Monte Carlo and analytic modeling of an Elekta Infinity linac with Agility MLC: Investigating the significance of accurate model parameters for small radiation fields

Purpose: To explain the deviation observed between measured and Monaco calculated dose profiles for a small field (i.e., alternating open-closed MLC pattern). A Monte Carlo (MC) model of an Elekta Infinity linac with Agility MLC was created and validated against measurements. In addition, an analytic model which predicts the fluence at the isocenter plane was used to study the impact of multiple beam parameters on the accuracy of dose calculations for small fields. Methods: A detailed MC model of a 6 MV Elekta Infinity linac with Agility MLC was created in EGSnrc/BEAMnrc and validated against measurements. An analytic model using primary and secondary virtual photon sources was created and benchmarked against the MC simulations and the impact of multiple beam parameters on the accuracy of the model for a small field was investigated. Both models were used to explain discrepancies observed between measured/EGSnrc simulated and Monaco calculated dose profiles for alternating open-closed MLC leaves. Results: MC-simulated dose profiles (PDDs, cross- and in-line profiles, etc.) were found to be in very good agreements with measurements. The bes

Web-based system for quality assurance of radiation oncology equipment and procedures

In a radiation therapy department, several periodic (daily, monthly, quarterly, yearly, etc.) and on-request quality control tests are performed as part of the quality assurance program. The lack of a commercial solution to unify all these tests in one single system was the motivation for this project. The goal of this thesis work was to develop a web-based quality assurance software tool for the radiation oncology division of the Jewish General Hospital that would be easily expendable and manageable. The tool that was created allows easy access to the tests through a simple web interface yet allowing advanced management of user rights, processing of complex numerical data, warning users through email alerts and reports, scheduling tests, keeping trends of the test results and providing safe storage for the collected data. Our system is based on Drupal, an open source web content management system. Several customizations were done to the basic Drupal system to adapt it to our needs: several scripts and specialized modules were used to enter and analyse collected data (text and images) as well as exchange data with the radiotherapy electronic medical record database. In this thesis work we have selected and implemented in our system a limited collection of quality control tests (9) that are representative of all types of tests that are performed in a radiotherapy clinic, as a full implementation would be beyond the time frame of this project. They are the bases for a future complete implementation and can be used as a model for other similar tests. The implemented tests are now being introduced in the clinic simplifying data entry, access, and analysis.Dans un département de radiothérapie plusieurs tests de contrôle de qualité sont exécutés de façon périodique (journalière, mensuelle, trimestrielle, annuelle, etc.) où sur demande dans le cadre du programme d'assurance qualité. L'absence d'une solution commerciale pour unifier tous ces tests dans un seul système informatique est la motivation de ce projet. L'objectif de ce travail de thèse était de développer un outil logiciel web d'assurance qualité pour la division de radio-oncologie de l'Hôpital général juif qui serait facilement extensible et facile à gérer. L'outil qui a été créé permet un accès facile à des tests via une interface web simple tout en permettant une gestion avancée des droits des utilisateurs, du traitement des données numériques complexes, permet l'envoie d'alertes e-mail et de rapports, la planification temporelle des tests, l'analyse des tendances des résultats et le stockage des données recueillies.Notre système est basé sur un logiciel libre de gestion de contenu, Drupal. Plusieurs adaptations ont été apportées au système Drupal de base pour l'adapter à nos besoins: plusieurs scripts et modules spécialisés ont été programmés et utilisés pour saisir et analyser les données recueillies (texte et images) ainsi que l'échange de données avec la base de données de dossiers médicaux électroniques de radiothérapie. Dans ce travail de thèse, nous avons sélectionné et implémenté dans notre système une collection limitée de tests de contrôle de qualité (9) qui sont représentatifs de tous les types de tests qui sont effectués dans une clinique de radiothérapie puisque la mise en œuvre complète de tous les tests est au-delà du délai de cette projet. Les tests implémentés peuvent facilement être utilisés comme modèles pour les autres tests. Les tests présentement implémentés sont en cours d'introduction dans la clinique et simplifie la saisie, l'accès et l'analyse aux données

Experimental verification of 4D Monte Carlo simulations of dose delivery to a moving anatomy

PURPOSE: To evaluate a novel 4D Monte Carlo simulation tool by comparing calculations to physical measurements using a respiratory motion phantom.METHODS: We used a dynamic Quasar phantom in both stationary and breathing states (sinusoidal motion of amplitude of 1.8 cm and period of 3.3 s) for dose measurements on an Elekta Agility linear accelerator. Gafchromic EBT3 film and the RADPOS 4D dosimetry system were placed inside the lung insert of the phantom to measure dose profiles and point-dose values at the center of the spherical tumor inside the insert. Both a static 4 × 4 cm2 field and a VMAT plan were delivered. Static and 4D Monte Carlo simulations of the treatment deliveries were performed using DOSXYZnrc and a modified version of the defDOSXYZnrc user code that allows modeling of the continuous motion of both machine and patient. DICOM treatment plan files and linac delivery log files were used to generate corresponding input files. The phantom motion recorded by RADPOS during beam delivery was incorporated into the input files for the 4DdefDOSXYZnrc simulations.RESULTS: For stationary phantom simulations, all point-dose values from MC simulations at the tumor center agreed within 1% with film and within 2% with RADPOS. More than 98% of the voxels from simulated dose profiles passed a 1D gamma of 2%/2-mm criteria against measured dose profiles. Similar results were observed when applying a 2D gamma analysis with a 2%/2-mm criteria to compare 2D dose distributions of Monte Carlo simulations against measurements. For simulations on the moving phantom, MC-calculated dose values at the center of the tumor were found to be within 1% of film and within 2σ of experimental uncertainties which are 2.8% of the RADPOS measurements. 1D gamma comparisons of the dose profiles were better than 91%, and 2D gamma comparisons of the 2D dose distributions were found to be better than 94%.CONCLUSION: Our 4D Monte Carlo method using defDOSXYZnrc can be used to accurately calculate the dose distribution in continuously moving anatomy for various treatment techniques. This work, if extended to deformable anatomies, can be used to reconstruct patient delivered dose for use in adaptive radiation therapy