Publications by authors named "Piotr Maras"

8 Publications

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Clinical radiotherapy application of N-vinylpyrrolidone-containing 3D polymer gel dosimeters with remote external MR-reading.

Phys Med 2020 Jan 3;69:134-146. Epub 2020 Jan 3.

Institute of Materials Science and Engineering, Lodz University of Technology, Lodz, Poland.

Purpose: Advanced 3D dosimetry is required for verifications of complex dose distributions in modern radiotherapy. Two 3D polymer gel dosimeters, coupled with magnetic resonance (MR) imaging (3 T MRI) readout and data processing with polyGeVero® software, were tested for the verification of calculated 3D dose distributions by a treatment planning system (TPS) and ArcCHECK®-3DVH®, related to eradication of a lung tumour.

Methods: N-vinylpyrrolidone-containing 3D polymer gel dosimeters were used: VIC (containing ascorbic acid and copper sulfate pentahydrate) and VIC-T (containing tetrakis(hydroxymethyl)phosphonium chloride). Three remote centers were involved in the dosimeters preparation and irradiation (Poland), and MRI (Austria). Cross beam calibration of the dosimeters and verification of a 3D dose distribution calculated with an Eclipse External Beam TPS and ArcCHECK®-3DVH® were performed. The 3D-to-3D comparisons of the VIC and VIC-T with TPS and ArcCHECK®-3DVH® along with ArcCHECK®-3DVH® versus TPS dose matrixes were performed with the aid of the polyGeVero® by analyzing dose profiles, isodoses lines, gamma index, gamma angle, dose difference, and related histograms.

Results: The measured MR-relaxation rate (R = 1/T) for the dosimeters relates to the dose, as follows: R = 0.0928 ± 0.0008 [Gy s] × D [Gy] + 2.985 ± 0.012 [s] (VIC) and 0.1839 ± 0.0044 [Gy s] × D [Gy] + 2.519 ± 0.053 [s] (VIC-T). The 3D-to-3D comparisons revealed a good agreement between the measured and calculated 3D dose distributions.

Conclusions: VIC and VIC-T with 3T MRI readout and polyGeVero® showed potential for verifications of calculated irradiation plans. The results obtained suggest the implementation of the irradiation plan for eradication of the lung tumour.
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http://dx.doi.org/10.1016/j.ejmp.2019.11.014DOI Listing
January 2020

Leuco crystal violet-Pluronic F-127 3D radiochromic gel dosimeter.

Phys Med Biol 2019 09 5;64(17):175017. Epub 2019 Sep 5.

Medical School, National and Kapodistrian University of Athens, Athens, Greece.

This work reports results related to the manufacturing and optimisation of a leuco crystal violet (LCV)-Pluronic F-127 radiochromic gel dosimeter suitable for 3D radiotherapy dosimetry. A feature of this gel is that the natural gelatine polymer, which is most often used as a matrix in 3D dosimeters, is substituted with Pluronic F-127 synthetic copolymer (poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide). Pluronic F-127 ensures a higher transparency than gelatine, which may be beneficial for optical computed tomography readout, and improves the thermal properties in the temperature range above ~30 °C at which the gelatine physical gel converts to a solution. The optimal composition obtained comprises 2 mM LCV, 4 mM 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100), 17 mM trichloroacetic acid (TCAA) and 25% Pluronic F-127. Its main dose-response features are 4‒150 Gy linear dose range (150 Gy was the maximal dose applied to gels in this work), 0.0070 Gy cm dose sensitivity (derived from absorbance (600 nm)  =  f (dose) for 6 MeV electrons, 0.88(3) Gy s and 0.0156 Gy cm derived from optical density (Δµ)  =  f (dose) for 6 MV x-rays, 0.1010 Gy s), low initial colour (initial absorbance  =  0.0429) and a diffusion coefficient of crystal violet (CV) in LCV-Pluronic of 0.054  ±  0.023 mm h. Raman spectroscopy was used to characterize LCV-Pluronic chemical changes after irradiation. Differential scanning calorimetry (DSC) revealed that LCV-Pluronic is stable in temperatures between approximately 11 °C and 56 °C. Irradiation of LCV-Pluronic gel impacts on its first sol-gel transition temperature and the thermal effect of this process-both increased with absorbed dose, which might be related to the degradation of Pluronic. LCV-Pluronic is a promising 3D dosimeter for ionising radiation applications. Further work is needed to improve LCV-Pluronic response in the low dose region, and characterize potential effects of pH, temperature during irradiation, and radiation quality/dose rate on dose response characteristics.
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http://dx.doi.org/10.1088/1361-6560/ab2f5dDOI Listing
September 2019

Examination of THPC as an oxygen scavenger impacting VIC dosimeter thermal stability and comparison of NVP-containing polymer gel dosimeters.

Phys Med Biol 2019 01 31;64(3):035019. Epub 2019 Jan 31.

Institute of Materials Science and Engineering, Lodz University of Technology, Lodz, Poland.

This work reports on the impact of tetrakis(hydroxymethyl)phosphonium chloride (THPC) on the properties of a VIC gel dosimeter (VIC is an abbreviated acronym of VIPAR). THPC was used as a substitute oxygen scavenger in VIC (17% N-vinylpyrrolidone, 8% N,N'-methylenebisacrylamide, 12% tert-butyl alcohol, 7.5% gelatine, 0.02% hydroquinone and an oxygen scavenger of 0.007% ascorbic acid and 0.0008% CuSO  ×  5HO). THPC reduced the gelation time of VIC from hours to minutes. The best composition (VIC-T) contained 14 mM THPC and a reduced gelatine concentration (5%) with respect to VIC, which allowed for gelation in about 3 min. VIC-T was characterised by the same dose sensitivity (0.176  ±  0.003 Gy s for VIC-T and 0.171  ±  0.002 Gy s for VIC), dose threshold (0.5 Gy) and dynamic dose range (0.5‒50 Gy) as VIC, and a lower linear dose range (20 Gy for VIC-T, 30 Gy for VIC) (0.47 T NMR measurements). VIC-T was stable for at least 10 days after irradiation, and 3D dose distribution was stable for over 4 months after irradiation. The dose response of VIC-T was independent of the radiation dose rate, type and energy of radiation for 6 and 15 MV photons and 12 MeV electrons. This is an improvement with respect to VIC which showed a different dose response for 6 MV photons than for 12 MeV electrons and 15 MV photons. Raman spectroscopy showed similarity in the rate of radiation-induced conversion of monomers in VIC and VIC-T, indicating interaction of THPC with gelatine in VIC-T, and showed ageing of gelatine in both dosimeters. Differential scanning calorimetry showed VIC-T stability at 0 °C-80 °C (VIC: 0 °C‒29.5 °C). The chemical polymerisation and crosslinking of gelatine with THPC is reported, the mechanism of which was analysed in detail. A comparison of N-vinylpyrrolidone-containing dosimeters is presented in this work.
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http://dx.doi.org/10.1088/1361-6560/aafa86DOI Listing
January 2019

Substituting gelatine with Pluronic F-127 matrix in 3D polymer gel dosimeters can improve nuclear magnetic resonance, thermal and optical properties.

Phys Med Biol 2018 09 6;63(17):175010. Epub 2018 Sep 6.

Institute of Materials Science and Engineering, Lodz University of Technology, Lodz, Poland.

This work discusses the substitution of a gelatine physical gel matrix with a matrix made of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127) in five 3D radiotherapy polymer gel dosimeters: MAGAT, PAGAT, NIPAM, VIPAR (VIP) and VIPAR (VIC). The current research outcomes showed that not each polymer gel dosimeter could be manufactured with Pluronic F-127. Two of the polymer gel dosimeters (PAGAT and VIP) containing the Pluronic F-127 matrix allowed for some proper dose response for radiotherapy dosimetry (a response to a dose range of e.g. 0‒50 Gy). The new best performing Pluronic-based polymer gel dosimeters were characterised by improved nuclear magnetic resonance properties, when being compared to gels with gelatine matrix at the same monomer content. These are: (i) a ~33% higher dose sensitivity; (ii) a comparable or slightly higher linear and dynamic dose range and (iii) a lower (new VIP composition, VIP3) or equivocal (new PAGAT composition, PAGAT2-Pluronic) dose threshold. However, there might be optimised gelatine based polymer dosimeters demonstrating even better sensitivity. UV-vis spectrophotometry measurements revealed that Pluronic matrices ensure six-times lower (VIP3-Pluronic) and eight-times lower (PAGAT2-Pluronic) absorbance (at 400 nm) of non-irradiated gels compared to gelatine matrices, which makes the new polymer gel dosimeters optically improved in comparison to their corresponding gelatine-based compositions. The differences in absorption reduce for higher wavelengths. Differential scanning calorimetry measurements revealed the following temperature stability ranges for the gels: (i) VIP with gelatine matrix: 0 °C‒26 °C, (ii) VIP3 with Pluronic matrix: 13.8 °C-55.2 °C, (iii) PAGAT2 with gelatine matrix: 0 °C-80 °C and (iv) PAGAT2 with Pluronic matrix: 21.4 °C-55.2 °C. In conclusion, Pluronic F-127 is an attractive co-polymer to serve as a substitute for the gelatine matrix in some 3D polymer gel dosimeters.
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http://dx.doi.org/10.1088/1361-6560/aad9d5DOI Listing
September 2018

Tetrazolium salts-Pluronic F-127 gels for 3D radiotherapy dosimetry.

Phys Med Biol 2018 05 4;63(9):095012. Epub 2018 May 4.

Department of Man-Made Fibres, Lodz University of Technology, Lodz, Poland.

This work is a follow-up study for a recently-proposed 3D radiochromic gel dosimeter that contains a tetrazolium salt and a physical gel matrix made of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127). Several tetrazolium salts were examined in this work, including tetrazolium violet, blue tetrazolium chloride, nitro blue tetrazolium chloride (NBT), tetranitro blue tetrazolium chloride (tNBT) and thiazolyl blue tetrazolium bromide (TBTB). The salt-containing gel dosimeters were compared with the first Pluronic gel composition that contained 2,3,5-triphenyltetrazolium chloride (TTC) as the radiation-sensitive component (dose sensitivity of 0.0023 (Gy cm)). The Pluronic gels with NBT and tNBT outperformed the other gels, including the TTC-containing gel, with respect to their dose sensitivity and low dose-response. The NBT gels were found to have better stability over time than tNBT gels. Sensitization of the gels to ionizing radiation was examined by addition of tert-butyl alcohol and sodium formate. The best composition was 0.0818% NBT (1 mM), 25% Pluronic F-127 and 0.136  ×  10% sodium formate. This gel dosimeter was insensitive to changes in dose rate for photons of different energies. The mean dose sensitivity amounted to 0.0047  ±  0.1  ×  10 (Gy cm). A diversion in the dose-response was observed for the gel irradiated with electrons. Additional characteristics of the NBT gel were a linear-dose range and a dynamic-dose range between  <1 and  ⩾150 Gy and a dose threshold of  <1 Gy. The dose distribution registered for the NBT-Pluronic gel was stable after irradiation for over 7 d with no visible diffusion of the irradiated part, which is analogous to the original TTC-Pluronic gel.
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http://dx.doi.org/10.1088/1361-6560/aabbb6DOI Listing
May 2018

On the development of a VIPAR radiotherapy 3D polymer gel dosimeter.

Phys Med Biol 2017 02 12;62(3):986-1008. Epub 2017 Jan 12.

Department of Man-Made Fibres, Lodz University of Technology, Lodz, Poland. GeVero Co., Lodz, Poland.

This work presents an improvement of the VIPAR ('nd' stands for 'normoxic, double', or VIP) polymer gel dosimeter. The gel composition was altered by increasing the concentration of the monomeric components, N-vinylpyrrolidone (NVP) and N,N'-methylenebisacrylamide (MBA), in co-solvent solutions. The optimal composition (VIPAR, where 'CT' stands for computed tomography, or VIC) comprised: 17% NVP, 8% MBA, 12% t-BuOH, 7.5% gelatine, 0.007% ascorbic acid, 0.0008% CuSO  ×  5HO and 0.02% hydroquinone. The following characteristics of VIC were achieved: (i) linear dose range of 0.930 Gy, (ii) saturation for radiation doses of over 50 Gy, (iii) threshold dose of about 0.5 Gy, (iv) dose sensitivity of 0.171 Gy s, which is roughly 2.2 times higher than that of VIP (for nuclear magnetic resonance measurements). It was also found that VIC is dose- rate-independent, and its dose response does not alter if the radiation source is changed from electrons to photons for external beam radiotherapy. The gel responded similarly to irradiation with small changes in radiation energy but was sensitive to larger energy changes. The VIC gel retained temporal stability from 20 h until at least 10 d after irradiation, whereas spatial stability was retained from 20 h until at least 6 d after irradiation. The scheme adopted for VIC manufacturing yields repeatable gels in terms of radiation dose response. The VIC was also shown to perform better than VIP using x-ray computed tomography as a readout method; the dose sensitivity of VIC (0.397 HU Gy) was 1.5 times higher than that of VIP. Also, the dose resolution of VIC was better than that of VIP in the whole dose range examined.
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http://dx.doi.org/10.1088/1361-6560/aa5089DOI Listing
February 2017

Software for 3D radiotherapy dosimetry. Validation.

Phys Med Biol 2014 Aug 8;59(15):4111-36. Epub 2014 Jul 8.

GeVero Co., Tansmana St. 2/11, 92-548 Lodz, Poland.

The subject of this work is polyGeVero(®) software (GeVero Co., Poland), which has been developed to fill the requirements of fast calculations of 3D dosimetry data with the emphasis on polymer gel dosimetry for radiotherapy. This software comprises four workspaces that have been prepared for: (i) calculating calibration curves and calibration equations, (ii) storing the calibration characteristics of the 3D dosimeters, (iii) calculating 3D dose distributions in irradiated 3D dosimeters, and (iv) comparing 3D dose distributions obtained from measurements with the aid of 3D dosimeters and calculated with the aid of treatment planning systems (TPSs). The main features and functions of the software are described in this work. Moreover, the core algorithms were validated and the results are presented. The validation was performed using the data of the new PABIG(nx) polymer gel dosimeter. The polyGeVero(®) software simplifies and greatly accelerates the calculations of raw 3D dosimetry data. It is an effective tool for fast verification of TPS-generated plans for tumor irradiation when combined with a 3D dosimeter. Consequently, the software may facilitate calculations by the 3D dosimetry community. In this work, the calibration characteristics of the PABIG(nx) obtained through four calibration methods: multi vial, cross beam, depth dose, and brachytherapy, are discussed as well.
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http://dx.doi.org/10.1088/0031-9155/59/15/4111DOI Listing
August 2014

Optical scanner for 3D radiotherapy polymer gel dosimetry.

Acta Phys Pol A 2012 Nov;122(5):969-974

Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland.

Sophisticated techniques employed in radiotherapy for irradiation of tumours require comprehensive dosimetry allowing for precise, high resolution measurements of radiation dose distribution in three dimensions and verification of treatment planning systems. Polymer gel dosimetry has been shown to be a unique technique for three-dimensional high resolution measurements of absorbed radiation dose distributions. If exposed to ionizing radiation, radical polymerisation and crosslinking of monomeric components take place in a 3D polymer gel dosimeter, leading to the formation of large polymeric structures that scatter visible light. This feature allows for optical observation of the effects of the absorbed dose and its distribution. Presently, magnetic resonance imaging is employed the most often for analysis of 3D polymer gel dosimeters. However, much attention is also being given to the development of optical computed tomography since this technique is hoped to serve as a substitute for expensive and not easily available magnetic resonance imaging. The optical scanner presented in this work consists of a laser diode, a scanning system and a signal detector. A 3D polymer gel dosimeter is measured in an immersion liquid in order to reduce deflection of the light from the dosimeter phantom. The very first results were obtained with the newly constructed scanner for PABIG 3D polymer gel dosimeter, which was inhomogeneously irradiated with Ir brachytherapy source. The results have been contrasted with those for magnetic resonance imaging and are presented in this work together with the description of the optical scanner. Currently, optimization of the optical scanner is performed.
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http://dx.doi.org/10.12693/APhysPolA.122.969DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6101184PMC
November 2012