Sharpening the edge in pencil-beam proton therapy: an aftermarket collimation system to better spare normal tissue during radiation treatment

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Abstract/Summary Proton arc therapy has lagged behind photon arc therapy, which is now commonplace in the clinic, due mostly to slow proton energy switching times which make treatment durations impractical. Fast energy modulation systems are now clinically available, and, by applying delivery optimization tools that intelligently change beam energy as the gantry rotates, proton arc therapy is on the verge of becoming a clinical reality that can improve plan delivery speed and robustness to range uncertainties relative to conventional fixed field proton therapy. Without dynamic lateral beam collimation, however, proton arc therapy tumor dose conformity will be inferior to fixed field collimated proton therapy plans. This is a major problem especially for brain and head and neck cancer patients whose normal tissues could be spared significant radiation dose using beam collimation. The long-term goal is to develop the next generation of pencil beam scanning (PBS) proton therapy delivery systems that maximize the achievable tumor dose conformity, robustness, and delivery speed. The overall objective of this proposal is to develop dynamically collimated arc-based PBS by expanding the dynamic collimation system (DCS) technology developed in the first part of this R37 proposal, providing the capability for rapid, tumor-conformal delivery of dose distributions that are more robust to uncertainties in Bragg Peak position placement than those delivered with fixed field proton therapy. The rationale for this project is that superior treatment plans will result from the combination of energy-specific collimation and rotational arc delivery than either of the individual technologies, thus improving the quality of care of proton therapy. Guided by strong preliminary data from our in-silico treatment planning studies and constructed DCS prototype, development of collimated proton arc therapy will be carried out by pursuing three specific aims: 1) develop arc-based treatment planning and delivery methods for dynamically collimated proton therapy, 2) enhance the clinical DCS prototype to perform proton arc treatments, and 3) adapt existing treatment verification methodologies for quality assurance. Under specific aim 1, established multi-field treatment planning techniques, both dose calculation and optimization, will be extended to include the optimization of trimmer and energy sequencing for the case of a rotating gantry. Under specific aim 2, real-time feedback mechanisms will be incorporated to monitor and synchronize gantry angle to the sequencing of the high-speed trimmer blades. Under specific aim 3, experimental and computational techniques will be developed and demonstrated to enable successful commissioning of dynamic collimated proton arc therapy. The research proposed in this application is innovative because it represents a new combination of two promising and synergistic technologies: dynamic collimation and proton arc therapy. This contribution is expected to be significant since the two technologies together can preserve conformity improvements gained by collimated PBS while adding the robustness and delivery speed benefits achievable with arc therapy, improving treatment outcomes.