SU-E-T-646: Feasibility Study of Proton Arc Therapy for the Treatment of Para-Aortic Lymph Node Tumor

To test feasibility of proton arc therapy (PAT) in the treatment of para-aortic lymph node tumor and compare its dosimetric properties with advanced radiotherapy techniques such as intensity modulated radiation therapy (IMRT) and conventional 3D conformal proton beam therapy (PBT).

The treatment plans for para-aortic lymph node tumor were planned for 9 patients treated at our institution using IMRT, PBT, and PAT. Feasibility test and dosimetric evaluation were based on comparisons of dose volume histograms (DVHs) which reveal mean dose, D30%, D60%, D90%, V30%, V60%, V90%, organ equivalent doses (OEDs), normal tissue complication probability (NTCP), homogeneity index (HI) and conformity index (CI).

The average doses delivered by PAT to the liver, kidney, small bowel, duodenum, stomach were 7.6%, 3%, 17.3%, 26.7%, and 14.4%, of the prescription dose (PD), respectively, which is higher than the doses delivered by IMRT (0.4%, 7.2%, 14.2%, 15.9%, and 12.8%, respectively) and PBT (4.9%, 0.5%, 14.12%, 16.1% 9.9%, respectively). The average homogeneity index and conformity index of tumor using PAT were 12.1 and 1.21, respectively which were much better than IMRT (21.5 and 1.47, respectively) and comparable to PBT (13.1 and 1.23, respectively). The Result shows that both NTCP and OED of PAT are generally lower than IMRT and PBT.

This study demonstrates that PAT is better in target conformity and homogeneity than IMRT and PBT but worse than IMRT and PBT for most of dosimetric factor which indicate that PAT is not recommended for the treatment of para-aortic lymph node tumor.