Biomedical subjects

A Kosunen

Publications and source records attributed to A Kosunen.

12 recordsLinked to original sources

PubMed2006

Monte Carlo simulations of occupational radiation doses in interventional radiology.

Occupational radiation doses in interventional radiology can potentially be high. Therefore, reliable methods to assess the effective dose are needed. In the present work, the relationship between the personal dose equivalent, H(p)(10), the reading of a personal dosimeter and the effective dose of the radiologist were studied using Monte Carlo simulations. In particular, the protection provided by a lead apron was investigated. Emphasis was placed on sensitivity of the results to changes in irradiation conditions. In our simulations a 0.35 mm thick lead apron and thyroid shield reduced the effective dose, on average, by a factor of 27 (the range of these data was 15-41). Without the thyroid shield the average reduction factor was 15 (range 6-22). The reduction sensitively depended on the projection and the X-ray tube voltage. The dosimeter reading, when the dosimeter was worn above the apron and a thyroid shield was used, overestimated the effective dose on average by a factor of 130 (range 44-258) when the dosimeter was located on the breast closest to the primary X-ray beam. Without the thyroid shield the average overestimation was 69 (range 32-127). If the dosimeter was worn under the apron its reading generally underestimated the effective dose (on average by 20% with the thyroid shield). Our study indicates that, even though large variations are present, the often used conversion coefficient from the dosimeter reading above the apron to the effective dose, around 1/30, generally overestimates the effective dose by a factor of two or more.

Brain↗

PubMed2006

CD44 expression and its relationship with MMP-9, clinicopathological factors and survival in oral squamous cell carcinoma.

We investigated the expression of CD44 and MMP-9 in primary oral squamous cell carcinoma (OSCC) and evaluated their association with each other and clinicopathological factors as well as their prognostic value during long term follow up. Histological samples from 138 OSCC patients were immunohistochemically stained for the expression of CD44 and MMP-9. The staining results were compared with conventional prognostic factors and their impacts to patients' prognosis were also studied with survival analyses. Irregular staining of CD44 in tumour cells was associated with poor tumour differentiation (p=0.003), higher clinical stage (III-IV) (p=0.049), and the presence of T3-4 tumour stage (p=0.03). Strong stromal MMP-9 staining intensity was correlated with poor tumour differentiation (p=0.03). In univariate survival analysis irregular staining of CD44 in tumour cells was related to poor disease free and overall survival (p=0.001 and p<0.001, respectively). In multivariate analysis CD44 staining was a significant independent predictor for overall (p=0.03) and disease free survival (p=0.003). MMP-9 expression showed no statistical significance in survival analyses. Strong stromal staining intensity of MMP-9 correlated with irregular staining of CD44 in tumour cells, but had no prognostic significance in the present cohort. However, irregular staining of CD44 predicted more advanced disease and shortened survival of the patients.

Adolescent↗

PubMed2006

Evaluation of methods to estimate the patient dose in interventional radiology.

Dosimetric methods used for interventional and diagnostic radiology are reviewed and evaluated, including terms, quantities, equipment, calibration and measurements. Measurement of local skin dose and estimation of maximum local skin dose are emphasised. Aspects related to dosimetry in computed tomography and to methods of determining organ and tissue doses are not considered.

Calibration↗

PubMed2004

Measurement of free beam neutron spectra at eight BNCT facilities worldwide.

Eight epithermal neutron beams, constructed for clinical or preclinical studies of NCT, have been dosimetrically characterized by in-air measurements with a set of activation foils for the determination of the neutron energy spectra in free beam. Measurements have been made on the already closed epithermal BNCT facility at the BMRR of the Brookhaven National Laboratory, on the HFR at JRC in Petten, The Netherlands, on the epithermal mode beam at KURRI, Japan, on the fission converter beam at MIT, USA, on the epithermal beam of the RA-6 facility in Bariloche, Argentina, on the epithermal beam at WSU, USA, on the mixed mode beam at JRR-4 at JAERI, Japan, as well as on the epithermal beam at FiR 1 at VTT, Espoo, Finland.

Animals↗

PubMed2004

Dosimetric comparison at FiR 1 using microdosimetry, ionisation chambers and computer simulation.

Tissue equivalent proportional counter microdosimetry has been applied in the dosimetry of epithermal neutron beams as they can provide an independent and accurate method to determine gamma ray and neutron absorbed doses. Dosimetric comparison has been performed using a tissue equivalent proportional counter, dual ionisation chambers and DORT computer code at FiR 1 boron neutron capture therapy facility in Espoo, Finland. The three methods were applied to determine neutron and gamma ray absorbed doses at 25, 40, 60 and 120 mm depths along the beam centerline in a water-filled PMMA phantom. The determined absorbed doses were found to agree within the limits of the estimated uncertainties.

Boron Neutron Capture Therapy↗

PubMed2004

Reduced expression of hyaluronan is a strong indicator of poor survival in oral squamous cell carcinoma.

Several malignant tumours accumulate hyaluronan (HA), a matrix component suggested to promote cancer cell growth and migration. The expression and prognostic value of HA was analysed in a cohort of 151 oral squamous cell carcinoma (SCC) patients with adequate archival tumour material and follow-up data. The tumour samples were stained using a biotinylated HA-specific probe. Normal squamous epithelium showed a strong and homogeneously distributed staining for HA. The most superficial layers were HA-negative. In moderate (n=11) and high grade (n=16) dysplasias an irregular HA staining was observed around invasive cancer. Malignant transformation in oral squamous cell epithelium changed the staining toward irregular with focal reduction of HA. The well (n=92) or moderately differentiated (n=47) carcinomas had a strong HA staining intensity. In poorly differentiated tumours (n=12) the HA staining was weaker and mainly intracellular. The stromal tissue showed usually moderate (n=69) or strong (n=67) HA staining intensity with no statistically significant correlation with the degree of tumour differentiation. At the end of the follow-up (median 52 months) 66 (43%) patients had died because of an oral SCC. A significant difference in overall survival (OS) and disease free survival (DFS) (P=0.0002 and 0.0020, respectively) was noticed between the patients with the different epithelial staining patterns for HA. The reduction of HA staining was associated with poor survival. In Cox's multivariate analysis HA staining was a significant independent predictor of OS (P=0.011) and DFS (P=0.013). These results suggest that HA is a prognostic marker in oral squamous cell carcinoma.

Adolescent↗

PubMed2004

Calibration of dosemeters used in mammography with different X ray qualities: EUROMET project no. 526.

The effect of different X ray radiation qualities on the calibration of mammographic dosemeters was investigated within the framework of a EUROMET (European Collaboration in Measurement Standards) project. The calibration coefficients for two ionization chambers and two semiconductor detectors were established in 13 dosimetry calibration laboratories for radiation qualities used in mammography. They were compared with coefficients for other radiation qualities, including those defined in ISO 4037-1, with first half value layers in the mammographic range. The results indicate that the choice of the radiation quality is not crucial for instruments with a small energy dependence of the response. However, the radiation quality has to be chosen carefully if instruments with a marked dependence of their response to the radiation energy are calibrated.

Calibration↗

PubMed2004

Calibration of a scintillation dosemeter for beta rays using an extrapolation ionization chamber.

A scintillation dosemeter is calibrated for 90Sr/90Y beta rays from an ophthalmic applicator, using an extrapolation ionization chamber as a reference instrument. The calibration factor for the scintillation dosemeter agrees with that given by the manufacturer of the dosemeter within ca. 2%. The estimated overall uncertainty of the present calibration is ca. 6% (2 sd). A calibrated beta-ray ophthalmic applicator can be used as a reference source for further calibrations performed in the laboratory or in the hospital.

Beta Particles↗

PubMed2003

Computational study of the required dimensions for standard sized phantoms in boron neutron capture therapy dosimetry.

The minimum size of a water phantom used for calibration of an epithermal neutron beam of the boron neutron capture therapy (BNCT) facility at the VTT FiR 1 research reactor is studied by Monte Carlo simulations. The criteria for the size of the phantom were established relative to the neutron and photon radiation fields present at the thermal neutron fluence maximum in the central beam axis (considered as the reference point). At the reference point, for the most commonly used beam aperture size at FiR 1 (14 cm diameter), less than 1% disturbance of the neutron and gamma radiation fields in a phantom were achieved with a minimum a 30 cm x 30 cm cross section of the phantom. For the largest 20 cm diameter beam aperture size, a minimum 40 cm x 40 cm cross-section of the phantom and depth of 20 cm was required to achieve undisturbed radiation field. This size can be considered as the minimum requirement for a reference phantom for dosimetry at FiR 1. The secondary objective was to determine the phantom dimensions for full characterization of the FiR 1 beam in a rectangular water phantom. In the water scanning phantom, isodoses down to the 5% level are measured for the verifications of the beam model in the dosimetric and treatment planning calculations. The dose distribution results without effects caused by the limited phantom size were achieved for the maximum aperture diameter (20 cm) with a 56 cm x 56 cm x 28 cm rectangular phantom. A similar approach to study the required minimum dimensions of the reference and water scanning phantoms can be used for epithermal neutron beams at the other BNCT facilities.

Boron Neutron Capture Therapy↗

PubMed2003

Characterisation of projectiles composed of depleted uranium.

Projectiles suspected to be composed of depleted uranium (DU) were found in Kosovo. Their properties were analysed using alpha and gamma ray spectrometry, mass spectrometry and electron microscopy. They were found to be composed of DU with small amounts of other elements such as Ti. 236U was detected in the penetrators, reflecting the use of reprocessed fuel. No transuranium elements were detected. The typical external dose rate meter is not the best option for mapping the location of penetrators from the ground. Monte Carlo calculations were performed in estimating possible skin doses. Penetrators in long-lasting contact with skin may cause a notable equivalent dose to skin.

Environmental Exposure↗

PubMed1993

Intercomparison of radiotherapy treatment planning systems for external photon and electron beam dose calculations.

Dose distributions calculated by six different treatment planning systems (TPSs), used by the hospitals in Finland or in Russia, were compared with measured dose distributions. Five typical cases of irradiation were selected: regular fields, oblique incidence, irregular field, wedge field and inhomogeneity in a water equivalent phantom. The beam data for each TPS where those pertaining to the beam where the comparative relative measurements were performed. The results indicate that the dose distributions produced by different TPSs can differ from each other as well as from the measured dose distributions up to a level which is not acceptable in terms of the ICRU recommendations. Greatest differences seem to be related to the omission or undue consideration of the scatter components of the beam.

Algorithms↗

PubMedDate not supplied

Beam quality specification for photon beam dosimetry.

It is argued that %dd(10), the percentage depth dose at 10 cm in a 10 x 10 cm2 photon beam at a SSD of 100 cm, is a better beam quality specifier for radiotherapy beams than the commonly used values of TPR10(20) or nominal accelerating potential (NAP). For radiation dosimetry purposes, TPR10(20) is not an ideal beam quality specifier because (i) stopping-power ratios for the same value of TPR10(20) can vary by up to 0.7% for thick-target bremsstrahlung beams; (ii) the value of TPR10(20) becomes insensitive to beam quality changes for high-energy beams; and (iii) it has little intuitive meaning. In contrast, %dd(10) in a pure photon beam specifies stopping-power ratios within 0.2% for all thick-target bremsstrahlung beams, maintains its sensitivity for high-energy beams, and has a simple physical and clinical meaning. It is shown that for all thick-target bremsstrahlung beams the spr (water/air) = 1.2676-0.002 224[%dd(10)] with a rms deviation of 0.1%. The effects of electron contamination in typical high-energy clinical beams can be corrected for using previously published experimental results or by reducing electron contamination using lead scattering foils.

Biophysical Phenomena↗