Development of optimized radiation therapy using external electron and photon beams
Sammanfattning: The development of new intensity modulated radiation therapy (IMRT) techniques and treatment optimization tools makes it desirable to further improve modulation methods by using scanned photon and electron beams. It is shown that the narrowest possible photon beams have the potential to improve the flexibility in dose delivery, speed up the dose delivery and improve the treatment outcome. The combination of intensity modulated electron and photon beams through the same or separate beam portals has the potential to improve the treatment outcome. The advantages of the calculated optimal dose distributions can almost always be explained in terms of traditional dose distribution concepts such as therapeutic range, exit dose and penumbra, even though the new IMRT techniques often are associated with strongly varying dose distributions. In addition, fluence and energy modulation techniques using electron beams can be used to practically eliminate the dose heterogeneities normally introduced by inhomogeneities in the patient geometry.To calculate the absolute dose in the patient per unit monitor reading it is necessary to account for all important characteristics of the beam incident on the patient. A dose per monitor unit formalism is presented capable of including all characteristics of an arbitrary beam. After the treatment head the beam is divided into two parts depending on the location in the beam phase space or with which treatment head components the particles have interacted. The dose formalism uses the concept of a generalized fluence, and is applicable to most radiation modalities used for external beam radiation therapy. The collimator-scattered contribution is calculated using collimator scatter kernels, describing the scattered contribution per unit length irradiated collimator. Collimator scatter kernels can be expressed in terms of fluence or dose, and both representations are investigated.
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