A unified method of calculating the dose rate and dose distribution for therapeutic x-ray beams.
There is a growing expectation that radiotherapy can be made more effective by conforming the dose distribution more closely to the volume of diseased tissue. Higher doses could then be given, without increasing the risks associated with the irradiation of the surrounding healthy tissue. The goal of...
| Publicado en: | Unified Method of Calculating the Dose Rate & Dose Distribution for Therapeutic X-ray Beams pp. 166 p - 167 |
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| Autor principal: | |
| Formato: | research Doctoral Dissertation |
| Publicado: |
UNIVERSITY OF WESTERN ONTARIO (CANADA)
1997
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| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=ccm&AN=109873409&site=ehost-live header: @attributes: shortDbName: ccm uiTerm: 109873409 longDbName: CINAHL Complete uiTag: AN controlInfo: bkinfo: dissinfo: disstl: A unified method of calculating the dose rate and dose distribution for therapeutic x-ray beams. dissinst: UNIVERSITY OF WESTERN ONTARIO (CANADA) jinfo: jid: IGOT jtl: Unified Method of Calculating the Dose Rate & Dose Distribution for Therapeutic X-ray Beams maglogo: N pubinfo: dt: 1997 pub: UNIVERSITY OF WESTERN ONTARIO (CANADA) artinfo: ui: 109873409 109873409 1999058287 UMI Order PVZNQ21313 109873409 ppf: 166 p ppct: 1 formats: tig: atl: A unified method of calculating the dose rate and dose distribution for therapeutic x-ray beams. aug: au: Sharpe MB sug: subj: Radiotherapy Therapy, Computer Assisted Dose-Response Relationship, Radiation Human ab: There is a growing expectation that radiotherapy can be made more effective by conforming the dose distribution more closely to the volume of diseased tissue. Higher doses could then be given, without increasing the risks associated with the irradiation of the surrounding healthy tissue. The goal of this thesis was to develop a dose calculation algorithm to support accurate treatment planning for conformal x-ray beam radiotherapy. Dose is calculated as the superposition of a dose spread kernel with the distribution of energy released by x-rays interacting in an absorber. When variations in the density of the irradiated tissues perturb the path of scattered radiation, a scaling approximation is used to distort the kernel. Studies were also performed to understand how the kernel is affected by beam hardening and beam divergence. It was determined that it is acceptable to use a polyenergetic kernel that is unaffected by beam hardening, and that kernels oriented parallel to the beam axis are an acceptable approximation in a divergent beam. The errors introduced by these approximations are generally less than 4% of the local dose. However, parallel kernels can produce larger errors under extreme conditions of a short source-to-surface distance, large field size, and high photon energy. Finally, a two component x-ray source model was developed. The x-ray source is modelled as a small but intense focal spot located in the x-ray target, and a broadly distributed extrafocal component of low intensity located at the base of the flattening filter. The extrafocal component is so broad that it can be 'eclipsed' by the field-defining collimators. It accounts for up to 12% of the energy fluence on the central axis of the 6 MVp x-ray beam studied. The extrafocal source model and superposition algorithm are used together to predict the dose delivered per monitor unit in an absorber (i.e., the 'output' factor). This method can also be used predict the beam penumbra for arbitrary field shapes, including those formed with a multi-leaf collimator. It is believed that this methodology can support accurate planning of conformal radiotherapy treatments. [Scientific symbols modified in accordance with CINAHL policy] pubtype: Dissertation doctype: research Doctoral Dissertation ougenre: Unknown language: English refInfo: holdings: @attributes: islocal: N |
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