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Biomedical subjects

P Fessenden

Publications and source records attributed to P Fessenden.

33 records · Page 2Linked to original sources
PubMed1982

The PIOTRON: initial performance, preparation and experience with pion therapy.

The PIOTRON is a large solid angle superconducting channel built for the use of negative pi-mesons in radiotherapy. The pions are produced by protons of 590 MeV striking a target of molybdenum or beryllium. The pions are divided into 60 channels and deflected twice to enter the treatment volume radially. The momentum and the momentum band for all 60 channels can be chosen and the beam spot of Bragg peak pions at the isocenter of the applicator is a few centimeters in each direction. Dynamic scanning can thus achieve 3-dimensionally shaped treatment volumes. Two different methods are available: the ring scan, using changes of pion range; and the spot scan, involving translation of the patient through the fixed beam spot. Dose distributions of individual and multiple beams were plotted in a cylindrical water phantom. Radiobiological experiments with mammalian cells in gel and with mouse feet were performed. A special beam geometry using a sector of 15 beams was selected for the first treatments of patients with metastatic skin nodules. Six patients were treated. Acute skin reactions were scored and compared with those from orthovoltage therapy with comparable beam geometry. The RBE for 10 fractions is between 1.4 and 1.5. The next step involved treatment of patients inside water-bolus rings in preparation for dynamic therapy. Patients were then treated with the spot scan dynamic mode in the water bolus. The initial responses and reactions are favorable and confirm the feasibility and accuracy of dynamic pion therapy.

Elementary Particles↗
PubMed1978

Dosimetry for tangential chest wall irradiation.

The skin-sparing effect of megavoltage photons is lost to a varying extent when tangential beams are used to irradiate the chest wall. The skin dose for this technique, with and without a bolus, was investigated for 4- and 6-MV photons using film, thermoluminescent dosimeters, and an ionization chamber. Metal/tissue interface effects were observed when a flexible brass fabric material was used as a bolus.

Humans↗
PubMed1977

Initial performance of the Stanford Medical pion generator.

A novel, cylindrical geometry, superconducting pion channel has been constructed at Stanford. It can simultaneously deliver up to 60 radially converging pion beams of the same mean momentum but with individually variable momentum spread (0.0-4.3%). Virtually no tuning of the pion beam is required Preliminary tests have demonstrated many of the performance characteristics which facilitate the treatment of selected human tumors.

Cold Temperature↗
PubMedDate not supplied

Introduction to hyperthermia device evaluation.

From 10/81 to 1/87, the National Cancer Institute (NCI) of the U.S. Department of Public Health Services (PHS) contracted with four institutions to evaluate hyperthermia technology to be applied in the treatment of human malignancy. During the five year period 1981-1986, data were collected which now reside in a consensus database representing treatments of 792 separate sites or fields in a total of 573 patients. These patients were treated with one or more of 49 devices by the four institutions. Sixteen ultrasound (US) devices were evaluated in 195 sites. Nine magnetic induction (MI) devices were evaluated in 208 sites. Twenty radiative electromagnetic (EM) devices were evaluated in 488 sites. Four interstitial (IRF) devices were evaluated in 37 sites. Many sites were treated with multiple hyperthermia modalities. This first in a series of 13 reports describes the general objectives of the Contractors' Group, basic methods of device evaluation and brief details of the large variety of devices tested.

Electromagnetic Phenomena↗
PubMedDate not supplied

Stanford University institutional report. Phase I evaluation of equipment for hyperthermia treatment of cancer.

From September 16, 1981, through April 4, 1986, a total of 21 radiative electromagnetic (microwave and radiofrequency), ultrasound and interstitial radio-frequency hyperthermia applicators and three types of thermometry systems underwent extensive phantom and clinical testing at Stanford University. A total of 996 treatment sessions involving 268 separate treatment fields in 131 patients was performed. Thermal profiles were obtained in 847 of these treatment sessions by multipoint and/or mapping techniques involving mechanical translation. The ability of these devices to heat superficial, eccentrically located and deep-seated tumours at the major anatomical locations is evaluated and the temperature distributions, acute and subacute toxicities, and chronic complications compared. Average measured tumour temperatures between 42 degrees C and 43 degrees C were obtained with many of the devices used for superficial heating; average tumour temperatures of 39.6 degrees C to 42.1 degrees C were achieved with the three deep-heating devices. When compared to the goal of obtaining minimum tumour temperatures of 43.0 degrees C, all devices performed poorly. Only 14 per cent (118/847) of treatments with measured thermal profiles achieved minimum intratumoural temperatures of 41 degrees C. Fifty-six per cent of all treatments had associated acute toxicity; 14 per cent of all treatments necessitated power reduction resulting in maximum steady-state temperatures of less than 42.5 degrees C. Direct comparisons between two or more devices utilized to treat the same field were made in 67 instances, including 19 treatment fields in which two or more devices were compared at the same treatment session. The analyses from direct comparisons consistently showed that the static spiral and larger area scanning spiral applicators resulted in more favourable temperature distributions. Three fibreoptic thermometry systems (Luxtron single channel, four channel and eight channel multiple [four] probe array), the BSD Bowman thermistor system and a thermocouple system were evaluated with respect to accuracy, stability and artifacts. The clinical reliability, durability, and patient tolerance of the thermometry systems were investigated. The BSD Bowman and third generation Luxtron systems were found clinically useful, with the former meeting all of our established criteria.

Adult↗
PubMedDate not supplied

Heat loss and blood flow during hyperthermia in normal canine brain. I: Empirical study and analysis.

The effects of blood flow and thermal conduction during microwave hyperthermia were investigated in normal canine brain. Heating was accomplished with an external microstrip spiral antenna and temperature measurements were made using a multichannel fluoroptic thermometry system. In order to determine cooling rates, temperature measurements made during cooling were fitted with a model consisting of a constant value and an exponential term. Data from experiments in both perfused and non-perfused brains could be fitted with this simple model. The resulting cooling rates indicated that heat loss by conduction is comparable to that by blood flow. In another series of experiments, temperature measurements were made during several 1 min cooling intervals in which the power was shut off intermittently during a 35 min heating episode. Results were consistent with a 2-3-fold increase in blood flow rate which occurred gradually throughout the course of heating. Parameters that affect the determination of cooling rates are discussed in terms of the bioheat transfer equation. These investigations demonstrate that a simple heat sink model provides a good representation of the cooling data for the thermal distributions obtained.

Animals↗
PubMedDate not supplied

Heat loss and blood flow during hyperthermia in normal canine brain. II: Mathematical model.

A mathematical model for heating and cooling during hyperthermia has been developed from an appropriate solution of a bioheat transfer equation. Predicted cooling rates obtained from the model have been compared with cooling rates obtained from experiments performed on both perfused and non-perfused normal canine brain tissue. The agreement between the predicted and observed cooling rates in non-perfused tissue is satisfactory (within 6-11 per cent) and provides confidence that the conduction process is being accurately represented. The model is then used to estimate the relative contribution of conductive and convective (blood flow) heat loss during cooling for the in vivo experiments. Estimates of blood flow dynamics are made from cooling data taken early and late in a heating course using the model to correct for conductive heat loss. Simplified forms of the bioheat transfer equation are examined. An adequate model for the observed cooling data is one that treats heat loss (both conduction and blood flow) as a heat sink (i.e. an effective perfusion model) rather than an effective thermal conductivity model.

Animals↗
PubMedDate not supplied

Automation of temperature control for large-array microwave surface applicators.

An adaptive temperature control system has been developed for the microstrip antenna array applicators used for large area superficial hyperthermia. A recursive algorithm which allows rapid power updating even for large antenna arrays and accounts for coupling between neighbouring antennas has been developed, based on a first-order difference equation model. Surface temperatures from the centre of each antenna element are the primary feedback information. Also used are temperatures from additional surface probes placed within the treatment field to protect locations vulnerable to excessive temperatures. In addition, temperatures at depth are observed by mappers and utilized to restrain power to reduce treatment-related complications. Experiments on a tissue-equivalent phantom capable of dynamic differential cooling have successfully verified this temperature control system. The results with the 25 (5 x 5) antenna array have demonstrated that during dynamic water cooling changes and other experimentally simulated disturbances, the controlled temperatures converge to desired temperature patterns with a precision close to the resolution of the thermometry system (0.1 degree C).

Algorithms↗
PubMedDate not supplied

Mammalian cell survival studies characterizing multiport negative pi-meson irradiation with the Stanford Medical Pion Generator (SMPG).

Radiobiological measurements have been made under various conditions of muliport pion irradiation using the Stanford Medical Pion Generator (SMPG). Chinese hamster cells (HA-1) were suspended in a tissue-equivalent 25% gelatin/medium solution. Hypoxic and aerobic HA-1 cells were irradiated simultaneously in a cylindrical water tank at either 4 or 16 degrees C. Irradiation at the focus of 60 converging pion beams, at a peak dose rate of 6 rads/min, gave relative biological effectiveness (RBEs) of 2.8, 1.8 and 1.4 at 50, 20 and 5% survival, respectively, and an oxygen enhancement ratio (OER) of 1.7. Plateau irradiation with crossing pion beams, at a peak dose-rate of 3 rads/min, resulted in survival values very close to those obtained with similar doses of 85 kV X-rays. Preliminary studies with large irradiation volumes in broadened pion stopping regions indicate RBEs significantly > 1 for survival > 50%. Supporting microdosimetric data with the SMPG are consistent with the radiobiological results.

Animals↗