Biomedical subjects

M A Duch

Publications and source records attributed to M A Duch.

7 recordsLinked to original sources

PubMed2006

Comparison of two extremity dosemeters based on LiF:Mg,Cu,P thin detectors for mixed beta-gamma fields.

Two types of thin LiF:Mg,Cu,P detectors, GR-200F and MCP-Ns, have been characterised for use in the design of an extremity dosemeter for mixed beta-photon radiation fields. Both detectors consist of an extremely thin layer of sensitive material with effective thicknesses of 5 and 8 mg cm(-2), respectively, held in a 5 mg cm(-2) PVC ring holder. Dosimetric performance was analysed according to the ISO 12794 standard and compared with 240 mg cm(-2) TLD-100 measurements. In particular, the energy response was obtained for ISO narrow X-ray spectra, (137)Cs, (60)Co, (204)Tl and (90)Sr/(90)Y. From these measurements a mean calibration factor was calculated to estimate H(p)(0.07). Subsequently, the performance of the dosemeters was checked for a set of 10 different mixed photon and beta-photon fields. The study shows that the proposed dosemeters can estimate H(p)(0.07) in a wide range of mixed beta-photon fields with a maximum deviation from the given dose of 30% and an overall uncertainty of the order of 25% (k = 1). However, the results also highlight a large variability among the different thin detectors and, thus, the standard TLD-100 material is recommended whenever the workplace does not include low-energy beta radiation.

Beta Particles↗

PubMed2006

Dose evaluation in lung-equivalent media in high-energy photon external radiotherapy.

In high-energy photon external radiotherapy treatment planning systems (TPSs) are used to calculate the dose to the target volume and the dose distribution around it. Commonly used TPSs include algorithms based on measurements in water and often fail in the estimate of dose in the presence of heterogeneities. In this study TL detectors were used to study the reliability of the Cadplan (Varian) TPS in the presence of low-density heterogeneities such as the lung for 6 and 18 MV photon beams at different field sizes. TL measurements were compared with TPS calculations and Monte Carlo simulations performed with the PENELOPE MC code. In a phantom with lung heterogeneity, TL measurements and MC simulations agreed, with an average deviation inside the lung of 2%. In contrast, TPS results overestimated the dose inside the lung, with a maximum deviation of 39% for the 18 MV photon beam and a field size of 2 x 2 cm(2).

Algorithms↗

PubMed2004

Comparison of dose calculation algorithms in phantoms with lung equivalent heterogeneities under conditions of lateral electronic disequilibrium.

An extensive set of benchmark measurement of PDDs and beam profiles was performed in a heterogeneous layer phantom, including a lung equivalent heterogeneity, by means of several detectors and compared against the predicted dose values by different calculation algorithms in two treatment planning systems. PDDs were measured with TLDs, plane parallel and cylindrical ionization chambers and beam profiles with films. Additionally, Monte Carlo simulations by means of the PENELOPE code were performed. Four different field sizes (10 x 10, 5 x 5, 2 x 2, and 1 x 1 cm2) and two lung equivalent materials (CIRS, p(w)e=0.195 and St. Bartholomew Hospital, London, p(w)e=0.244-0.322) were studied. The performance of four correction-based algorithms and one based on convolution-superposition was analyzed. The correction-based algorithms were the Batho, the Modified Batho, and the Equivalent TAR implemented in the Cadplan (Varian) treatment planning system and the TMS Pencil Beam from the Helax-TMS (Nucletron) treatment planning system. The convolution-superposition algorithm was the Collapsed Cone implemented in the Helax-TMS. The only studied calculation methods that correlated successfully with the measured values with a 2% average inside all media were the Collapsed Cone and the Monte Carlo simulation. The biggest difference between the predicted and the delivered dose in the beam axis was found for the EqTAR algorithm inside the CIRS lung equivalent material in a 2 x 2 cm2 18 MV x-ray beam. In these conditions, average and maximum difference against the TLD measurements were 32% and 39%, respectively. In the water equivalent part of the phantom every algorithm correctly predicted the dose (within 2%) everywhere except very close to the interfaces where differences up to 24% were found for 2 x 2 cm2 18 MV photon beams. Consistent values were found between the reference detector (ionization chamber in water and TLD in lung) and Monte Carlo simulations, yielding minimal differences (0.4%+/-1.2%). The penumbra broadening effect in low density media was not predicted by any of the correction-based algorithms, and the only one that matched the experimental values and the Monte Carlo simulations within the estimated uncertainties was the Collapsed Cone Algorithm.

Algorithms↗

PubMed2002

Extremity and whole-body dosemeters for beta and beta gamma fields based on LiF:Mg,Cu,P thin detectors.

This study aims at proposing two TL dosemeters: one for the whole body and another for the extremities, for beta and gamma fields. Selected sensible material consists of 5 mg x cm(-2) LiF:Mg,Cu,P film (GR-200F) manufactured in China. Calibration was carried out according to ISO 4037-3, in terms of Hp(0.07), and dosimetric performance was analysed on the basis of IEC-1066 and ISO-12794 Standards. Experiments showed a satisfactory sensitivity of the proposed dosemeters for detecting beta radiation at protection levels and a very good energy response; thus, highly recommending their use for weakly penetrating radiation measurements. However, the homogeneity and the reproducibility of GR-200F are not found to be as reliable as in standard materials.

Arm↗

PubMed2001

Implementing new recommendations for calibrating personal dosemeters.

This paper analyses the differences between the calibration procedures for personal dosemeters recommended by ICRU 47 and ISO 4037-3. The tissue equivalence of the PMMA and the ISO water slab phantoms are analysed by means of the Penelope Monte Carlo code for monoenergetic and filtered X ray photon beams and compared with the results of two other independent codes. The influence of the calibration method is also verified experimentally, both on a thermoluminescence and an electronic personal dosemeter. Good consistency between both calibration procedures is shown provided that a correction factor for backscatter differences between the PMMA and the ICRU phantom is introduced. The Monte Carlo simulation is used to determine this correction to a greater accuracy.

Calibration↗

PubMed1998

Thermoluminescence dosimetry applied to in vivo dose measurements for total body irradiation techniques.

BACKGROUND AND PURPOSE: In total body irradiation (TBI) treatments in vivo dosimetry is recommended because it makes it possible to ensure the accuracy and quality control of dose delivery. The aim of this work is to set up an in vivo thermoluminescence dosimetry (TLD) system to measure the dose distribution during the TBI technique used prior to bone marrow transplant. Some technical problems due to the presence of lung shielding blocks are discussed. MATERIALS AND METHODS: Irradiations were performed in the Hospital de la Santa Creu i Sant Pau by means of a Varian Clinac-1800 linear accelerator with 18 MV X-ray beams. Different TLD calibration experiments were set up to optimize in vivo dose assessment and to analyze the influence on dose measurement of shielding blocks. An algorithm to estimate midplane doses from entrance and exit doses is proposed and the estimated dose in critical organs is compared to internal dose measurements performed in an Alderson anthropomorphic phantom. RESULTS: The predictions of the dose algorithm, even in heterogeneous zones of the body such as the lungs, are in good agreement with the experimental results obtained with and without shielding blocks. The differences between measured and predicted values are in all cases lower than 2%. CONCLUSIONS: The TLD system described in this work has been proven to be appropriate for in vivo dosimetry in TBI irradiations. The described calibration experiments point out the difficulty of calibrating an in vivo dosimetry system when lung shielding blocks are used.

Algorithms↗

PubMed1998

Midplane dose determination during total body irradiation using in vivo dosimetry.

BACKGROUND AND PURPOSE: During TBI techniques an accurate determination of the dose distribution is very difficult when using commercial treatment planning systems. In order to determine the midplane dose, an algorithm was developed based on the use of in vivo dosimetry. MATERIALS AND METHODS: Scanditronix EDP-30 diodes were placed at the entrance and the exit surface for in vivo dosimetry. The proposed algorithm was validated firstly in a regular and homogeneous phantom of different thickness with an ionization chamber and TL dosimeters and secondly in an Alderson anthropomorphic phantom with TL dosimeters. In this study, in vivo measurements were evaluated in 60 patients and furthermore, in 20 of them, the midplane dose calculated with this algorithm was compared with the method described by Rizzotti A, Compri C, Garusi GF. Dose evaluation to patients irradiated by 60Co beams, by means of direct measurement on the incident and on the exit surfaces. Radiother. Oncol. 1985;3:279-283. RESULTS: No differences were found between the two methods. The differences between dose values calculated with both methods and dose values measured with the ionization chamber and TL dosimeters were within +/-22% and +/-4%, respectively, in the regular and homogeneous phantom and within +/-2% in the Alderson phantom. The algorithm was useful in calculating the midplane dose when heterogeneities as lungs were present. Even when partial transmission blocks were used to reduce the dose to the lungs, the algorithm with modified correction factors gave a midplane lung dose in the Alderson phantom within 1.3% of the measurements with TL dosimeters. For 360 patients' measurements in each A-P and P-A field, the relative deviations were analyzed between the measured and calculated entrance, exit dose and midplane dose and the prescribed dose, always applying the temperature correction factor. These deviations at the entrance dose were within +/-4%. Greater deviations were found for the exit dose measurements. Deviations larger than +/-10% corresponded in general to obese patients, with a thickness over 25 cm. The relative deviations between the total received and prescribed midplane doses in 60 patients were within +/-3%. CONCLUSIONS: The results indicate excellent correspondence between the total prescribed and calculated midplane doses using this algorithm while also no significant differences were found when the Rizzotti method was used. Comparison between doses measured with TL dosimeters in the core of Alderson phantom lungs and doses calculated from in vivo measurements showed that the proposed algorithm could be used in the presence of heterogeneities even when partial transmission blocks were used. The temperature correction factor must be applied in order to avoid a 2-3% dose overestimation.

Humans↗