Abstract
Purpose:To develop a delivery‐efficient proton spot‐scanning arc therapy technique with robust plan quality.Methods:We developed a Scanning Proton Arc(SPArc) optimization algorithm integrated with (1)Control point re‐sampling by splitting control point into adjacent sub‐control points; (2)Energy layer re‐distribution by assigning the original energy layers to the new sub‐control points; (3)Energy layer filtration by deleting low MU weighting energy layers; (4)Energy layer re‐sampling by sampling additional layers to ensure the optimal solution. A bilateral head and neck oropharynx case and a non‐mobile lung target case were tested. Plan quality and total estimated delivery time were compared to original robust optimized multi‐field step‐and‐shoot arc plan without SPArc optimization (Arcmulti‐field) and standard robust optimized Intensity Modulated Proton Therapy(IMPT) plans. Dose‐Volume‐Histograms (DVH) of target and Organ‐at‐Risks (OARs) were analyzed along with all worst case scenarios. Total delivery time was calculated based on the assumption of a 360 degree gantry room with 1 RPM rotation speed, 2ms spot switching time, beam current 1nA, minimum spot weighting 0.01 MU, energy‐layer‐switching‐time (ELST) from 0.5 to 4s.Results:Compared to IMPT, SPArc delivered less integral dose(−14% lung and −8% oropharynx). For lung case, SPArc reduced 60% of skin max dose, 35% of rib max dose and 15% of lung mean dose. Conformity Index is improved from 7.6(IMPT) to 4.0(SPArc). Compared to Arcmulti‐field, SPArc reduced number of energy layers by 61%(276 layers in lung) and 80%(1008 layers in oropharynx) while kept the same robust plan quality. With ELST from 0.5s to 4s, it reduced 55%–60% of Arcmulti‐field delivery time for the lung case and 56%–67% for the oropharynx case.Conclusion:SPArc is the first robust and delivery‐efficient proton spot‐scanning arc therapy technique which could be implemented in routine clinic. For modern proton machine with ELST close to 0.5s, SPArc would be a popular treatment option for both single and multi‐room center.
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