ESTRO 2024 - Abstract Book

S4704

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

Purpose/Objective:

Proton spatially fractionated RT (SFRT) can potentially synergize the unique advantages from using proton Bragg peak and SFRT peak-valley dose ratio (PVDR) to spare normal tissues. Uniform-target-dose (UTD) proton GRID is a proton SFRT modality that can be clinically desirable or conveniently adopted for its UTD resembling target dose distribution in conventional proton RT (CONV). However, UTD proton GRID is not clinically used currently, for which a very hurdle is the lack of effective treatment planning method. This work will develop a novel treatment planning method using scissor beams (SB) for UTD proton GRID, with the joint optimization of PVDR and dose objectives.

Material/Methods:

The principle of the SB method to modulate the spatial dose distribution in normal tissues is illustrated in Fig. 1(b). For the demonstration purpose, conventional proton RT method (CONV) is shown in Fig.1(a) serving as the comparison benchmark, in which two planes of interest (the OAR plane and the CTV plane) are irradiated with proton beamlets (called the primary beam (PB)). As a result of uniform irradiation, both OAR and CTV planes have uniform dose, i.e., the peak dose. Compared to CONV, SB has two primary changes as shown in Fib. 1(b): (1) in Step 1, PB is essentially halved, i.e., the beamlets are interleaved, so that the OAR has the peak-valley dose pattern (however, the CTV also has the valley dose); (2) in Step 2, the complementary beam (CB) is added with half complementary beamlets to fill in the valley-dose positions at CTV during Step 1, so that the CTV dose becomes uniform, while on the other hand, CB is angled slightly from PB, i.e., θ=tan -1 d/D (d is the spot spacing, i.e., the center-to-center distance of adjacent spots and D is the distance from the OAR plane to the CTV plane, as shown in Fig. 1(a)) so that the OAR still has the peak-valley dose pattern. A treatment planning method with PVDR optimization via the joint total variation and L1 (TVL1) regularization is developed to jointly optimize PVDR and dose objectives. The plan optimization solution is obtained using iterative convex relaxation algorithm.