[Electronic portal imaging (EPI) on linear accelerator] / Elektronikus mezôellenôrzés lineáris gyorsítón. (EPI: Electronic Portal Imaging).

The EPI has become available recently in the Oncoradiological Centre of Budapest. The purpose of this paper is to review the construction and operation of the electronic portal imaging devices (EPIDs). The different EPID systems as well the EPID technique vs. portal films are compared. The advantages in patient set-up and the detection of the set-up errors are discussed. The use of the EPID technique in the clinical everyday practice is detailed. Recommendations of the set-up error correction for the most often occurring failures is given.

[Field matching in breast irradiation] / Mezôillesztés mammatumorok posztoperatív besugárzásánál.

INTRODUCTION: In this paper the authors have combined different irradiation techniques for breast and adjacent supraclavicular lymph nodes. The aim was to reduce inhomogeneity in the match-line. METHODS: The CadPlan 6.1.5 three-dimensional treatment planning system was applied in this study for CT based plan using a standard medial and lateral wedged tangential breast portals with the adjacent supraclavicular field. Isocenter is placed at depth on the match-line, where asymmetric jaws are used to produce non-divergent field edges. The tangential fields are shaped using multi-leaf collimator (MLC), by following the curvature of the thorax. In this way the cranial vertical match plane is maintaned without using the breast board. The prescribed dose was 50 Gy at the isocentre. RESULTS: The calculated dose distributions were evaluated in three dimension in the match region of supraclavicular field and the two opposing tangential fields. This method produces a more uniform dose distribution in the target volume and in the match-line. Set-up is fast, this is done without the need for table rotation, or vertical cephalad blocks. The average dose to the ipsilateral lung is reduced using the IMRT (intensity modulated radiotherapy) technique by approximately 10% compared with the conventional technique. Furthermore, this new technique has the possibility to improve the field match between the tangential fields and the parasternal field, while maintaning the field match between the tangential fields and the axillary and supraclavicular fields.

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]).

[The brachytherapy of carcinoma of the external auditory canal]. / Die Brachytherapie des äusseren Gehörgangskarzinoms.

Brachytherapy is advantageous in the initial carcinomas of external auditory canal. The radiation charge of the surrounding tissues is much lower in spite of millivoltage irradiation because of its higher dosage gradient. It is stated according to the recent experiences and results on seven treated patients, that with LDR treatment of 5 x 10 Gy on consecutive days and with HDR treatment of 6 x 6 Gy on weekly interruptions (in both cases the dose means a depth of 5 mm). It is impossible to give the analysis because of the small number of cases. On base of our own patients it could be proved that lasting recovery of bone involving tumours is due to radical surgery and postoperative millivoltage irradiation.

[Radiation moulage therapy of gingival tumors]. / Moulage-kezelés gingivatumornál.

An irradiation treatment technique, long ago known yet seldom employed, is reported on. With a patient, because of an inoperable gingiva-tumor, after percutan irradiation for complementary purpose radium-moulage treatment was employed. Due to the irradiation treatment the patient became symptomless.

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.

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.

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.

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.

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.

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.

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.

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.