Martin Glegg - Academia.edu (original) (raw)
Papers by Martin Glegg
The accuracy of electron dose calculations performed by two commercially available treatment plan... more The accuracy of electron dose calculations performed by two commercially available treatment planning computers, Varian Cadplan and Helax TMS, has been assessed. Measured values of absorbed dose delivered by a Varian 2100C linear accelerator, under a wide variety of irradiation conditions, were compared with doses calculated by the treatment planning computers. Much of the motivation for this work was provided by a requirement to verify the accuracy of calculated electron dose distributions in situations encountered clinically at Glasgow's Beatson Oncology Centre. Calculated dose distributions are required in a significant minority of electron treatments, usually in cases involving treatment to the head and neck. Here, therapeutic electron beams are subject to factors which may cause non-uniformity in the distribution of dose, and which may complicate the calculation of dose. The beam shape is often irregular, the beam may enter the patient at an oblique angle or at an extended ...
Journal of Thoracic Oncology
Background: The main reason for a low progressionfree survival rate in radiotherapy for NSCLC is ... more Background: The main reason for a low progressionfree survival rate in radiotherapy for NSCLC is that the lung is sensitive to radiation, and radiation-induced lung injury is closely related to the exposed volume of the lung tissues. A large irradiation field resulted in difficulty in increasing target dose, so clinically complete remission is very difficult in the primary lesion of the lung cancer. Therefore, as opinions are currently divided on whether it is necessary to delineate the CTV, this study aimed to study the impact of delineating CTV on the treatment of lung cancer. Methods: A total of 177 patients with medium and late stages of NSCLC diagnosed by pathology and/or cytology were selected. These patients received three-dimensional conformal radiation therapy (3-DCRT) or intensity modulated radiation therapy (IMRT) were divided into an undelineated CTV group (A group) and delineated CTV group (B group). Gross tumor volume (GTV) and planning target volume (PTV) were delineated in the A group, while CTV was additionally delineated in the B group. Dose was fractionated in pulmonary lesions in the two groups: 200-220 cGy/time, 5 times per week, and the radiation dose was DT5600-6600 cGy. The mean lung tumor doses were comparable between the two groups. Results: The short-term overall response rate had a trend to be higher in group B, while the 1-year, 2-year and 3-year distant metastasis rates, progression-free survival and overall survival rates had a trend to be higher in group A, but none of the differences were significant. The incidence of radiation pneumonitis was higher in group B (33.33% vs. 16.30%, P¼0.017), but none were Grade-4 or worse. Conclusion: Undelineating the CTV in radiotherapy of lung tumors tends to reduce the radiation field and significantly reduce the incidence of radiation pneumonitis, but it don't reduce overall response rate, the progression-free survival and overall survival rate.
Radiother Oncol, 2011
The study was performed to investigate how tumor shrinkage affects the dose given to head and nec... more The study was performed to investigate how tumor shrinkage affects the dose given to head and neck patients' spinal cord when treated with RapidArc. Materials: The study included 20 patients receiving radiotherapy for cancer in the head and neck area. All the patients were treated with arc-treatment (RapidArc, Varian). Cone-BeamCT scans (CBCT) were acquired daily with the On-Board Imager (Varian), and used for verifying the patient setup and to correct the position before each daily treatment session. The contour for the spinal cord was transferred off-line from the planning CT to the CBCT scans. The original plan was thereafter recalculated on the CBCT scans, where monitor units and MLC movements were kept fixed. This was done to estimate the effect of the size of the patient's tumor on the dose given to the spinal cord in each daily session. The maximum dose to the spinal cord (Dmax,spinal cord) was found on each of the CBCT scans, where Dmax,spinal cord was the maximum dose given to at least 2% of the contoured volume of the spinal cord. As a first approximation, was the size of the tumor indicated with the distance d defined in Fig 1, where d was taken as the largest measured distance from the tumor surface to the spinal cord. Results: Dmax,spinal cord and d were found for each patient on all the daily CBCT scans. The results for two of the patients are shown in Fig 1. The figure shows how Dmax,spinal cord is weakly dependent on the change in d (Δd) and therefore on the change in the size of the tumor. The results for the other patients show similar dependency on d. For different patients the planned Dmax,spinal cord will be different and thus give different fitted curves for each patient. If, on the other hand, the results for the patient group studied are normalized in that way that Dmax,spinal cord (0) =100% for all the patients, the results can be fitted with one linear curve, similar as can be seen in Fig 1. These results will be shown and discussed in further details, as well as threshold for Δd to keep Dmax,spinal cord below the allowed limit, will be presented.
Nuclear Medicine Communications, 1992
The British Journal of Radiology, 2015
This study describes a two dimensional electronic portal imaging device (EPID) transit dosimetry ... more This study describes a two dimensional electronic portal imaging device (EPID) transit dosimetry model that can predict either: (1) in-phantom exit dose, or (2) EPID transit dose, for treatment verification. The model was based on a quadratic equation that relates the reduction in intensity to the equivalent path length (EPL) of the attenuator. In this study, two sets of quadratic equation coefficients were derived from calibration dose planes measured with EPID and ionization chamber in water under reference conditions. With two sets of coefficients, EPL can be calculated from either EPID or treatment planning system (TPS) dose planes. Consequently, either the in-phantom exit dose or the EPID transit dose can be predicted from the EPL. The model was tested with two open, five wedge and seven sliding window prostate and head and neck intensity-modulated radiation therapy (IMRT) fields on phantoms. Results were analysed using absolute gamma analysis (3%/3 mm). The open fields gamma pass rates were >96.8% for all comparisons. For wedge and IMRT fields, comparisons between predicted and TPS-computed in-phantom exit dose resulted in mean gamma pass rate of 97.4% (range, 92.3-100%). As for the comparisons between predicted and measured EPID transit dose, the mean gamma pass rate was 97.5% (range, 92.6-100%). An EPID transit dosimetry model that can predict in-phantom exit dose and EPID transit dose was described and proven to be valid. The described model is practical, generic and flexible to encourage widespread implementation of EPID dosimetry for the improvement of patients' safety in radiotherapy.
The British journal of radiology, 1999
Left-sided post-operative radiotherapy fields for the treatment of breast cancer inevitably encom... more Left-sided post-operative radiotherapy fields for the treatment of breast cancer inevitably encompass the heart within the treatment volume, resulting in late mortality which may negate the cause-specific survival advantage of the therapy. The effect of positioning was studied in 11 patients with left-sided tumours and five with right-sided tumours receiving routine post-operative radiotherapy to the breast or chest wall as part of primary therapy for breast cancer. Using the same arrangement of glancing fields for each patient treatment position, the optimum patient positioning resulted in a reduction in cardiac dose compared to our standard patient treatment position. On the left side the reduction in mean cardiac dose was 60% (p < 0.001) and the reduction in maximum dose was 32% (p < 0.001); on the right it was 17% and 31%, respectively. The volume of cardiac tissue irradiated was also reduced for all patients. Using this optimum treatment position, cardiac dose was investi...
The Breast, 1997
it does not arise from either MCF or overlooked tumour, respectively. We propose that local recur... more it does not arise from either MCF or overlooked tumour, respectively. We propose that local recurrence arises a) from circulating metastatic cancer cells (local relapse does harbinger a poorer prognosis) or b) from local transfection of surrounding breast epithelium by nuclear material released from the original malignant clone resulting in insertional mutagenesis. The recent report of the loss of heterozygocity in morphologically normal tissue around breast cancer supports the latter view. In any case. if MCF do not give rise to breast recurrence then why should we treat them with either mastectomy or whole breast radiotherapy? It is as necessary or as unnecessary as treating the contralateral breast! We have begun pilot studies of a clinical trial to test whether radiotherapy to the index quadrant alone can achieve good local control.
Cancer Treatment Reviews, 1997
Journal of Cardiovascular Magnetic Resonance, 2016
Radiotherapy and Oncology, 2015
Nuclear Medicine Communications, 1992
Medical dosimetry : official journal of the American Association of Medical Dosimetrists, 2003
The accuracy of electron dose calculations performed by two commercially available treatment plan... more The accuracy of electron dose calculations performed by two commercially available treatment planning systems, Varian Cadplan and MDS Nordion Helax-TMS, were assessed. Three tests designed to reproduce clinical treatments likely to result in dose nonuniformity have been carried out. The tests examined oblique incidence of the electron beam; incidence on a surface containing a step shape; and incidence on a phantom containing a small air cavity. Dose calculations performed by the planning systems were compared with thermoluminescence dosimetry (TLD) measurements in a WTe electron solid water phantom. A Varian 2100C linear accelerator was used. In most situations, the discrepancy between calculated and measured dose was within the tolerance specified by the ICRU; however, some exceptions were noted. Helax-TMS produced errors of 5 mm in the position of the 10% isodose line in the penumbra of the obliquely incident beam. Both Cadplan and Helax-TMS overestimated the surface dose adjacent...
Physics in medicine and biology, Jan 21, 2010
In vivo dosimetry is one of the quality assurance tools used in radiotherapy to monitor the dose ... more In vivo dosimetry is one of the quality assurance tools used in radiotherapy to monitor the dose delivered to the patient. Electronic portal imaging device (EPID) images for a set of solid water phantoms of varying thicknesses were acquired and the data fitted onto a quadratic equation, which relates the reduction in photon beam intensity to the attenuation coefficient and material thickness at a reference condition. The quadratic model is used to convert the measured grey scale value into water equivalent path length (EPL) at each pixel for any material imaged by the detector. For any other non-reference conditions, scatter, field size and MU variation effects on the image were corrected by relative measurements using an ionization chamber and an EPID. The 2D EPL is linked to the percentage exit dose table, for different thicknesses and field sizes, thereby converting the plane pixel values at each point into a 2D dose map. The off-axis ratio is corrected using envelope and boundar...
Journal of applied clinical medical physics / American College of Medical Physics, 2011
In this study, we use the quadratic calibration method (QCM), in which an EPID image is converted... more In this study, we use the quadratic calibration method (QCM), in which an EPID image is converted into a matrix of equivalent path lengths (EPLs) and, therefore, exit doses, so as to model doses in conformal and enhanced dynamic wedge (EDW) fields. The QCM involves acquiring series of EPID images at a reference field size for different thicknesses of homogeneous solid water blocks. From these, a set of coefficients is established that is used to compute the EPL of any other irradiated material. To determine the EPL, the irradiated area must be known in order to establish the appropriate scatter correction. A method was devised for the automatic calculation of areas from the EPID image that facilitated the calculation of EPL for any field and exit dose. For EDW fields, the fitting coefficients were modified by utilizing the linac manufacturer's golden segmented treatment tables (GSTT) methodology and MU fraction model. The nonlinear response of the EPL with lower monitor units (M...
Radiation Oncology, 2013
Background: The purpose of this study was to demonstrate how magnetic resonance imaging (MRI) pat... more Background: The purpose of this study was to demonstrate how magnetic resonance imaging (MRI) patient position protocols influence registration quality in patients with oropharyngeal cancer undergoing radical radiotherapy and the consequences for gross tumour volume (GTV) definition and radiotherapy planning. Methods and materials: Twenty-two oropharyngeal patients underwent a computed tomography (CT), a diagnostic MRI (MRI D ) and an MRI in the radiotherapy position within an immobilization mask (MRI RT ). Clinicians delineated the GTV on the CT viewing the MRI D separately (GTV C ); on the CT registered to MRI D (GTV D ) and on the CT registered to MRI RT (GTV RT ). Planning target volumes (PTVs) were denoted similarly. Registration quality was assessed by measuring disparity between structures in the three set-ups. Volumetric modulated arc therapy (VMAT) radiotherapy planning was performed for PTV C , PTV D and PTV RT . To determine the dose received by the reference PTV RT , we optimized for PTV C and PTV D while calculating the dose to PTV RT . Statistical significance was determined using the two-tailed Mann-Whitney or two-tailed paired student t-tests. Results: A significant improvement in registration accuracy was found between CT and MRI RT versus the MRI D measuring distances from the centre of structures (geometric mean error of 2.2 mm versus 6.6 mm). The mean GTV C (44.1 cm 3 ) was significantly larger than GTV D (33.7 cm 3 , p value = 0.027) or GTV RT (30.5 cm 3 , p value = 0.014). When optimizing the VMAT plans for PTV C and investigating the mean dose to PTV RT neither the dose to 99% (58.8%) nor 95% of the PTV (84.7%) were found to meet the required clinical dose constraints of 90% and 95% respectively. Similarly, when optimizing for PTV D the mean dose to PTV RT did not meet clinical dose constraints for 99% (14.9%) nor 95% of the PTV (66.2%). Only by optimizing for PTV RT were all clinical dose constraints achieved.
Journal of applied clinical medical physics / American College of Medical Physics, 2014
Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected v... more Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected values, usually generated by the treatment planning system (TPS), to verify accuracy of treatment delivery. This report aims to evaluate the accuracy of six TPS algorithms in computing entrance and exit doses for a 6 MV beam. The algorithms tested were: pencil beam convolution (Eclipse PBC), analytical anisotropic algorithm (Eclipse AAA), AcurosXB (Eclipse AXB), FFT convolution (XiO Convolution), multigrid superposition (XiO Superposition), and Monte Carlo photon (Monaco MC). Measurements with ionization chamber (IC) and diode detector in water phantoms were used as a reference. Comparisons were done in terms of central axis point dose, 1D relative profiles, and 2D absolute gamma analysis. Entrance doses computed by all TPS algorithms agreed to within 2% of the measured values. Exit doses computed by XiO Convolution, XiO Superposition, Eclipse AXB, and Monaco MC agreed with the IC measure...
Physics in Medicine and Biology, 2009
This study investigated the compatibility of a head and neck immobilization device with magnetic ... more This study investigated the compatibility of a head and neck immobilization device with magnetic resonance imaging (MRI). The immobilization device is used to position a patient in the same way as when receiving a computed tomography (CT) scan for radiotherapy planning and radiation treatment. The advantage of using immobilization in MR is improved accuracy in CT/MR image registration enabling greater confidence in the delineation of structures. The main practical difficulty in using an immobilization device in MRI is that physical constraints make their use incompatible with head imaging coils. Within this paper we describe a method for MR imaging of the brain which allows the use of head and neck immobilization devices. By a series of image quality tests we obtained the same or better image quality as a multi-channel head coil.
Radiotherapy and Oncology, 2011
Physics in Medicine and Biology, 2008
Dosimetrical characteristics of 11 Varian a-Si-500 electronic portal imaging devices (EPIDs) in c... more Dosimetrical characteristics of 11 Varian a-Si-500 electronic portal imaging devices (EPIDs) in clinical use for periods ranging between 10 and 86 months were investigated for consistency of performance and portal dosimetry implications. Properties studied include short-term reproducibility, signal linearity with monitor units, response to reference beam, signal uniformity across the detector panel, signal dependence on field size, dose-rate influence, memory effects and image profiles as a function of monitor units. The EPID measurements were also compared with those of the ionization chambers&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; to ensure stability of the linear accelerators. Depending on their clinical installation date, the EPIDs were interfaced with one of the two different acquisition control software packages, IAS2/IDU-II or IAS3/IDU-20. Both the EPID age and image acquisition system influenced the dosimetric characteristics with the newer version (IAS3 with IDU-20) giving better data reproducibility and linearity fit than the older version (IAS2 with IDU-II). The relative signal response (uniformity) after 50 MU was better than 95% of the central value and independent of detector. Sensitivity for all EPIDs reduced continuously with increasing dose rates for the newer image acquisition software. In the dose-rate range 100-600 MU min(-1), the maximum variation in sensitivity ranged between 1 and 1.8% for different EPIDs. For memory effects, the increase in the measured signal at the centre of the irradiated field for successive images was within 1.8% and 1.0% for the older and newer acquisition systems, respectively. Image profiles acquired at a lower MU in the radial plane (gun-target) had gradients in measured pixel values of up to 25% for the older system. Detectors with software/hardware versions IAS3/IDU-20 have a high degree of accuracy and are more suitable for routine quantitative IMRT dosimetrical verification.
The accuracy of electron dose calculations performed by two commercially available treatment plan... more The accuracy of electron dose calculations performed by two commercially available treatment planning computers, Varian Cadplan and Helax TMS, has been assessed. Measured values of absorbed dose delivered by a Varian 2100C linear accelerator, under a wide variety of irradiation conditions, were compared with doses calculated by the treatment planning computers. Much of the motivation for this work was provided by a requirement to verify the accuracy of calculated electron dose distributions in situations encountered clinically at Glasgow's Beatson Oncology Centre. Calculated dose distributions are required in a significant minority of electron treatments, usually in cases involving treatment to the head and neck. Here, therapeutic electron beams are subject to factors which may cause non-uniformity in the distribution of dose, and which may complicate the calculation of dose. The beam shape is often irregular, the beam may enter the patient at an oblique angle or at an extended ...
Journal of Thoracic Oncology
Background: The main reason for a low progressionfree survival rate in radiotherapy for NSCLC is ... more Background: The main reason for a low progressionfree survival rate in radiotherapy for NSCLC is that the lung is sensitive to radiation, and radiation-induced lung injury is closely related to the exposed volume of the lung tissues. A large irradiation field resulted in difficulty in increasing target dose, so clinically complete remission is very difficult in the primary lesion of the lung cancer. Therefore, as opinions are currently divided on whether it is necessary to delineate the CTV, this study aimed to study the impact of delineating CTV on the treatment of lung cancer. Methods: A total of 177 patients with medium and late stages of NSCLC diagnosed by pathology and/or cytology were selected. These patients received three-dimensional conformal radiation therapy (3-DCRT) or intensity modulated radiation therapy (IMRT) were divided into an undelineated CTV group (A group) and delineated CTV group (B group). Gross tumor volume (GTV) and planning target volume (PTV) were delineated in the A group, while CTV was additionally delineated in the B group. Dose was fractionated in pulmonary lesions in the two groups: 200-220 cGy/time, 5 times per week, and the radiation dose was DT5600-6600 cGy. The mean lung tumor doses were comparable between the two groups. Results: The short-term overall response rate had a trend to be higher in group B, while the 1-year, 2-year and 3-year distant metastasis rates, progression-free survival and overall survival rates had a trend to be higher in group A, but none of the differences were significant. The incidence of radiation pneumonitis was higher in group B (33.33% vs. 16.30%, P¼0.017), but none were Grade-4 or worse. Conclusion: Undelineating the CTV in radiotherapy of lung tumors tends to reduce the radiation field and significantly reduce the incidence of radiation pneumonitis, but it don't reduce overall response rate, the progression-free survival and overall survival rate.
Radiother Oncol, 2011
The study was performed to investigate how tumor shrinkage affects the dose given to head and nec... more The study was performed to investigate how tumor shrinkage affects the dose given to head and neck patients' spinal cord when treated with RapidArc. Materials: The study included 20 patients receiving radiotherapy for cancer in the head and neck area. All the patients were treated with arc-treatment (RapidArc, Varian). Cone-BeamCT scans (CBCT) were acquired daily with the On-Board Imager (Varian), and used for verifying the patient setup and to correct the position before each daily treatment session. The contour for the spinal cord was transferred off-line from the planning CT to the CBCT scans. The original plan was thereafter recalculated on the CBCT scans, where monitor units and MLC movements were kept fixed. This was done to estimate the effect of the size of the patient's tumor on the dose given to the spinal cord in each daily session. The maximum dose to the spinal cord (Dmax,spinal cord) was found on each of the CBCT scans, where Dmax,spinal cord was the maximum dose given to at least 2% of the contoured volume of the spinal cord. As a first approximation, was the size of the tumor indicated with the distance d defined in Fig 1, where d was taken as the largest measured distance from the tumor surface to the spinal cord. Results: Dmax,spinal cord and d were found for each patient on all the daily CBCT scans. The results for two of the patients are shown in Fig 1. The figure shows how Dmax,spinal cord is weakly dependent on the change in d (Δd) and therefore on the change in the size of the tumor. The results for the other patients show similar dependency on d. For different patients the planned Dmax,spinal cord will be different and thus give different fitted curves for each patient. If, on the other hand, the results for the patient group studied are normalized in that way that Dmax,spinal cord (0) =100% for all the patients, the results can be fitted with one linear curve, similar as can be seen in Fig 1. These results will be shown and discussed in further details, as well as threshold for Δd to keep Dmax,spinal cord below the allowed limit, will be presented.
Nuclear Medicine Communications, 1992
The British Journal of Radiology, 2015
This study describes a two dimensional electronic portal imaging device (EPID) transit dosimetry ... more This study describes a two dimensional electronic portal imaging device (EPID) transit dosimetry model that can predict either: (1) in-phantom exit dose, or (2) EPID transit dose, for treatment verification. The model was based on a quadratic equation that relates the reduction in intensity to the equivalent path length (EPL) of the attenuator. In this study, two sets of quadratic equation coefficients were derived from calibration dose planes measured with EPID and ionization chamber in water under reference conditions. With two sets of coefficients, EPL can be calculated from either EPID or treatment planning system (TPS) dose planes. Consequently, either the in-phantom exit dose or the EPID transit dose can be predicted from the EPL. The model was tested with two open, five wedge and seven sliding window prostate and head and neck intensity-modulated radiation therapy (IMRT) fields on phantoms. Results were analysed using absolute gamma analysis (3%/3 mm). The open fields gamma pass rates were >96.8% for all comparisons. For wedge and IMRT fields, comparisons between predicted and TPS-computed in-phantom exit dose resulted in mean gamma pass rate of 97.4% (range, 92.3-100%). As for the comparisons between predicted and measured EPID transit dose, the mean gamma pass rate was 97.5% (range, 92.6-100%). An EPID transit dosimetry model that can predict in-phantom exit dose and EPID transit dose was described and proven to be valid. The described model is practical, generic and flexible to encourage widespread implementation of EPID dosimetry for the improvement of patients' safety in radiotherapy.
The British journal of radiology, 1999
Left-sided post-operative radiotherapy fields for the treatment of breast cancer inevitably encom... more Left-sided post-operative radiotherapy fields for the treatment of breast cancer inevitably encompass the heart within the treatment volume, resulting in late mortality which may negate the cause-specific survival advantage of the therapy. The effect of positioning was studied in 11 patients with left-sided tumours and five with right-sided tumours receiving routine post-operative radiotherapy to the breast or chest wall as part of primary therapy for breast cancer. Using the same arrangement of glancing fields for each patient treatment position, the optimum patient positioning resulted in a reduction in cardiac dose compared to our standard patient treatment position. On the left side the reduction in mean cardiac dose was 60% (p < 0.001) and the reduction in maximum dose was 32% (p < 0.001); on the right it was 17% and 31%, respectively. The volume of cardiac tissue irradiated was also reduced for all patients. Using this optimum treatment position, cardiac dose was investi...
The Breast, 1997
it does not arise from either MCF or overlooked tumour, respectively. We propose that local recur... more it does not arise from either MCF or overlooked tumour, respectively. We propose that local recurrence arises a) from circulating metastatic cancer cells (local relapse does harbinger a poorer prognosis) or b) from local transfection of surrounding breast epithelium by nuclear material released from the original malignant clone resulting in insertional mutagenesis. The recent report of the loss of heterozygocity in morphologically normal tissue around breast cancer supports the latter view. In any case. if MCF do not give rise to breast recurrence then why should we treat them with either mastectomy or whole breast radiotherapy? It is as necessary or as unnecessary as treating the contralateral breast! We have begun pilot studies of a clinical trial to test whether radiotherapy to the index quadrant alone can achieve good local control.
Cancer Treatment Reviews, 1997
Journal of Cardiovascular Magnetic Resonance, 2016
Radiotherapy and Oncology, 2015
Nuclear Medicine Communications, 1992
Medical dosimetry : official journal of the American Association of Medical Dosimetrists, 2003
The accuracy of electron dose calculations performed by two commercially available treatment plan... more The accuracy of electron dose calculations performed by two commercially available treatment planning systems, Varian Cadplan and MDS Nordion Helax-TMS, were assessed. Three tests designed to reproduce clinical treatments likely to result in dose nonuniformity have been carried out. The tests examined oblique incidence of the electron beam; incidence on a surface containing a step shape; and incidence on a phantom containing a small air cavity. Dose calculations performed by the planning systems were compared with thermoluminescence dosimetry (TLD) measurements in a WTe electron solid water phantom. A Varian 2100C linear accelerator was used. In most situations, the discrepancy between calculated and measured dose was within the tolerance specified by the ICRU; however, some exceptions were noted. Helax-TMS produced errors of 5 mm in the position of the 10% isodose line in the penumbra of the obliquely incident beam. Both Cadplan and Helax-TMS overestimated the surface dose adjacent...
Physics in medicine and biology, Jan 21, 2010
In vivo dosimetry is one of the quality assurance tools used in radiotherapy to monitor the dose ... more In vivo dosimetry is one of the quality assurance tools used in radiotherapy to monitor the dose delivered to the patient. Electronic portal imaging device (EPID) images for a set of solid water phantoms of varying thicknesses were acquired and the data fitted onto a quadratic equation, which relates the reduction in photon beam intensity to the attenuation coefficient and material thickness at a reference condition. The quadratic model is used to convert the measured grey scale value into water equivalent path length (EPL) at each pixel for any material imaged by the detector. For any other non-reference conditions, scatter, field size and MU variation effects on the image were corrected by relative measurements using an ionization chamber and an EPID. The 2D EPL is linked to the percentage exit dose table, for different thicknesses and field sizes, thereby converting the plane pixel values at each point into a 2D dose map. The off-axis ratio is corrected using envelope and boundar...
Journal of applied clinical medical physics / American College of Medical Physics, 2011
In this study, we use the quadratic calibration method (QCM), in which an EPID image is converted... more In this study, we use the quadratic calibration method (QCM), in which an EPID image is converted into a matrix of equivalent path lengths (EPLs) and, therefore, exit doses, so as to model doses in conformal and enhanced dynamic wedge (EDW) fields. The QCM involves acquiring series of EPID images at a reference field size for different thicknesses of homogeneous solid water blocks. From these, a set of coefficients is established that is used to compute the EPL of any other irradiated material. To determine the EPL, the irradiated area must be known in order to establish the appropriate scatter correction. A method was devised for the automatic calculation of areas from the EPID image that facilitated the calculation of EPL for any field and exit dose. For EDW fields, the fitting coefficients were modified by utilizing the linac manufacturer's golden segmented treatment tables (GSTT) methodology and MU fraction model. The nonlinear response of the EPL with lower monitor units (M...
Radiation Oncology, 2013
Background: The purpose of this study was to demonstrate how magnetic resonance imaging (MRI) pat... more Background: The purpose of this study was to demonstrate how magnetic resonance imaging (MRI) patient position protocols influence registration quality in patients with oropharyngeal cancer undergoing radical radiotherapy and the consequences for gross tumour volume (GTV) definition and radiotherapy planning. Methods and materials: Twenty-two oropharyngeal patients underwent a computed tomography (CT), a diagnostic MRI (MRI D ) and an MRI in the radiotherapy position within an immobilization mask (MRI RT ). Clinicians delineated the GTV on the CT viewing the MRI D separately (GTV C ); on the CT registered to MRI D (GTV D ) and on the CT registered to MRI RT (GTV RT ). Planning target volumes (PTVs) were denoted similarly. Registration quality was assessed by measuring disparity between structures in the three set-ups. Volumetric modulated arc therapy (VMAT) radiotherapy planning was performed for PTV C , PTV D and PTV RT . To determine the dose received by the reference PTV RT , we optimized for PTV C and PTV D while calculating the dose to PTV RT . Statistical significance was determined using the two-tailed Mann-Whitney or two-tailed paired student t-tests. Results: A significant improvement in registration accuracy was found between CT and MRI RT versus the MRI D measuring distances from the centre of structures (geometric mean error of 2.2 mm versus 6.6 mm). The mean GTV C (44.1 cm 3 ) was significantly larger than GTV D (33.7 cm 3 , p value = 0.027) or GTV RT (30.5 cm 3 , p value = 0.014). When optimizing the VMAT plans for PTV C and investigating the mean dose to PTV RT neither the dose to 99% (58.8%) nor 95% of the PTV (84.7%) were found to meet the required clinical dose constraints of 90% and 95% respectively. Similarly, when optimizing for PTV D the mean dose to PTV RT did not meet clinical dose constraints for 99% (14.9%) nor 95% of the PTV (66.2%). Only by optimizing for PTV RT were all clinical dose constraints achieved.
Journal of applied clinical medical physics / American College of Medical Physics, 2014
Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected v... more Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected values, usually generated by the treatment planning system (TPS), to verify accuracy of treatment delivery. This report aims to evaluate the accuracy of six TPS algorithms in computing entrance and exit doses for a 6 MV beam. The algorithms tested were: pencil beam convolution (Eclipse PBC), analytical anisotropic algorithm (Eclipse AAA), AcurosXB (Eclipse AXB), FFT convolution (XiO Convolution), multigrid superposition (XiO Superposition), and Monte Carlo photon (Monaco MC). Measurements with ionization chamber (IC) and diode detector in water phantoms were used as a reference. Comparisons were done in terms of central axis point dose, 1D relative profiles, and 2D absolute gamma analysis. Entrance doses computed by all TPS algorithms agreed to within 2% of the measured values. Exit doses computed by XiO Convolution, XiO Superposition, Eclipse AXB, and Monaco MC agreed with the IC measure...
Physics in Medicine and Biology, 2009
This study investigated the compatibility of a head and neck immobilization device with magnetic ... more This study investigated the compatibility of a head and neck immobilization device with magnetic resonance imaging (MRI). The immobilization device is used to position a patient in the same way as when receiving a computed tomography (CT) scan for radiotherapy planning and radiation treatment. The advantage of using immobilization in MR is improved accuracy in CT/MR image registration enabling greater confidence in the delineation of structures. The main practical difficulty in using an immobilization device in MRI is that physical constraints make their use incompatible with head imaging coils. Within this paper we describe a method for MR imaging of the brain which allows the use of head and neck immobilization devices. By a series of image quality tests we obtained the same or better image quality as a multi-channel head coil.
Radiotherapy and Oncology, 2011
Physics in Medicine and Biology, 2008
Dosimetrical characteristics of 11 Varian a-Si-500 electronic portal imaging devices (EPIDs) in c... more Dosimetrical characteristics of 11 Varian a-Si-500 electronic portal imaging devices (EPIDs) in clinical use for periods ranging between 10 and 86 months were investigated for consistency of performance and portal dosimetry implications. Properties studied include short-term reproducibility, signal linearity with monitor units, response to reference beam, signal uniformity across the detector panel, signal dependence on field size, dose-rate influence, memory effects and image profiles as a function of monitor units. The EPID measurements were also compared with those of the ionization chambers&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; to ensure stability of the linear accelerators. Depending on their clinical installation date, the EPIDs were interfaced with one of the two different acquisition control software packages, IAS2/IDU-II or IAS3/IDU-20. Both the EPID age and image acquisition system influenced the dosimetric characteristics with the newer version (IAS3 with IDU-20) giving better data reproducibility and linearity fit than the older version (IAS2 with IDU-II). The relative signal response (uniformity) after 50 MU was better than 95% of the central value and independent of detector. Sensitivity for all EPIDs reduced continuously with increasing dose rates for the newer image acquisition software. In the dose-rate range 100-600 MU min(-1), the maximum variation in sensitivity ranged between 1 and 1.8% for different EPIDs. For memory effects, the increase in the measured signal at the centre of the irradiated field for successive images was within 1.8% and 1.0% for the older and newer acquisition systems, respectively. Image profiles acquired at a lower MU in the radial plane (gun-target) had gradients in measured pixel values of up to 25% for the older system. Detectors with software/hardware versions IAS3/IDU-20 have a high degree of accuracy and are more suitable for routine quantitative IMRT dosimetrical verification.