The Generation and Application

The use of beamlets as a dose calculation tool in Intensity Modulated Radiation Therapy (IMRT) treatment planning is widespread and well documented. A beamlet can simply be defined as the contribution of radiation passing through a particular geometrically defined subdivision of a given linear accelerator¿s emerging radiation field. The most common classes of algorithms used today to calculate the dose distributions deposited by beamlets are the pencil beam convolution and collapsed cone classes of algorithms. Using BEAMnrc, a Monte Carlo (MC) based radiation transport simulation software package, this book presents a novel method of calculating MC Beamlet dose distributions with a level of accuracy not achievable using the above analytic dose calculation methods. In a first application, the MC beamlet dose distributions generated in this book are used to fine-tune the output of the MC or ¿virtual¿ linear accelerator from which they are produced. This is achieved through the adjustment of individual beamlet weights to align the output of the virtual accelerator to the experimentally measured output of the modeled accelerator in water.