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dc.contributor.advisorDu Plessis, F. C. P.
dc.contributor.authorStrauss, Lourens Jochemus
dc.date.accessioned2015-08-11T10:02:30Z
dc.date.available2015-08-11T10:02:30Z
dc.date.issued2015-01
dc.identifier.urihttp://hdl.handle.net/11660/811
dc.description.abstractEnglish: Cancer treatment with external beam radiotherapy using the specialized technique of intensity modulation is a complex modality. The Treatment Planning System (TPS) is responsible for accurate calculation of dose to allow the radiotherapy team to make decisions on the patient treatment. The commercial TPS, XiO, utilizes a Multigrid Superposition algorithm as dose calculation engine, which is model based. Several approximations are inherent in this method. In-depth quality assurance (QA) of Intensity Modulated Radiation Therapy (IMRT) plans is necessary, and these tests are time-consuming and reduce the available clinical treatment time. Monte Carlo (MC) has been proven to be the most accurate method of radiation dose calculation. MC is a direct dose calculation method, and the EGSnrc codes are well suited for linear accelerator (linac) simulations. This study aims to be a first step towards full MC-based dose verification for IMRT dose distributions produced on XiO: developing the system and demonstrating the accuracy thereof. A generic virtual linac based on a typical Elekta linac was constructed using the EGSnrc MC software (BEAMnrc and DOSXYZnrc), for beam energies of 6 and 10 MV respectively. Simulations were either run on a watertank model or in air to produce beam data required for commissioning on XiO. Beam profiles, Percentage Depth Dose (PDD) curves and scatter factors for collimator and total scatter were extracted from the data. Software was developed to convert data to a format readable by the TPS. Modelling was done on XiO for all fields. A software graphical user interface (GUI) was developed to extract necessary information from dicom files required for MC calculations. This included CT data extracting and converting to EGSnrc format, reading all plan details, and creating scripts for automatic MC dose calculation execution. IMRT plans were created for 3 different treatment sites using the newly commissioned model on XiO. The modelling and simulation process was verified with MC dose calculations in scanned phantoms. After simulation, the IMRT plans were evaluated with isodose/profiles and 2D gamma analysis, as well as dose difference maps and Dose Volume Histogram (DVH) comparisons. The generic linac could successfully be created on BEAMnrc, and produced clinically acceptable beams. The data for commissioning was also generated successfully, and could be extracted and read into XiO after some de-noising filters were applied. Modelling on the TPS was done to an overall agreement level of 3%/3mm and 2%/2mm for small fields. Doses in the Prostate and Head-and-Neck IMRT plans compared well between XiO and MC for both energies. Gamma pass rates were above 90% for a criterion of 3%/2mm in a region of interest (ROI) covering the target and critical organs. Only slight overestimation of dose in bony regions was observed. The Esophagus IMRT plans however indicated some discrepancies in the dose calculation of XiO, especially in the low density regions, like lung. The 2D gamma pass rates were low, and DVH comparison indicated large overestimation of dose in the target volume, as well as in the Spine, as a direct consequence of errors in dose calculation of low density media. It is concluded that a dose verification system could successfully be developed for comparison of IMRT plans. Accurate modelling on the TPS was a vital step, and some possible issues were addressed. The system can be used routinely, and doses are calculated in a reasonable time with differences presented in a practical manner. The dose calculation of IMRT plans on XiO was compared to MC dose and found to be accurate for most treatment sites, independent of beam energy. However, caution is advised for cases where beams are directed through low density media, as clinically significant effects can possibly occur in patients.en_ZA
dc.description.abstractAfrikaans: Die behandeling van kanker met eksterne bundel bestraling d.m.v. die gespesialiseerde tegniek van intensiteit modulasie is 'n komplekse modaliteit. Die Behandelings Beplanning Stelsel (BBS) is verantwoordelik vir die akkurate berekening van dosis sodat die bestralings span besluite kan neem oor die pasiënt se behandeling. Die kommersiële BBS, XiO, maak gebruik van 'n veelvuldige-rooster Superposisie algoritme as dosis berekening enjin, wat model-gebaseerd is. Verskeie benaderings is deel van hierdie metode. Deeglike gehalteversekering (GV) is nodig in Intensiteit Gemoduleerde Radioterapie (IGR) planne, en hierdie toetse is tydrowend en verminder die beskikbare kliniese behandeling tyd. Monte Carlo (MC) is al bewys om die mees akkurate metode van stralingsdosis berekening te wees. MC is 'n direkte dosis berekening metode, en die EGSnrc kodes is geskik vir lineêre versneller simulasies. Hierdie studie het ten doel om 'n eerste stap tot volledige MC-gebaseerde dosis verifikasie vir IGR dosis verspreidings te wees op XiO: die stelsel te ontwikkel en die akkuraatheid daarvan te demonstreer. 'n Generiese virtuele versneller gebaseer op 'n tipiese Elekta versneller is gebou met behulp van die EGSnrc MC sagteware (BEAMnrc en DOSXYZnrc) met energieë van 6 en 10 MV onderskeidelik. Simulasies was óf op 'n water tenk model of in lug gedoen om die nodige data vir ingebruikneming op XiO te produseer. Bundel profiele, Persentasie Diepte Dosis (PDD) kurwes en verstrooïngs faktore vir kollimator en totale verstrooïng is uit die data verkry. Sagteware is ontwikkel om data te omskep in 'n formaat geskik vir die BBS. Modellering is gedoen op XiO vir alle velde. 'n Sagteware grafiese gebruikerskoppelvlak (GGK) is ontwikkel om die nodige inligting van DICOM lêers vir MC berekeninge te verkry. Dit sluit in die verkryging van RT data en die omskakeling na EGSnrc formaat, inlees van alle plan besonderhede, en die skep van roetines vir outomatiese MC dosis berekening uitvoering. IGR planne vir 3 verskillende behandeling areas is geskep met behulp van díe nuwe model op XiO. Die modellering en simulasie proses is geverifieer met MC dosis berekeninge in geskandeerde fantome. Na simulasie is die IGR planne geëvalueer met isodosisse/profiele en 2D gamma analise, asook dosis-verskil kaarte en Dosis Volume Histogram (DVH) vergelykings. Die generiese versneller kon suksesvol geskep word op BEAMnrc, en produseer klinies aanvaarbare bundels. Die data vir ingebruikneming is ook suksesvol gegenereer, en kon verkry en ingelees word in XiO nadat 'n paar vergladdings filters toegepas is. Modellering van die BBS is gedoen tot 'n algehele ooreenkoms vlak van 3%/3mm en 2%/2mm vir klein velde. Dosisse in die Prostaat en Kop- en-nek IGR planne het goed vergelyk tussen XiO en MC vir beide energieë. Die gamma slaagsyfers was bo 90 % vir 'n maatstaf van 3%/2mm in 'n gebied van belang wat die teiken en kritiese organe insluit. Slegs effense oorskatting van dosis in been is waargeneem. Die Esofagus IGR planne het egter teenstrydighede in die dosis berekening van XiO aangedui, veral in die lae digtheid gebiede soos die longe. Die 2D gamma slaagsyfers was laag, en DVH vergelyking het groot oorskatting van dosis in die teiken volume aangedui, sowel as in die spinaalkoord, as 'n direkte gevolg van foute in die dosis berekening van lae digtheid media. Dit is die gevolgtrekking dat 'n dosis verifikasie stelsel suksesvol vir die verifikasie van IGR planne ontwikkel kon word. Akkurate modelle op die BBS was 'n belangrike stap, en 'n paar moontlike kwessies is aangespreek. Die stelsel kan gereeld gebruik word, en dosisse word bereken in 'n redelike tyd met verskille wat in 'n praktiese wyse vertoon word. Die dosis berekening van IGR planne op XiO is vergelyk met MC dosis berekeninge en gevind om akkuraat vir die meeste behandeling areas te wees, onafhanklik van bundel energie. Dit word egter aanbeveel om versigtig te wees in gevalle waar strale deur lae digtheid media beplan word, aangesien klinies beduidende effekte moontlik in pasiënte kan voorkom.
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectTreatment Planning Systemen_ZA
dc.subjectMonte Carloen_ZA
dc.subjectDose verification toolen_ZA
dc.subjectEGSnrcen_ZA
dc.subjectBEAMnrcen_ZA
dc.subjectDOSXYZnrcen_ZA
dc.subjectXiOen_ZA
dc.subjectIntensity Modulated Radiation Therapyen_ZA
dc.subjectRadiation -- Dosageen_ZA
dc.subjectMonte Carlo methoden_ZA
dc.subjectRadiotherapyen_ZA
dc.subjectDissertation (M.Med.Sc. (Medical Physics))--University of the Free State, 2015en_ZA
dc.titleVerification of a commercial treatment planning system based on Monte Carlo radiation dose calculations in intensity modulated radiation therapyen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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