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Biomedical subjects

R O Kornelsen

Publications and source records attributed to R O Kornelsen.

At least 19 recordsLinked to original sources
PubMed1994

Dosimetry for asymmetric x-ray fields.

Conventional linear accelerators have four field-defining jaws or collimators. Usually, one set of the two opposing jaws moves concurrently to define the field width and the other set defines the field length. The resultant square or rectangular field will have the field centerline coincide with the collimator axis. However, some modern linacs have independent collimators or jaws that can be set asymmetrically. In this case, one of the two opposing jaws can be closed down independently of the other one to define an asymmetric field of smaller dimension. The field center now does not coincide with the collimator axis. Asymmetric collimators have found many clinical applications, but have complicated the dosimetry for physicists. Data acquisition and treatment planning implementations are tedious and complicated. An algorithm has been developed to correct for the reduced dose in the smaller asymmetric field. The approach used is similar in principle to the Day's equivalent field calculation. The difference in dose between an asymmetric and a symmetric radiation field is accounted for by a correction factor that is a function of the asymmetric and symmetric field sizes, off axis distance, and depth of measurement. The correction method presented here applies only to the closing down of one independent jaw. Beam profiles for asymmetric fields are measured for both the 6 and 10 MV photon beams.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1989

Clinical results in carcinoma of the cervix: radium compared to caesium using remote afterloading.

In 1979 the Cancer Control Agency of British Columbia changed from radium to remote controlled afterloaded caesium in the treatment of carcinoma of the cervix. In the 3 years prior to the change, 139 patients received radium as part of their treatment and in the 3 years after the change, 158 patients received caesium. Overall referral patterns, patient and cancer demographics, and treatment policies were stable throughout the 6-year period. Radiotherapy technique, dose, dose distribution and dose rate were comparable for both radium and caesium treated patients. The results of treatment in the two time periods showed no difference in survival, local tumour control or complications. The use of afterloading has not compromised treatment results and has allowed better nursing care for patients and protection from radiation for all staff.

Brachytherapy↗
PubMed1985

Preparatory clinical studies of Pi-mesons at TRIUMF.

Eighty patients have been treated with Pi-mesons (pions) at TRIUMF between 1979-1984. The patients had tumors rarely curable by standard methods and had no prior radiotherapy. The distribution by site included skin, metastatic nodules (13), brain, glioblastoma multiforme (32), pelvis, rectosigmoid (15), prostate (12), bladder (7), and ovary (1). The studies involve serial escalations of pion dose until maximum tissue tolerance is reached, monitoring the response at each dose increment. Sites were chosen for study where lack of local control is a significant cause of treatment failure with conventional radiation therapy. The low dose rate and the available beam access at TRIUMF limit the number of patients treated and the volume treatable. A 3-D treatment planning program is in use, and a 3-D display of the dose distribution delivered in brain tumor treatments has been developed using the PET scanner. In practice, new methods introduced for measurement of tissue response include tumor growth delay curves, fine-needle biopsy mapping, and PET scanning of brain tumors. The use of endoscopic assessment of the rectosigmoid region is emphasized. Treatment results of glioblastoma multiforme show that the median survival for patients treated to 125 pion cGy/fx is in the range of 187-198 days; for patients receiving 170 cGy per dose/fraction (fx) the range is 290-315 days, and for those receiving 200-220 cGy/fx the median survival is in excess of 290 days. For pelvic malignancies the local control obtained with doses of 2500 cGy or less was 50% in 12 assessable patients; it was 75% in 20 patients who had 3000 cGy or more.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

In vitro and in vivo studies of the TRIUMF pion therapy beam.

Patient treatments at TRIUMF (Tri-University Meson Facility, Vancouver, B. C.) use a moving spot raster scan technique where the pion range is modulated in depth for each position of the moving spot. The spot scans in a stepwise fashion and can produce any desired field shape. This approach provides very good dose uniformity across the treatment field and allows maximum flexibility in shaping the treatment volume. Survival of cultured cells has been used as a biological dosimeter to test the isoeffectiveness of the pion dose distributions, which must be shaped in depth to compensate for the depth-dependent LET distribution. Isoeffectiveness across the treatment field has also been verified using this system, which involves irradiating cells supported in a gelatin matrix. The response of pig skin to pion irradiation at TRIUMF has provided a check on the in vivo RBE for acute effects derived from our earlier studies with mouse foot. In addition, the pig skin reactions have been followed for several months to assess the later dermal response. The RBE of our pion beam relative to 270 kVp X rays is approximately 1.5 for both the acute epidermal and the later dermal responses.

Animals↗
PubMed1984

Application of moiré topography to mantle treatment.

We believe moiré topography is a particularly suitable technique for establishing contours on patients receiving mantle treatment. We derive the fundamental moiré equation from a novel, but simple, consideration of moiré phenomena. Our apparatus is designed to give a difference in height of approximately 1.0 cm between successive moiré fringes. Using an inclined plane test object, an accuracy of better than 3 mm is obtained.

Anthropometry↗
PubMed1982

Pions, Vancouver.

Clinical treatments at TRIUMF started in November, 1979. Ten patients with malignant subcutaneous nodules had 14 lesions treated with pions and 37 other nodules treated with 280 kV X rays. Three different fractionation regimens were used with X ray doses spanning the expected RBE range of pions. The RBE for pions for acute skin reaction for 10 fractions had a mean value about 1.5, while for 3 fractions it was 1.3 maximum. No dissociation of acute and late skin effects was seen with follow-up to 27 months after treatment. Phase 1-2 studies of Pion-Boost Therapy for patients with glioblastoma multiforme will begin in May, 1982. These will be followed in August with treatments of advanced pelvic malignancies using pions only. The existing beam line at TRIUMF will be upgraded and commitments have been given to go to higher beam currents. As a result, the dose rate should increase by a factor of at least two, allowing treatment of clinically relevant volumes in acceptable times by 1983-1984.

Brain Neoplasms↗
PubMed1975

Empirical equations for the representation of depth dose data for computerized treatment planning.

Equations of the form (see article) have been used to represent the variation of central axis percentage depth dose P or tissue-air ratio (TAR) with depth d below the dose maximum. The equations were originally developed for the representation of cobalt 60 depth dose data but have also been fitted to the central axis depth dose data published in the British Journal of Radiology Supplement 11, for radiations ranging in energy from 1-5 mm Cu HVT to 8 MV. Values of the constants Q and M for standard field sizes are presented together with an estimate of the goodness of fit in each case. Two different approaches have been used in determining the dose at points other than those on the central axis. In the simpler method, used for rotation techniques, the off-axis ratio (OAR) is calculated from the equation. (see article) where x is the off-axis distance, w the field width at the depth and k1 and k2 are constants. In the more accurate method, used for fixed field techniques, different equations are used within the main beam, within the geometrical penumbra and outside the beam.

Computers↗
PubMedDate not supplied

Dose corrections for low-density tissue inhomogeneities and air channels for 10-MV x rays.

Methods of correcting for tissue inhomogeneities which consider only changes in the photon fluence are of limited usefulness for 10-MV x rays. Although there is normally transient electronic equilibrium on the central axis beyond the depth of maximum buildup in soft tissue, when the beam enters a low-density material the beam profile is degraded and there is a loss of lateral electron equilibrium which reduces the dose both within and beyond the inhomogeneity. This paper describes experimental measurements of the dose within and near large, low-density inhomogeneities simulating lungs and also behind air channels (where similar effects occur). Methods of calculating correction factors are discussed.

Lung↗
PubMedDate not supplied

A differential method for inhomogeneity correction on dose in a photon beam.

For a uniform slab of inhomogeneity in a supervoltage beam, correction factors can be calculated from the Batho equation. In this report, we present a method for calculating the effect of an annular inhomogeneity, concentric about the beam axis, upon the dose at a point on the axis and below the annulus. A derivation of the equation required in the calculation for supervoltage radiation is given. Results from measurements made in 60Co beams for polystyrene foam, cedar, and aluminum annuli, all having 3.0 x 2.0 cm2 in cross section but with different inside diameters, are compared with correction values calculated by the method. For situations where the annulus is just submerged in the phantom, measured and calculated values are in good agreement. For a general situation, two calculation types are proposed and the data show that in general the measured scatter perturbation lies between the calculated values of the two types. Application of our technique predicts a sign reversal in the scatter perturbation due to an inhomogeneity. This reversal has previously been observed and reported and is also demonstrated in our measurements.

Cobalt Radioisotopes↗
PubMedDate not supplied

Practical application of the differential Batho method for inhomogeneity correction on kerma in a photon beam.

The Batho equation gives a satisfactory method to correct the dose for points in the electronic equilibrium region for a uniform slab of inhomogeneity in a photon beam. In spite of the many investigations, we believe no simple and adequate method has been found for routine clinical dose calculations which require dose correction of a small-volume inhomogeneity in an arbitrary location. In the present report, we combine the values of the two calculation types of the differential Batho method, which we have developed previously, to give a new calculated value for the scatter perturbation due to an annulus of inhomogeneity. The coefficients in the combination, which we derived from a detailed analysis of the scatter perturbation, are simple geometrical ratios. The new calculated values are in good agreement with measured values. We believe this application of the differential Batho method can provide a practical and accurate method of correcting for inhomogeneities of any size and shape in clinical dose calculations.

Humans↗
PubMedDate not supplied

Detection of pion-induced radioactivity by autoradiography and positron emission tomography.

An autoradiographic technique incorporating a new imaging system was used to detect pion-induced radioactivity in Plexiglass and the results were compared with aluminium activation and PET imaging. The activity distribution in the region of the pion-stopping peak was similar in all three cases. Another large signal in the entrance region due to in-flight interactions [12C(pi-, pi- n) 11C] was detected by autoradiography and by PET but was not reflected in the aluminium activation measurements. This new technique is capable of defining the stopping region in phantoms with a better resolution than PET scanning and is useful as a complementary technique to other methods of pion dosimetry.

Autoradiography↗