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Detalles de la revista
Formato
Revista
eISSN
1898-0309
Publicado por primera vez
30 Dec 2008
Periodo de publicación
4 veces al año
Idiomas
Inglés

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Volumen 28 (2022): Edición 4 (December 2022)

Detalles de la revista
Formato
Revista
eISSN
1898-0309
Publicado por primera vez
30 Dec 2008
Periodo de publicación
4 veces al año
Idiomas
Inglés

Buscar

6 Artículos
Acceso abierto

Development of a standard phantom for diffusion-weighted magnetic resonance imaging quality control studies: A review

Publicado en línea: 17 Nov 2022
Páginas: 169 - 179

Resumen

Abstract

Various materials and compounds have been used in the design of diffusion-weighted magnetic resonance imaging (DWMRI) phantoms to mimic biological tissue properties, including diffusion. This review thus provides an overview of the preparations of the various DW-MRI phantoms available in relation to the limitations and strengths of materials/solutions used to fill them. The narrative review conducted from relevant databases shows that synthesizing all relevant compounds from individual liquids, gels, and solutions based on their identified strengths could contribute to the development of a novel multifunctional DW-MRI phantom. The proposed multifunctional material at varied concentrations, when filled into a multi-compartment Perspex container of cylindrical or spherical geometry, could serve as a standard DW-MRI phantom. The standard multifunctional phantom could potentially provide DW-MRI quality control test parameters in one study session.

Palabras clave

  • diffusion-weighted magnetic resonance imaging
  • apparent diffusion coefficient
  • phantom
  • quality control
Acceso abierto

Local diagnostic reference levels in diagnostic and therapeutic pediatric cardiology at a specialist pediatric hospital in South Africa

Publicado en línea: 17 Nov 2022
Páginas: 180 - 187

Resumen

Abstract

Introduction: Children may be at a higher risk of experiencing the detrimental effects of ionizing radiation arising from medical radiation imaging. Dose optimisation is therefore recommended to provide assurance that their exposure is as low as reasonably achievable. To this end, periodic assessment of dose levels and establishment of Local Diagnostic Reference Levels (LDRLs) in medical facilities is necessary. There is a general paucity in the literature of data pertaining to dose levels in pediatric interventional radiology. This study establishes LDRLs in diagnostic and therapeutic heart catheterization procedures at a specialist pediatric hospital in a resource constrained country.

Material and methods: Dose indicators from actual patient procedures were collected from the archive and analyzed retrospectively to determine the median, 25th, and 75th percentiles of the total Air Kerma Area Product (KAP), Cumulative Air Kerma (CAK), total Fluoroscopy Time (FT), and a total number of Cine Images (CI) of selected interventional procedures. The dose indicators were also age-stratified into five age groups defined by the International Commission on Radiation Protection publication 135. The results were compared to values available from similar studies in the literature to benchmark our dose levels. Local Dose Reference Levels were set as the 75th percentile values.

Results: For diagnostic procedures (n = 80), the 75th percentiles of KAP, CAK, FT, and CI were 4.0 Gy·cm2, 31.5 mGy, 14.3 min, and 315 frames, respectively and 3.2 Gy·cm2, 30.5 mGy, 17.5 min, and 606 frames, respectively for therapeutic procedures (n = 143).

Conclusions: The LDRLs from this study did not vary significantly from those published in the literature, suggesting that practices at our center were comparable to international norms. Regular reviews of the LDRLs must be conducted to check that the dose levels do not deviate considerably.

Palabras clave

  • pediatric cardiology
  • interventional
  • diagnostic reference levels
  • cathlab
Acceso abierto

Construction and pre-evaluation of an in-house cylindrical ionization chamber fabricated from locally available materials

Publicado en línea: 17 Nov 2022
Páginas: 188 - 199

Resumen

Abstract

Introduction: The objectives of this study were to construct a very robust in-house cylindrical ionization chamber from locally available materials to minimize cost, and to assess its suitability for use in a clinical setting.

Materials and Methods: The entire body of the constructed IC was composed of Perspex (PMMA). Other components of the IC were made from locally available materials, such as paper and discarded items. The in-house IC was made waterproof by passing the triaxial cable connecting its various electrodes through a plastic tube which once served as a drainage tube of a urine bag. This connection was made such that the chamber was vented to the environment. The completed in-house IC was evaluated for: polarity effect, ion recombination, ion collection efficiency, stability, dose linearity, stem effect, leakage current, angular, dose rate and energy dependences.

Results: Although the pre-evaluation results confirmed that the in-house IC satisfied the stipulated international standards for ICs, there was a need to enhance the stem effect and leakage current characteristics of the IC. The in-house IC was found to have an absorbed dose to water calibration coefficient of 4.475 x 107 Gy/C (uncertainty of 1.6%) for cobalt 60 through a cross-calibration with a commercial 0.6 cc cylindrical IC with traceability to the Germany National Dosimetry Laboratory. Using a Jaffé diagram, the in-house IC was also found to have a recombination correction factor of 1.0078 when operated at the calibration voltage of + 400 V. In terms of beam quality correction factors for megavoltage beams, the in-house IC was found to exhibit characteristics similar to those of Scanditronix-Wellhofer IC 70 Farmer type IC.

Conclusion: The constructed in-house Farmer-type IC was able to meet all the recommended characteristics for an IC, and therefore, the in-house IC is suitable for beam output calibration in external beam radiotherapy.

Palabras clave

  • in-house ionization chamber
  • beam output calibration
  • Perspex
  • stem effect
  • leakage current
Acceso abierto

Dosimetric impact of rotational set-up errors in high-risk prostate cancer

Publicado en línea: 15 Dec 2022
Páginas: 200 - 206

Resumen

Abstract

Introduction: Cone-beam computed tomography (CBCT) provides an excellent solution to quantitative assessment and correction of patient set-up errors during radiotherapy. However, most linear accelerators are equipped with conventional therapy tables that can be moved in three translational directions and perform only yaw rotation. Uncorrected roll and pitch result in rotational set-up errors, particularly when the distance from the isocenter to the target border is large. The aim of this study was to investigate the impact of rotational errors on the dose delivered to the clinical target volume (CTV), the planning target volume (PTV) and organs at risk (OAR).

Material and methods: 30 patients with prostate cancer treated with VMAT technique had daily CBCT scans (840 CBCTs in total) prior to treatment delivery. The rotational errors remaining after on-line correction were retrospectively analysed. The sum plans simulating the dose distribution during the treatment course were calculated for selected patients with significant rotational errors.

Results: The dose delivered to the prostate bed CTV reported in the sum plan was not lower than in the original plan for all selected patients. For four patients from the selected group, the D98% for prostate bed PTV was less than 95%. The V47.88Gy for pelvic lymph nodes PTV was less than 98% for two of the selected patients.

Conclusions: The analysis of the dosimetric parameters showed that the impact of uncorrected rotations is not clinically significant in terms of the dose delivered to OAR and the dose coverage of CTV. However, the PTV dose coverage is correlated with distance away from the isocenter and is smaller than planned.

Palabras clave

  • rotational set-up errors
  • IGRT
  • prostate cancer
  • pelvic irradiation
Acceso abierto

Automated patient centering of computed tomography images and its implementation to evaluate clinical practices in three hospitals in Indonesia

Publicado en línea: 15 Dec 2022
Páginas: 207 - 214

Resumen

Abstract

Purpose: This study aims to develop a software tool for investigating patient centering profiles of axial CT images and to implement it to evaluate practices in three hospitals in Indonesia.

Methods: The evaluation of patient centering accuracy was conducted by comparing the center coordinate of the patient’s image to the center coordinates of the axial CT image. This process was iterated for all slices to yield an average patient mis-centering in both the x- and y-axis. We implemented the software to evaluate the profile of centering on 268 patient images from the head, thorax, and abdomen examinations taken from three hospitals.

Results: We found that 82% of patients were mis-centered in the y-axis (i.e., placed more than 5 mm from the iso-center), with 49% of patients placed 10–35 mm from the iso-center. Most of the patients had a tendency to be placed below the iso-centers. In head examinations, patients were more precisely positioned than in the other examinations. We did not find any significant difference in mis-centering between males and females. We found that there was a slight difference between mis-centering in adult and pediatric patients.

Conclusion: Software for automated patient centering was successfully developed. Patients in three hospitals in Indonesia had a tendency to be placed under the iso-center of the gantry.

Palabras clave

  • iso-center
  • mis-centering
  • centering profile
Acceso abierto

Characterization of a commercial EPID-based in-vivo dosimetry and its feasibility and implementation for treatment verification in Malaysia

Publicado en línea: 15 Dec 2022
Páginas: 215 - 221

Resumen

Abstract

Introduction: In vivo dosimetry verification is currently a necessity in radiotherapy centres in Europe countries as one of the tools for patient-specific QA, and now its demand is currently rising in developed countries, such as Malaysia. The aim of this study is to characterize commercial EPID-based dosimetry and its implementation for radiotherapy treatment verification in Malaysia.

Materials and Methods: In this work, the sensitivity and performance of a commercially available in vivo dosimetry system, EPIgray® (DOSIsoft, Cachan, France), were qualitatively evaluated prior to its use at our centre. EPIgray response to dose linearity, field size, off-axis, position, and angle dependency tests were performed against TPS calculated dose for 6 MV and 10 MV photon beams. Relative deviations of the total dose were evaluated at isocentre and different depths in the water. EPIgray measured dose was validated by using IMRT and VMAT prostate plan. All calculation points were at the beam isocentre and at points suggested by TG-119 with accepted tolerance of ±10% dose threshold.

Results: EPIgray reported good agreement for linearity, field size, off-axis, and position dependency with TPS dose, being within 5% tolerance for both energy ranges. The average deviation was less than ±2% and ±7% in 6 MV and 10 MV photon beams, respectively, for the angle dependency test. A clinical evaluation performed for the IMRT prostate plan gave average agreement within ±3% at the plan isocentre for both energies. While for the VMAT plan, 95% and 100% of all points created lie below ±5% for 6 MV and 10 MV photon beam energy, respectively.

Conclusion: In summary, based on the results of preliminary characterization, EPID-based dosimetry is believed as an important tool and beneficial to be implemented for IMRT/VMAT plans verification in Malaysia, especially for in vivo verification, alongside existing pre-treatment verification.

Palabras clave

  • real-time
  • in vivo
  • EPID-based dosimetry
  • patient-specific QA
6 Artículos
Acceso abierto

Development of a standard phantom for diffusion-weighted magnetic resonance imaging quality control studies: A review

Publicado en línea: 17 Nov 2022
Páginas: 169 - 179

Resumen

Abstract

Various materials and compounds have been used in the design of diffusion-weighted magnetic resonance imaging (DWMRI) phantoms to mimic biological tissue properties, including diffusion. This review thus provides an overview of the preparations of the various DW-MRI phantoms available in relation to the limitations and strengths of materials/solutions used to fill them. The narrative review conducted from relevant databases shows that synthesizing all relevant compounds from individual liquids, gels, and solutions based on their identified strengths could contribute to the development of a novel multifunctional DW-MRI phantom. The proposed multifunctional material at varied concentrations, when filled into a multi-compartment Perspex container of cylindrical or spherical geometry, could serve as a standard DW-MRI phantom. The standard multifunctional phantom could potentially provide DW-MRI quality control test parameters in one study session.

Palabras clave

  • diffusion-weighted magnetic resonance imaging
  • apparent diffusion coefficient
  • phantom
  • quality control
Acceso abierto

Local diagnostic reference levels in diagnostic and therapeutic pediatric cardiology at a specialist pediatric hospital in South Africa

Publicado en línea: 17 Nov 2022
Páginas: 180 - 187

Resumen

Abstract

Introduction: Children may be at a higher risk of experiencing the detrimental effects of ionizing radiation arising from medical radiation imaging. Dose optimisation is therefore recommended to provide assurance that their exposure is as low as reasonably achievable. To this end, periodic assessment of dose levels and establishment of Local Diagnostic Reference Levels (LDRLs) in medical facilities is necessary. There is a general paucity in the literature of data pertaining to dose levels in pediatric interventional radiology. This study establishes LDRLs in diagnostic and therapeutic heart catheterization procedures at a specialist pediatric hospital in a resource constrained country.

Material and methods: Dose indicators from actual patient procedures were collected from the archive and analyzed retrospectively to determine the median, 25th, and 75th percentiles of the total Air Kerma Area Product (KAP), Cumulative Air Kerma (CAK), total Fluoroscopy Time (FT), and a total number of Cine Images (CI) of selected interventional procedures. The dose indicators were also age-stratified into five age groups defined by the International Commission on Radiation Protection publication 135. The results were compared to values available from similar studies in the literature to benchmark our dose levels. Local Dose Reference Levels were set as the 75th percentile values.

Results: For diagnostic procedures (n = 80), the 75th percentiles of KAP, CAK, FT, and CI were 4.0 Gy·cm2, 31.5 mGy, 14.3 min, and 315 frames, respectively and 3.2 Gy·cm2, 30.5 mGy, 17.5 min, and 606 frames, respectively for therapeutic procedures (n = 143).

Conclusions: The LDRLs from this study did not vary significantly from those published in the literature, suggesting that practices at our center were comparable to international norms. Regular reviews of the LDRLs must be conducted to check that the dose levels do not deviate considerably.

Palabras clave

  • pediatric cardiology
  • interventional
  • diagnostic reference levels
  • cathlab
Acceso abierto

Construction and pre-evaluation of an in-house cylindrical ionization chamber fabricated from locally available materials

Publicado en línea: 17 Nov 2022
Páginas: 188 - 199

Resumen

Abstract

Introduction: The objectives of this study were to construct a very robust in-house cylindrical ionization chamber from locally available materials to minimize cost, and to assess its suitability for use in a clinical setting.

Materials and Methods: The entire body of the constructed IC was composed of Perspex (PMMA). Other components of the IC were made from locally available materials, such as paper and discarded items. The in-house IC was made waterproof by passing the triaxial cable connecting its various electrodes through a plastic tube which once served as a drainage tube of a urine bag. This connection was made such that the chamber was vented to the environment. The completed in-house IC was evaluated for: polarity effect, ion recombination, ion collection efficiency, stability, dose linearity, stem effect, leakage current, angular, dose rate and energy dependences.

Results: Although the pre-evaluation results confirmed that the in-house IC satisfied the stipulated international standards for ICs, there was a need to enhance the stem effect and leakage current characteristics of the IC. The in-house IC was found to have an absorbed dose to water calibration coefficient of 4.475 x 107 Gy/C (uncertainty of 1.6%) for cobalt 60 through a cross-calibration with a commercial 0.6 cc cylindrical IC with traceability to the Germany National Dosimetry Laboratory. Using a Jaffé diagram, the in-house IC was also found to have a recombination correction factor of 1.0078 when operated at the calibration voltage of + 400 V. In terms of beam quality correction factors for megavoltage beams, the in-house IC was found to exhibit characteristics similar to those of Scanditronix-Wellhofer IC 70 Farmer type IC.

Conclusion: The constructed in-house Farmer-type IC was able to meet all the recommended characteristics for an IC, and therefore, the in-house IC is suitable for beam output calibration in external beam radiotherapy.

Palabras clave

  • in-house ionization chamber
  • beam output calibration
  • Perspex
  • stem effect
  • leakage current
Acceso abierto

Dosimetric impact of rotational set-up errors in high-risk prostate cancer

Publicado en línea: 15 Dec 2022
Páginas: 200 - 206

Resumen

Abstract

Introduction: Cone-beam computed tomography (CBCT) provides an excellent solution to quantitative assessment and correction of patient set-up errors during radiotherapy. However, most linear accelerators are equipped with conventional therapy tables that can be moved in three translational directions and perform only yaw rotation. Uncorrected roll and pitch result in rotational set-up errors, particularly when the distance from the isocenter to the target border is large. The aim of this study was to investigate the impact of rotational errors on the dose delivered to the clinical target volume (CTV), the planning target volume (PTV) and organs at risk (OAR).

Material and methods: 30 patients with prostate cancer treated with VMAT technique had daily CBCT scans (840 CBCTs in total) prior to treatment delivery. The rotational errors remaining after on-line correction were retrospectively analysed. The sum plans simulating the dose distribution during the treatment course were calculated for selected patients with significant rotational errors.

Results: The dose delivered to the prostate bed CTV reported in the sum plan was not lower than in the original plan for all selected patients. For four patients from the selected group, the D98% for prostate bed PTV was less than 95%. The V47.88Gy for pelvic lymph nodes PTV was less than 98% for two of the selected patients.

Conclusions: The analysis of the dosimetric parameters showed that the impact of uncorrected rotations is not clinically significant in terms of the dose delivered to OAR and the dose coverage of CTV. However, the PTV dose coverage is correlated with distance away from the isocenter and is smaller than planned.

Palabras clave

  • rotational set-up errors
  • IGRT
  • prostate cancer
  • pelvic irradiation
Acceso abierto

Automated patient centering of computed tomography images and its implementation to evaluate clinical practices in three hospitals in Indonesia

Publicado en línea: 15 Dec 2022
Páginas: 207 - 214

Resumen

Abstract

Purpose: This study aims to develop a software tool for investigating patient centering profiles of axial CT images and to implement it to evaluate practices in three hospitals in Indonesia.

Methods: The evaluation of patient centering accuracy was conducted by comparing the center coordinate of the patient’s image to the center coordinates of the axial CT image. This process was iterated for all slices to yield an average patient mis-centering in both the x- and y-axis. We implemented the software to evaluate the profile of centering on 268 patient images from the head, thorax, and abdomen examinations taken from three hospitals.

Results: We found that 82% of patients were mis-centered in the y-axis (i.e., placed more than 5 mm from the iso-center), with 49% of patients placed 10–35 mm from the iso-center. Most of the patients had a tendency to be placed below the iso-centers. In head examinations, patients were more precisely positioned than in the other examinations. We did not find any significant difference in mis-centering between males and females. We found that there was a slight difference between mis-centering in adult and pediatric patients.

Conclusion: Software for automated patient centering was successfully developed. Patients in three hospitals in Indonesia had a tendency to be placed under the iso-center of the gantry.

Palabras clave

  • iso-center
  • mis-centering
  • centering profile
Acceso abierto

Characterization of a commercial EPID-based in-vivo dosimetry and its feasibility and implementation for treatment verification in Malaysia

Publicado en línea: 15 Dec 2022
Páginas: 215 - 221

Resumen

Abstract

Introduction: In vivo dosimetry verification is currently a necessity in radiotherapy centres in Europe countries as one of the tools for patient-specific QA, and now its demand is currently rising in developed countries, such as Malaysia. The aim of this study is to characterize commercial EPID-based dosimetry and its implementation for radiotherapy treatment verification in Malaysia.

Materials and Methods: In this work, the sensitivity and performance of a commercially available in vivo dosimetry system, EPIgray® (DOSIsoft, Cachan, France), were qualitatively evaluated prior to its use at our centre. EPIgray response to dose linearity, field size, off-axis, position, and angle dependency tests were performed against TPS calculated dose for 6 MV and 10 MV photon beams. Relative deviations of the total dose were evaluated at isocentre and different depths in the water. EPIgray measured dose was validated by using IMRT and VMAT prostate plan. All calculation points were at the beam isocentre and at points suggested by TG-119 with accepted tolerance of ±10% dose threshold.

Results: EPIgray reported good agreement for linearity, field size, off-axis, and position dependency with TPS dose, being within 5% tolerance for both energy ranges. The average deviation was less than ±2% and ±7% in 6 MV and 10 MV photon beams, respectively, for the angle dependency test. A clinical evaluation performed for the IMRT prostate plan gave average agreement within ±3% at the plan isocentre for both energies. While for the VMAT plan, 95% and 100% of all points created lie below ±5% for 6 MV and 10 MV photon beam energy, respectively.

Conclusion: In summary, based on the results of preliminary characterization, EPID-based dosimetry is believed as an important tool and beneficial to be implemented for IMRT/VMAT plans verification in Malaysia, especially for in vivo verification, alongside existing pre-treatment verification.

Palabras clave

  • real-time
  • in vivo
  • EPID-based dosimetry
  • patient-specific QA

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