Fast robust optimization of proton PBS arc therapy plans using early energy layer selection and spot assignment

Abstract

Objective: Proton pencil-beam scanning arcs (PBS arcs) have gained much attention during the past years, due to its potential for increased clinical benefit compared to conventional proton therapy. Previous studies on PBS arcs have primarily been focused on plan quality, and lately efforts have been made to reduce the delivery time. However, the methods presented so far suffer from slow optimization processes. Approach: We present a new method for fast robust optimization of PBS arc plans. The new method assigns a single energy layer per discretized direction prior to spot weight optimization and reduces the number of initial spots considerably compared to conventional methods. We used the new method for three prostate cancer patients with a prescribed dose to the CTV of 77 GyRBE in 35 fractions. For each of the patients, four plans were created: 2-beam IMPT (2IMPT), 1-beam PBS arc (1Arc), 1-beam PBS arc without focus on reducing upward energy jumps (1Arc_unseq) and two-beam PBS arc (2Arc). Main results: All PBS arc plans show a reduced integral dose compared to their respective 2IMPT plans. In the nominal case, the average CTV D98 and D2 metrics over the three patients were best for the 2Arc, followed by 2IMPT (D98/D2: 7523/7986 cGyRBE (2IMPT), 7478/7984 cGy (1Arc), 7486/7951 cGy (1Arc_unseq), 7531/7951 cGyRBE (2Arc)). The average robust target coverage in terms of V95 of the voxelwise minimum dose distribution (evaluated over 42 scenarios) was: 98.0% (2IMPT), 88.6% (1Arc), 92.5% (1Arc_unseq), 97.3% (2Arc). The optimization time, including spot selection and spot dose computation, is longest for the 2Arc plan, but is below 6 minutes for all patients. The maximum estimated delivery time for all types of arc plans is just above 5 minutes. Significance: The ability for efficient treatment planning constitutes an important step towards clinical introduction of proton PBS arcs.

Beam angle optimization for proton therapy via group‐sparsity based angle generation method

“…Spot-scanning arc therapy is an emerging proton modality 56 and rapidly developing [57][58][59][60] as a viable alternative to fixed-beam IMPT that can potentially offer a combination of advantages in plan quality and delivery efficiency, compared to fixed beam IMPT. But currently fixed-beam IMPT remains to be the mainstream for proton treatments, for which BAO is still relevant.…”

Bi-criteria Pareto optimization to balance irradiation time and dosimetric objectives in proton arc therapy

“…In this study, uncertainties have voluntarily been neglected in the treatment planning optimization and, consequently, no robustness evaluation was performed. However, robustness planning and evaluation are of utmost importance for proton therapy due to dose distributions sensitivity to the uncertainties of the position of the Bragg peaks (Albertini et al 2011, Fredriksson 2012. However, the integration of robustness in proton arc therapy treatment optimization is extremely difficult and also computationally too intensive at this time, when using optimizers with no restrictive pre-selection of the energy layers, i.e., using the full available set of degrees of freedom.…”

“…The other previous published paper, however, do not directly optimize the energy sequence simultaneously with the spot intensities yet. For instance, RaySearch (RaySearch Laboratories AB, Stockholm, Sweden) has recently published a method of selecting energy layers and spots, as a proof of concept coined ELSA (Early Layer and Spot Assignment), prior to spot weight optimization (Engwall et al 2022). Additionally, Ding et al (2016) developed the Spot-Scanning Proton Arc (SPArc) algorithm, an iterative greedy approach based on robust optimization.…”

FLASH instead of proton arc therapy is a more promising advancement for the next generation proton radiotherapy

“…Multiple international consortiums have been established, aiming to join‐force in pushing the technique forward 66,67 . The proton system manufacturers such as IBA are taking the key steps to such development, while the Treatment Planning System (TPS) providers such as RaySearch and Elekta are also providing the proton arc module in support of future clinical implementations 68,69 . Additionally, many ideas have been formed to optimize particle arc therapy in a more efficient way 70–75 .…”

“…66,67 The proton system manufacturers such as IBA are taking the key steps to such development, while the Treatment Planning System (TPS) providers such as RaySearch and Elekta are also providing the proton arc module in support of future clinical implementations. 68,69 Additionally, many ideas have been formed to optimize particle arc therapy in a more efficient way. [70][71][72][73][74][75] In recent years, we saw exponentially increased publications on the topic of particle arc therapy.These encouraging trends and global efforts might suggest that the proton RT is at an important turning point, similar to the invention of VMAT in the 2000s in the photon world.…”