Proton therapy delivery: what is needed in the next ten years?

Abstract

Proton radiation therapy has been used clinically since 1952, and major advancements in the last 10 years have helped establish protons as a major clinical modality in the cancer-fighting arsenal. Technologies will always evolve, but enough major breakthroughs have been accomplished over the past 10 years to allow for a major revolution in proton therapy. This paper summarizes the major technology advancements with respect to beam delivery that are now ready for mass implementation in the proton therapy space and encourages vendors to bring these to market to benefit the cancer population worldwide. We state why these technologies are essential and ready for implementation, and we discuss how future systems should be designed to accommodate their required features.

Figure 1.

A robust optimized IMPT treatment plan for a prostate (A) compared to a SPArc plan (B). The dose distribution advantages are illustrated in the DVH (C) and dose difference (D) panels. (Used with permission from Ding et al. DVH, dose–volume histogram; IMPT, intensity-modulated proton therapy; SPArc, spot-scanning proton arc.

Figure 2.

A proton radiograph of a CATHPHAN line pair phantom obtained with the ProtonVDA system at our facility. A 0.2 mm-thick plastic tape used to hold the phantom in place is clearly visible in the image: see the horizontal streak across the image.

Figure 3.

A two-field mediastinal plan reoptimized for two different isocenters using the same optimization constraints and objectives. The isocenter for the second plan was shifted by +10 mm in X, Y, and Z, and a 1° roll was applied relatively to the first plan. The total number of monitor units per energy layer for the two plans for the second beam is compared in the bottom right panel. The DVH curves are compared in the upper right panel. DVH, dose–volume histogram

Figure 4.

Penumbra (P) as a function of proton range (R) for a spot-scanning beam with MLC collimation and uniform spot weights (square) and for spot scanning beam without MLC and variable spot weight (circle). Data are provided for 3 Bragg peak depths (4, 10 and 20 cm) corresponding to proton energies of 72, 118 and 174 MeV, respectively. Analytical fits to the data are provided in order to estimate the crossing point at R. 17.5 cm, corresponding to a proton energy of 159 MeV. (Used with permission from Bues et al. MLC, multi leaf collimator.