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P Zaránd

Publications and source records attributed to P Zaránd.

At least 19 recordsLinked to original sources
PubMed1996

On the measurement of the effective linear attenuation coefficient mueff in 60Co wedge fields.

PURPOSE: It is difficult to obtain a correct measurement of mueff. Moreover, wedge calculations using a single mueff value are not correct. We present a program for the analysis of wedge measurements. MATERIALS AND METHODS: The program employs parameters of an open field to correct the dosimetry of a wedge field. For this the ASCII export files of an MP3 (PTW) system are automatically imported into our program. The principle is illustrated for ionization measurements from a Chisobalt 2B75 cobalt unit. The wedge field dose profiles are corrected by the off-centre ratio of the open field and mueff is analysed as well as its dependents on geometry. RESULTS: We found that the dose attenuation by a wedge can be described by the product of wedge thickness and the effective linear attenuation coefficient mueff. However, mueff values for a given field size decrease with depth. This is interpreted as an effect of beam hardening. For the usual fields in radiotherapy this effect is independent of field size and can be described as an exponential function of wedge thickness. CONCLUSION: The effective linear attenuation coefficient mu(eff) is depth-dependent. A correction could be added to planning programmes, i.e.: exp. (delta mu.tw.[d-dmax]).

Cobalt Radioisotopes↗
PubMed1990

On the use of NHZ-203C Thermoluminescence (TL) reader in clinical dosimetry.

The sensitivity vs. dose characteristics of two TL readers (Harshaw 2000 A + B and NHZ-203C) was compared both in the range of small doses (10 microGy to 100 mGy) as well as in the radiation therapy level by using individually calibrated LiF:Mg, Ti detectors manufactured in Poland. The performance of both systems can be predicted by a three parameter theoretical model. The very good reproducibility of the NHZ-203C reader (sigma/D = 0.6%) is important in radiation therapy while the high sensitivity (the lowest detectable dose limit = 3 S.D. of the background = 27 microGy) is useful for radiation protection measurements.

Evaluation Studies as Topic↗
PubMed1989

Quality control of X-ray orthovoltage therapy units with a dual TL system.

More than 40 orthovoltage X-ray therapy units are monitored by calibrated thermoluminescent dosimeters (TLD). Three pairs of LiF:Mg,Ti and CaSO4:Dy pellets are irradiated in air in a polypropane capsule. The range between 0.2 to 3.0 mm Cu the half-value layer (HVL) is determined from the CaSO4-LiF ratio. In this range, the response of the LiF dosimeters is corrected for energy dependence. We are using a fixed sensitivity for LiF in the MVL range of 2 mm Al to 0.2 mm Cu. In the first two years 173 monitorings were performed by using 485 badges. Usually not more then two different radiation qualities (in the HVL ranges 2 mm Al to 0.2 mm Cu and 0.9-2.5 mm Cu) or two beams used on a therapy unit are measured by using 2-3 badges per monitoring. In 134 cases (77.5%) the dose rates were within acceptable limits (+/- 10%). In 23 cases (13.3%) a failure of the X-ray unit was detected. We think that our system is simple enough and may be used for the dosimetric monitoring of orthovoltage X-ray therapy units. In some cases even the type of malfunction can be determined.

Quality Control↗
PubMed1989

A new type of sorting program for plotting of isodose curves.

The determination of isoeffect curves (sometimes within given contours) from data given in an n x m matrix is a general scientific problem. The algorithm to be described is useful e.g. for pen plotters not only in the case of brachytherapy but in teletherapy too. It takes into consideration the effect of the body contour (isodose curves are not plotted outside the contour). The points with the desired dose value are rearranged into continuous line segments. The segments are characterized by the serial number of their start point and that of their extremity and by a variable the value of which can be 0 or 1 depending on whether the segment is closed or not. The number of the unconnected segments is the fourth variable characterizing the isodose line. The sorting algorithm ensures the less motion of the pen and the less tests during the plotting process. The algorithm has been implemented on IBM compatible PC's.

Algorithms↗
PubMed1987

Dose reconstruction of x-ray irradiation of the larynx.

The authors have determined the dose distribution in the neck for parallel opposed and three field orthovoltage X-ray irradiation techniques of the larynx. LiF:Mg, Ti rods and pellets combined with film densitometry were used. Absorbed dose measured in the region of vocal chords is about 20% lower than that assessed by assuming full backscatter (perpendicular incidence) and by using standard isodose tables.

Film Dosimetry↗
PubMed1986

Source localization in intracavitary 60Co therapy with semiconductor and TL detectors.

Thermoluminescence and p-type semiconductor detectors were used for localization of the source in intracavitary (modified Stockholm method) treatment. The results were compared with X-ray films, and especially good agreement was obtained if the detectors were positioned on both sides of the patients. The measurements performed on Stage III to IV carcinoma cervix uteri patients indicate that the intracavitary source can deviate to both sides with equal probability. The magnitude of the deviation is described by a Gaussian distribution with an expected value of zero and S.D. of 8mm.

Brachytherapy↗
PubMed1985

The effect of external regeneration on the performance of CaSO4:Dy discs.

The authors have investigated the effect of annealing on the reproducibility of CaSO4: Dy dosimeters. The dosimeters cannot be used without external thermal treatment in high precision therapy level dosimetry while a 600 degrees C-1 h external regeneration resulted in a better reproducibility than a 400 degrees C-1 h treatment (which may be used if the absorbed dose in water does not exceed a few Gy). The background of the dosimeters increased considerably even in a 10 X 1 mGy exposure as a result of irradiation history if no external regeneration was used.

Calcium Sulfate↗
PubMed1984

On the effect of the discrete nature of the photoelectric emission in the thermoluminescence measurements (pulse counting method).

The discrete nature of the photoelectric emission cannot be neglected at low reading levels. The effect of A/D conversion after photomultiplication were both calculated and measured. The reading and its standard deviation were considerably different from those expected on the basis of a simple Poisson distribution and this should be taken into account at low reading levels. The authors describe a simple method which permits the experimental determination of photoelectron/digit conversion factor necessary for the prediction of the variation coefficient of TL measurements.

Analog-Digital Conversion↗
PubMed1983

On the statistics of 32P enrichment in skin tumours.

The authors have determined the distribution of 32P in normal skin and in the case of certain skin tumours (basalioma and spinalioma). In both groups a lognormal distribution was found. It may be assumed that the enrichment is governed by similar distribution in the case of melanoma malignum.

Basal Cell Carcinoma↗
PubMed1981

An experimental check of published depth dose tables (HVL: 0.8-2.5 mm Cu).

The author has compared the absorbed dose rate (at a depth of 5 cm in water) of 89 different X-ray beams (HVL: 0.8-2.5 mm Cu) determined from the free-in-air exposure rate values with those measured directly in a water phantom. A total of 16 X-ray units from the four different types used in Hungary were involved in the intercomparison. The ratio of the two dose values were 1.005 if depth dose tables of Brit. J. Radiol., Suppl. 11. (open ended applicators) were used, for Wachsmann-Drexler tables it was 1.019. The agreement was poor (0.898) if the absorbed dose rate was determined on the base of the Hungarian Standard (the tables of it are taken from the Brit. J. Radiol., Suppl. 10., closed ended applicators). The difference was explained mainly by the different relative depth dose values.

Mathematics↗
PubMed1981

On a possible use of point detectors in intracavitary therapy (Stockholm method).

The authors discuss the possible use of point detectors for the determination of source movements in the Stockholm method of intracavitary therapy. It was demonstrated that the displacement of the source may be seen from the reading of only two point detectors. The average position of the source can be assessed from the dose determined at two points if an appropriate correction term is used.

Brachytherapy↗
PubMed1981

[Radiotherapy problems by skin tumors in the facial folds].

The clinical observations of the higher incidence of recurrence after irradiation of skin cancer in the more furrowed and more articulated regions of the face are explained in part by physical-dosimetric measurements. We believe that the higher ratio of recurrences in these areas is attributable to several factors, such as the unfavorable patho-anatomical structure and the inherent difficulties in radiation therapy and to the inadequate determination of the tumor's depth extension.

Eyelid Neoplasms↗
PubMed1981

Dose reduction in the low-energy X-ray diagnostics of extremities.

The authors determined the surface absorbed dose (Ds = 67-68 mGy) and the average absorbed dose (Dav = 13-15 mGy) by means of non-screen film radiography of the extremities. The authors recommend the use of xeroradiography (with a tungsten anode tube) or, first of all, a rare-earth screen - film combination (e.g. Kodak min-R + Nuklearmedizin NMB film). The two methods permit the dose values to be decreased by a factor of about 4 and 15, respectively. The dose values are smaller, at least for the 8 cm thick tissue equivalent phantom, when a tungsten anode is used instead of a Mo anode.

Extremities↗
PubMed1980

The focus-to-detector distance as a source of systematical errors in the measurement of Chaoul therapy units.

The skin exposure rates measured on 22 Chaoul units in two consecutive years were compared and their variance was analysed. The statistical fluctuation of the ionization method was 3.1% by a factor of about 2 to 2.5 smaller than the variations due to lack of reproducibility of the Chaoul units. The authors observed systematical errors among exposure rate measurement performed at different focus-to-detector distances. The effective source-to-detector distance is different for various ionization chambers. It is the sum of nominal focus-to-detector distance plus a geometrical constant. The geometrical constant is for a particular chamber only to a small extent dependent on the front wall thickness and on the focus-to detector distance. Sufficient standardization of both calibration procedure and construction of ionization chambers may help in avoiding this effect.

Analysis of Variance↗