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Intensity modulated radiation therapy with electrons using algorithm based energy/range selection methods.
Umeå University, Faculty of Medicine, Radiation Sciences, Radiation Physics.
Umeå University, Faculty of Medicine, Radiation Sciences, Oncology.
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2004 (English)In: Radiotherapy and Oncology, ISSN 0167-8140, E-ISSN 1879-0887, Vol. 73, no 2, 223-231 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND AND PURPOSE: In recent years photon intensity modulated radiation therapy (IMRT) has gained attention due to its ability to improve conformity of dose distributions. A potential advantage of electron-IMRT is that the dose fall off in the depth dose curve makes it possible to modulate the dose distribution in the direction of the beam by selecting different electron energies. This paper examines the use of a computer based energy selection in combination with the IMRT technique to optimise the electron dose distribution. MATERIALS AND METHODS: One centimetre square electron beamlets ranging from 2.5 to 50 MeV were pre-calculated in water using Monte Carlo methods. A modified IMRT optimisation tool was then used to find an optimum mix of electron energies and intensities. The main principles used are illustrated in some simple geometries and tested on two clinical cases of post-operated ca. mam. RESULTS: It is clearly illustrated that the energy optimisation procedure lowers the dose to lung and heart and makes the dose in the target more homogeneous. Increasing the energy at steep gradients compensates for lack of target coverage at beam edges and steep gradients. Comparison with a clinically acceptable four segment plan indicates the advantage of the used electron IMRT technique. CONCLUSIONS: Using an intensity optimised mix of computer selected electron energies has the potential to improve electron treatments for mastectomy patients with good target coverage and reduced dose to normal tissue such as lung and heart.

Place, publisher, year, edition, pages
2004. Vol. 73, no 2, 223-231 p.
Keyword [en]
Radiotherapy, conformal therapy, IMRT, electrons
Identifiers
URN: urn:nbn:se:umu:diva-14818DOI: 10.1016/j.radonc.2004.08.020PubMedID: 15542170OAI: oai:DiVA.org:umu-14818DiVA: diva2:154490
Available from: 2007-02-27 Created: 2007-02-27 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Energy and intensity modulated radiation therapy with electrons
Open this publication in new window or tab >>Energy and intensity modulated radiation therapy with electrons
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In recent years intensity modulated radiation therapy with photons (xIMRT) has gained attention due to its ability to reduce the dose in the tissues close to the tumour volume. However, this technique also results in a large low dose volume. Electron IMRT (eIMRT) has the potential to reduce the integral dose to the patient due to the dose fall off in the electron depth dose curves. This dose fall off makes it possible to modulate the dose distribution in the direction of the beam by selecting appropriate electron energies. The use of a computer based energy selection method was examined in combination with the IMRT technique to optimise the electron dose distribution. It is clearly illustrated that the energy optimisation procedure reduces the dose to lung and heart in a breast cancer treatment.

To shape the multiple electron subfields (beamlets) that are used in eIMRT, an electron multi leaf collimator (eMLC) is needed. However, photons produced in a conventional electron treatment head could penetrate such an added eMLC, thus producing an undesirable dose contribution. The leakage levels normally achieved are acceptable for standard single electron field treatments but could become unacceptably high in eIMRT treatments where a lot of small subfields are combined. To limit this photon contribution, the photon MLC (xMLC) was used to shield off large parts of the photon leakage.

The effect of this xMLC shielding on the reduction of photon leakage, the electron beam penumbras, and electron output (dose level), was studied using Monte Carlo methods for different electron treatment head designs. The use of helium as a mean to reduce the electron scatter in the treatment head, and thus the perturbating effect of the xMLC on electron beam penumbra and output, was also investigated.

This thesis shows that the effect of the xMLC shielding on the electron beam penumbra and output can be made negligible while still obtaining a significantly reduced x-ray leakage dose contribution. The result is a large gain in radiation protection of the patient and a better dynamic range for the eIMRT dose optimisation. For this optimisation a computer based electron energy selection method was developed and tested on two clinical cases.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2005. 48 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 947
Keyword
Radiation sciences, Radiation therapy, Conformal therapy, IMRT, Electrons, Electron treatment head, Electron MLC, Bremsstrahlung reduction, Integral dose, Penumbra, Output factor, Strålningsvetenskap
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-491 (URN)91-7305-839-4 (ISBN)
Public defence
2005-04-15, sal 244, by 7, Norrlands universitetssjukhus, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2005-04-01 Created: 2005-04-01 Last updated: 2012-04-03Bibliographically approved

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