Piotr Tulik

Introduction: Three cylindrical graphite ionization chambers have been constructed, one of which, DW3, participated in the BIPM.RI(I)-K4 key comparisons for absorbed dose to water in a gamma radiation field of the ⁶⁰ Co radionuclide, achieving a positive result. This prompted us to attempt to use the experimental DW2 chamber (twin to DW3 chamber) for dosimetry of high-energy photon beams used clinically with the aim of reducing the value of the total standard uncertainty of the measured radiation dose. Material and methods: The performance of the DW2 chamber was first tested in gamma ray fields of ¹³⁷ Cs and ⁶⁰ Co. Subsequently, the chamber was calibrated in a ⁶⁰ Co beam relative to the GUM primary standard (DW3). Then, the kQ factors for 6, 10, and 15 MV photon beams produced by Versa HD, Elekta accelerators were determined using Monte Carlo methods. Next, for the same beams, the correction factors for saturation ( ks ) and the polarity ( kpol ) were experimentally determined. Finally, the DW2 chamber was used to measure the absorbed dose to water under reference conditions. The obtained results were compared to those of a commercial Farmer-type ionization chamber, model 30013 by PTW. A metrological conformity test was used for evaluation. Results: The relative differences between the two chambers (DW2 vs Farmer chamber) in measured absorbed dose to water for 6, 10, and 15 MV photon beams were −0.1 %, 0.2 %, and 0.7 %, respectively. The relative standard uncertainties of the dose measurement under reference conditions using the DW2 chamber were approximately 0.6 % which are lower than those for the commercial chamber (Farmer) of 0.89 %. Conclusions: The obtained results confirm that the DW2 ionization chamber is an accurate tool for measuring absorbed dose to water under reference conditions for therapeutic photon beams. Lower measurement uncertainty will translate into higher precision in monitoring and calibration of the accelerator’s output.

Background: Existing calibration procedures of ionization chambers refer to the cobalt 60 (⁶⁰Co) beam and require a k_Q quality conversion factor for therapeutic photon beams. This factor has the largest contribution to the total standard uncertainty of dose measurement. The main objective of our work is to verify the performance of the experimental DW2 ionization chamber for the absorbed dose to water measurements using Monte Carlo (MC) calculations instead of calibration in the Secondary Standard Dosimetry Laboratory (SSDL). Materials and methods: To calculate the absorbed dose to water based on the signal from the experimental DW2 ionization chamber, its active volume was determined. Using experimental methods, the correction factors for polarisation and ion recombination were established. Additionally, MC methods were employed to determine the factors for converting the ionization charge in the chamber cavity to the absorbed dose to water. Subsequently, the chamber's performance was verified against ionometric and calorimetric Central Office of Measures (GUM) standards under reference conditions. Results: The difference between the dose measured by the DW2 chamber and the GUM ionometric standard for the ⁶⁰Co beam was –0.09%. The differences for the 6, 10 and 15 MV photon beams relative to the graphite calorimeter were –0.30%, 0.40%, and 0.45%, respectively. The maximum expanded (k = 2) standard uncertainty of the chamber was 0.57%. Conclusions: This work demonstrates that it is possible to obtain accurate measurements of the absorbed dose to water for high-energy photon beams under reference conditions using an ionization chamber without calibrating it in a ⁶⁰Co source but only using correction factors determined by MC calculations. Keywords: reference dosimetry ionization chamber calibration high-energy photon beam

Dosimetry based on gas detectors operating in the recombination and saturation region provides unique research opportunities but requires high-quality electrometers with a measuring range below 1 pA (10⁻¹² A). The standard approach in electrometry is to strive to increase the accuracy and precision of the measurement, ignoring the importance of its duration. The article presents an algorithm for the measurement of low current values (from 100 fA) that allows both a fast measurement (with a step of 2.3 ms) and high accuracy (measurement error below 0.1%), depending on the measurement conditions and the expected results. A series of tests and validations of the algorithm were carried out in a measurement system with a Keithley 6517B electrometer and a REM-2 recombination chamber under conditions of constant and time-varying radiation fields. The result of the work is a set of parameters that allow for the optimisation of the operation of the algorithm, maximising the quality of the measurements according to needs and the expected results. The algorithm can be used in low current measurement systems, e.g., for dosimetry of mixed radiation fields using recombination methods and chambers.

Background: The purpose was to assess the impact of irradiation technique type and beam energy on the mixed radiation field around the medical linear accelerator (linac) in terms of radiation quality and related radiation protection quantities. Materials and methods: Seven radiotherapeutic plans with Alderson-Rando anthropomorphic phantom [different techniques: conventional three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT) and intensity modulated arc therapy (IMAT), different beams: 6 MV or 18 MV, and their arrangements) were prepared for the case of prostate malignancy. Recombination chambers REM-2 and GW2 were positioned on the treatment couch 100 cm from the beam axis at the height of the isocentre. Recombination chambers REM-2 and GW2 were used for recombination index of radiation quality Q₄ determination, measurement of total tissue dose D_t and calculation of gamma and neutron components to D_t. Estimation of D_t and Q₄ allowed for the ambient dose equivalent H*(10) calculations for each plan. Results: For plans prepared with 6 MV beams, Q₄ values within the limits of uncertainty were equal to one, which confirms the correctness of the measurement method. For plans implemented with 18 MV beams, the value of Q₄ was in the range of 3.7–5.7. Comparison between treatment techniques indicates that the lowest exposure resulting from out-of-field doses comes from 6 MV IMAT (0.7 mSv), whereas the highest one is from 18 MV IMRT (55.1 mSv). Conclusion: With the recombination chambers technique it was confirmed that the choice of beam energy directly affects the generation of photoneutrons. The treatment plan technique can have a significant impact on the out-of-field dose. Keywords: photon external beam radiotherapy recombination chambers radiation quality secondary radiation radiation protection

Background: The inadvertent detachment of stent retrievers during mechanical thrombectomy is an extremely rare but feared complication associated with poor clinical outcomes. We discuss management considerations after an unexpected disconnection of the pRESET stent retriever during mechanical thrombectomy, based on clinical experience and mechanical and phantom studies. Methods: We present a clinical course of rare accidents of stent-retriever separation inside an intracranial vessel that occurred in patients in a comprehensive stroke centre between 2018 and 2020. We designed a phantom study to assess the Tigertriever’s ability to remove a detached stent retriever from intercranial vessels. In the mechanical study, several types of stent retrievers were evaluated in order to find the weakest point at which detachment occurred. Results: Two patients (~0.7%) with inadvertent stent-retriever detachment were found in our database. Failed attempts of endovascular removal with no recanalization at the end of procedure were reported in both cases. mRS after 3 months was three and four respectively. In the mechanical study, the Tigertriever was the most resistant to detachment and was followed by Embotrap > pRESET > 3D Separator. In the phantom study, the pRESET device detached in a configuration resembling the M1 segment was successfully removed with the Tigertriever. Conclusions: Conservative management of the inadvertent detachment of stent retrievers during mechanical thrombectomy in large vessel occlusion may be acceptable in order to avoid further periprocedural complications after unsuccessful device removal attempts. Based on the phantom and mechanical studies, the Tigertriever may be a useful tool for the removal of detached pRESET devices.

Introduction The purpose of this study was to present the optimization process of CT parameters to reduce patient exposure during bone SPECT/CT without affecting the quality of SPECT images with attenuation correction (AC). Material and methods A fillable phantom reflecting realistic bone scintigraphy conditions was developed and acquired on an AnyScan SC. SPECT/CT scans were carried out with different x-ray tube current values (10, 20, 30, 40, 50, 60, 70, 90, 110, 130, 150, and 200 mA) at three different high-voltage values (80, 100, and 120 kV). The contrast (C) and coefficients of variation (CV) in the SPECT images as well as the signal-to-noise ratio (SNR) and noise (SDCT) in the CT images with CTDIvol were measured. An optimal acquisition protocol that obtained SPECT/CT images with no artifacts on both CT and SPECT images, acceptable C, SNR, CV, and SDCT values, and the largest reduction in patient exposure compared to the reference acquisition procedure was sought. Results The optimal set of parameters for bone SPECT/CT was determined based on a phantom study. It has been implemented in clinical practice. Two groups of patients were examined according to the baseline and optimized protocols, respectively. The new SPECT/CT protocol substantially reduced patients' radiation exposure compared to the old protocol while maintaining the required diagnostic quality of SPECT and CT images. Conclusions In the study, we present a methodology that finds a compromise between diagnostic information and patient exposure during bone SPECT/CT procedures.

X-ray computed tomography (CT) is increasingly recognized as a promising measuring technique for dimensional metrology. Various methods are being developed to improve measurement accuracy. Tests of new methods for such applications include accuracy evaluation with the use of calibrated workpieces; however, the internal algorithms of image acquisition and data processing might influence the experimental error, and then also the comparison of methods at different CTs. The accuracy of the results of tomographic measurements is influenced by many factors, one of which is the setting of the threshold value. The article presents the results of an attempt to use Monte Carlo simulated images to estimate deviations to determine threshold values to improve measurement accuracy and additionally, to estimate the impact of data processing. The differences of the results obtained from the simulated images were up to 4 % larger than those from tomographic images. It was caused by degradation of the image contrast by scattered radiation.

The calibration laboratory revises periodically the dosimetric properties of its calibration fields. For reference neutron fields based on radionuclide sources, it is due to presence of isotopic impurities in the source ingredients. Consequently, in long term, the admixtures and their decay products become significant. Neglecting the impact of such effect leads to inconsistencies between the neutron emission rate observed during the measurements and the emission rate derived from the decay curve of the main isotope. In the Radiation Protection Measurements Laboratory at the National Centre for Nuclear Research the neutron fields of the bare sources of ²⁵²Cf, ²⁴¹AmBe and ²³⁹PuBe have been examined for nearly 30 years, regularly, in fixed geometry. Additionally, at the particular point of a calibration bench, determination of neutron fluence rate, ambient dose equivalent rate and its scattered component, total neutron and gamma dose rate, gamma to total dose ratio, radiation quality factor and total tissue kerma are occasionally determined. In this article, we would like to present recently achieved results and their comparison with the measurement data formerly presented. The growth of the neutron emission of ²³⁹PuBe source, as well as discrepancies between the decay curves of relevant isotopes and the emission rate of ²⁵²Cf and ²⁴¹AmBe will be presented.

The aim of this study is to investigate secondary mixed radiation field around linac, as the first part of an overall assessment of out-of-field contribution of neutron dose for new advanced radiation dose delivery techniques. All measurements were performed around Varian Clinic 2300 C/D accelerator at Maria Sklodowska-Curie Memorial, Cancer Center and Institute of Oncology, Krakow Branch. Recombination chambers REM-2 and GW2 were used for recombination index of radiation quality Q₄ determination (as an estimate of quality factor Q), measurement of total tissue dose D_t and calculation of gamma and neutron components to D_t. Estimation of D_t and Q₄ allowed for the ambient dose equivalent H*(10) per monitor unit (MU) calculations. Measurements around linac were performed on the height of the middle of the linac’s head (three positions) and on the height of the linac’s isocentre (five positions). Estimation of secondary radiation level was carried out for seven different configurations of upper and lower jaws position and multileaf collimator set open or closed in each position. Study includes the use of two photon beam modes: 6 and 18 MV. Spatial distribution of ambient dose equivalent H*(10) per MU on the height of the linac’s head and on the standard couch height for patients during the routine treatment, as well as relative contribution of gamma and neutron secondary radiation inside treatment room were evaluated.

This paper presents the results of radiation level measurements at workplaces in a nuclear medicine facility performing PET/CT examinations. This study meticulously determines the staff radiation exposure in a PET/CT facility by tracking the path of patient movement. The measurements of the instantaneous radiation exposure were performed using an electronic radiometer with a proportional counter that was equipped with the option of recording the results on line. The measurements allowed for visualisation of the staff's instantaneous exposure caused by a patient walking through the department after the administration of ¹⁸ F-FDG. An estimation of low doses associated with each working step and the exposure during a routine day in the department was possible. The measurements were completed by determining the average radiation level using highly sensitive thermoluminescent detectors.