A modified method of planning and delivery for dynamic multileaf collimator intensity-modulated radiation therapy

PURPOSE

To develop a modified planning and delivery technique that reduces dose nonuniformity for tomographic delivery of intensity-modulated radiation therapy (IMRT).

METHODS AND MATERIALS

The NOMOS-CORVUS system delivers IMRT in a tomographic paradigm. This type of delivery is prone to create multiple dose nonuniformity regions at the arc abutment regions. The modified technique was based on the cyclical behavior of arc positions as a function of a target length. With the modified technique, two plans are developed for the same patient, one with the original target and the second with a slightly increased target length and the abutment regions shifted by approximately 5 mm compared to the first plan. Each plan is designed to deliver half of the target prescription dose delivered on alternate days, resulting in periodic shifts of abutment regions. This method was experimentally tested in phantoms with and without intentionally introduced errors in couch indexing.

RESULTS

With the modified technique, the degree of dose nonuniformity was reduced. For example, with 1 mm error in couch indexing, the degree of dose nonuniformity changed from approximately 25% to approximately 12%.

CONCLUSION

Use of the modified technique reduces dose nonuniformity due to periodic shifts of abutment regions during treatment delivery.

The lateral fixation screw in implant dentistry

This clinical report presents a means of retaining implant supported superstructures using lateral fixation screws (Novadent). 244 lateral fixation screws have been used for the retention of a variety of restorations including single teeth, short span and full arch bridgework as well as overdenture bars. Over a period of observation of 4 years, the authors have found the restorations to have effective retention, ease of retrievability, good aesthetics and occlusal contours.

Extended survival of carcinoma head of pancreas following palliative treatment

A 48 year old woman presented with obstructive jaundice 10 years back. Upper gastrointestinal endoscopy revealed a growth infiltrating the ampulla of Vater, which was confirmed to be adenocarcinoma on cytology. At laparotomy, a large nodular growth was seen in the head of pancreas. Surgical resection could not be done because of encasement of superior mesenteric vessels, hence a cholecystojejunostomy was performed. The patient remained asymptomatic for 9 years, when she developed cholangitis. Duodenoscopy at this stage revealed an ulcerated growth at the ampulla and biopsy from the growth confirmed a well differentiated adenocarcinoma. A straight flap 10 F stent was placed in the common bile duct. Thereafter the patient has remained asymptomatic for more than a year.

Calculation of depth dose and dose per monitor unit for irregularly shaped electron fields

A new dosimetric quantity, the lateral build-up ratio (LBR), has been introduced to calculate depth dose distribution for any shaped field. Factors to account for change in incident fluence with collimation are applied separately. The LBR data for a small circular field are used to extract radial spread of the pencil beam, sigma(r), as a function of depth and energy. By using the relationship between LBR, sigma(r), energy and depth, a formalism is developed to calculate dose per monitor unit for any shaped field. Criteria for lateral scatter equilibrium are also developed which are useful in clinical dosimetry.

Initial results of the Osteo Ti implant system in general dental practice

It is the purpose of this paper to present the preliminary results of 370 consecutively placed Osieo-Ti implants. Two stage screw form endosseous implants ranging in length from 7mm to 20mm in one mm increments were used. Four diameters of implant 2.75mm, 3.00mm, 3.75mm and 4.50mm were used to engage the maximum available width of bone. The larger, 3.75mm and 4.50mm diameter, implants were made from commercially pure titanium and the two smaller diameter, 2.75mm and 3.00mm, implants were manufactured from titanium alloy. The overall success rate for 370 exposed functioning Osteo-Ti implants was 98.6%.

Inferior alveolar nerve repositioning in implant dentistry: a preliminary report

The surgical repositioning of the inferior alveolar nerve facilitates the placement of implants in the posterior mandible. The entire height of the posterior mandible is made available and enables implants to be anchored in two cortical plates, improving the primary fixation and increasing the area of the bone-implant interface. The posterior mandible can thus be predictably treated with implants in those cases where posterior support is considered important for occlusal stability and masticatory efficiency. The rapid and total recovery of sensation to the lip following nerve repositioning renders the procedure more acceptable to both the patient and the clinician.

Incorporation of diaphyseal sequestra in chronic haematogenous osteomyelitis

Seventeen patients with haematogenous osteomyelitis and long diaphyseal sequestra are reported. Treatment was incision and drainage with antibiotics for at least 6 to 8 weeks, the limb being protected in plaster for a long time. The sequestra became incorporated in every case. Sequestrectomy should only be undertaken when successive radiographs show no reduction in size of the sequestrum and an increase in the amount of the involucrum.

Predicting esthetics in implant dentistry using multiplanar angulation: a technical note

Although the permucosal site of implants can be made to coincide with tooth position, the problem of aligning multiple abutments remains. To use the maximum amount of available bone, an implant must often be placed at an angle to the long axis of the prosthetic replacement tooth, and it also can deviate mesiodistally. This paper discusses a technique using trial abutments to create parallelism while ensuring that each abutment is ideally positioned with respect to the final restoration. The procedure also encourages patient acceptance by transferring the appearance created by a preliminary diagnostic waxup through to the finished prosthesis.

Surgical treatment of complete acromioclavicular dislocation using the coracoacromial ligament and coracoclavicular fixation: report of a technique in 14 patients

Fourteen cases of a complete dislocation of the acromioclavicular joint were treated using a modified technique of surgical repair involving the transfer of the coracoacromial ligament to reconstruct the coracoclavicular ligaments and coracoclavicular fixation with a screw. In addition, the lateral 2 cm of the clavicle was removed and the coracoacromial ligament attached to the raw surface. Eleven patients underwent surgery < 2 weeks after injury, whereas three underwent surgery 6 months after the initial episode. Follow-up of 2-4 years showed excellent results in 12 and good in two cases. It is our recommendation that coracoclavicular ligament reconstruction should be supplemented with clavicular fixation to the coracoid to ensure acromioclavicular alignment.

Sensory nerve conduction during cold pressor response in humans

A study was carried out to find the correlation, if any of autonomic responses and experimental pain induced during the cold pressor test (CPT) with the median nerve sensory conduction velocity (SCV). In 19 healthy subjects who volunteered for the study, the nondominant hand of each was subjected to the CPT and, pain parameters, heart rate, blood pressure and SCV were recorded. Dominant median nerve SCV was measured by orthodromic stimulation of the index finger and evoked responses were recorded at the wrist. In each subject, 32 evoked action potential responses were averaged to determine the SCV. Median nerve SCV of 57.8 +/- 5.2, 56.6 +/- 5.1, 57.0 +/- 5.2 and 57.8 +/- 5.1 m/sec were recorded before, during, immediately after and after ten minutes of the CPT, respectively. The SCV and the amplitude of the evoked response were significantly (P < 0.001 and P < 0.01 respectively) decreased during the CPT. A significant relationship (P < 0.05) was found between nerve conduction parameters and diastolic blood pressure recorded before the CPT. These findings suggest that sympathetic overactivity and/or cold induced pain interacts with sensory conduction in the contralateral median nerve so as to decrease its conduction velocity. There also exists a relationship between SCV and vasomotor mechanisms controlling peripheral resistance, and hence the diastolic pressure.

Brain stem auditory evoked responses during the cold pressor test

This study was conducted to determine changes, if any, in Brain stem auditory evoked responses (BAEP's) during the cold pressor test (CPT) in healthy human subjects. Thirteen subjects (age 18-25 yrs) were selected for the study. Their BAEP's were recorded using standardized technique employing 10-20 international electrode placement system and sound click stimuli of specified intensity, duration and frequency. The standard CPT was performed in the non-dominant hand and the BAEP's, heart rate and blood pressure were recorded before and during the CPT. The values of absolute peak latencies and amplitude of evoked responses were statistically analysed. The amplitude of wave V showed a significant increase (P < 0.05) during the CPT (0.47 +/- 0.203 and 0.37 +/- 0.174 mu v before and during CPT respectively). This could be due to interaction of activated central ascending monoaminergic pathways or nociceptive afferents with the midbrain auditory generator so as to increase it's activity.

Restoration of the maxillary arch using implants, natural teeth and the Konus crown: a case study

Restoring the maxillary arch by using a suprastructure retained by a Konus crown means that the patient can remove the crown for oral hygiene. This construction enables large embrasure spaces to be avoided without compromising phonetics, that is, without adversely affecting the patient's speech. It also enables the dental surgeon to monitor the tooth and implant abutments and the soft tissues around them. In this article we demonstrate successful restoration of the maxillary arch by the use of Konus crowns on a combination of implants and natural teeth.

Allograft in the treatment of benign cystic lesions of bone

Seventeen patients with benign cystic osseous lesions were treated by curettage and grafting using allogenic decalcified bone. Human bones were partially decalcified using 0.6 N HCl and preserved in 90% ethanol in a deep freezer at -16 degrees C. The cystic lesions were: 5 cases of fibrous dysplasia, 4 aneurysmal bone cysts, 3 simple bone cysts, 2 giant-cell tumours, 1 chondromyxoid fibroma, 1 non-ossifying fibroma and 1 fibrous cortical defect. The bones involved were: femur, tibia, humerus, fibula and calcaneum. Infection was a complication in three patients. In two of these it did not interfere with healing, but in one it persisted for more than 1 year with partial resorption of the graft. The time to adequate incorporation of the graft varied from 6 to 9 months in children and 9 to 15 months in adults. The overall response compares favourably with that to allograft from more sophisticated bone banks.

Inferior alveolar nerve repositioning in implant dentistry: clinical report

Repositioning the inferior alveolar neurovascular bundle is a high risk procedure which can result in permanent damage. It must be justified by the need for posterior mandibular support to stabilize the dentition and provide function. A clinical report is presented.

Childhood neurocysticercosis--epidemiology, diagnosis and course

Neurocysticercosis was diagnosed in 0.89% of children enrolled in our Child Neurology Clinic in the years 1979 to 1990. The commonest presenting symptom was seizures (90%) followed by raised intracranial pressure (44%). CT scans revealed a variety of lesions including low and high attenuation cysts, periventricular edema, hydrocephalus and calcification. ELISA was useful in substantiating the diagnosis in almost 70% of cases. Only 18 patients who had active disease merited treatment with praziquantel. The clinical and CT response was good. Follow-up revealed spontaneous quiescence in many patients with inactive disease.

Oxidative metabolic response of peripheral blood monocytes of monkeys during primary and chronic Plasmodium knowlesi infection

The oxygen free radical generation (as determined by cytochrome c reduction) and respiratory burst enzyme activities were measured in the peripheral blood monocytes before infecting normal animals, during primary Plasmodium knowlesi infection, after treatment of primary infection with chloroquine, after administration of various subcurative doses following reinfection and after establishment of chronicity. For all the parameters of the oxidative response, no significant difference was observed during primary infection and after curing of primary infection. However, the response was significantly increased in the reinfected monkeys given subcurative therapy; this was followed by a sharp decline after the 4th subcurative dose, after which the response continued to be low until the attainment of chronicity. The results of the present study exclude the possibility of the increase in oxidative metabolism being the effect of the drug (i.e. chloroquine), since no significant difference was observed during primary infection and after its cure. The sustained low grade parasitaemia in the chronic stage, in spite of the sharp decrease in the oxidative response, suggests that some nonoxidant parasitic killing mechanism might be playing a role in the regulation of parasitaemia.

The role of a critical care unit in an epidemic

The role of a critical care unit in life-threatening situations is well established. The management of 52 children with acute gastroenteritis and 22 children with acute paralytic poliomyelitis as part of recent epidemics is described. The solutions to the problems in the critical care management of these 74 victims (out of a total of 6197 patients admitted during the epidemics) are discussed.

Thymosin alpha 1 enhancement of human lymphocyte proliferation is not mediated by prostaglandin E2

Prostaglandins of the E series have been implicated as possible mediators of thymosin alpha 1 (TA-1) effect on mitogen stimulated lymphoproliferation. In the present study human peripheral blood mononuclear cells were stimulated with concanavalin A in the presence of TA-1, prostaglandin E2 and indomethacin individually, or in combination. Both TA-1 and indomethacin significantly enhanced the proliferative response over that seen with mitogen alone (less than 0.001). The magnitude of enhancement observed with indomethacin (20 microM) was considerably less than that of TA-1 and it was abolished with prostaglandin E2. The combination of indomethacin and TA-1 did not alter TA-1 effect and prostaglandin E2 (up to 250 ng/ml) did not abolish thymosin effect. These results suggest that TA-1 and prostaglandin E2 have opposite effects and that thymosin enhancement of mitogen induced proliferation is not mediated by prostaglandin E2.

Stimulation of the human immunodeficiency virus type 2 (HIV-2) gene expression by the cytomegalovirus and HIV-2 transactivator gene

Human immunodeficiency virus (HIV) often causes latent infection. Transactivation by some DNA viruses has been implicated in inducing HIV-1 replication and pathogenesis. The transactivator (IE-2) gene of the human cytomegalovirus (CMV) can enhance HIV-2 as well as HIV-1 gene expression in vitro. This inducer can act in concert with the HIV-2 tat gene and T-cell activation in enhancing gene expression in human CD4+ lymphocytes. While the HIV-2 and HIV-1 tat genes and T-cell activators apparently employ independent modes of action, the CMV transactivator in combination with the HIV-2 tat or T-cell activators may employ a gene activation pathway with some common and some distinct components. Both HIV-2 and CMV transactivators enhance HIV-2 gene expression by transcriptional activation involving transcript initiation as well as elongation, with CMV transactivator affecting elongation more than the initiation. A significant proportion of transcripts appear to terminate prematurely in the absence of transactivators. Deletion mutation analysis of the HIV-2 long terminal repeat (LTR) suggests that the element that responds to CMV transactivation in human CD4+ lymphocytes is either a diffuse one or located downstream of the HIV-2 enhancer element.

Immunological profile in neonatal hyperbilirubinemia

Thirty cases of neonatal hyperbilirubinemia of varying etiology, severity and duration; and twenty six normal healthy newborns were subjected to various tests of cellular and humoral immunity. The results revealed a significant depression of all the parameters of cellular immunity in neonatal hyperbilirubinemia of greater than or equal to 10 mg/dl as compared to the control values. The depression of immunological profile in these newborns was seen to be more pronounced with increasing duration and severity of jaundice. A limited assessment of the humoral immunity by the B cell count and serum immunoglobulin IgG levels, however, showed no significant difference from the control.

An analysis of Memnet—an experiment in high-speed shared-memory local networking

Memnet is a shared-memory local area network under development at the University of Delaware that provides close coupling to the processors of a physically distributed multiprocessor system. The Memnet local network appears as memory in the physical address space of each processor (host) on the network.

This paper describes an analysis of the Memnet system performed to predict the possible performance levels attainable by a Memnet system. One objective of this analysis is to provide analytic results demonstrating the intrinsic soundness of the Memnet architecture. This is in support of the intuitive arguments of the shared-memory network model over the I/O modeled local network schemes. Another function of this analysis has been to provide design feedback for the choice of values for parameters such as page size.

The analysis results indicate that the Memnet approach to networking should significantly speed communication compared to alternative networking schemes.

Due to space limitations, the details of the analysis have not been included. The full text is available as TR-88-6-1 from: Department of Electrical Engineering, University of Delaware, Newark DE, 19716.

An unusual case of Holt-Oram syndrome

An unusual case of Holt-Oram syndrome with arachnodactyly, high arch palate, thoracic scoliosis and hypoplasia of the left radial artery is reported. The relevant literature is discussed and the importance of vascular hypoplasia in genesis and localization of the skeletal deformities of this syndrome is stressed.