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Use of gafchromic EBT3 for characterization of dose distributions in intraoperative electron radiotherapy (IOERT)
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Abstracts / Physica Medica 30 (2014) e75ee121
for LE, HE and DE images, respectively for both contrast and CNR). The calibration results may further serving as a reference for analyzing contrast enhancement for patient participating the dual energy CEDM procedures.
Fig 4. CNR as a function of iodine area density for LE , HE and DE images.Ă
Fig 1. Custom-made phantom.Ă
A NOVEL NON-INVASIVE METHOD SUBSTITUTING BREAST CANCER BIOPSIES N. Martini a, V. Koukou a, P. Sotiropoulou a, C. Michail b, I. Kandarakis b, G. Nikiforidis a, G. Fountos b. a Department of Medical Physics, Medical School, University of Patras, 265 00 Patras, Greece; b Department of Biomedical Engineering, Technological Educational Institution of Athens, Egaleo, 122 10 Athens, Greece
Fig 2. MPV ratios for the LE , HE and DE images.Ă
Dual-energy digital mammography (DEDM), where low- and high energy images are acquired and synthesized in order to cancel out the tissue structures, may improve the ability of enhancing the visibility of certain elements (calcifications) in the subtracted X-ray image. According to former researches, microcalcifications are mainly composed of calcite (CaCO3), calcium oxalate (CaC2O4), and apatite (a calciumphosphate mineral form). It has also been considered that any pathologic alteration (carcinogenesis) of the breast may produce apatite. A method using a quantitative parameter which characterizes the calcification, such as Calcium/Phosphorus (Ca/P) mass ratio, is of interest. This method will be able to sufficiently discriminate between malignant and benign lesions, reducing the need for invasive methods, such as biopsies. A simulation study, using dual energy method, was accomplished for the determination of Ca/P mass ratio in calcifications in order to distinguish between malignant and non-malignant lesions. In this study, the Ca/P mass ratio of calcifications larger than 300mm was calculated. The simulation was performed for hydroxyapatite calcifications, indicating malignancy, and compared with calcite calcifications. The Ca/P mass ratio appeared to be at least 20% higher in case of hydroxyapatite, indicating that this method can be used in breast cancer diagnosis. Acknowledgement This research has been co-funded by the European Union (European Social Fund) and Greek national resources under the framework of the “Archimedes III: Funding of Research Groups in TEI of Athens” project of the “Education & Lifelong Learning” Operational Programme.
USE OF GAFCHROMIC EBT3 FOR CHARACTERIZATION OF DOSE DISTRIBUTIONS IN INTRAOPERATIVE ELECTRON RADIOTHERAPY (IOERT)
Fig 3. Contrast as a function of iodine area density for LE, HE and DE images.Ă
es de Oncologia do Filipa Costa a, Sandra Sarmento a, b. a Instituto Portugu^ ~o, Rua Dr. Anto nio Porto, Francisco Gentil, EPE, Centro de Investigaça Bernardino de Almeida, 4200-072 Porto; b Instituto Portugu^ es de Oncologia do Porto, Francisco Gentil, EPE, Serviço de nio Bernardino de Almeida, 4200-072 Porto Física Medica, Rua Dr. Anto
Abstracts / Physica Medica 30 (2014) e75ee121
IntraOperative Electron Radiation Therapy (IOERT) consists of delivering a single high radiation dose directly to the malignant tissue, after the removal of a neoplastic mass, with minimal exposure of the surrounding healthy tissues. Unlike conventional external beam radiotherapy, the dosimetric determinations in IOERT are not based on a Treatment Planning System (TPS). Treatment planning for IOERT is limited to manual calculations. The volume to be irradiated is visually estimated at the operating theatre, and the electron energy is chosen considering the depth of tissue to be treated and the isodose curves measured in reference conditions. Software is used to generate isodoses curves, by interpolation, from the dose profiles measured in a water phantom. This process is time consuming and does not provide much detail, especially near the surface. Film dosimetry is generally a good alternative to obtain 2D dose distributions, when compared with point dose detector as ion chambers, diodes and others, even though the use of solid phantoms for electron dosimetry is generally not recommended. In this work, we have investigated the possibility of using Gafchromic EBT3 film and a solid water phantom to obtain complete 2D dose distributions parallel to the beam. This is usually a challenge due to the effect of air gaps which may easily cause artefacts in the dose distribution. The setup is crucial to obtain good results, particularly near the surface where the air gap effect is more evident. We studied several setups and optimized a practical and easy methodology for irradiation of films parallel to the beam in a solid water phantom. The irradiated films were digitized and the resultant image processed to obtain detailed and uninterrupted dose distributions, to be used during a surgery by the radio-oncologist, for a better visual estimation of the irradiated volume. Good agreement was observed between the dose distributions obtained with gafchromic film in a solid water phantom and with a diode in the water tank phantom, between 1mm below the surface and 60% isodose, for 9MeV.
THEORETICAL MODELING OF THE DETECTOR OPTICAL GAIN (DOG) AND THE ANGULAR DISTRIBUTION OF COLUMNAR PHOSPHORS USED IN MEDICAL X e RAY IMAGING. AN ANALYTICAL METHOD AND THE APPLICATION TO CSI:TL
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SYSTEMATIC INVESTIGATION OF THE DOSIMETRIC EFFECT OF BEAM ANGLES IN IMRT OF THE PROSTATE Spiridon V. Spirou PhD, George Loudos PhD. Dept. of Biomedical Engineering, TEI Athens, Greece Purpose: To systematically investigate how the choice of beam angles in IMRT of the prostate affects the dosimetry of the PTV and each OAR, as well as how the dosimetry of each structure is correlated with that of other structures. Methods and Materials: Five prostate patients, previously treated with a 5-beam IMRT plan to 86.4 Gy, were selected for this study. Candidate beams were defined in a 360 arc around the isocenter. Treatment plans were generated for each set of 5 beams taken out from the set of the candidate beams. First, all the optimization constraints, as well as all other algorithmic parameters, were kept fixed as in the clinical plan. Subsequently, additional constraints were placed on the rectum and bladder, in order to bring forth any differences between the beam sets. Preliminary Results: The methodology described previously has been manually applied to a single prostate patient for 9 candidate beams, equally spaced every 40 . Altogether 252 (126 x 2) plans were generated for this patient. All plans were normalized so that the maximum dose to the rectal wall is 99%. The envelope DVHs describe all the DVHs obtained from the 126 plans (Fig. 1). The clinical DVHs may or may not lie within the envelope because the clinical beam arrangement was not among the 126 examined. The envelope DVHs for the PTV is fairly narrow, indicating that coverage was not an issue for this patient, regardless of the beam arrangement used. However, the envelope DVHs for the rectum, bladder and, especially, the large bowel are much wider, suggesting that the choice of beam directions may have a significant impact on the treatment plan. The use of additional constraints improves the range of DVHs for the rectum, bladder and, especially, the large bowel. Conclusion: The choice of beam directions may have a significant impact on the dosimetry of the rectum, bladder and, especially, large bowel. Furthermore, the use of additional constraints has the potential to improve current treatment plans. These may, in turn, affect the patient’s quality of life and post-treatment disease management.
K. Psichis a, N. Kalyvas b, H. Delis a, I. Kandarakis b, G. Panayiotakis a. a Department of Medical Physics, School of Medicine, University of Patras, Patras 26500, Greece; b Department of Biomedical Engineering, Technological Educational Institution of Athens, Agiou Spyridonos, 122 10, Egaleo, Athens, Greece Phosphor screens have been used extensively in medical imaging either in the form of powdered phosphors or in the form of columnar phosphors. In digital medical imaging, the broad use of columnar phosphors has lead to the development of many theoretical models for the propagation of light inside these phosphors. A two dimensional model for light propagation inside columnar phosphors has been developed and was used for the prediction of the Detector Optical Gain (DOG) and the angular distribution of these crystals. DOG is defined as the ratio of the total number of optical photons that exit the crystal to the total number of x-ray photons that enter the crystal. The model for light propagation is based on optical photon propagation physical and geometrical principles and takes into account the attenuation of x-rays inside the crystal bulk, the conversion of x-ray energy to optical photon beams, the propagation of these light photon beams inside the crystal where the multiple reflections on the sides of the crystal column, the infinite forward and backward reflections as well as the attenuation of photon beams during these reflections are taken into account. This theoretical model was applied to CsI:Tl columnar crystals, it was compared to results found in literature and good correlation with them was observed. It was found that DOG is affected by the length of the columns of the crystal as well as the incident x-ray energy spectrum. The results of the angular distribution are in accordance with the theory that the longer crystal columns have more directional light distribution.
Fig. 1. Envelope DVHs for the PTV (cyan), rectum (pink), bladder (orange) and large bowel (green). Top row: the optimization constraints are the ones used in the clinical plan. Bottom row: additional constraints are placed on the rectum and bladder. The solid black lines are the DVHs obtained using the clinical beam directions.
Abstracts / Physica Medica 30 (2014) e75ee121
for LE, HE and DE images, respectively for both contrast and CNR). The calibration results may further serving as a reference for analyzing contrast enhancement for patient participating the dual energy CEDM procedures.
Fig 4. CNR as a function of iodine area density for LE , HE and DE images.Ă
Fig 1. Custom-made phantom.Ă
A NOVEL NON-INVASIVE METHOD SUBSTITUTING BREAST CANCER BIOPSIES N. Martini a, V. Koukou a, P. Sotiropoulou a, C. Michail b, I. Kandarakis b, G. Nikiforidis a, G. Fountos b. a Department of Medical Physics, Medical School, University of Patras, 265 00 Patras, Greece; b Department of Biomedical Engineering, Technological Educational Institution of Athens, Egaleo, 122 10 Athens, Greece
Fig 2. MPV ratios for the LE , HE and DE images.Ă
Dual-energy digital mammography (DEDM), where low- and high energy images are acquired and synthesized in order to cancel out the tissue structures, may improve the ability of enhancing the visibility of certain elements (calcifications) in the subtracted X-ray image. According to former researches, microcalcifications are mainly composed of calcite (CaCO3), calcium oxalate (CaC2O4), and apatite (a calciumphosphate mineral form). It has also been considered that any pathologic alteration (carcinogenesis) of the breast may produce apatite. A method using a quantitative parameter which characterizes the calcification, such as Calcium/Phosphorus (Ca/P) mass ratio, is of interest. This method will be able to sufficiently discriminate between malignant and benign lesions, reducing the need for invasive methods, such as biopsies. A simulation study, using dual energy method, was accomplished for the determination of Ca/P mass ratio in calcifications in order to distinguish between malignant and non-malignant lesions. In this study, the Ca/P mass ratio of calcifications larger than 300mm was calculated. The simulation was performed for hydroxyapatite calcifications, indicating malignancy, and compared with calcite calcifications. The Ca/P mass ratio appeared to be at least 20% higher in case of hydroxyapatite, indicating that this method can be used in breast cancer diagnosis. Acknowledgement This research has been co-funded by the European Union (European Social Fund) and Greek national resources under the framework of the “Archimedes III: Funding of Research Groups in TEI of Athens” project of the “Education & Lifelong Learning” Operational Programme.
USE OF GAFCHROMIC EBT3 FOR CHARACTERIZATION OF DOSE DISTRIBUTIONS IN INTRAOPERATIVE ELECTRON RADIOTHERAPY (IOERT)
Fig 3. Contrast as a function of iodine area density for LE, HE and DE images.Ă
es de Oncologia do Filipa Costa a, Sandra Sarmento a, b. a Instituto Portugu^ ~o, Rua Dr. Anto nio Porto, Francisco Gentil, EPE, Centro de Investigaça Bernardino de Almeida, 4200-072 Porto; b Instituto Portugu^ es de Oncologia do Porto, Francisco Gentil, EPE, Serviço de nio Bernardino de Almeida, 4200-072 Porto Física Medica, Rua Dr. Anto
Abstracts / Physica Medica 30 (2014) e75ee121
IntraOperative Electron Radiation Therapy (IOERT) consists of delivering a single high radiation dose directly to the malignant tissue, after the removal of a neoplastic mass, with minimal exposure of the surrounding healthy tissues. Unlike conventional external beam radiotherapy, the dosimetric determinations in IOERT are not based on a Treatment Planning System (TPS). Treatment planning for IOERT is limited to manual calculations. The volume to be irradiated is visually estimated at the operating theatre, and the electron energy is chosen considering the depth of tissue to be treated and the isodose curves measured in reference conditions. Software is used to generate isodoses curves, by interpolation, from the dose profiles measured in a water phantom. This process is time consuming and does not provide much detail, especially near the surface. Film dosimetry is generally a good alternative to obtain 2D dose distributions, when compared with point dose detector as ion chambers, diodes and others, even though the use of solid phantoms for electron dosimetry is generally not recommended. In this work, we have investigated the possibility of using Gafchromic EBT3 film and a solid water phantom to obtain complete 2D dose distributions parallel to the beam. This is usually a challenge due to the effect of air gaps which may easily cause artefacts in the dose distribution. The setup is crucial to obtain good results, particularly near the surface where the air gap effect is more evident. We studied several setups and optimized a practical and easy methodology for irradiation of films parallel to the beam in a solid water phantom. The irradiated films were digitized and the resultant image processed to obtain detailed and uninterrupted dose distributions, to be used during a surgery by the radio-oncologist, for a better visual estimation of the irradiated volume. Good agreement was observed between the dose distributions obtained with gafchromic film in a solid water phantom and with a diode in the water tank phantom, between 1mm below the surface and 60% isodose, for 9MeV.
THEORETICAL MODELING OF THE DETECTOR OPTICAL GAIN (DOG) AND THE ANGULAR DISTRIBUTION OF COLUMNAR PHOSPHORS USED IN MEDICAL X e RAY IMAGING. AN ANALYTICAL METHOD AND THE APPLICATION TO CSI:TL
e85
SYSTEMATIC INVESTIGATION OF THE DOSIMETRIC EFFECT OF BEAM ANGLES IN IMRT OF THE PROSTATE Spiridon V. Spirou PhD, George Loudos PhD. Dept. of Biomedical Engineering, TEI Athens, Greece Purpose: To systematically investigate how the choice of beam angles in IMRT of the prostate affects the dosimetry of the PTV and each OAR, as well as how the dosimetry of each structure is correlated with that of other structures. Methods and Materials: Five prostate patients, previously treated with a 5-beam IMRT plan to 86.4 Gy, were selected for this study. Candidate beams were defined in a 360 arc around the isocenter. Treatment plans were generated for each set of 5 beams taken out from the set of the candidate beams. First, all the optimization constraints, as well as all other algorithmic parameters, were kept fixed as in the clinical plan. Subsequently, additional constraints were placed on the rectum and bladder, in order to bring forth any differences between the beam sets. Preliminary Results: The methodology described previously has been manually applied to a single prostate patient for 9 candidate beams, equally spaced every 40 . Altogether 252 (126 x 2) plans were generated for this patient. All plans were normalized so that the maximum dose to the rectal wall is 99%. The envelope DVHs describe all the DVHs obtained from the 126 plans (Fig. 1). The clinical DVHs may or may not lie within the envelope because the clinical beam arrangement was not among the 126 examined. The envelope DVHs for the PTV is fairly narrow, indicating that coverage was not an issue for this patient, regardless of the beam arrangement used. However, the envelope DVHs for the rectum, bladder and, especially, the large bowel are much wider, suggesting that the choice of beam directions may have a significant impact on the treatment plan. The use of additional constraints improves the range of DVHs for the rectum, bladder and, especially, the large bowel. Conclusion: The choice of beam directions may have a significant impact on the dosimetry of the rectum, bladder and, especially, large bowel. Furthermore, the use of additional constraints has the potential to improve current treatment plans. These may, in turn, affect the patient’s quality of life and post-treatment disease management.
K. Psichis a, N. Kalyvas b, H. Delis a, I. Kandarakis b, G. Panayiotakis a. a Department of Medical Physics, School of Medicine, University of Patras, Patras 26500, Greece; b Department of Biomedical Engineering, Technological Educational Institution of Athens, Agiou Spyridonos, 122 10, Egaleo, Athens, Greece Phosphor screens have been used extensively in medical imaging either in the form of powdered phosphors or in the form of columnar phosphors. In digital medical imaging, the broad use of columnar phosphors has lead to the development of many theoretical models for the propagation of light inside these phosphors. A two dimensional model for light propagation inside columnar phosphors has been developed and was used for the prediction of the Detector Optical Gain (DOG) and the angular distribution of these crystals. DOG is defined as the ratio of the total number of optical photons that exit the crystal to the total number of x-ray photons that enter the crystal. The model for light propagation is based on optical photon propagation physical and geometrical principles and takes into account the attenuation of x-rays inside the crystal bulk, the conversion of x-ray energy to optical photon beams, the propagation of these light photon beams inside the crystal where the multiple reflections on the sides of the crystal column, the infinite forward and backward reflections as well as the attenuation of photon beams during these reflections are taken into account. This theoretical model was applied to CsI:Tl columnar crystals, it was compared to results found in literature and good correlation with them was observed. It was found that DOG is affected by the length of the columns of the crystal as well as the incident x-ray energy spectrum. The results of the angular distribution are in accordance with the theory that the longer crystal columns have more directional light distribution.
Fig. 1. Envelope DVHs for the PTV (cyan), rectum (pink), bladder (orange) and large bowel (green). Top row: the optimization constraints are the ones used in the clinical plan. Bottom row: additional constraints are placed on the rectum and bladder. The solid black lines are the DVHs obtained using the clinical beam directions.