Dosimetric comparison of intensity-modulated proton therapy and proton arc therapy for pediatric ependymoma.

Background and purpose: Proton Arc Therapy (PAT) is an emerging proton therapy treatment modality with the potential to reduce radiation exposure to healthy tissues compared to conventional Intensity-Modulated Proton Therapy (IMPT) with fewer beams. This is an attractive option for treating pediatric patients, who are vulnerable to radiation-induced side effects. There is, however, a need to investigate the redistribution of dose to the target volume and organs at risk. In this study, we therefore explored the potential of PAT in proton therapy of pediatric ependymoma.

Methods and materials: Three-field IMPT and PAT treatment plans for 10 pediatric ependymoma patients were optimized using the Eclipse treatment planning system. The PAT plans consisted of 8 fields, spanning 170 degrees. Both modalities were robustly optimized with a ± 2 mm isocenter shift and a ± 3% range uncertainty.

Results: PAT showed improved CTV coverage compared to three-field IMPT, with a distinct increase in D98%. A clear dose reduction was found for the cochleae, with median values of 9.32 Gy(Relative Biological Effectiveness [RBE]) [0.76 - 30.40 Gy(RBE)] and 18.30 Gy(RBE) [1.24 - 29.75 Gy(RBE)] for PAT and IMPT, respectively, for the right cochlea. For the left cochlea, the respective doses were 12.34 Gy(RBE) [2.81 - 30.94 Gy(RBE)] and 18.49 Gy(RBE) [4.27 - 31.97 Gy(RBE)]. No significant difference for the brain integral dose was found between the two modalities.

Interpretation: PAT can improve the dosimetric outcome of proton therapy in pediatric ependymoma patients. Organs at risk dose varied on a patient-to-patient basis; thus, individual treatment plan comparisons are recommended.