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D R Dickson

Publications and source records attributed to D R Dickson.

At least 19 recordsLinked to original sources
PubMed1993

Estimation of tissue volume irradiated by intracavitary implants.

PURPOSE: The volume of space enclosed by a specified isodose surface arising from an intracavitary implant may correlate with clinical outcome. Several investigators have proposed using the product of the three maximum orthogonal dimensions of the isodose surface as a measure of this volume. We have examined the accuracy of this proposal and compared it to a simpler model for estimating volume which requires only knowledge of the mgRaEq-hrs (total reference air kerma) and the dose level. METHODS AND MATERIALS: Orthogonal films from 204 intracavitary implants of 128 patients with carcinoma of the cervix were used to reconstruct the 137Cs-source coordinates. The source location, strength and duration data were used to calculate dose-volume histograms, yielding the volume enclosed by each dose level as well as its orthogonal dimensions: thickness, width, and height. Using bony landmarks to align films for different insertions in the same patient, similar calculations were repeated for composite implant source coordinates. RESULTS: Curve-fitting techniques revealed that the volume encompassed by each isodose level could be predicted by a modified power-law function of the mgRaEq-hr/dose ratio: predicted volume = [104.8 - 8.103.(M/D) + 0.437.(M/D)2].(M/D)1.635 where M/D = mgRaEq-hr/cGy. The volume predicted by this simple model is accurate within +/- 10% in 95% of the implants when mgRaEq-hr/cGy = 0.8. Accuracy increases with increasing mgRaEq-hr/cGy. In contrast, the ratio, product of orthogonal dimensions/actual volume, varies widely from implant-to-implant, as well as differing systematically from one implant type to another. Investigation of the individual orthogonal dimensions demonstrated that width and height, but not thickness, were moderately well correlated with corresponding maximum implant dimensions. However, in all cases the dimensions were more sensitive to changes in mgRaEq-hr/cGy than to changes in implant geometry. CONCLUSIONS: The product of the orthogonal dimensions is an unsatisfactory estimator of the actual irradiated volume encompassed by an isodose surface. Isodose surface volumes can be accurately estimated knowing only mgRaEq-hr. Prescribing intracavitary brachytherapy by mgRaEq-hr, or its derivative, total reference air kerma, is equivalent to requiring that an isodose surface encompass a specified volume which does not depend on the implant geometry. Constraining the mgRaEq-hr delivered therefore serves to limit the volume of tissue irradiated to high doses.

Brachytherapy↗
PubMed1983

Tomographic assessment of craniofacial structures: cleft lip/palate.

The purpose of the investigation was to develop software and hardware modifications for computed tomography to provide high-resolution thin sections for the assessment of craniofacial anomalies in the pediatric population. Modifications were undertaken on an EMI 5005 head scanner. Section thickness of two millimeters and resolution of greater than ten lines per centimeter were achieved. Since this study was concerned with reduction of slice thickness and increase in resolution, radiation dose was not of immediate concern, but would be addressed subsequent to achievement of desired initial results. Initial results on investigation of a full-term human fetus with bilateral cleft lip, cleft of the posterior palate, and micrognathia are presented. The interrelationships of the affected structures are shown clearly. Soft tissues are visualized which cannot be seen by conventional tomography.

Cleft Lip↗
PubMed1980

Anatomy and physiology related to cleft palate: current research and clinical implications.

The most important areas for future research related to the anatomy and physiology of cleft palate are thus: (1) the role of the tensor tympani muscle in auditory tube clearance; (2) the specific etiology of auditory tube dysfunction associated with cleft palate; (3) the nature and extent of variability in the muscular deformities associated with various types of cleft palate; (4) the nature and extent of vascular abnormalities associated with clefts of the palate; and (5) the investigation of cleft palate as one aspect of a craniofacial syndrome.

Cleft Palate↗
PubMed1979

Comparison of dosimetry and image quality in computed and conventional tomography.

Comparison was made of tomograms of a phantom head and a normal adult cadaver head on GE CT/T, Delta 50, EMI 5005, and CGR Stratomatic units. Image quality was ranked as follows: First, GE CT/T 8800 system; second, EMI; third, GE CT/T 7800 and Delta. The GE CT/T 7800 imaged 3.7 line pairs at high contrast with an exposure to the head phantom of 2.5 R (6.5 X 10(-4) C kg-1). The EMI exposure level was 5 R (13 X 10(-4) C kg-1) in the fast mode and 12 R (31 X 10(-4) C kg-1) in the slow mode, while the Delta 50 exposure level was fixed at 2 R (5.2 X 10(-4) C kg-1). The GE CT/T 8800 could image 6.1 line pairs/cm in a high-contrast phantom with exposures as low as 100 mR (25.8 muC/kg) but a typical operating exposure would be about 1--2 R (2.58 -5.2 X 10 (-4) C kg-1). Dosimetry ranged from 1.1 to 5.5 R/scan section (2.8--14.2 x 10(-4) C kg-1) in the CT units but never increased by a factor of more than 2, irrespective of the number of sections scanned. In conventional tomography, however, exposure increased almost arithmetically with the number of contiguous sections scanned.

Humans↗
PubMedDate not supplied

Anatomy of the normal and cleft palate Eustachian tube.

This report presents preliminary findings from a study of cleft palate and noncleft palate human fetuses to determine whether differences in Eustachian tube and cranial base structures could be found which might explain the universal appearance of otitis media in infants with cleft palate. Differences were found which are consistent with the previous hypothesis of reduced elasticity in the Eustachian tube. Principal findings included medial to lateral compression of the tube and reduced tubal width.

Abnormalities, Multiple↗