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T J Jordan

Publications and source records attributed to T J Jordan.

18 recordsLinked to original sources
PubMed2001

The design and evaluation of a phantom for the audit of the treatment chain for prostate radiotherapy.

BACKGROUND AND PURPOSE: A phantom has been designed and built for a multi-institutional technique audit of the planning and delivery for radiotherapy to the prostate. The phantom was designed to test both the geometric and dosimetric accuracy of each aspect of the process. MATERIALS AND METHODS: The phantom consists of two curved water filled perspex tanks either side of a central block of solid water equivalent material. There are two options for the central section; a target defining block and a dose measurement block. The target defining block uses air holes to define a 3-D target volume for imaging via a CT scanner or a simulator. These holes can subsequently be filled with steel pins to allow megavoltage imaging. The dose measurement block allows thimble chamber measurements to be made at pre-selected points in a 5x5mm array. Five dose measurement points, typical for a prostate planning target volume (PTV) were selected. Initial evaluation of the phantom was performed by auditing the prostate radiotherapy planning and treatment chain at one institution. RESULTS: Agreement between the phantom and planned geometry confirmed that the stages of image acquisition, transfer and manipulation were accurately performed. Agreement within 0.5% was found between phantom and water tank measurements for dose calibration at a reference point. The measured dose delivered was within 2% of the dose calculated by the planning computer for all of the selected measurement points. The target volume marked by the steel pins was visible using electronic portal imaging. CONCLUSIONS: The phantom is a useful tool for the technique audit of prostate radiotherapy.

Humans↗
PubMed1997

Management after exposure to tuberculosis.

The increased incidence of tuberculosis-coupled with the emergence of mycobacterial strains resistant to the most effective drugs-has highlighted the importance of identifying transmission and preventing active disease. Skin test conversion can document infection, except in most patients vaccinated with bacille Calmette-Guérin. Prophylactic medication is effective, but not without complications.

Adult↗
PubMed1997

Quality control aspects of the Philips multileaf collimator.

BACKGROUND AND PURPOSE: Linear accelerators equipped with multileaf collimators (MLCs) are becoming more common and are widely available from most commercial manufacturers. There is a need to ensure they retain their commissioning specification using a preventative maintenance and quality control (QC) programme. This paper considers the design criteria of the Philips MLC which are important to the production of a comprehensive quality control programme. MATERIALS AND METHODS: The specific QC problems related to MLCs are identified as the positional accuracy of the leaves and their relationship to the back-up collimators, leakage considerations, the relationship of X-ray to light field and the influence of gravity on the positioning and leakage characteristics of the leaves. These problems are considered in relation to the general design considerations of the MLC, and methods of performing routine quality control checks are discussed. RESULTS AND CONCLUSIONS: The introduction of MLCs into clinical use results in new QC procedures being developed but it can be concluded that for the Philips MLC only an extra 30 min of QC time is needed per month and that its use has added little to the general down-time of this department.

Calibration↗
PubMed1994

The design and performance characteristics of a multileaf collimator.

A multileaf collimator, which has been in routine clinical use for both conventional and conformal radiotherapy for over four years, is described in detail. The collimator replaces the conventional treatment head of a Philips SL series linear accelerator and comprises 80 tungsten leaves and two orthogonal pairs of back-up collimators. Each leaf projects a width of 1 cm in the isocentric plane, allowing shaped photon treatment beams of up to 40 cm square. The performance of the prototype and first production model have been thoroughly tested against the design specifications and the requirements of IEC standards. Radiation attenuation by the collimator components has been measured and substantially exceeds those requirements. The irregular portion of a field (shielded by the leaves only) receives, on average, a dose of less than 2% of the tumour dose. The effect on the penumbra of using leaves which translate linearly and have curved faces has been assessed and found not to degrade the sharpness of the beam fall-off significantly. The reproducibility of the video system used in positioning the leaves has been measured and gave a root mean square deviation of less than 0.3 mm in repeat setting of a 10 cm square field, and an accuracy always within 1 mm. The rationale for clinical use of the device is discussed and its effect on treatment quality control and reliability, is considered.

Computers↗
PubMed1991

Isoniazid as preventive therapy in HIV-infected intravenous drug abusers. A decision analysis.

Tuberculin skin testing is a notoriously poor marker of tuberculosis infection in patients who are serologically positive for the human immunodeficiency virus. A decision analysis was performed to determine if and when isoniazid should be prescribed to prevent tuberculosis in these patients. The decision was analyzed for an intravenous drug abuser who may have been anergic, while tuberculin test status, race, and gender were varied. The assumptions and parameter estimates selected for this investigation represent a highly conservative vantage point opposing the use of isoniazid as a preventive therapy. Nevertheless, results showed a benefit from the use of isoniazid as a preventive therapy for all groups, even without tuberculin testing, except tuberculin-negative black women. This benefit of isoniazid therapy increased patient life expectancy as much as 285 days. Further, the decisions continue to favor prescribing isoniazid even when the suspected incidence of tuberculosis infection falls as low as 3% to 8%. Tuberculin testing appears important primarily for black women, since those who have negative tuberculin skin tests may not be candidates for isoniazid therapy.

Adult↗
PubMed1991

Isoniazid preventive therapy for tuberculosis. Decision analysis considering ethnicity and gender.

The decision to prescribe or withhold isoniazid (INH) preventive therapy for low-risk tuberculin reactors has been highly controversial, primarily due to isoniazid's possible hepatotoxic effects. Previous analyses have explored the INH decision only from the perspective of patient age, recognizing that the risks of INH-induced hepatotoxicity are age related. Decision analyses presented in this paper assess the impact of gender and ethnic group, as well as age, on the INH decision. Results for low-risk patients favor prescribing INH preventive therapy for all 20-yr-olds, all 35-yr-olds except black women, and no 50-yr-olds, projecting life expectancy benefits that range from 3 to 19 days. A comparison set of analyses performed for high-risk patients favors prescribing INH for all groups except 50-yr-old black women. These findings suggest that ethnicity, gender, and age should be considered when making the decision to prescribe or withhold INH preventive therapy.

Adult↗
PubMed1991

Methodological issues in the study of confidentiality: a reinterpretation of findings.

Investigations of confidentiality management have been constrained by an inability to obtain direct measures of clinicians' behaviors when deciding whether to breach or safeguard a confidence. Some researchers have used responses to hypothetical case vignettes to derive approximations of how clinicians manage confidences entrusted to them by their patients. However, these studies have focused primarily on total confidentiality scores, without exploring the possibility that subsets of clinical cases might elicit different confidentiality decisions. In this investigation, reanalysis of responses to case vignettes obtained from 436 psychologists, psychiatrists, and internists revealed that on the issue of confidentiality management, these health care providers discriminate among cases involving: Premeditated harm to others, socially irresponsible acts with possible dire consequences to self or others, and minor theft. Of these three categories of cases, those involving social irresponsibility elicited the greatest disagreement among the clinician groups studied.

Confidentiality↗
PubMed1990

Lack of late skin necrosis in man after high-dose irradiation using small field sizes: experiences of grid therapy.

Out of a total of 437 patients with superior vena caval syndrome or advanced malignancy, given single-dose grid radiotherapy, four survived to 7 years. The dose to the skin under each of the 77 holes in the grid was approximately 58 Gy. The lack of skin necrosis in the total of 308 skin circles of 1 cm diameter among these survivors, compared with known necrosis rates in larger irradiated areas, implies that there is a marked field-size effect for late necrosis in small areas of irradiated skin.

Adult↗
PubMed1989

Once-daily versus twice-daily dosing of theophylline. A decision analysis approach to evaluating theophylline blood levels and compliance.

The question of whether to prescribe once-daily or twice-daily theophylline was investigated using decision-analysis techniques with sensitivity procedures. While the relative efficacies of the two theophylline preparations have been examined in a number of studies, previous efforts have not assessed the impact of compliance on therapeutic effectiveness. When a blood theophylline level of 10 to 20 micrograms is taken to constitute the therapeutic range, twice-daily has been shown to yield 15% greater efficacy than once-daily dosing. However, results of the present investigation suggest that a drop in compliance greater than 4 to 14%, associated with once- versus twice-daily dosing, would be sufficient to obliterate the apparent advantage of the twice-daily preparation. The existing empirical evidence suggests that selecting twice-daily over once-daily dosing will incur a drop in compliance that is substantially greater than 14%. Consequently, when the impact of compliance is incorporated into a decision analysis, once-daily dosing is favored over twice-daily dosing for most patients. The decision will favor twice-daily theophylline only in the unusual case in which continuity of contact with a given patient provides strong evidence that he/she is more than 80% likely to comply with the twice-daily regimen. Decision analyses applied to this topic would benefit greatly from better studies of compliance in asthmatic patients and more careful correlations of symptoms with varying medication usage.

Asthma↗
PubMed1987

Tuberculin reaction size measurement by the pen method compared to traditional palpation.

A prospective, double blind study was conducted to determine the degree of concordance of pen and palpation methods of measuring skin induration to Mantoux tuberculin tests. One hundred thirty-five skin tests were performed in patients with previously bacteriologically proved tuberculous disease. An experienced reader who was only able to see the forearm of the patient measured the induration by the palpation technique. The measurement was then repeated by the pen method under the same conditions, on the same day. Results of the study indicated that the pen method yielded statistically the same frequency distribution of indurations as the palpation method and the pen method appeared to be more sensitive.

Double-Blind Method↗
PubMed1984

A comparison of low and high dose-rate radiation for recipient mice in spleen-colony studies.

Over the last 15 years, endogenous spleen-colony formation in our mice, following lethal irradiation, has increased to an unacceptable level. It has been found necessary, therefore, to introduce a new method of preparing recipient mice for spleen-colony studies. Irradiation with low dose-rate 60Cobalt gamma rays has been compared with high dose-rate linear accelerator electrons, and their effects on endogenous spleen colony formation compared with earlier X and gamma ray dose-response data. It was found that a large dose (13.5 Gy) of gamma rays results in fewer endogenous colonies than 8.5 Gy of electrons, yet because of its low dose rate (14.1 X 10(-3) Gy/min) it has a marked sparing of the intestinal tissue as measured by the intestinal microcolony technique. This in turn permits better survival and, therefore, a 'healthier' animal for spleen-colony work. Exogenous colony formation is also lower in the low dose-rate, gamma-irradiated recipients and this is shown to be due to a reduced spleen-seeding efficiency. It is concluded that very low dose-rate radiation is preferable for haemopoietic ablation, that a mouse colony requires constant monitoring for changes of endogenous spleen-colony formation and that the spleen-seeding efficiency of CFU-s depends on the irradiation technique used--there is no absolute value for a given strain of mouse.

Animals↗