Optimization of 3D conformal electron beam therapy in inhomogeneous media by concomitant fluence and energy modulation

Abstract

The possibilities of using simultaneous fluence and energy modulation techniques in electron beam therapy to shape the dose distribution and almost eliminate the influences of tissue inhomogeneities have been investigated. By using a radiobiologically based optimization algorithm the radiobiological properties of the tissues can be taken into account when trying to find the best possible dose delivery. First water phantoms with differently shaped surfaces were used to study the effect of surface irregularities. We also studied water phantoms with internal inhomogeneities consisting of air or cortical bone. It was possible to improve substantially the dose distribution by fluence modulation in these cases. In addition to the fluence modulation the most suitable single electron energy in each case was also determined. Finally, the simultaneous use of several preselected electron beam energies was also tested, each with an individually optimized fluence profile. One to six electron energies were used, resulting in a slow improvement in complication-free cure with increasing number of beam energies. To apply these techniques to a more clinically relevant situation a post-operative breast cancer patient was studied. For simplicity this patient was treated with only one anterior beam portal to clearly illustrate the effect of inhomogeneities like bone and lung on the dose distribution. It is shown that by using fluence modulation the influence of dose inhomogeneities can be significantly reduced. When two or more electron beam energies with individually optimized fluence profiles are used the dose conformality to the internal target volume is further increased, particularly for targets with complex shapes.

Can Photon IMRT be improved by combination with mixed electron and photon techniques?

“…This property has been used in the treatment of breast cancer with segmented electron beams (9,10), a 3-D bolus technique (11), and intensity modulated electron beams (12,13). However, the depth dependent penumbra, the small effective field size, and the high skin dose limit the use of pure electron therapy in many other clinical situations.…”

Introduction to passive electron intensity modulation

“…MERT utilizes multiple intensity modulated electron fields of varying angle and energy 35–39 . Ma et al reports MERT being delivered using an eMLC 39 ; however, PRIME might be able to be used for MERT.…”

Monte Carlo electron source model validation for an Elekta Precise linac

“…Dose calculation algorithms used for electron dose calculations, such as 3-D pencil beam algorithms, [13][14][15] have been proven not to be accurate enough, particularly in heterogeneous media, where the electron dose distribution can change markedly. One of the challenges of MC electron beam simulations is to benchmark this data against measurements as the simulation requires more detailed and accurate treatment head data.…”