Medium Energy X-ray Research Articles

Revisiting the dead time effects of Insight-HXMT/ME on timing analysis

ABSTRACT Dead time is a common instrumental effect of X-ray detectors, which would alter the behaviour of timing properties of astronomical signals, such as distorting the shape of power density spectra (PDS), affecting the root-mean-square of potential quasi-periodic oscillation signals, etc. We revisit the effects of the dead time of Medium Energy X-ray telescope (ME) onboard Insight-HXMT based on the simulation of electronic read-out mechanism that causes the dead time and the real data. We investigate dead time effects on the pulse profile as well as the quasi–periodic oscillation (QPO) signals. The dead time coefficient suggests a linear correlation with the observed count rate in each phase bin of the pulse profile according to the simulation of periodic signal as well as the real data observed on Swift J0243.6+6124. The Fourier-amplitude-difference (FAD) method could well recover the intrinsic shape of the observed PDS in the case that the PDS is from two identical detectors. We apply this technique on ME, by splitting the nine FPGA modules into two groups. The results indicate that the FAD technique suits the case when two groups of detectors are not largely different; and the recovered PDS of Sco X-1 observed by ME slightly enhances the significance of the previously known QPO signal, meanwhile the root-mean-square of QPO is significantly improved. We provide the FAD correction tool implemented in HXMTDAS for users in the future to better analyse QPO signals.

Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the PTB, Germany, and the BIPM in medium-energy x-rays

Main textA key comparison has been made between the air-kerma standards of the PTB, Germany, and the BIPM in the medium-energy x-ray range. The results show the standards to be in agreement at the limit of the expanded uncertainty of the comparison of 5.8 parts in 103. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

SSRMP Recommendations No 9: Reference dosimetry in low and medium energy x-ray beams

The SSRMP recommendations on reference dosimetry in kilovolt beams as used in radiation therapy were revised to establish current practice in Switzerland.The recommendations specify the dosimetry formalism, reference class dosimeter systems and conditions used for the calibration of low and medium energy x-ray beams. Practical guidance is provided on the determination of the beam quality specifier and all corrections required for converting instrument readings to absorbed dose to water. Guidance is also provided on the determination of relative dose under non-reference conditions and on the cross calibration of instruments.The effect of lack of electron equilibrium and influence of contaminant electrons when using thin window plane parallel chambers at x-ray tube potentials higher than 50kV is elaborated in an appendix. In Switzerland the calibration of the reference system used for dosimetry is regulated by law. METAS and IRA are the authorities providing this calibration service to the radiotherapy departments. The last appendix of these recommendations summarise this calibration chain.

PO-1795 Energy-dependence of the Exradin W1 scintillator for low and medium-energy x-ray beams

PO-1795 Energy-dependence of the Exradin W1 scintillator for low and medium-energy x-ray beams

In-orbit performance of ME onboard Insight-HXMT in the first 5 years

The medium-energy X-ray telescope (ME) is a collimated X-ray telescope onboard the Insight hard X-ray modulation telescope (Insight-HXMT) satellite. It has 1728 Si-PIN pixels readout using 54 low noise application-specific integrated circuits (ASICs). ME covers the energy range of 5–30 keV and has a total detection area of 952 cm $$^2$$ . The typical energy resolution of ME at the beginning of the mission is 3 keV at 17.8 keV (full width at half maximum, FWHM), and the time resolution is 255 $$\mu $$ s. In this study, we present the in-orbit performance of ME in its first 5 years of operation. The performance of ME was monitored using onboard radioactive sources and astronomical X-ray objects. ME carries six $$^{241}$$ Am radioactive sources for onboard calibration, which can continuously illuminate the calibration pixels. The long-term performance evolution of ME can be quantified using the properties of the accumulated spectra of the calibration pixels. In addition, observations of the Crab Nebula and the pulsar were used to check the long-term evolution of the detection efficiency as a function of energy. After 5 years of operation, 742 cm $$^2$$ of the Si-PIN pixels were still working normally. The peak positions of $$^{241}$$ Am emission lines gradually shifted to the high-energy region, implying a slow increase in ME gain of $$1.43\%$$ . A comparison of the ME spectra of the Crab Nebula and the pulsar shows that the E–C relations and the redistribution matrix file are still acceptable for most data analysis works, and there is no detectable variation in the detection efficiency.

Characterization of Inorganic Scintillator Detectors for Dosimetry in Image-Guided Small Animal Radiotherapy Platforms.

The purpose of the study was to characterize a detection system based on inorganic scintillators and determine its suitability for dosimetry in preclinical radiation research. Dose rate, linearity, and repeatability of the response (among others) were assessed for medium-energy X-ray beam qualities. The response's variation with temperature and beam angle incidence was also evaluated. Absorbed dose quality-dependent calibration coefficients, based on a cross-calibration against air kerma secondary standard ionization chambers, were determined. Relative output factors (ROF) for small, collimated fields (≤10 mm × 10 mm) were measured and compared with Gafchromic film and to a CMOS imaging sensor. Independently of the beam quality, the scintillator signal repeatability was adequate and linear with dose. Compared with EBT3 films and CMOS, ROF was within 5% (except for smaller circular fields). We demonstrated that when the detector is cross-calibrated in the user's beam, it is a useful tool for dosimetry in medium-energy X-rays with small fields delivered by Image-Guided Small Animal Radiotherapy Platforms. It supports the development of procedures for independent "live" dose verification of complex preclinical radiotherapy plans with the possibility to insert the detectors in phantoms.

Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the BFKH, Hungary, and the BIPM in medium-energy x-rays

Main text A key comparison has been made between the air-kerma standards of the BFKH, Hungary, and the BIPM in the medium-energy x-ray range. The results show the standards to be in agreement at the level of the expanded uncertainty of the comparison of 6.2 parts in 103. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

APMP/TCRI key comparison report of measurement of air kerma for medium-energy x-rays (APMP.RI(I)-K3.2013)

Main textThe APMP/TCRI Dosimetry Working Group initiated the APMP.RI(I)-K3.2013 key comparison of measurement of air kerma for medium-energy x-rays (100 kV to 250 kV); measurements took place between 2015 and 2017. In total, 11 institutes took part in the comparison, among which 8 were APMP member laboratories, two from AFRIMETS and one from SIM. Three commercial cavity ionization chambers were used as transfer standards circulated among the participants. All the participants established 100, 135, 180 and 250 kV x-ray beam qualities equivalent to those of the BIPM. The ARPANSA and the NMIJ were linking laboratories and two participants subsequently made comparisons with the BIPM. The 7 other participants' degrees of equivalence fell within 11 parts in 103 of unity, well within the relevant expanded uncertainty (k = 2) in all cases. Excluding the BARC, the results were within 5.7 parts in 103, well within the relevant combined standard uncertainty. These results indicated that the calibration capabilities of most laboratories were in very good agreement and there were no serious discrepancies between them. The effect of implementing the recommendations of ICRU Report 90, which occurred on 1 January 2018 (after this comparison), is discussed and we deduce that the effect on the degrees of equivalence is negligible. The increase in the uncertainty in Wair has been added to all laboratories so that the degrees of equivalence and the uncertainties published here are applicable to post-ICRU 90 measurement results.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Correction Factors for the LSDG Free-Air Ionization Chamber for Low and Medium-Energy X-Rays with Monte Carlo Calculations

Advances in radiation dosimetry continue to improve the accuracy of calibrating photon and electron beams of radiotherapy. This accuracy in the dose delivery to the patient in radiotherapy depends to a large extent on the absolute dosimetry of the irradiation unit. This necessitates the use of an ionization chamber such as Free air ionization chambers (FAC), calibrated in a recognised Standard Dosimetry Laboratory [1]. FACs are widely used by Primary Standard Dosimetry Labs (PSDL) as primary standard for absolute measurement of air kerma in beam of low and medium energy x-rays. It can accurately measure air kerma of x-ray beams of energy up to about 300kV. The purpose of this investigation, was to determine the correction factors of the Free Air Chamber (FAC) using the Monte Carlo calculations.

In-orbit Timing Calibration of the Insight-Hard X-Ray Modulation Telescope

Abstract We describe the timing system and the timing calibration results of the three payloads on board the Insight-Hard X-ray Modulation Telescope (Insight-HXMT). These three payloads are the High Energy X-ray telescope (HE; 20–250 keV), the Medium Energy X-ray telescope (ME; 5–30 keV), and the Low Energy X-ray telescope (LE; 1–10 keV). We present a method to correct the temperature-dependent period response and the long-term variation of the onboard crystal oscillator, especially for ME, which does not carry a temperature-compensated crystal oscillator. The times of arrival (ToAs) of the Crab pulsar are measured to evaluate the accuracy of the timing system. As the ephemeris of the Crab pulsar given by the Jodrell Bank Observatory has systematic errors around (Rots et al. 2004) 40 μs, we use the quasi-simultaneous observations of the X-ray Timing Instrument (XTI) on board the Neutron star Interior Composition Explorer (NICER) to produce the Crab ephemerides and to verify the timing system of Insight-HXMT. The energy-dependent ToAs’ offsets relative to the NICER measurements including the physical and instrumental origins are about 24.7 μs, 10.1 μs, and 864.7 μs, and the systematic errors of the timing system are determined to be 12.1 μs, 8.6 μs, and 15.8 μs, for HE, ME, and LE, respectively.

Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the KRISS, Republic of Korea, and the BIPM in medium-energy x-rays

Main textA key comparison has been made between the air-kerma standards of the KRISS, Republic of Korea, and the BIPM in the medium-energy x-ray range. The results show the standards to be in agreement at the limit of the expanded uncertainty of the comparison of 4.4 parts in 103. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Evaluation of a micro ionization chamber for dosimetric measurements in image-guided preclinical irradiation platforms

Image-guided small animal irradiation platforms deliver small radiation fields in the medium energy x-ray range. Commissioning of such platforms, followed by dosimetric verification of treatment planning, are mostly performed with radiochromic film. There is a need for independent measurement methods, traceable to primary standards, with the added advantage of immediacy in obtaining results. This investigation characterizes a small volume ionization chamber in medium energy x-rays for reference dosimetry in preclinical irradiation research platforms. The detector was exposed to a set of reference x-ray beams (0.5–4 mm Cu HVL). Leakage, reproducibility, linearity, response to detector’s orientation, dose rate, and energy dependence were determined for a 3D PinPoint ionization chamber (PTW 31022). Polarity and ion recombination were also studied. Absorbed doses at 2 cm depth were compared, derived either by applying the experimentally determined cross-calibration coefficient at a typical small animal radiation platform ‘user’s’ quality (0.84 mm Cu HVL) or by interpolation from air kerma calibration coefficients in a set of reference beam qualities. In the range of reference x-ray beams, correction for ion recombination was less than 0.1%. The largest polarity correction was 1.4% (for 4 mm Cu HVL). Calibration and correction factors were experimentally determined. Measurements of absorbed dose with the PTW 31022, in conditions different from reference were successfully compared to measurements with a secondary standard ionization chamber. The implementation of an End-to-End test for delivery of image-targeted small field plans resulted in differences smaller than 3% between measured and treatment planning calculated doses. The investigation of the properties and response of a PTW 31022 small volume ionization chamber in medium energy x-rays and small fields can contribute to improve measurement uncertainties evaluation for reference and relative dosimetry of small fields delivered by preclinical irradiators while maintaining the traceability chain to primary standards.

OD49 - Advancing the Italian national standard of absorbed dose to water in medium energy x-rays

OD49 - Advancing the Italian national standard of absorbed dose to water in medium energy x-rays

Determination of an ionization chamber response using quality index for kilovoltage x-ray beams

This study aims to investigate the energy response of a Farmer-type ionization chamber for kilovoltage x-ray beams. The chamber response in free air and at depths of 1 to 15 cm in a water phantom was calculated using the Monte Carlo method. The response in the phantom was evaluated using a beam quality conversion factor, kQx, for x-ray beams Qx to a 60Co beam. The response was expressed as a function of the effective energy or a half-value layer (HVL, mm Al) for x-ray beams with given quality index (QI) values of 0.4, 0.5, and 0.6 and for monoenergetic photon beams. QI is defined as the ratio of the effective energy to the tube voltage. The response for 25 fluence spectra of x-ray beams was calculated for the beam qualities with HVL of 1.39-10.4 mm Al and tube voltages of 50-137.6 kVp, as classified by QI. The chamber response calculated in free air for the given QI values agreed with 1% of that provided by secondary standard laboratories. The kQx values depended on depth at the lower energy levels. The depth dependence was less than 1% for an HVL (mm Al) of more than 6 mm. The dose to water obtained from kQx and a 60Co absorbed dose-to-water calibration coefficient ND,wC60o was within 1.5% at depths of 1 to 15 cm with that determined by the AAPM TG-61 for HVL of 2.9 to 10.8 mm Al. This method can reduce the uncertainty of doses in the phantom without any correction using PQ,cham and [(μ‾en/ρ)airw]w, and can directly determine the absorbed dose to water from the ionization chamber reading for medium-energy x-ray beams, including kilovoltage x-ray CT and image-guided cone beam CT in radiotherapy.

Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the VNIIM, Russian Federation, and the BIPM in medium-energy x-rays

Main textA key comparison has been made between the air-kerma standards of the VNIIM and the BIPM in the medium-energy x-ray range. The results show the standards to be in agreement at the level of the standard uncertainty of the comparison of 1.9 parts in 103. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the ARPANSA, Australia, and the BIPM in medium-energy x-rays

Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the GUM, Poland, and the BIPM in medium-energy x-rays

Main textA key comparison has been made between the air-kerma standards of the GUM and the BIPM in the medium-energy x-ray range. The results show the standards to be in agreement at the level of the expanded uncertainty of the comparison of 6.0 parts in 103. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The determination of correction factors for free-air ionization chamber calculation using monte carlo method

A free-air ionization chamber is used as the primary standard instrument for absolute measurement of air kerma for of X-ray beams. The evaluation of correction factors is a key importance for establishing the standard. Photon-scattering, and diaphragm transmission and scattering were taken into the accounts to reduce some photon phenomena. On the other hand, electron-loss factor which scatter from an electrode were used for electron compensates. In this research, Correction factors were calculated for each mono-energetic photon from 2 to 60 keV for low energy x-rays and 10 to 320 keV for medium energy x-rays by EGS5 code. The calculated corrections from a mono-energetic photon of W/Mo mammography x-rays were compared between effective energy and spectrum method. There is no significant difference between two methods.

Monte Carlo calculation of quality correction factors based on air kerma and absorbed dose to water in medium energy x-ray beams

Clinical dosimetry is typically performed using ion chambers calibrated in terms of absorbed dose to water. As primary measurement standards for this quantity for low and medium energy x-rays are available only since a few years, most dosimetry protocols for this photon energy range are still based on air kerma calibration. For that reason, data for beam quality correction factors , necessary for the application of dose to water based protocols, are scarce in literature. Currently the international IAEA TRS-398 Code of Practice is under revision and new factors for a large number of ion chambers will be introduced in the update of this protocol. Several international groups provided the IAEA with experimental and Monte Carlo based data for this revision. Within the European Community the EURAMET 16NRM03 RTNORM project was initiated for that purpose. In the present study, Monte Carlo based results for the beam quality correction factors in medium energy x-ray beams for six ion chambers applying different Monte Carlo codes are presented. Additionally, the perturbation factor p Q , necessary for the calculation of dose to water from an air kerma calibration coefficient, was determined.The beam quality correction factor for the chambers varied in the investigated energy range by about 4%–5%, and for five out of six chambers the data could be fitted by a simple logarithmic function, if the half-value-layer was used as the beam quality specifier. Corresponding data using different Monte Carlo codes for the same ion chamber agreed within 0.5%. For the perturbation factor p Q , the data did not obey a comparable simple relationship with the beam quality specifier. The variation of p Q for all ion chambers was in the range of 3%–4%. Compared to recently published data, our p Q data is around 1% larger, although the same Monte Carlo code has been used. Compared to the latest experimental data, there are even deviations in the range of 2%.

PO-1334: Feasibility of the kQQ0 formalism for Farmertype chambers in medium-energy kV x-ray beams

PO-1334: Feasibility of the kQQ0 formalism for Farmertype chambers in medium-energy kV x-ray beams