Investigation of irregular radiation field-based proton therapy using conformal dose layer stacking method

Background: Dose modulaton is a key factor in practcal proton therapy. This study investgates the dose modulaton methodology of irregular radiaton field (IRF)-based proton therapy using forward radiaton treatment planning and conformal dose layer stacking (CDLS) methods. Materials and Methods: The geometric configuraton of a virtual mult-leaf system was constructed to generate IRFs during Monte Carlo simulatons. Two patent geometries-lymphatc metastasis and brain tumors-were configured to investgate the dosimetric feasibility and applicatons of IRF-based proton therapy in ideal patent anatomies. The investgated tumors were divided into slices perpendicular to proton beam axis. Segments were designed to be conformal to the profiles of these tumor slices. Conformal dose layers were produced by modulatng the proton intensites and energies of the predesigned segments. Then, these dose layers were stacked throughout the tumors to obtain sufficient and conformal tumor doses. Results: From the proposed IRF-based proton therapy, tumors with 4-7 cm extents along the depth directon could be treated with fewer than 10 segments. The lymphatc metastasis and brain tumors were sufficiently covered by 95% dose lines, while appropriate distal and proximal dose conformites were achieved. The maximum tumor doses did not exceed 110%. Conclusions: Theoretcally, the proposed IRF-based proton therapy using forward planning and CDLS methods is feasible from the viewpoint of dosimetry. This study can serve as a foundaton for future investgatons of potental proton therapy methods based on fast conformal dose layer stacking using radiaton fields with irregular shapes.