Pencil beam scanning proton lattice radiotherapy: single-field versus multi-field optimization

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Pencil beam scanning (PBS) proton lattice radiotherapy (LRT) is an advanced technique for treating bulky tumors.
• Optimizing dose distribution is crucial for maximizing therapeutic ratio in LRT.

Purpose of the Study:

• To compare the clinical advantages and disadvantages of single-field optimization (SFO) versus multi-field optimization (MFO) for PBS proton LRT.
• To assess plan quality and robustness for both optimization techniques.

Main Methods:

• Retrospective planning for 12 patients with bulky head-and-neck, thoracic, or abdominal tumors using RayStation (v2023B).
• Dose prescription: 18 Gy to each of 6-8 vertices and 3 Gy to the gross tumor volume (GTV).
• Evaluation of dosimetric parameters (GTV Dmean, D95%, gEUD; vertex D90%; PVDR; skin D1%) and plan robustness under varying scenarios.

Main Results:

• Both SFO and MFO achieved a peak-to-valley dose ratio (PVDR) near 4.
• Multi-field optimization (MFO) significantly reduced skin dose (D1%) by 25% compared to single-field optimization (SFO).
• MFO plans showed greater deviations in PVDR, GTV Dmean, and skin D1% under robust analysis compared to SFO plans.

Conclusions:

• Both SFO and MFO are clinically implementable with current proton therapy technology and planning systems.
• SFO demonstrates superior plan robustness, maintaining optimized metrics under treatment uncertainties.
• MFO offers an advantage in sparing critical organs, particularly reducing skin dose.