Panayiotis Mavroidis - Academia.edu (original) (raw)

Papers by Panayiotis Mavroidis

Research paper thumbnail of Dosimetric correlations with urinary quality of life in patients receiving post-prostatectomy radiation therapy

Journal of Radiation Oncology, 2020

Objective Acute urinary toxicity is well-documented in individuals receiving post-prostatectomy r... more Objective Acute urinary toxicity is well-documented in individuals receiving post-prostatectomy radiation. However, dosimetric correlations between bladder dose and acute urinary symptoms in the post-prostatectomy setting have not been well-studied. We examined the relationship between bladder dosimetry and acute changes in individual urinary symptoms among men receiving post-prostatectomy radiation therapy. Methods Patient-reported urinary symptoms were prospectively collected for 90 consecutive prostate cancer patients receiving post-prostatectomy radiation using the validated quality of life instrument Prostate Cancer Symptom Indices. Data were collected prior to treatment and weekly during treatment. Individual symptom scores were examined and a change in severity of an individual symptom (from baseline) of ≥ 2 points was considered clinically significant. DVHs were generated for all the patients. Receiver operating characteristic curves were generated to evaluate the ability of different dose-volume metrics to identify patients who developed individual urinary symptoms during radiation treatment from those who did not. Logistic regression was used to examine the relationship between dose-volume parameters and worsening of individual urinary symptoms. Results Worsening of individual urinary symptoms during radiation treatment was reported by 7% (urinary flow) to 29% (urgency) of patients. The relative bladder volume receiving moderate doses of radiation was associated with urgency (AUC 0.67 for V30 Gy). Dose-volume parameters were not significantly associated with flow, frequency, nocturia, or dysuria. Conclusion There is an acute worsening of urinary symptoms among men receiving modern post-prostatectomy radiation. Worsening of urgency is associated with bladder dosimetry while flow, frequency, nocturia, and dysuria are not. This data can be used during treatment planning to reduce acute urinary toxicity during post-prostatectomy radiation.

Research paper thumbnail of Evaluation of the Dose Delivery Consistency and Its Dependence on Imaging Modality and Deformable Image Registration Algorithm in Prostate Cancer Patients

Journal of Medical and Biological Engineering, 2021

Research paper thumbnail of Thorax artifacts in CT – air embolism or other causes?

International Journal of Radiation Research, 2021

Background: The existence of air in hollow organs in the thoracic cavity constitutes a life-threa... more Background: The existence of air in hollow organs in the thoracic cavity constitutes a life-threatening situation most of the times. However, sometimes in thoracic Computed Tomography (CT) there are artifacts from different sources that could mimic air densities, disorientating the diagnosis. Materials and Methods: 100 patients (46 females and 54 males, mean age: 60 years, range: 20-90 years), who had been routinely scanned in the area of thorax using three different imaging protocols (follow up, aorta, pulmonary vessels) were retrospectively studied. In 67 cases, contrast agent was used during the examination. Every case was studied by two specialists. Results: Artifacts in pulmonary veins were observed in 38 of the cases. Of these artifacts 27 stemmed from contrast agent, calcifications in the vessels, metallic implants, movement of the patient, malfunction of a detector due to the size of field of view (FOV) or due to the existence of contrast agent on the examination table of the CT scanner. In 11 cases, small amounts of air had been inserted into blood circulation during contrast injection. Conclusions: This study characterized and classified many artifacts related to thorax CT in order to separate them from other serious thoracic pathologies (e.g. aortic dissection, ulcer of veins or arteries). The knowledge and identification of the different types of artifacts is very important in order to avoid the risk of misdiagnosis.

Research paper thumbnail of SU-F-I-29: Investigating the Impact of the Amount of Contrast Material Used in Abdominal CT Examinations Regarding the Diagnosis of Appendicolith

Medical Physics, Jun 1, 2016

Acute appendicitis is a clinical emergency and is one of the more common causes of acute abdomina... more Acute appendicitis is a clinical emergency and is one of the more common causes of acute abdominal pain. Consequently, to avoid significant unpleasant consequences it is necessary have early diagnosis and treatment. Commonly, in patients with signs of appendicitis an abdominal computed tomography (CT) examination should be performed. Materials/methods: Out of 12 cases of patients with acute appendicitis. The presence of an appendicolith was one common finding in the CTs of those cases. Almost one third of patients show the presence of appendicoliths, which may have prognostic importance since their presence has been associated with increased likelihood for appendiceal perforation. Results: In the first case, a young adult underwent a CT examination with incomplete oral administration of contrast material. This revealed the existence of an appendicolith, which caused acute appendicitis. The second patient with acute appendicitis is an adult who was diagnosed 40 days after his CT pyelography, in which small appedicoliths were not observed.

Research paper thumbnail of Strategies for Evaluation of Daily Delivered Dose Using Cone Beam CT (CBCT)

International Journal of Radiation Oncology*Biology*Physics, 2014

Research paper thumbnail of OA24.03 Cardiac Toxicity after Radiation for Stage III NSCLC: Pooled Analysis of Dose-Escalation Trials Delivering 70-90 Gy

Journal of Thoracic Oncology, 2017

Research paper thumbnail of SU-E-T-372: Evaluation and Comparison of Second-Check Monitor Unit Calculation Software with Pinnacle Treatment Planning System

Medical Physics, 2015

ABSTRACT

Research paper thumbnail of SU-E-I-67: Arachnoid Cysts: The Role of the BLADE Technique

Medical Physics, 2015

ABSTRACT The purpose of this study is first to show the extent by which BLADE sequences can reduc... more ABSTRACT The purpose of this study is first to show the extent by which BLADE sequences can reduce all the image artifacts and second to verify that the usefulness of this technique in certain pathological conditions is significant. In this study, fourteen consecutive patients (5 females, 9 males), who routinely underwent MRI brain examination, between 2010-2014, were selected. The applied routine protocols for brain MR examination included the following sequences: 1) T2-W FLAIR axial; 2) T2-W TSE axial; 3) T2*-W axial, 4) T1-W TSE sagittal; 5) DWI-W axial; 6) T1-W TSE axial; 7) T1-W TSE axial+contrast. In cases of cystic tumors, the T2-W FLAIR BLADE sequence was added to the protocol. All the images were evaluated independently at two separate settings with 3 weeks interval by two radiologists. The radiologists also evaluated the presence of image artifacts (motion, flow, chemical shift, Gibbs ringing). To evaluate the size of the cyst, the two radiologists compared the two techniques (conventional and BLADE) by assessing the extent of the divergence in the measurements of the cysts. Regarding the extent of the cyst size, BLADE measurements were found to be more reliable than the conventional ones with the differences being statistically significant (p<0.01). The qualitative measurements indicated that the T2 FLAIR BLADE sequences were superior to the conventional T2 FLAIR with statistically significant differences (p<0.001) in the following characteristics: 1) overall image quality, 2) CSF nulling; 3) contrast at the pathology and its surrounding; 4) limits of the pathology; 5) motion artifacts; 6) flow artifacts; 7) chemical shift artifacts and 8) Gibbs ringing artifacts. BLADE sequence was found to decrease both flow artifacts in the temporal lobes and motion artifacts from the orbits and it is proposed for clinical use.

Research paper thumbnail of Evaluation of the generalized gamma as a tool for treatment planning optimization

International Journal of Cancer Therapy and Oncology, 2014

The aim of that work is to study the theoretical behavior and merits of the Generalized Gamma (ge... more The aim of that work is to study the theoretical behavior and merits of the Generalized Gamma (generalized dose response gradient) as well as to investigate the usefulness of this concept in practical radiobiological treatment planning. Methods: In this study, the treatment planning system RayStation 1.9 (Raysearch Laboratories AB, Stockholm, Sweden) was used. Furthermore, radiobiological models that provide the tumor control probability (TCP), normal tissue complication probability (NTCP), complication-free tumor control probability (P+) and the Generalized Gamma were employed. The Generalized Gammas of TCP and NTCP, respectively were calculated for given heterogeneous dose distributions to different organs in order to verify the TCP and NTCP computations of the treatment planning system. In this process, a treatment plan was created, where the target and the organs at risk were included in the same ROI in order to check the validity of the system regarding the objective function P+ and the Generalized Gamma. Subsequently, six additional treatment plans were created with the target organ and the organs at risk placed in the same or different ROIs. In these plans, the mean dose was increased in order to investigate the behavior of dose change on tissue response and on Generalized Gamma before and after the change in dose. By theoretically calculating these quantities, the agreement of different theoretical expressions compared to the values that the treatment planning system provides could be evaluated. Finally, the relative error between the real and approximate response values using the Poisson and the Probit models, for the case of having a target organ consisting of two compartments in a parallel architecture and with the same number of clonogens could be investigated and quantified. Results: The computations of the RayStation regarding the values of the Generalized Gamma and the objective function (P+) were verified by using an independent software. Furthermore, it was proved that after a small change in dose, the organ that is being affected most is the organ with the highest Generalized Gamma. Apart from that, the validity of the theoretical expressions that describe the change in response and the associated Generalized Gamma was verified but only for the case of small change in dose. Especially for the case of 50% TCP and NTCP, the theoretical values (ΔPapprox.) and those calculated by the RayStation show close agreement, which proves the high importance of the D50 parameter in specifying clinical response levels. Finally, the presented findings show that the behavior of ΔPapprox. looks sensible because, for both of the models that were used (Poisson and Probit), it significantly approaches the real ΔP around the region of 37% and 50% response. The present study managed to evaluate the mathematical expression of Generalized Gamma for the case of non-uniform dose delivery and the accuracy of the RayStation to calculate its values for different organs. Conclusion: A very important finding of this work is the establishment of the usefulness and clinical relevance of Generalized Gamma. That is because it gives the planner the opportunity to precisely determine which organ will be affected most after a small increase in dose and as a result an optimal treatment plan regarding tumor control and normal tissue complications can be found.

Research paper thumbnail of 157 oral 4D U/S-BASED PROSTATE HDR BRACHYTHERAPY TREATMENT PLANNING: ANALYSIS OF INFLUENCE OF PATIENT MOVEMENT AND ANATOMY ALTERATION ON THE PLAN QUALITY AND TREATMENT DELIVERY

Radiotherapy and Oncology, 2011

Research paper thumbnail of Determination and use of radiobiological response parameters in radiation therapy optimization (in English)

Medical Physics, 2002

Professor Anders Brahme who inspired me through his deep theoretical knowledge and taught me how ... more Professor Anders Brahme who inspired me through his deep theoretical knowledge and taught me how to present my thoughts in a nice and comprehensive way. Dr. Bo Nilsson for the very nice discussions we had, for being so kind and helpful whenever I needed him and for the great educational work he caries out at our department. Dr. Constantin Kappas for his friendship most of all, scientific guidance and the opportunities he offered me.

Research paper thumbnail of Elimination of motion and pulsation artifacts using BLADE sequences in knee MR imaging

Magnetic Resonance Imaging, 2012

The purpose of this study is to evaluate the ability of proton density (PD)-BLADE sequences in re... more The purpose of this study is to evaluate the ability of proton density (PD)-BLADE sequences in reducing or even eliminating motion and pulsatile flow artifacts in knee magnetic resonance imaging examinations. Eighty consecutive patients, who had been routinely scanned for knee examination, participated in the study. The following pairs of sequences with and without BLADE were compared: (a) PD turbo spin echo (TSE) sagittal (SAG) fat saturation (FS) in 35 patients, (b) PD TSE coronal (COR) FS in 19 patients, (c) T2 TSE axial in 13 patients and (d) PD TSE SAG in 13 patients. Both qualitative and quantitative analyses were performed based on the signal-to-noise ratio (SNR), contrastto-noise ratio (CNR) and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of image motion and pulsation artifacts was evaluated. Based on the results of the SNR, CRN and ReCon for the different sequences and anatomical structures, the BLADE sequences were significantly superior in 19 cases, whereas the corresponding conventional sequences were significantly superior in only 6 cases. BLADE sequences eliminated motion artifacts in all the cases. However, motion artifacts were shown in (a) six PD TSE SAG FS, (b) three PD TSE COR FS, (c) three PD TSE SAG and (d) two T2 TSE axial conventional sequences. In our results, it was found that, in PD FS sequences (sagittal and coronal), the differences between the BLADE and conventional sequences regarding the elimination of motion and pulsatile flow artifacts were statistically significant. In all the comparisons, the PD FS BLADE sequences (coronal and sagittal) were significantly superior to the corresponding conventional sequences regarding the classification of their image quality. In conclusion, this technique appears to be capable to potentially eliminate motion and pulsatile flow artifacts in MR images.

Research paper thumbnail of Comparison of 3D-CRT, MLC-based IMRT and Helical Tomotherapy for Lung Cancer Radiotherapy

International Journal of Radiation Oncology*Biology*Physics, 2008

a critical F-value of 148.50 giving a p value of 0.001; for a period of 4s and an amplitude of 15... more a critical F-value of 148.50 giving a p value of 0.001; for a period of 4s and an amplitude of 15 mm the F-value was 3.70 for a critical F-value 3.55 giving a p value of 0.13; for a period of 6s and an amplitude of 15mm the F-value was 41.17 for a critical F-value 30.81 giving a p value of 0.01; for a period of 8s and an amplitude of 15 mm the F-value was 2.92 for a critical F-value 2.89 giving a p value of 0.20. Conclusions: Active scanning is more dose sensitive to both the variation in breathing period and initial breathing phase compared to passive scattering. Comparatively, the greater dose sensitivity is to initial breathing phase. Management of intrafraction motion error and its amelioration is required for active proton beam scanning system treatment of moving lung cancer.

Research paper thumbnail of γ+ index: A new evaluation parameter for quantitative quality assurance

Computer Methods and Programs in Biomedicine, 2014

I Non-binary low-density parity-check decoding 7 1 State of the art of non-binary low-density par... more I Non-binary low-density parity-check decoding 7 1 State of the art of non-binary low-density parity-check decoding algorithms 9 1.1 Background concepts of non-binary low-density parity-check codes. .. .. . 9

Research paper thumbnail of Comparison of the helical tomotherapy against the multileaf collimator-based intensity-modulated radiotherapy and 3D conformal radiation modalities in lung cancer radiotherapy

British Journal of Radiology, 2011

Research paper thumbnail of 4D analysis of influence of patient movement and anatomy alteration on the quality of 3D U/S-based prostate HDR brachytherapy treatment delivery

Medical Physics, 2011

Purpose: Modern HDR brachytherapy treatment for prostate cancer based on the 3D ultrasound (U/S) ... more Purpose: Modern HDR brachytherapy treatment for prostate cancer based on the 3D ultrasound (U/S) plays increasingly important role. The purpose of this study is to investigate possible patient movement and anatomy alteration between the clinical image set acquisition, made after the needle implantation, and the patient irradiation and their influence on the quality of treatment. Methods: The authors used 3D U/S image sets and the corresponding treatment plans based on a 4D-treatment planning procedure: plans of 25 patients are obtained right after the needle implantation (clinical plan is based on this 3D image set) and just before and after the treatment delivery. The authors notice the slight decrease of treatment quality with increase of time gap between the clinical image set acquisition and the patient irradiation. 4D analysis of dose-volume-histograms (DVHs) for prostate: CTV1 ¼ PTV, and urethra, rectum, and bladder as organs at risk (OARs) and conformity index (COIN) is presented, demonstrating the effect of prostate, OARs, and needles displacement. Results: The authors show that in the case that the patient body movement/anatomy alteration takes place, this results in modification of DVHs and radiobiological parameters, hence the plan quality. The observed average displacement of needles (1 mm) and of prostate (0.57 mm) is quite small as compared with the average displacement noted in several other reports [A. A.

Research paper thumbnail of Evaluation of the Elekta Agility MLC performance using high-resolution log files

Medical Physics

PURPOSE With the advent of volumetric modulated arc therapy (VMAT) and intensity-modulated radiat... more PURPOSE With the advent of volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) treatment techniques, the requirement for more elaborate approaches in reviewing linac components' integrity has become even more stringent. A possible solution to this challenge is to employ the usage of log files generated during treatment. The log files generated by the new generation of Elekta linacs record events at a higher frequency (25 Hz) than their predecessors, which allows for retrospective analysis and identification of subtle changes and provides another means of quality assurance. The ability to track machine components based on log files for each treatment can allow for constant monitoring of fraction consistency in addition to machine reliability. Using Elekta Agility log files, a set of tests were developed to evaluate the reliability and robustness of the multileaf collimators (MLCs). METHODS To evaluate Elekta log file utilization for linac MLC QA effectiveness, five MLC test patterns were constructed to review the effects of leaf velocity and acceleration on positional accuracy, including gravitational effects for the Elekta MLC system. Each test was run five times in a particular setting to obtain reproducibility data and statistical averages. This study was performed on two identical Versa HD machines, each delivering a full set of test plans with all possible variations. Plans were delivered using Elekta's iCOMcat software and recorded log files were extracted. Log files were reformatted for readability and automatically analyzed in Matlab® . RESULTS The Elekta Agility MLC system was shown to be capable of obtaining speeds within the range of 5-35 mm/s. MLC step and shoot tests have demonstrated the MLC system's capability of having positional repeatability, averaging 0.03- and 0.08-mm offsets with and without gravitational effects, respectively. The IMRT-specific tests have shown that gravitational effects are negligible with all positional tests averaging 0.5-mm offsets. The largest speed root-mean-square error (RMSE) for the MLC system was found at the maximum speed of 35 mm/s with an average error of 0.8 mm. For slower speeds, the value was found to be much lower. CONCLUSION Utilizing log files has demonstrated the feasibility for higher precision of MLC motions to be reviewed, based on the performance tests that were instituted. Log files provide insight on the effects of friction, acceleration, and gravity, with MU's delivered that previously could not be reviewed in such detail. Based on our results, log file-based QA has enhanced our ability to review performance, functionality, and perform QA on Elekta's MLC system.

Research paper thumbnail of SU-F-T-411: A Quantitative Parameter for Treatment Plan Quality

Medical physics, 2016

To create an IMRT treatment plan quantitative score using QUANTEC dose/volume parameters to asses... more To create an IMRT treatment plan quantitative score using QUANTEC dose/volume parameters to assess plan quality. 132 IMRT patient plans of various treatment sites were evaluated. The optimized plan's dose volume histogram (DVH) was exported to Velocity for evaluation. The proposed scoring was based on calculating the shortest distance from the QUANTEC objective to the DVH line of each organ. Each plan was normalized against the "perfect" plan where the organs at risk (OAR) received no dose and hence the distance between the QUANTEC objective and the DVH line was maximized. The normalized scores allowed comparing the quality of plans across the treatment sites, dosimetrists, and physicians. The scores were plotted and statistically analyzed to serve as basis for future plans. The score for each site was evaluated and the average percentage score resulted in the abdomen having an average percent score of 1.68 ± 1.49, 34.61 ± 35.19, 11.00 ± 15.39, 28.44 ± 25.13, 1.99 ± 5....

Research paper thumbnail of SU-E-T-94: Daily Fraction Dose Recalculation Based On Rigid Registration Using Cone Beam CT

Medical Physics, 2014

PURPOSE To calculate the daily fraction dose for a CBCT recalculation based on rigid registration... more PURPOSE To calculate the daily fraction dose for a CBCT recalculation based on rigid registration and compare it to the planned CT dose. METHODS For this study, 30 patients that were previously treated (10 SBRT lung, 10 prostate and 10 abdomen) were considered. The daily CBCT images were imported into the Pinnacle treatment planning system from Mosaic. The prescribing physician contoured the regions of interest (ROI) on each CBCT and then dose was computed on each CBCT. Each CBCT dose distribution was then compared against the plan. The evaluation was based on isodose line comparison and Dose Volume Histogram comparison. RESULTS In the case of lung patients the dose differences between daily dose and plan dose were considered small. The PTV coverage was not compromised and the dose to the organs at risk had negligible differences. Larger differences were observed for prostate and abdomen patients. In these cases, although the PTV doses did not change on a daily basis, the doses to the organs at risk had significant differences. For a prostate patient, the bladder dose at 35% volume was 2714.444 cGy for the CT plan and 2844.747, 2801.556, 3552.37, and 2970.968 cGy for subsequent CBCTs. For the PTV on a SBRT patient, however, the CT plan had a dose at 35% volume of 6917.71 cGy and 6815.385, 6892.5, 6896.25, and 6922.9 cGy for the CBCTs. CONCLUSION Daily dose validation is feasible using CBCT and treatment planning system. It provides means to evaluate the course of treatment for the patient undergoing radiation therapy and can assist in the decision of the need of adaptation of the treatment plan.

Research paper thumbnail of SU-EI-51: Use of Blade Sequences in Cervical Spine MR Imaging for Eliminating Motion, Truncation and Flow Artifacts

ABSTRACT Purpose: To assess the efficacy of the BLADE technique to eliminate motion, truncation, ... more ABSTRACT Purpose: To assess the efficacy of the BLADE technique to eliminate motion, truncation, flow and other artifacts in Cervical Spine MRI compared to the conventional technique. To study the ability of the examined sequences to reduce the indetention and wrap artifacts, which have been reported in BLADE sagittal sequences.

Research paper thumbnail of Dosimetric correlations with urinary quality of life in patients receiving post-prostatectomy radiation therapy

Journal of Radiation Oncology, 2020

Objective Acute urinary toxicity is well-documented in individuals receiving post-prostatectomy r... more Objective Acute urinary toxicity is well-documented in individuals receiving post-prostatectomy radiation. However, dosimetric correlations between bladder dose and acute urinary symptoms in the post-prostatectomy setting have not been well-studied. We examined the relationship between bladder dosimetry and acute changes in individual urinary symptoms among men receiving post-prostatectomy radiation therapy. Methods Patient-reported urinary symptoms were prospectively collected for 90 consecutive prostate cancer patients receiving post-prostatectomy radiation using the validated quality of life instrument Prostate Cancer Symptom Indices. Data were collected prior to treatment and weekly during treatment. Individual symptom scores were examined and a change in severity of an individual symptom (from baseline) of ≥ 2 points was considered clinically significant. DVHs were generated for all the patients. Receiver operating characteristic curves were generated to evaluate the ability of different dose-volume metrics to identify patients who developed individual urinary symptoms during radiation treatment from those who did not. Logistic regression was used to examine the relationship between dose-volume parameters and worsening of individual urinary symptoms. Results Worsening of individual urinary symptoms during radiation treatment was reported by 7% (urinary flow) to 29% (urgency) of patients. The relative bladder volume receiving moderate doses of radiation was associated with urgency (AUC 0.67 for V30 Gy). Dose-volume parameters were not significantly associated with flow, frequency, nocturia, or dysuria. Conclusion There is an acute worsening of urinary symptoms among men receiving modern post-prostatectomy radiation. Worsening of urgency is associated with bladder dosimetry while flow, frequency, nocturia, and dysuria are not. This data can be used during treatment planning to reduce acute urinary toxicity during post-prostatectomy radiation.

Research paper thumbnail of Evaluation of the Dose Delivery Consistency and Its Dependence on Imaging Modality and Deformable Image Registration Algorithm in Prostate Cancer Patients

Journal of Medical and Biological Engineering, 2021

Research paper thumbnail of Thorax artifacts in CT – air embolism or other causes?

International Journal of Radiation Research, 2021

Background: The existence of air in hollow organs in the thoracic cavity constitutes a life-threa... more Background: The existence of air in hollow organs in the thoracic cavity constitutes a life-threatening situation most of the times. However, sometimes in thoracic Computed Tomography (CT) there are artifacts from different sources that could mimic air densities, disorientating the diagnosis. Materials and Methods: 100 patients (46 females and 54 males, mean age: 60 years, range: 20-90 years), who had been routinely scanned in the area of thorax using three different imaging protocols (follow up, aorta, pulmonary vessels) were retrospectively studied. In 67 cases, contrast agent was used during the examination. Every case was studied by two specialists. Results: Artifacts in pulmonary veins were observed in 38 of the cases. Of these artifacts 27 stemmed from contrast agent, calcifications in the vessels, metallic implants, movement of the patient, malfunction of a detector due to the size of field of view (FOV) or due to the existence of contrast agent on the examination table of the CT scanner. In 11 cases, small amounts of air had been inserted into blood circulation during contrast injection. Conclusions: This study characterized and classified many artifacts related to thorax CT in order to separate them from other serious thoracic pathologies (e.g. aortic dissection, ulcer of veins or arteries). The knowledge and identification of the different types of artifacts is very important in order to avoid the risk of misdiagnosis.

Research paper thumbnail of SU-F-I-29: Investigating the Impact of the Amount of Contrast Material Used in Abdominal CT Examinations Regarding the Diagnosis of Appendicolith

Medical Physics, Jun 1, 2016

Acute appendicitis is a clinical emergency and is one of the more common causes of acute abdomina... more Acute appendicitis is a clinical emergency and is one of the more common causes of acute abdominal pain. Consequently, to avoid significant unpleasant consequences it is necessary have early diagnosis and treatment. Commonly, in patients with signs of appendicitis an abdominal computed tomography (CT) examination should be performed. Materials/methods: Out of 12 cases of patients with acute appendicitis. The presence of an appendicolith was one common finding in the CTs of those cases. Almost one third of patients show the presence of appendicoliths, which may have prognostic importance since their presence has been associated with increased likelihood for appendiceal perforation. Results: In the first case, a young adult underwent a CT examination with incomplete oral administration of contrast material. This revealed the existence of an appendicolith, which caused acute appendicitis. The second patient with acute appendicitis is an adult who was diagnosed 40 days after his CT pyelography, in which small appedicoliths were not observed.

Research paper thumbnail of Strategies for Evaluation of Daily Delivered Dose Using Cone Beam CT (CBCT)

International Journal of Radiation Oncology*Biology*Physics, 2014

Research paper thumbnail of OA24.03 Cardiac Toxicity after Radiation for Stage III NSCLC: Pooled Analysis of Dose-Escalation Trials Delivering 70-90 Gy

Journal of Thoracic Oncology, 2017

Research paper thumbnail of SU-E-T-372: Evaluation and Comparison of Second-Check Monitor Unit Calculation Software with Pinnacle Treatment Planning System

Medical Physics, 2015

ABSTRACT

Research paper thumbnail of SU-E-I-67: Arachnoid Cysts: The Role of the BLADE Technique

Medical Physics, 2015

ABSTRACT The purpose of this study is first to show the extent by which BLADE sequences can reduc... more ABSTRACT The purpose of this study is first to show the extent by which BLADE sequences can reduce all the image artifacts and second to verify that the usefulness of this technique in certain pathological conditions is significant. In this study, fourteen consecutive patients (5 females, 9 males), who routinely underwent MRI brain examination, between 2010-2014, were selected. The applied routine protocols for brain MR examination included the following sequences: 1) T2-W FLAIR axial; 2) T2-W TSE axial; 3) T2*-W axial, 4) T1-W TSE sagittal; 5) DWI-W axial; 6) T1-W TSE axial; 7) T1-W TSE axial+contrast. In cases of cystic tumors, the T2-W FLAIR BLADE sequence was added to the protocol. All the images were evaluated independently at two separate settings with 3 weeks interval by two radiologists. The radiologists also evaluated the presence of image artifacts (motion, flow, chemical shift, Gibbs ringing). To evaluate the size of the cyst, the two radiologists compared the two techniques (conventional and BLADE) by assessing the extent of the divergence in the measurements of the cysts. Regarding the extent of the cyst size, BLADE measurements were found to be more reliable than the conventional ones with the differences being statistically significant (p<0.01). The qualitative measurements indicated that the T2 FLAIR BLADE sequences were superior to the conventional T2 FLAIR with statistically significant differences (p<0.001) in the following characteristics: 1) overall image quality, 2) CSF nulling; 3) contrast at the pathology and its surrounding; 4) limits of the pathology; 5) motion artifacts; 6) flow artifacts; 7) chemical shift artifacts and 8) Gibbs ringing artifacts. BLADE sequence was found to decrease both flow artifacts in the temporal lobes and motion artifacts from the orbits and it is proposed for clinical use.

Research paper thumbnail of Evaluation of the generalized gamma as a tool for treatment planning optimization

International Journal of Cancer Therapy and Oncology, 2014

The aim of that work is to study the theoretical behavior and merits of the Generalized Gamma (ge... more The aim of that work is to study the theoretical behavior and merits of the Generalized Gamma (generalized dose response gradient) as well as to investigate the usefulness of this concept in practical radiobiological treatment planning. Methods: In this study, the treatment planning system RayStation 1.9 (Raysearch Laboratories AB, Stockholm, Sweden) was used. Furthermore, radiobiological models that provide the tumor control probability (TCP), normal tissue complication probability (NTCP), complication-free tumor control probability (P+) and the Generalized Gamma were employed. The Generalized Gammas of TCP and NTCP, respectively were calculated for given heterogeneous dose distributions to different organs in order to verify the TCP and NTCP computations of the treatment planning system. In this process, a treatment plan was created, where the target and the organs at risk were included in the same ROI in order to check the validity of the system regarding the objective function P+ and the Generalized Gamma. Subsequently, six additional treatment plans were created with the target organ and the organs at risk placed in the same or different ROIs. In these plans, the mean dose was increased in order to investigate the behavior of dose change on tissue response and on Generalized Gamma before and after the change in dose. By theoretically calculating these quantities, the agreement of different theoretical expressions compared to the values that the treatment planning system provides could be evaluated. Finally, the relative error between the real and approximate response values using the Poisson and the Probit models, for the case of having a target organ consisting of two compartments in a parallel architecture and with the same number of clonogens could be investigated and quantified. Results: The computations of the RayStation regarding the values of the Generalized Gamma and the objective function (P+) were verified by using an independent software. Furthermore, it was proved that after a small change in dose, the organ that is being affected most is the organ with the highest Generalized Gamma. Apart from that, the validity of the theoretical expressions that describe the change in response and the associated Generalized Gamma was verified but only for the case of small change in dose. Especially for the case of 50% TCP and NTCP, the theoretical values (ΔPapprox.) and those calculated by the RayStation show close agreement, which proves the high importance of the D50 parameter in specifying clinical response levels. Finally, the presented findings show that the behavior of ΔPapprox. looks sensible because, for both of the models that were used (Poisson and Probit), it significantly approaches the real ΔP around the region of 37% and 50% response. The present study managed to evaluate the mathematical expression of Generalized Gamma for the case of non-uniform dose delivery and the accuracy of the RayStation to calculate its values for different organs. Conclusion: A very important finding of this work is the establishment of the usefulness and clinical relevance of Generalized Gamma. That is because it gives the planner the opportunity to precisely determine which organ will be affected most after a small increase in dose and as a result an optimal treatment plan regarding tumor control and normal tissue complications can be found.

Research paper thumbnail of 157 oral 4D U/S-BASED PROSTATE HDR BRACHYTHERAPY TREATMENT PLANNING: ANALYSIS OF INFLUENCE OF PATIENT MOVEMENT AND ANATOMY ALTERATION ON THE PLAN QUALITY AND TREATMENT DELIVERY

Radiotherapy and Oncology, 2011

Research paper thumbnail of Determination and use of radiobiological response parameters in radiation therapy optimization (in English)

Medical Physics, 2002

Professor Anders Brahme who inspired me through his deep theoretical knowledge and taught me how ... more Professor Anders Brahme who inspired me through his deep theoretical knowledge and taught me how to present my thoughts in a nice and comprehensive way. Dr. Bo Nilsson for the very nice discussions we had, for being so kind and helpful whenever I needed him and for the great educational work he caries out at our department. Dr. Constantin Kappas for his friendship most of all, scientific guidance and the opportunities he offered me.

Research paper thumbnail of Elimination of motion and pulsation artifacts using BLADE sequences in knee MR imaging

Magnetic Resonance Imaging, 2012

The purpose of this study is to evaluate the ability of proton density (PD)-BLADE sequences in re... more The purpose of this study is to evaluate the ability of proton density (PD)-BLADE sequences in reducing or even eliminating motion and pulsatile flow artifacts in knee magnetic resonance imaging examinations. Eighty consecutive patients, who had been routinely scanned for knee examination, participated in the study. The following pairs of sequences with and without BLADE were compared: (a) PD turbo spin echo (TSE) sagittal (SAG) fat saturation (FS) in 35 patients, (b) PD TSE coronal (COR) FS in 19 patients, (c) T2 TSE axial in 13 patients and (d) PD TSE SAG in 13 patients. Both qualitative and quantitative analyses were performed based on the signal-to-noise ratio (SNR), contrastto-noise ratio (CNR) and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of image motion and pulsation artifacts was evaluated. Based on the results of the SNR, CRN and ReCon for the different sequences and anatomical structures, the BLADE sequences were significantly superior in 19 cases, whereas the corresponding conventional sequences were significantly superior in only 6 cases. BLADE sequences eliminated motion artifacts in all the cases. However, motion artifacts were shown in (a) six PD TSE SAG FS, (b) three PD TSE COR FS, (c) three PD TSE SAG and (d) two T2 TSE axial conventional sequences. In our results, it was found that, in PD FS sequences (sagittal and coronal), the differences between the BLADE and conventional sequences regarding the elimination of motion and pulsatile flow artifacts were statistically significant. In all the comparisons, the PD FS BLADE sequences (coronal and sagittal) were significantly superior to the corresponding conventional sequences regarding the classification of their image quality. In conclusion, this technique appears to be capable to potentially eliminate motion and pulsatile flow artifacts in MR images.

Research paper thumbnail of Comparison of 3D-CRT, MLC-based IMRT and Helical Tomotherapy for Lung Cancer Radiotherapy

International Journal of Radiation Oncology*Biology*Physics, 2008

a critical F-value of 148.50 giving a p value of 0.001; for a period of 4s and an amplitude of 15... more a critical F-value of 148.50 giving a p value of 0.001; for a period of 4s and an amplitude of 15 mm the F-value was 3.70 for a critical F-value 3.55 giving a p value of 0.13; for a period of 6s and an amplitude of 15mm the F-value was 41.17 for a critical F-value 30.81 giving a p value of 0.01; for a period of 8s and an amplitude of 15 mm the F-value was 2.92 for a critical F-value 2.89 giving a p value of 0.20. Conclusions: Active scanning is more dose sensitive to both the variation in breathing period and initial breathing phase compared to passive scattering. Comparatively, the greater dose sensitivity is to initial breathing phase. Management of intrafraction motion error and its amelioration is required for active proton beam scanning system treatment of moving lung cancer.

Research paper thumbnail of γ+ index: A new evaluation parameter for quantitative quality assurance

Computer Methods and Programs in Biomedicine, 2014

I Non-binary low-density parity-check decoding 7 1 State of the art of non-binary low-density par... more I Non-binary low-density parity-check decoding 7 1 State of the art of non-binary low-density parity-check decoding algorithms 9 1.1 Background concepts of non-binary low-density parity-check codes. .. .. . 9

Research paper thumbnail of Comparison of the helical tomotherapy against the multileaf collimator-based intensity-modulated radiotherapy and 3D conformal radiation modalities in lung cancer radiotherapy

British Journal of Radiology, 2011

Research paper thumbnail of 4D analysis of influence of patient movement and anatomy alteration on the quality of 3D U/S-based prostate HDR brachytherapy treatment delivery

Medical Physics, 2011

Purpose: Modern HDR brachytherapy treatment for prostate cancer based on the 3D ultrasound (U/S) ... more Purpose: Modern HDR brachytherapy treatment for prostate cancer based on the 3D ultrasound (U/S) plays increasingly important role. The purpose of this study is to investigate possible patient movement and anatomy alteration between the clinical image set acquisition, made after the needle implantation, and the patient irradiation and their influence on the quality of treatment. Methods: The authors used 3D U/S image sets and the corresponding treatment plans based on a 4D-treatment planning procedure: plans of 25 patients are obtained right after the needle implantation (clinical plan is based on this 3D image set) and just before and after the treatment delivery. The authors notice the slight decrease of treatment quality with increase of time gap between the clinical image set acquisition and the patient irradiation. 4D analysis of dose-volume-histograms (DVHs) for prostate: CTV1 ¼ PTV, and urethra, rectum, and bladder as organs at risk (OARs) and conformity index (COIN) is presented, demonstrating the effect of prostate, OARs, and needles displacement. Results: The authors show that in the case that the patient body movement/anatomy alteration takes place, this results in modification of DVHs and radiobiological parameters, hence the plan quality. The observed average displacement of needles (1 mm) and of prostate (0.57 mm) is quite small as compared with the average displacement noted in several other reports [A. A.

Research paper thumbnail of Evaluation of the Elekta Agility MLC performance using high-resolution log files

Medical Physics

PURPOSE With the advent of volumetric modulated arc therapy (VMAT) and intensity-modulated radiat... more PURPOSE With the advent of volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) treatment techniques, the requirement for more elaborate approaches in reviewing linac components' integrity has become even more stringent. A possible solution to this challenge is to employ the usage of log files generated during treatment. The log files generated by the new generation of Elekta linacs record events at a higher frequency (25 Hz) than their predecessors, which allows for retrospective analysis and identification of subtle changes and provides another means of quality assurance. The ability to track machine components based on log files for each treatment can allow for constant monitoring of fraction consistency in addition to machine reliability. Using Elekta Agility log files, a set of tests were developed to evaluate the reliability and robustness of the multileaf collimators (MLCs). METHODS To evaluate Elekta log file utilization for linac MLC QA effectiveness, five MLC test patterns were constructed to review the effects of leaf velocity and acceleration on positional accuracy, including gravitational effects for the Elekta MLC system. Each test was run five times in a particular setting to obtain reproducibility data and statistical averages. This study was performed on two identical Versa HD machines, each delivering a full set of test plans with all possible variations. Plans were delivered using Elekta's iCOMcat software and recorded log files were extracted. Log files were reformatted for readability and automatically analyzed in Matlab® . RESULTS The Elekta Agility MLC system was shown to be capable of obtaining speeds within the range of 5-35 mm/s. MLC step and shoot tests have demonstrated the MLC system's capability of having positional repeatability, averaging 0.03- and 0.08-mm offsets with and without gravitational effects, respectively. The IMRT-specific tests have shown that gravitational effects are negligible with all positional tests averaging 0.5-mm offsets. The largest speed root-mean-square error (RMSE) for the MLC system was found at the maximum speed of 35 mm/s with an average error of 0.8 mm. For slower speeds, the value was found to be much lower. CONCLUSION Utilizing log files has demonstrated the feasibility for higher precision of MLC motions to be reviewed, based on the performance tests that were instituted. Log files provide insight on the effects of friction, acceleration, and gravity, with MU's delivered that previously could not be reviewed in such detail. Based on our results, log file-based QA has enhanced our ability to review performance, functionality, and perform QA on Elekta's MLC system.

Research paper thumbnail of SU-F-T-411: A Quantitative Parameter for Treatment Plan Quality

Medical physics, 2016

To create an IMRT treatment plan quantitative score using QUANTEC dose/volume parameters to asses... more To create an IMRT treatment plan quantitative score using QUANTEC dose/volume parameters to assess plan quality. 132 IMRT patient plans of various treatment sites were evaluated. The optimized plan's dose volume histogram (DVH) was exported to Velocity for evaluation. The proposed scoring was based on calculating the shortest distance from the QUANTEC objective to the DVH line of each organ. Each plan was normalized against the "perfect" plan where the organs at risk (OAR) received no dose and hence the distance between the QUANTEC objective and the DVH line was maximized. The normalized scores allowed comparing the quality of plans across the treatment sites, dosimetrists, and physicians. The scores were plotted and statistically analyzed to serve as basis for future plans. The score for each site was evaluated and the average percentage score resulted in the abdomen having an average percent score of 1.68 ± 1.49, 34.61 ± 35.19, 11.00 ± 15.39, 28.44 ± 25.13, 1.99 ± 5....

Research paper thumbnail of SU-E-T-94: Daily Fraction Dose Recalculation Based On Rigid Registration Using Cone Beam CT

Medical Physics, 2014

PURPOSE To calculate the daily fraction dose for a CBCT recalculation based on rigid registration... more PURPOSE To calculate the daily fraction dose for a CBCT recalculation based on rigid registration and compare it to the planned CT dose. METHODS For this study, 30 patients that were previously treated (10 SBRT lung, 10 prostate and 10 abdomen) were considered. The daily CBCT images were imported into the Pinnacle treatment planning system from Mosaic. The prescribing physician contoured the regions of interest (ROI) on each CBCT and then dose was computed on each CBCT. Each CBCT dose distribution was then compared against the plan. The evaluation was based on isodose line comparison and Dose Volume Histogram comparison. RESULTS In the case of lung patients the dose differences between daily dose and plan dose were considered small. The PTV coverage was not compromised and the dose to the organs at risk had negligible differences. Larger differences were observed for prostate and abdomen patients. In these cases, although the PTV doses did not change on a daily basis, the doses to the organs at risk had significant differences. For a prostate patient, the bladder dose at 35% volume was 2714.444 cGy for the CT plan and 2844.747, 2801.556, 3552.37, and 2970.968 cGy for subsequent CBCTs. For the PTV on a SBRT patient, however, the CT plan had a dose at 35% volume of 6917.71 cGy and 6815.385, 6892.5, 6896.25, and 6922.9 cGy for the CBCTs. CONCLUSION Daily dose validation is feasible using CBCT and treatment planning system. It provides means to evaluate the course of treatment for the patient undergoing radiation therapy and can assist in the decision of the need of adaptation of the treatment plan.

Research paper thumbnail of SU-EI-51: Use of Blade Sequences in Cervical Spine MR Imaging for Eliminating Motion, Truncation and Flow Artifacts

ABSTRACT Purpose: To assess the efficacy of the BLADE technique to eliminate motion, truncation, ... more ABSTRACT Purpose: To assess the efficacy of the BLADE technique to eliminate motion, truncation, flow and other artifacts in Cervical Spine MRI compared to the conventional technique. To study the ability of the examined sequences to reduce the indetention and wrap artifacts, which have been reported in BLADE sagittal sequences.