Theoretical shape of cavity to locate ovoid sources

A mathematical technique is described for calculating the shape of a cavity required to position an ovoid source in its appropriate location within an applicator. This locus depends only on the assumption of a fixed angle between the source and wall that the source is touching. This technique has enabled us to avoid the problems of constructing ovoid cavities where the source sticks mid-course or does not seat properly, and has therefore resulted in a considerable saving of machine shop time and hence cost.

The forward production of high-energy electrons from megavoltage photon beams

The forward production of high-energy electrons from materials with various atomic numbers from carbon to lead has been measured for megavoltage photon beams from 4- to 25-MV peak bremsstrahlung energy by placing a thin-window parallel-plate ionization chamber directly behind foils of the various materials. The relative forward production of electrons decreases with atomic number for energies less than or equal to 10 MV until about Z = 50, after which it rises. For photon energies greater than or equal to 15 MV, forward production increases with atomic number with a break point at Z approximately 50, beyond which the curve becomes steeper.

Malignant rhabdoid tumor of the central nervous system

Originally described and most frequently reported in association with the kidney, the malignant rhabdoid tumor (MRT) is a highly aggressive neoplasm with distinctive morphologic features. Extrarenal sites reported for this neoplasm include the liver, thymus, and various soft tissue sites. Young infants are affected with rare exceptions. We report the case of a 3-month-old boy who presented with hyperirritability and increasing head size over several weeks. The patient died following a two-week hospital stay marked by development of seizures, paralysis, and apnea. At autopsy, significant findings were limited to the central nervous system. The subarachnoid space contained neoplasm throughout, with multiple areas of parenchymal invasion. A predominating intraparenchymal mass was present in the inferior cerebellum contiguous with the neoplasm in the subarachnoid space and probably represented the site of origin. Microscopically, the neoplasm was composed of a highly cellular monomorphic population of polygonal cells with roughly ovoid vesicular nuclei and conspicuous nucleoli. Variable amounts of cytoplasm were present, and many cells contained a single, well-demarcated eosinophilic hyaline globule adjacent to the nucleus. Ultrastructurally, the cytoplasmic globules were composed of whorled aggregates of intermediate filaments. Immunoperoxidase studies confirmed that the filaments were composed, at least in part, of vimentin. The morphologic and immunohistochemical features are diagnostic of MRT, an entity of unknown histogenesis that has not been reported previously as a primary neoplasm of the CNS.

Preoperative irradiation, lymphadenectomy, and 125iodine implantation for patients with localized carcinoma of the prostate

Fifty-four patients with clinically and surgically localized prostatic carcinoma were treated with low-dose preoperative irradiation (1,050 cGy), pelvic lymphadenectomy, and interstitial 125Iodine implantation. The follow-up range is 2 to 9 years with a median follow-up of 5 years. Overall local tumor control is 92%. Actuarial 5-year survival is 86% and the actuarial disease-free survival at 5 years is 73%. Patients with poorly differentiated tumors have a significantly worse actuarial survival (62%) at 5 years than patients with well (95%) or moderately well differentiated tumors (93%), p = 0.04. Disease-free survival at 5 years was influenced by grade: well (100%), moderate (60%), and poor (48%), p = 0.03. Multivariate regression analysis indicates that only the degree of differentiation (p = 0.05) significantly impacts on survival. Both degree of differentiation (p = 0.04) and nodal status (p = 0.03) significantly influence disease-free survival. Potency has been maintained in 71% of patients potent at the time of implantation. Late reactions have been acceptable to date: bladder outlet obstruction (13%), mild proctitis (13%), cystourethritis (6%), incontinence (2%), and prostatic calculi (2%).

Phaeohyphomycosis complicating compound skull fracture

Intracranial infection is a well-recognized complication of compound skull fractures. In most cases various bacteria are identified as the etiologic agents. Fungal infection complicating open head trauma is unusual. We describe a patient who contracted fatal meningoencephalitis due to Drechslera spicifera, a rarely pathogenic soil saprophyte, after open head trauma.

An afterloading vaginal applicator

An afterloading vaginal applicator has been built that incorporates two ovoid sources and two tandem sources arranged in the shape of a T, the tandems forming the upright and the ovoids, orthogonal to the tandems, located at the ends of the crossbar. The body of the applicator was designed and constructed to correspond to the 90 cGy/hr contour for a source loading of 10 mg Ra Eq 137Cs for the ovoids and 15 mg Ra Eq 137Cs for the tandems. TLD measurements made at various points located around the applicator in the AP and lateral planes indicate agreement with the dose calculated by computer to within +/- 1%.

A beam width improving device for a 25 MV X ray beam

We have made a device that improves the dose distributions of X ray fields from a 25 MV accelerator by increasing the width of the 95% dose relative to the 50%. This device, called a beam width improving device, is a specially designed "compensator," consisting of two lead sheets taped onto a plastic blocking tray and is tailored for each field so that it can accommodate square fields, rectangular fields and fields with corner cuts. Comparison of profiles with and without this compensator indicates an increase in the width of the 95% dose of approximately 8 mm for small fields to approximately 14 mm for large fields.

Unilateral adrenal hemorrhage: an unusual presentation

An asymptomatic adrenal mass was discovered in an elderly patient during evaluation of an abnormal urinary sediment. Exploratory laparotomy revealed an adrenal hematoma as the cause of the mass. No clear cause of the adrenal hemorrhage was identified, and postoperatively there was no evidence of adrenal insufficiency. Though rare, signs of adrenal hemorrhage may include an asymptomatic adrenal mass, and should be considered in the differential diagnosis of this problem.

A diagnostic X ray field verification device for a 10 MV linear accelerator

The quality of portal films taken at megavoltage energies is frequently poor, despite the use of various techniques such as lead screens to improve the image. When critical structures, such as the spinal cord, are to be blocked out of the treatment field, it is frequently difficult to determine whether the block is correctly placed. To solve this problem, a diagnostic X ray source has been mounted on the side of a 10 MV linear accelerator to provide accurate verification of patient positioning and location of shielding blocks. The coincidence between the mechanical, 10 MV and diagnostic X ray isocenters is about 1 mm. The system has been designed so that procedures to monitor this coincidence, and adjustment procedures to maintain it, are easily performed.

A simple digitizer technique for determining the effective center of spoke shots

A method is described for computing the effective center of an x-ray spoke shot pattern and determining its separation from a given reference point, such as the mechanical isocenter. This method is as quick as, but more accurate than, the standard technique of using a ruler.

The effect of beam angulation on central axis per cent depth dose for 4-29 MeV electrons

Electron beams are playing an increasing role in the areas of intraoral and intraoperative radiotherapy. Because of the way the electron beams are used in these two procedures, they are rarely incident normally on the surface of the tissue to be treated, but are inclined at some angle. Previous work has shown that when low-energy electron beams are used in this way, the per cent depth-dose curves, when measured along the oblique axis (the central axis of the beam) show a decrease compared with normal incidence. To quantify this effect in detail the per cent depth dose distributions of electron beams in the energy range 4-29 MeV have been studied as a function of their angle of incidence with respect to the normal (phi) between 0 and 60 degrees. The curves for different phi are compared by plotting the per cent depth dose along the central axis in each case: at low energies, this decreases as phi increases, while at the highest energies, the change is very small. The surface dose also changes, increasing with phi at low energies and decreasing at high energies.

Progressive Multifocal Leukoencephalopathy Occurring With the Acquired Immune Deficiency Syndrome

A 33-year-old homosexual man with symptoms and signs of a focal brain process was subsequently found to have an acquired immune deficiency syndrome (AIDS) with biopsy-proven progressive multifocal leukoencephalopathy. This report reemphasizes the association of progressive multifocal leukoencephalopathy with AIDS and probably is best viewed as another example of an opportunistic CNS infection complicating deficient cell-mediated immunity.

Breakaway safety feature for an intra-oral cone system

With an increasing number of high energy accelerators in operation, intra-oral electron radiotherapy is likely to become a more widely-used modality in the treatment of lesions of the oral cavity. However, there is one potential problem associated with this modality which concerns patient safety. There must never be any uncontrolled movement of the couch or gantry while the cone is in the patient's mouth, otherwise serious consequences could occur. In an effort to overcome this problem, a set of cones previously constructed by us for use in intra-oral electron radiotherapy has been modified to include a breakaway safety feature. This modification consists of separating the plate into which each of the treatment cones screws, into two pieces, the dividing line being in the shape of a cone frustum flaring out in the upward direction. A set of four spring plungers projecting into a notch on the inner ring prevents the cone from being pushed upwards without the application of an upward force. The amount of force required to push the cone upwards can be changed by adjusting the pressure of the spring plungers.

Brain calcification in severely stressed neonates receiving parenteral calcium

Morphologic evidence for calcium salts within the brains of severely stressed neonates at autopsy correlated to the mean daily parenteral dose of calcium gluconate (P less than 0.01). Survival analysis indicated that parenteral administration of calcium contributed a negative effect to predicted survival (P less than 0.05).

Neuroblastic medulloblastoma with abundant cytoplasmic actin filaments

Routine light microscopic examination of a midline cerebellar medulloblastoma with unusual morphologic features disclosed features identical to those of classic medulloblastoma. Immunoperoxidase staining for glial fibrillary acidic protein (GFA), neurofilament protein (NF), and skeletal muscle actin showed diffuse cytoplasmic staining for actin, but not for GFA or NF. Ultrastructurally, the cells had many blunt cytoplasmic processes with abundant, often parallel, 4- to 5-nm filaments. Other ultrastructural features included scattered, clear, and dense-core vesicles (80 to 90 nm), microtubules, rare intermediate filaments, polyribosomes, rough endoplasmic reticulum, and cell junctions. Plasmalemmal densities and invaginations, occasionally associated with clusters of 40- to 50-nm clear vesicles, were encountered infrequently and were interpreted as immature or abortive synapses. The blunt cytoplasmic processes containing abundant actin filaments, several microtubules, and large clear vesicles resemble growth cones of developing nerve cells.

Sources of electron contamination for the Clinac-35 25-MV photon beam

A detailed Monte Carlo approach has been employed to investigate the sources of electron contamination for the 25-MV photon beam generated by Varian's Clinac-35. Three sources of contamination were examined: (a) the flattening filter and beam monitor chamber, (b) the fixed primary collimators downstream from the monitor chamber and the adjustable photon jaws, and (c) the air volume separating the treatment head from the observation point. Five source-to-surface distances (SSDs) were considered for a single field size, 28 cm in diameter at 80 cm SSD. It was found that for small SSDs (80-100 cm), the dominant sources of electron contamination were the flattening filter and the beam monitor chamber which accounted for 70% of the unwanted electrons. Thirteen percent of the remaining electrons originated in the downstream primary collimators and the photon jaws, and 17% were produced in air. At larger SSDs, the fraction of unwanted electrons originating in air increased. At 400 cm SSD, 61% of the contaminating electrons present in the beam were produced in air, 34% originated in the flattening filter and beam monitor chamber, and 5% were due to interactions in the fixed collimators downstream from the monitor chamber and the adjustable photon jaws. These calculated results are substantiated by recent experiments.

Polymethylmethacrylate blocking trays. The effects of repeated usage

Sheets of polymethylmethacrylate (Lucite), which are commonly used to hold low-melting-point alloy blocks for radiation therapy treatments, are frequently recycled; subsequently, they generally contain a substantial number of holes. Experiments which have been performed to measure the deflection of these plates under a load indicate that, even with many holes drilled through the plates, their strength is not diminished significantly.

An investigation into the presence of secondary electrons in megavoltage photon beams

The presence of secondary electrons in photon beams of 60Co and 4, 8, 10, 15 and 25 MV x-rays has been studied by measuring surface charge using thin window ionisation chambers. Measurements have been made for square fields from 4 X 4 cm2 to 35 X 35 cm2 for locations from the collimator head to a distance of 4 m from the target. In addition, measurements have been made for rectangular fields at 10 MV and 25 MV for fields of equivalent area from 5 X 5 cm2 to 25 X 25 cm2. By eliminating the inverse square effect, the presence of contaminants from the head and the effect of build-up in air are clearly seen and well separated. Comparison between the curves at different energies indicates an increasing effect of contamination from the head with energy and a decreasing effect of electron production in air with increasing energy.

Geometric reconstruction of seed implants using a three-film technique

A computer program has been written to reconstruct the three-dimensional distribution of radioactive seed implants. The technique requires the use of three rotated films with random input of the seeds. This algorithm differs from previous ones in the constraints that are applied, since no correlation is made between distances on the three films from the plane of rotation through the isocenter nor is there a correlation between the distances from the axis of rotation. Instead, projections from the x-ray source to the seed images on each of the three films are compared to see which combinations of seeds intersect at a point and therefore correspond to real seeds. This program has been written in Fortran IV for the PDP VAX 11/780 and 11/34 computers. Changes have been made to the TP11 program "QSEED" on the PDP 11/34 to accommodate the coordinate data from this program to produce the requisite isodose curves.

Intra-oral cone radiation therapy for selected carcinomas of the oral cavity

A study of 101 patients with early carcinomas of the oral cavity, T1 and T2, treated by external cobalt 60 beam and/or intra-oral cone (IOC) radiation therapy between 1964 through 1980 was made. The two year disease-free survival rate, including surgical salvage, was 88% and the local control rate was 85%. The incidence of radiation complications, i.e. soft tissue ulceration and/or osteoradionecrosis, was 14% and varied with various tumor sites and radiation doses delivered. The present review shows that local control and radiation complications are closely related to radiation doses and varies with different tumor sites of the oral cavity. Radiation therapy dosages expressed in terms of TDF values for these lesions are herein recommended. With proper selections of lesions arising from the oral cavity, combined external beam and IOC radiation therapy has been found extremely efficacious in achieving good local tumor control and high survival rates with excellent cosmetic and functional results and minimum radiation sequelae.

A linear accelerator couch attachment for extended SSD treatments

An attachment to an existing linear accelerator couch is described that extends the range of SSD's at which patients can be treated. This couch attachment, which is mounted on castors for ease of mobility, is attached to and locks into the rail of the accelerator couch such that the axis of the new device is normal to the existing couch. All motions of this assembly are then under the control of the existing couch. The overall size of the couch attachment is 215 cm x 90 cm, sufficiently large to treat all clinically used fields.

Tissue phantom ratios for a Clinac 4/100

Tissue phantom ratios (TPR), based on a normalization depth of 5 cm, have been measured in water for field sizes from 5 x 5 cm2 to approximately 40 x 40 cm2 and for depths from 1 to 40 cm for a Varian Clinac 4/100. These TPR's have been compared with those calculated from percent depth doses measured at the same time, and the two sets of data generally agree to better than 1%, with an average ratio of measured to calculated TPR of 0.999 +/- 0.013. Beam profiles have been measured for open and wedged fields, with particular concern for the often observed "horns," or the increase in dose at the corners of the field. The maximum dose at a depth of 1 cm, along the diagonal of the field for this machine, is approximately 5% higher than at the same depth on the central axis, whereas along the principal plane the maximum dose is only about 3% higher.