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Biomedical subjects

P F O'Brien

Publications and source records attributed to P F O'Brien.

24 records · Page 2Linked to original sources
PubMed1980

The ICTH/WFH study of the partial thromboplastin time in mild haemophilia.

A study has been carried out in two stages to compare the sensitivity of different Partial Thromboplastin Time (P.T.T.) methods to partial deficiencies of factor VIII. In Stage 1, 63 laboratories throughout the world compared their own methods with a reference method, all using samples of the same three mild haemophilic plasmas. Wide variation was found between laboratories using the same method, especially for those methods which were not well standardised. There was fairly good agreement for the reference method. All methods correctly diagnosed the three mild haemophilic plasmas, but their factor VIII levels were rather low. Stage 2 was restricted to seven laboratories in Great Britain, comparing seven well-standardised commercial methods and the same reference method. A much wider range of abnormal plasmas was tested, and a variety of normal ones. P.T.T.'s for all plasmas (factor VIII levels from 5 to 58 iu/dL) fell outside the normal range by all methods, with a few exceptions. It was not possible to rank the methods in any order.

Blood Coagulation Tests↗
PubMedDate not supplied

Characteristics of the photon beam from a new 25-MV linear accelerator.

The Therac 25 is a relatively compact therapy machine, the heart of which is a double-pass electron linear accelerator. The electron beam is injected into the accelerator at the treatment head end of the machine and is accelerated back down the arm to an energy of 13 MeV. At this end of the machine a magnet system reflects the beam back into the structure where it gains up to an additional 12 MeV of energy. After leaving the linear accelerator the beam is bent by an achromatic head magnet through 270 degrees to the treatment head. The machine produces eight electron beams and a 25-MV photon beam. In this work only the parameters of the photon beam are addressed based on measurements at the first two clinical sites. Percentage depth doses, tissue phantom ratios, and beam symmetry and stability are presented and discussed.

Humans↗
PubMedDate not supplied

Measurements in high-intensity beams from medical linear accelerators.

There is a potential to produce very high doses and dose rates on dual mode (electron and x-ray capability) medical electron accelerators [C. J. Karzmark, Br. J. Radiol. 40, 697 (1967)]. Measurements were taken on two accelerators to determine the size of the doses which were possible. The experiments demonstrate the limitations of many of the commonly used dosimeters when they are used outside of the dose and dose rate ranges normally encountered in a radiotherapy department. Dose rates from 110 to 165 cGy/pulse were measured using ionization chamber, ferrous sulphate and thermoluminescent dosimetry, and water calorimetry.

Calorimetry↗
PubMedDate not supplied

Radiosurgery with unflattened 6-MV photon beams.

One of the major drawbacks to doing stereotactic radiosurgery with a linear accelerator is the long time required to deliver the target dose. Single fractions of 25 Gy delivered at the isocenter and at depth in the skull may require beam times in excess of 15 min for a typical linear accelerator with a maximum dose rate of 250 cGy/min in tissue. In an effort to decrease the treatment time for this technique, the flattening filter has been removed from an AECL Therac-6 linear accelerator and the characteristics of the resulting beam have been measured. Flatness is acceptable for the field sizes used with this technique and the dose rate is increased by a factor of 2.75.

Brain Diseases↗
PubMedDate not supplied

Engineering modifications for dynamic stereotactically assisted radiotherapy.

To perform dynamic stereotactic radiotherapy, a number of modifications to the commercial linear accelerator were required and these are described in this report. A couch drive system was added to rotate the couch in synchrony with the gantry. A high dose rate beam for this technique is acquired through a head modification, which allows easy removal of the radiation field flattener. Because of these modifications, a number of changes and additions were required to the linac interlock system, including a complete new chain of interlocks for use with the stereotactic technique.

Biomedical Engineering↗