Segmented field electron conformal therapy planning algorithm

Purpose: Segmented-field electron conformal therapy (SFECT) is rarely used, or if used, used sub optimally, primarily due to inadequate tools for its planning. The development of SFECT planning tools could help begin to bring electron therapy to the same level of sophistication as x-ray and proton therapy, resulting in greater consideration by radiation oncologists. The purpose of this work was to develop a forward planning algorithm that will improve segmentation of the SFECT treatment field. It was hypothesized that a forward planning algorithm can produce segmented-field ECT fields that improve dose conformity as the number of beam energies is increased from one to five using the Varian beam set (6, 9, 12, 16, and 20 MeV). Methods: A planning algorithm that allowed each field segment to have its own energy, shape, size, and weighting was developed. The planning algorithm developed an initial plan and then went through several iterations of re-planning based on the dose distributions of each previous plan in order to converge the 90% dose surface to the distal PTV surface. The planning algorithm was used to develop SFECT plans for six hypothetical PTVs and two head and neck patient PTVs. These plans were compared to single-energy plans developed by the same planning algorithm. Results: Conformity improved little beyond allowing three energies due to energy overlap and field-size restrictions. For the hypothetical PTVs, non-PTV treated to 90% of the prescribed dose was reduced compared to the single-energy plans, resulting in improved dose conformity, supporting the hypothesis. The improved conformity came at the expense of increased dose heterogeneity within the PTV. One of the patient plans improved in conformity, supporting the hypothesis and indicating the planning algorithm has the potential to plan patient cases. The other patient case did not improve in conformity and therefore did not support the hypothesis. Conclusion: The planning algorithm was successful in developing plans that improved conformity while still treating the PTV to prescription dose. The planning algorithm has the potential to plan patient SFECT treatments. Future improvements to the algorithm may improve its ability to plan patient cases