. In this study a cell culture of dispersed rat anterior pituitary cells was exposed to single doses of radiation in the range of 100-1500 rad: Survival curves were obtained for the different anterior pituitary cell lines, and growth hormone secretion was measured in the tissue culture medium. Both survival and growth hormone secretion curves showed an initial shoulder in the range of 0-300 rad, followed by a decline between 300-750 rad.

A simple equivalent tissue-air ratio method for calculating absorbed dose in a heterogeneous medium.

Density correction factors for 60Co gamma rays and 8-MV x rays were measured with an ionization chamber in water-equivalent phantoms containing simulated lung or bone inhomogeneities larger or smaller than the beam (beam sizes, 5 x 5 to 30 x 30 cm). Measurements were compared with values calculated from the effective SSD method, the generalized Batho power law method, and a simplified equivalent tissue-air ratio (SETAR) method. The results indicate that the SETAR method gives the best overall agreement with experimental values, while the effective SSD and Batho algorithms are accurate only in certain situations.

Evaluation of density correction algorithms for photon-beam dose calculations.

The authors questioned whether more sophisticated density correction algorithms than those presently used for photon-beam dose calculations are necessary to take full advantage of CT in treatment planning. Predictions obtained with correction equations based on the radiological thickness (effective SSD) and generalized power-law TAR methods, as well as on the more complex equivalent-TAR method, we compared with ionization-chamber measurements in phantoms containing stimulated lung and soft tissues. Various geometric configurations were investigated for 60Co and 8-MV radiations.

An analog patient model derived from computed tomograms for three-dimensional radiotherapy planning.

An analog model of the part of a patient's body containing a tumor is constructed by drawing anatomical contours obtained from computed tomograms on a set of transparent plastic sheets. The coverage of radiotherapy fields in the patient is visualized in three dimensions using the model and the light beam from the radiotherapy machine or a simulator. A clinical example is presented.

Factors affecting sperm motility. III. Influence of visible light and other electromagnetic radiations on human sperm velocity and survival.

Specimens of semen from fertile and infertile patients were exposed to different electromagnetic radiations, including visible light, ultraviolet (UV) light, x-rays, and high-frequency radio waves. Sperm motility was analyzed before, during, and after irradiation by the multiple exposure photography (MEP) method. No significant difference was found between controls and specimens exposed to various doses of visible and UV light and x-rays either immediately or several hours after exposure.