Treating superficial tumors with megavoltage electron beams often requires usage of water equivalent bolus material for shifting the dose build-up region to the surface of the patient. Utilizing 3D printed boli not only improves physical fitting to the patient, but improved conformity of the prescribed dose to PTV can be achieved by further modulating the bolus shape. In Modulated Electron Radiation Therapy (MERT) the shape of the bolus is being optimized resulting in a 3D printed non-uniform thickness device which ultimately modulates the electron beam conforming the prescribed dose to the distal part of the PTV.
However, employing modulated electron bolus (MEB) may introduce a certain trade-off between the resulting dose conformity and homogeneity to the PTV due to the scattered component of the electron radiation originating from the modulated surface of the bolus.
Since beam energy, field aperture, optimization of the plan and bolus material are all pre-set for a particular electron treatment plan, the shape of the modulated surface of the bolus represents a feature preferred to be further optimized resulting in less scattered radiation and the overall reduction of hot-spots while maintaining the level of dose conformity of the original MEB treatment plan.