Search PubMed⌕ Search

Biomedical subjects

P J Harrington

Publications and source records attributed to P J Harrington.

8 recordsLinked to original sources
PubMed1999

Dissociation in the laboratory: a comparison of strategies.

Several methods for inducing dissociation in the laboratory were examined in a sample of 78 undergraduate students. Participants scoring high or low on the Dissociative Experiences Scale participated in three dissociation challenge conditions: (a) dot-staring task, (b) administration of pulsed photic and audio stimulation and (c) stimulus deprivation. Participants recorded their dissociative experiences both before and after each of the three challenge conditions. Across conditions, high DES participants reported significantly more dissociative sensations than low DES participants, even after controlling for pre-challenge dissociation. Moreover, regardless of DES status, pulsed photo and audio stimulation produced the greatest level of dissociative symptoms. The findings suggest that the induction of dissociative symptoms in a nonclinical sample is easily accomplished in the laboratory and that those who report more dissociative symptoms in their day-to-day life exhibit more pronounced dissociative symptoms when undergoing dissociative challenge in the laboratory. Implications for the study and treatment of dissociative symptoms are discussed.

Acoustic Stimulation↗
PubMed1998

Three-dimensional lookup tables for Henschke applicator cervix treatment by HDR 192IR remote afterloading.

PURPOSE: We have generated three-dimensional (3D) lookup tables for dosimetric analysis and optimization of high-dose rate (HDR) gynecological treatments using the Henschke applicator. The new dosimetry data have been compared with two-dimensional (2D) data currently in use. The 3D dosimetry tables have been implemented in an existing cervix treatment-planning system and have been evaluated through analysis of clinical cases. METHODS AND MATERIALS: A general Monte Carlo N-Particles (MCNP) transport code was used to compute absorbed dose distributions around the intrauterine tandem and tungsten-shielded ovoid separately. The dosimetry data are represented in the x-y coordinate system for the intrauterine tandem table. The 3D table for the ovoid contains a radial dose function and an anisotropy function, as formulated in the spherical coordinate system. Absorbed dose at a spatial point is calculated by applying bilinear interpolation for the anisotropy function and linear interpolation for the radial dose function. The geometry factor for a finite line source is used. 3D dose calculations and optimization were performed for 20 treatments of 10 patients. The absorbed dose to critical structures, bladder and rectum, was compared by applying both the 2D table currently in use and the new tables. RESULTS: The new 2D table for the intrauterine tandem yields doses different by less than 10% from those with the current table. The 3D table for the shielded ovoids shows as large as a factor of 4 reduction of dose behind the shield compared with the present 2D table. This shielding effect leads to 21.6 +/- 9.3% and 20.0 +/- 6.6% dose reduction at rectum and bladder, respectively, for actual treatments. CONCLUSION: Our analysis indicates a need for patient-specific 3D dosimetry to permit more accurate dosimetric evaluation of HDR cervix treatments using shielded applicators. We have also shown that a Monte Carlo simulation code enabled us to derive the lookup tables necessary for 3D planning.

Brachytherapy↗
PubMed1998

Experimental and Monte Carlo dosimetry of the Henschke applicator for high dose-rate 192Ir remote afterloading.

We have performed extensive computational and experimental dosimetry of the Henschke applicator with respect to high dose-rate 192Ir brachytherapy using a GAMMAMED remote afterloader. Our goal was to generate clinically useful two- and three-dimensional look-up tables. Dose measurements of the Henschke applicator involved using TLD chips placed in a polystyrene phantom. Monte Carlo simulations were performed using the MCNP code. The computational models included the detailed geometry of 192Ir source, tandem tube, and shielded ovoid. The measured dose rates were corrected for the dependence of TLD sensitivity on the distance of measurement points from the source. Transit dose delivered during source extension to and retraction from a given dwell position was estimated by Monte Carlo simulations, and a correction was applied to the experimental values. For the applicator tandem, the ratio of dose rates obtained by MCNP to those measured by TLD chips ranges from 0.92 to 1.10 with an average of 0.98 and a standard deviation of 0.02. The measured and calculated dose rates at 1 cm on the transverse axis are 1.10 cGy U-1 h-1. For the shielded ovoid, the ratio ranges from 0.88 to 1.16 with an average of 1.00 and a standard deviation of 0.07. Causes of the discrepancy between the Monte Carlo and TLD results were identified. We found that the combined uncertainty of measured dose rates due to these causes is 5.6% for the applicator tandem and 8.4% for the shielded ovoid. Therefore, the results of the Monte Carlo simulation are considered to have been validated by the measurements within the uncertainty involved in the calculation and measurements.

Brachytherapy↗
PubMed1996

Prospective evaluation of panic potentiation following 35% CO2 challenge in nonclinical subjects.

OBJECTIVE: The authors examined the effect of panic provocation on the subsequent development of panic attacks and panic disorder in nonclinical subjects with no history of spontaneous panic. METHOD: Sixty-two subjects who had completed a study examining fearful responses to a single vital capacity inhalation of 35% CO2 were reevaluated 1 year following the challenge test. RESULTS: Challenge-induced panic was not related to the later development of panic or panic disorder. According to the Structured Clinical Interview for DSM-III-R--Non-Patient Edition, none of the subjects met DSM-III-R criteria for panic disorder and only six subjects reported spontaneous panic during the year after panic provocation. Of the six subjects who experienced spontaneous panic, two had panicked in response to the CO2 challenge. CONCLUSIONS: The experimental provocation of panic in nonclinical subjects appears to be a safe research paradigm for exploring the psychopathogenicity of panic disorder.

Administration, Inhalation↗
PubMed1995

Impact of cognitive-behavioral treatment on quality of life in panic disorder patients.

Panic disorder (PD) is associated with significant social and health consequences. The present study examined the impact of treatment on PD patients' quality of life. Patients (N = 156) meeting DSM-III-R (Diagnostic and Statistical Manual of Mental Disorders [3rd ed., rev.]; American Psychiatric Association, 1987) criteria for PD with agoraphobia were randomly assigned to group cognitive-behavioral treatment (CBT) or a delayed-treatment control. An assessment battery measuring the major clinical features of PD as well as quality of life was administered at baseline (Week 0), post-treatment (Week 9) and 6-month follow-up (Week 35). Consistent with previous studies, PD patients displayed significant impairment in quality of life at intake. Compared with delayed-treatment control participants, CBT-treated participants showed significant reductions in impairment that were maintained at follow-up. Consistent with prediction, anxiety and phobic avoidance were significantly associated with quality of life, whereas frequency of panic attacks was not.

Adult↗
PubMed1993

A CT-based evaluation method for permanent implants: application to prostate.

A computerized tomography-based 3-dimensional evaluation scheme, using semi-automatic seed localization from transverse computerized tomography-images, has been developed for permanent implants. The treatment isodose contour is generated at each scan plane and overlaid on the corresponding target contour for coverage visualization. Volume and surface dose histograms are generated for the target and neighboring normal structures. Dose inhomogeneity within the target is also estimated from the full-width at half maximum of the differential volume dose histogram. The matched peripheral dose is calculated from the ellipsoidal volume approximation for the target. The present evaluation method has been applied here to 10 actual permanent I-125 prostatic implantations. Coverages by 150 Gy and 100 Gy levels are found to range from 78-96% and 91-99% of the target volume, respectively. The average matched peripheral dose is found to be about two times the average peripheral dose (the dose encompassing 99% target) and about three times the average minimum peripheral dose (the dose encompassing 100% target). The dose inhomogeneities within the target volume, in these 10 cases, range from 220-420 Gy.

Brachytherapy↗
PubMedDate not supplied

A versatile method for planning stereotactic brain implants.

Our approach to planning stereotactic 125I brachytherapy of brain tumors has involved least-squares optimization of individual seed positions within the target contour, followed by repeated combining of seeds from nearest-neighbor catheters in order to achieve an acceptably low number of catheters and an acceptable-separation of entry points. In one option, the catheters diverge from an extra-cranial point that can be close to the skull if all catheters are to be placed through a small craniectomy to treat a larger-diameter target. In another option, catheters converge toward a point beyond the target, to facilitate perpendicularity at the skull surface if a separate opening is to be drilled for each catheter. In either case, the fact that seed orientations are known, permits including anisotropy in dose calculations. Trial seed locations are constrained to a target region defined on a 1-mm mesh, both in the initial optimization of single-seed catheters and in subsequent combinations followed by tune-up optimizations. In the optimization process, sum-of-squares contributions are weighted more heavily when the dose rate is lower than the target dose rate; the weighting imbalance falls short of keeping all target points above the target dose rate and requires targeting on a dose rate about 25% higher than the desired minimum dose rate.

Biophysical Phenomena↗