Development of a particle source model for a synergy linear accelerator to be used in Monte Carlo radiation dose calculations for cancer therapy
| dc.contributor.advisor | Du Plessis, F. C. P. | |
| dc.contributor.author | Van Eeden, Dete | |
| dc.date.accessioned | 2016-01-08T11:37:42Z | |
| dc.date.available | 2016-01-08T11:37:42Z | |
| dc.date.issued | 2014-05 | |
| dc.description.abstract | English: In oncology patients are treated for cancer with various methods such as surgery, chemo therapy and radiation therapy. Accurate radiation treatment planning and dose delivery to the tumour is necessary for the successful outcome of cancer treatment. In order to achieve this goal accurate radiation dose calculation codes must be utilized. EGSnrc based Monte Carlo (MC) codes such as BEAMnrc and DOSXYZnrc have been developed for just this purpose. The problem that arises in using these MC codes is that they lack suitable x-ray beam source models. These models must be accurate in order to replicate the true clinical x-ray beam emanating from the linear accelerator. One such machine for which radiation source data must be derived is currently being used at the Oncology department in Universitas Hospital Annex. It is desirable to model this linear accelerator in order to perform MC based dose calculations for radiation treatment. The use of MC based dose calculations is certainly not new in the radiation physics environment. Various authors have studied the replication of radiation beam characteristics using source models to simulate the phase-space parameters of particles produced by the linear accelerator. These parameters include the charge, energy, direction, and position of each particle as it crosses a certain reference plane below the linear accelerator. An accurate source model should be able to re-generate particles with the exact set of above-mentioned parameters as would be produced by the real linear accelerator. Sources can be very simple such as a single point from which the particles are radiating with a single invariant energy spectrum. Studies have shown that these beam models can yield accurate beam data over relatively small field sizes and is not general enough to use over a whole range of clinically useful field sizes. A graphical user interface (GUI) was developed that can assist in the construction of the source model. The source model can describe energy and fluence distributions for photons and electrons as separate point sources each with their own SSD. The accuracy of the model was validated by comparing simulated profiles with measured data for an Elekta Synergy linear accelerator. The modified Schiff formula was used to derive the bremsstrahlung spectra emanating from the target. The x-ray fluence Gaussian distribution consisted of the primary fluence from the target, which was modified by the primary collimator, secondary collimators as well as the multileaf collimators. The truncation and beam scatter caused by the face of the collimators were modelled with error functions. Exponential functions were used to model off-axis collimator transmission. Profiles and percentage depth dose curves were obtained with the source for square field sizes of 1 × 1 cm2 up to a 40 × 40 cm2. Offset fields for 10 × 10 cm2, 15 × 15 cm2 and 20 × 20 cm2, rectangular fields as well as wedged fields were included. Irregular field shapes were simulated to evaluate the source model‘s capability of reproducing complex treatment fields. Film dose verification was done in an anthropomorphic Rando® phantom and compared with the MC source model for 6 MV x-ray beams. A criterion of 2% / 2 mm was used to compare MC data and measured data. This study demonstrated that a diversity of field sizes and percentage depth dose curves can be modelled within 2% / 2 mm. The model can replicate irregular field sizes used for complex treatments. Minor discrepancies were found for the relative dose comparisons between the MC and film data for the anthropomorphic phantom. | en_ZA |
| dc.description.abstract | Afrikaans: In onkologie word pasiënte behandel vir kanker met verskillende metodes soos chirurgie, chemoterapie en bestralings terapie. Akkurate bestralings beplanning en gelewerde dosis aan die tumor is noodsaaklik vir die suksesvolle uitkoms van die behandeling van kanker. Ten einde hierdie doel te bereik moet akkurate bestralings dosis berekening kodes gebruik word. EGSnrc gebaseerde Monte Carlo (MC) kodes soos BEAMnrc en DOSXYZnrc is ontwikkel vir hierdie doel. Die probleem wat ontstaan in die gebruik van hierdie MC kodes, is hulle gebrek aan geskikte x-straal bron modelle. Hierdie modelle moet akkuraat wees om die ware kliniese x-strale vanuit die lineêre versneller te herhaal. Een so 'n masjien waarvoor bestralings bron data afgelei moet word, word tans gebruik by die Onkologie-afdeling in Universitas Annex Hospitaal. Dit is wenslik om hierdie lineêre versneller te modelleer om MC gebaseerde dosis berekeninge uit te voer vir bestraling. Die gebruik van MC gebaseerde dosis berekeninge is beslis nie nuut in die mediese fisika gebied nie. Verskeie outeurs het die herhaling van bestralings eienskappe met behulp van bron-modelle met fase-ruimte parameters van deeltjies wat deur die lineêre versneller beweeg gebestudeer. Hierdie parameters sluit in die lading, energie, rigting, en die posisie van elke deeltjie by 'n sekere verwysings vlak onder die lineêre versneller. 'N akkurate bron model moet in staat wees om deeltjies te her-skep met die presiese stel van bogenoemde parameters soos geproduseer sal word deur die werklike lineêre versneller. Bronne kan baie eenvoudig wees soos 'n enkele puntbron van waar die deeltjies uitstraal met 'n enkele onafhanklike energie spektrum. Studies het getoon dat hierdie bundel modelle akkurate bundel data kan oplewer oor relatief klein veld groottes en is nie algemeen genoeg om te gebruik oor 'n hele reeks van klinies bruikbare veld groottes nie. 'N grafiese gebruikerskoppelvlak is ontwikkel wat kan help met die bou van die bron model. Die bron model kan energie en vloed distribusies vir fotone en elektrone beskryf as afsonderlike punt bronne, elk met hul eie FVA. Die akkuraatheid van die model is bevestig deur gesimuleerde profiele te vergelyk met gemete data vir 'n Elekta Synergy lineêre versneller. Die gemodifiseerde Schiff formule is gebruik om die bremsstrahlung spektrum afkomstig van die teiken, af te lei. Die x-straal vloed Gaussiese verspreiding bestaan uit die primêre vloed van die teiken, wat aangepas is by die primêre kollimator, sekondêre kollimators sowel as die multispleet kollimatore. Die vernouiing en bundel verstrooiing wat veroorsaak word deur die oppervlakte van die kollimators is gemodelleer met erfunksies. Eksponensiële funksies is gebruik om asimmetriese kollimator verstrooiing the modelleer . Profiele en persentasie diepte dosis kurwes is verkry met die bron vir vierkantige groottes van 1 x 1 cm2 tot 'n 40 × 40 cm2. Asimmetriese velde van 10 × 10 cm2, 15 × 15 cm2 en 20 × 20 cm2, reghoekige velde asook wig velde was ingesluit. Onreëlmatige veld groottes is gesimuleer om die bron model se vermoë van die kopiëring van komplekse behandeling velde te evalueer. Film dosis verifikasie is in 'n antropomorfiese Rando® fantoom gedoen en is vergelyking met die MC bron model vir 6 MV x-straal bundel. 'N maatstaf van 2% / 2 mm is gebruik om die MC data en gemete data te vergelyk. Hierdie studie het getoon dat 'n verskeidenheid van veld groottes en persentasie diepte dosis kurwes binne 2% / 2 mm gemodelleer kan word. Die model kan onreëlmatige veld groottes herhaal wat gebruik word vir komplekse behandelings. Geringe verskille is gevind vir die relatiewe dosis vergelykings tussen die MC en film data vir die antropomorfiese fantoom. | af |
| dc.identifier.uri | http://hdl.handle.net/11660/2082 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Monte Carlo | en_ZA |
| dc.subject | DOSXYZnrc | en_ZA |
| dc.subject | Schiff formula | en_ZA |
| dc.subject | Graphical user interface | en_ZA |
| dc.subject | Source model | en_ZA |
| dc.subject | Gamma criteria | en_ZA |
| dc.subject | Dose verification | en_ZA |
| dc.subject | Linear accelerator | en_ZA |
| dc.subject | Radiation dose calculations | en_ZA |
| dc.subject | Cancer therapy | en_ZA |
| dc.subject | Radiation dosimetry | en_ZA |
| dc.subject | Monte Carlo method | en_ZA |
| dc.subject | Radiation -- Measurement | en_ZA |
| dc.subject | Radiotherapy | en_ZA |
| dc.subject | Cancer -- Treatment | en_ZA |
| dc.subject | Dussertation (M.Med.Sc. (Medical Physics))--University of the Free State, 2014 | en_ZA |
| dc.title | Development of a particle source model for a synergy linear accelerator to be used in Monte Carlo radiation dose calculations for cancer therapy | en_ZA |
| dc.type | Dissertation | en_ZA |