Sotirios Stathakis

University of Texas Health Science Center at San Antonio | UT HSC · Department of Radiation Oncology

Purpose/Objective(s) The Radiation Oncology treatment planning process necessitates many moving parts. Highly specialized teams work in concert with many aspects of planning, contingent on the completion of one item before the start of the next. A delay caused by unplanned barriers to completion can have significant impact on the final production t...

Purpose/Objective(s) It is accepted that radiation therapy can have some effect on hemoglobin/hematocrit, but it is not very well documented. The purpose of this study is to explore the effect of radiation monotherapy on hematocrit levels. Materials/Methods Given that intensity modulated radiation therapy treats a large volume of normal tissue, we...

Purpose: To develop a simplified aluminum compensator system for total body irradiation (TBI) that is easy to assemble and modify in a short period of time for customized patient treatments. Methods: The compensator is composed of a combination of 0.3 cm thick aluminum bars, two aluminum T-tracks, spacers, and metal bolts. The system is mounted...

Aim: The aim of this study was to measure and compare the output factor (OF) of a CyberKnife Robotic Radiosurgery System with eight different small field detectors and validate with Technical Report Series (TRS) report 483. Background: Accurate dosimetry of CyberKnife system is limited due to the challenges in small field dosimetry. OF is a vita...

Purpose: To determine the severity of the effects on VMAT dose calculations caused by varying statistical uncertainties (SU) per control point in a Monte Carlo based treatment planning system (TPS) and to assess the impact of the uncertainty during dose volume histogram (DVH) evaluation. Methods: For this study, 13 archived patient plans were se...

Purpose: For mobile lung tumors, four-dimensional computer tomography (4D CT) is often used for simulation and treatment planning. Localization accuracy remains a challenge in lung stereotactic body radiation therapy (SBRT) treatments. An attractive image guidance method to increase localization accuracy is 4D cone-beam CT (CBCT) as it allows for...

Purpose: Studies have evaluated the viability of using open-face masks as an immobilization technique to treat intracranial and head and neck cancers. This method offers less stress to the patient with comparable accuracy to closed-face masks. Open-face masks permit implementation of surface guided radiation therapy (SGRT) to assist in positioning...

Dose enhancement due to gold nanoparticles (GNPs) has been quantified experimentally and through Monte Carlo simulations for external beam radiation therapy energies of 6 and 18 MV. The highest enhancement was observed for the 18 MV beam at the highest GNP concentration tested, amounting to a DEF of 1.02. DEF is shown to increase with increasing co...

The era of real‐time radiotherapy is upon us. Robotic and gimbaled linac tracking are clinically established technologies with the clinical realization of couch tracking in development. Multileaf collimators (MLCs) are standard equipment for most cancer radiotherapy systems, and therefore MLC tracking is a potentially widely available technology. M...

Purpose: To compare the accuracy of two separate models when calculating dose distributions in patients undergoing stereotactic radiosurgery (SRS) treatment for brain cancer. Methods: For this comparison, two dose calculation algorithms were evaluated on two different treatment planning systems (TPS): Elekta's Monaco Version 5.11.00 Monte Carlo...

Purpose: To create an open-source visualization program that allows one to find potential cone collisions while planning intracranial stereotactic radiosurgery cases. Methods: Measurements of physical components in the treatment room (gantry, cone, table, localization stereotactic radiation surgery frame, etc.) were incorporated into a script in...

Purpose: Single-isocenter multiple brain metastasis stereotactic radiosurgery is an efficient treatment modality increasing in clinical practice. The need to provide accurate, patient-specific quality assurance (QA) for these plans is met by several options. This study reviews some of these options and explores the use of the Octavius 4D as a solu...

Purpose: Monaco treatment planning system (TPS) version 5.1 uses a Monte-Carlo (MC)-based dose calculation engine. The aim of this study is to verify and compare the Monaco-based dose calculations with both Pinnacle3 collapsed cone convolution superposition (CCCS) and Eclipse anisotropic analytical algorithm (AAA) calculations. Materials and meth...

Background: The increased use of deformable registration algorithms in clinical practice has also increased the need for their validation. Aims and objectives: The purpose of the study was to investigate the quality, accuracy, and plausibility of three commercial image registration algorithms for 4-dimensional computed tomography (4DCT) datasets...

OBJECTIVES/GOALS: The Monte Carlo dose calculation method is often considered the “gold standard” for patient dose calculations and can be as radiation dose measurements. Our study aims to develop a true Monte Carlo model that can be implemented in our clinic as part of our routine patient-specific quality assurance. METHODS/STUDY POPULATION: We ha...

Gold nanoparticles (GNPs) have been studied extensively as promising radiation dose enhancing agents. In the current study, the dose enhancement effect of GNPs for Ir-192 HDR brachytherapy is studied using Monte Carlo N-Particle code, version 6.2 (MCNP6.2) and compared with experimental results obtained using Burlin cavity theory formalism. The Ir-...

Purpose: Dose-volume histogram (DVH) measurements have been integrated into commercially available quality assurance systems to provide a metric for evaluating accuracy of delivery in addition to gamma analysis. We hypothesize that tumor control probability and normal tissue complication probability calculations can provide additional insight beyo...

Monte Carlo N-Particle 6 (MCNP6) is the latest version of Los Alamos National Laboratory's powerful Monte Carlo software designed to compute general photon, neutron, and electron transport using stochastic algorithms. Here we provide a case study of modeling the photon beam of a Varian 600C Clinical Linear Accelerator (linac), which is used to deli...

The purpose is to calculate the composite 3D biological effective dose (BED) distribution in healthy liver, when multiple lesions are treated concurrently with different hypo-fractionated schemes and stereotactic body radiation therapy, and to investigate the potential of biological based plan optimization. Two patients, each having two tumors that...

Background: The prevention of radiation-induced liver disease (RILD) is very significant in ensuring a safe radiation treatment and high quality of life. Aims and objectives: The purpose of this study is to investigate the correlation of physical and biological effective dose (BED) metrics with liver toxicity from hypo-fractionated liver radioth...

We developed a dosimeter that measures biological damage following delivery of therapeutic beams in the form of double-strand breaks (DSBs) to DNA. The dosimeter contains DNA strands that are labeled on one end with biotin and on the other with fluorescein and attached to magnetic microbeads. Following irradiation, a magnet is used to separate brok...

This is a new book that covers the topics of practical medical physics in a distilled, informative manner. This book has a total of 24 chapters. The first 12 chapters deal with the technical aspects of medical physics, while the last 12 chapters cover various applications of medical physics to various radiation therapy modalities. The book is writt...

Introduction: Clinical evaluation of a two-dimensional (2D) liquid-filled ion chamber detector array used in the verification of highly modulated small beams of stereotactic body radiation therapy (SBRT) has been conducted. Materials and methods: Measurements with the Octavius 1000 SRS (PTW, Freiburg, Germany) detector with 977 liquid-filled ion...

Purpose: The purpose of this study was to investigate the dosimetric equivalency of dynamic conformal arc therapy (DCAT) against volumetric modulated arc therapy (VMAT) plans in stereotactic body radiation therapy (SBRT) of lung and liver lesions and to examine if efficiency can be increased. Methods: Nineteen patients previously treated for lun...

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...

Introduction This research quantifies and compares the effect of hip prostheses on dose distributions calculated using collapsed cone convolution superposition and Monte Carlo (with and without correcting for the density of the implant and surrounding tissues). The use of full volumetric modulated arc therapy arcs versus volumetric modulated arc th...

Purpose: The Brainlab Elements treatment planning system utilizes distinct modules for treatment planning specific to stereotactic treatment sites including single or multiple brain lesions as well as spine. This work investigates the hypothesis that an optimization tailored specifically to spine can in fact create dosimetrically superior plans to...

Background and purpose: With the increasingly prominent role of stereotactic radiosurgery in radiation therapy, there is a clinical need for robust, efficient, and accurate solutions for targeting multiple sites with one patient setup. The end-to-end accuracy of high definition dynamic radiosurgery with Elekta treatment planning and delivery syste...

Purpose: To develop and validate an intensity modulated radiation therapy (IMRT) treatment plan quantitative score using QUANTEC dose/volume parameters to assess plan quality. Methods: 132 IMRT and volumetric modulated Arc therapy (VMAT) patient plans of various treatment sites were evaluated. The optimized plan's dose volume histogram (DVH) was...

The purpose of the study is to evaluate the accuracy of two deformable image registration algorithms by examining their influence on the dose summation results obtained using 4DCT (four dimensional computed tomography) dose distributions based on ‘4D’ planned and ‘4D optimal’ IMRT (intensity modulated radiation therapy) plans. For ten lung cancer p...

Purpose: While external beam radiotherapy treatment planning determines nearly every mechanical and dosimetric parameter of the linear accelerator (LINAC), the table coordinates in all three dimensions are generally unknown until initial patient setup at the LINAC. Knowing these parameters in advance could help verify the direction of patient shif...

Streaking artifacts in computed tomography (CT) scans caused by metallic dental implants (MDIs) can lead to inaccuracies in dose calculations. This study quantifies and compares the effect of MDIs on dose distributions using the collapsed cone convolution superposition (CCCS) and Monte Carlo (MC) algorithms, with and without correcting for the dens...

Purpose: Many types of dosimeters are used to measure radiation dose and calibrate radiotherapy equipment, but none directly measure the biological effect of this dose. The purpose here is to create a dosimeter that can measure the probability of double-strand breaks (DSB) for DNA, which is directly related to the biological effect of radiation....

Purpose: Electronic portal imaging devices (EPIDs) are an integral part of the radiation oncology workflow for treatment setup verification. Several commercial EPID implementations are currently available, each with varying capabilities. To standardize performance evaluation, Task Group Report 58 (TG-58) and TG-142 outline specific image quality me...

Purpose: Electronic portal imaging devices (EPIDs) are an integral part of the radiation oncology workflow for treatment setup verification. Several commercial EPID implementations are currently available, each with varying capabilities. To standardize performance evaluation, Task Group Report 58 (TG-58) and TG-142 outline specific image quality m...

The purpose of this study was to evaluate and compare the accuracy of dose calculations in second check softwares (Diamond, IMSure, MuCheck, and RadCalc) against the Phillips Pinnacle³ treatment planning system. Eighteen previously treated patients’ treatment planning files consisting of a total of 204 beams were exported from the Pinnacle³ TPS to...

Introduction This study evaluates treatment plans aiming at determining the expected impact of daily patient setup corrections on the delivered dose distribution and plan parameters in head-and-neck radiotherapy. Materials and Methods In this study, 10 head-and-neck cancer patients are evaluated. For the evaluation of daily changes of the patient...

Purpose To quantify and compare the effect of metallic dental implants (MDI) on dose distributions calculated using Collapsed Cone Convolution Superposition (CCCS) algorithm or a Monte Carlo algorithm (with and without correcting for the density of the MDI). Methods Seven previously treated patients to the head and neck region were included in thi...

The purpose of this study is to perform dosimetric validation of Monaco treatment planning system version 5.1. The Elekta VersaHD linear accelerator with high dose rate flattening filter-free photon modes and electron energies was used in this study. The dosimetric output of the new Agility head combined with the FFF photon modes warranted this inv...

A multiphase, approximate biological effective dose (BEDA) equation was introduced because most treatment planning systems (TPS) are incapable of calculating the true BED (BEDT). This work investigates the accuracy and precision of the multiphase BEDA relative to the BEDT in clinical cases. Ten patients with head and neck cancer and 10 patients wit...

The purpose of this study is to evaluate the clinical efficacy of both step-and-shoot IMRT and 3D-Conformal Radiation Therapy modalities (CRT) in treating prostate cancer using radiobiological measures. Another aim was to estimate the risks for developing secondary malignancies in bladder and rectum due to radiotherapy from the corresponding modali...

A patient specific quality assurance (QA) should detect errors that originate anywhere in the treatment planning process. However, the increasing complexity of treatment plans has increased the need for improvements in the accuracy of the patient specific pretreatment verification process. This has led to the utilization of higher resolution QA met...

Contour comparison, landmark tracking, and image similarity are methods that can be used to perform a patient-specific evaluation for the accuracy of deformable image registration (DIR), but they are not necessarily a true measurement of DIR accuracy. The purpose of this work is to evaluate how the calculated errors from these methods compare to th...

The primary purpose of the study was to determine how detailed deformable image registration (DIR) phantoms need to adequately simulate human anatomy and accurately assess the quality of DIR algorithms. In particular, how many distinct tissues are required in a phantom to simulate complex human anatomy? Pelvis and head-and-neck patient CT images we...

Introduction Radiation treatment planning, delivery and patient monitoring have been enriched with the increased use of MRI in radiotherapy clinical practice. MRI Polymer gel dosimetry has been proposed as a sensitive 3D dosimetry and QA tool. Purpose To develop and implement a QA test for the validation of spatial and dosimetric accuracy of a rec...

Purpose To investigate the viability of patient specific IMRT QA method which uses MLC log files to recreate a delivered fluence and compare to the planned fluence. Materials and methods A Varian Novalis Tx equipped with a HD120 MLC was used in this study. A total of 40 patients of both VMAT and step and shoot of various sites were used. Error con...

Prostate cases commonly consist of dual phase planning with a primary plan followed by a boost. Traditionally, the boost phase is planned independently from the primary plan with the risk of generating hot or cold spots in the composite plan. Alternatively, boost phase can be planned taking into account the primary dose. The aim of this study was t...

Background: In this treatment planning study, we compare the plan quality and delivery parameters for the treatment of multiple brain metastases using 2 monoisocentric techniques: the Multiple Metastases Element from Brainlab and the RapidArc volumetric-modulated arc therapy from Varian Medical Systems. Methods: Eight patients who were treated in...

Objective The purposes of this work are to investigate the influence of breathing motion on the quality of delivered radiation therapy treatment for lung cancer patients, to study the effect of tumor volume movement and anatomy change (due to the breathing motion) on the dose distribution through a radiobiological analysis, and finally, to examine...

Purpose:A DNA double-strand break (DSB) dosimeter was developed to measure the biological effect of radiation. The goal here is to refine the fabrication method of this dosimeter to reproducibly create a low coefficient of variation (CoV) and reduce the cost for the dosimeter. Methods:Our dosimeter consists of 4 kilo-base pair DNA strands (labeled...

Purpose:There is a variety of treatment planning systems (TPS) available for clinical use all with highly variable settings to calculate patient dose. Patient specific IMRT QA is often a daily procedure at most clinics and each clinic devises their own policy on the TPS settings for testing the quality of the patient plan against a measured dose on...

Purpose:As modern linacs have become more technologically advanced with the implementation of IGRT and IMRT with HDMLCs, a requirement for more elaborate tracking techniques to monitor components’ integrity is paramount. ElektaLog files are generated every 40 milliseconds, which can be analyzed to track subtle changes and provide another aspect of...

Purpose:To quantify and compare the effect of metallic dental implants (MDI) on dose distributions calculated using Collapsed Cone Convolution Superposition (CCCS) algorithm or a Monte Carlo algorithm (with and without correcting for the density of the MDI). Methods:Seven previously treated patients to the head and neck region were included in this...

Purpose:To create an IMRT treatment plan quantitative score using QUANTEC dose/volume parameters to assess plan quality. Methods: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 distan...

Purpose:The use of radiation as a treatment modality for skin cancer has increased significantly over the last decade with standardized applicators. Utilizing 3D printing, the ability to make applicators specifically designed for each patient’s anatomy has become economically feasible. With this in mind it was the aim of this study to determine the...

Purpose:Deep inspiration breath-hold (DIBH) is used for left-sided breast radiotherapy to spare the heart and lung. The magnitude of sparing has been shown to be significant. Monte Carlo, furthermore, has the potential to calculate most accurately the dose in the heterogeneous lung medium at the interface with the lung wall. The lung dose was inves...

Purpose:Spatially fractionated radiation therapy, also known as GRID therapy, is used to treat large solid tumors by irradiating the target to a single dose of 10–20Gy through spatially distributed beamlets. We have investigated the use of a 3D gel for dosimetric characterization of GRID therapy. Methods:GRID therapy is an external beam analog of v...

Purpose:SBRT is proving to be a very efficacious treatment modality for an increasing number of indications, including spine lesions. We have developed a novel phantom to serve as an end-to-end QA tool for either patient specific QA or commissioning QA of SBRT for spine lesions. Methods:In this feasibility study, we have selected a patient with a s...

Purpose:To present treatment statistics of a Varian Novalis Tx using more than 90,000 Varian Dynalog files collected over the past 2 years. Methods:Varian Dynalog files are recorded for every patient treated on our Varian Novalis Tx. The files are collected and analyzed daily to check interfraction agreement of treatment deliveries. This is accompl...

Purpose:The purpose of this study was to evaluate, compare and investigate the differences of SBRT treatment plans on dose calculation and plan metrics between Pinnacle and Monaco treatment planning systems (TPS). Methods:14 previously treated patients’ files were exported from the Pinnacle treatment planning system to Monaco. All of the treatment...

Purpose:Stereotactic radiosurgery (SRS) outcomes are related to the delivered dose to the target and to surrounding tissue. We have commissioned a Monte Carlo based dose calculation algorithm to recalculated the delivered dose planned using pencil beam calculation dose engine. Methods:Twenty consecutive previously treated patients have been selecte...

Purpose:With increasing QA demands of medical physicists in clinical radiation oncology, the need for an effective method of tracking clinical data has become paramount. A tool was produced which scans through data automatically recorded by a 2D chamber array and extracts relevant information recommended by TG-142. Using this extracted information...

Purpose:To validate dose calculation and delivery accuracy of a recently introduced mono-isocentric technique for the treatment of multiple brain metastases in a realistic clinical case. Methods:Anonymized CT scans of a patient were used to model a hollow phantom that duplicates anatomy of the skull. A 3D printer was used to construct the phantom o...

Purpose:This study aims at estimating the dosimetric differences of Pinnacle and Monte Carlo (MC) calculation algorithms in computing the dose distributions in lung cancer SBRT cases. Furthermore, to interpret the dosimetric findings into expected tissue response rates in order to estimate their clinical impact. Methods:17 patients were studied and...

Purpose:To investigate inter-fraction differences of dose delivery by analyzing portal images acquired during treatment and implement an automated system to generate a report for each fraction. Large differences in images between fractions can alert the physicist of possible machine performance issues or patient set-up errors. Methods:A Varian Nova...

Purpose:To evaluate a commercial system for patient specific quality assurance using measurements and re-calculated dose volume histograms. Methods:The PTW OCTAVIUS4D was used to physically measure the dose distribution from previously accepted IMRT patient plans for a variety of sites. PTW VeriSoft was used to for the IMRT QA evaluation. Patient p...

Purpose:Radiotherapy treatment is specified by radiation dose prescriptions, but biological DNA damage actually controls treatment effectiveness. It is impractical to directly measure dose in the clinic, so we measure quantities, such as collected charge, and calculate the relationship to dose. At small fields, such as those in stereotactic radiosu...