Dosimetric Assessment Of Intraoperative Radiation Therapy Utilizing Xoft Axxent Electronic Brachytherapy for Intracranial Tumors

Abstract Purpose: The present study aimed to evaluate low-energy balloon electronic intraoperative radiation therapy (IORT) in terms of dosimetry, gradient indices (GI) and normal tissue complication probability (NTCP) for the treatment of intracranial tumors. Materials and Methods: Non-coplanar volumetric modulated arc therapy (ncVMAT) plans were generated for 23 patients with a single brain lesion in order to cover 95% of target volume with a prescription dose 20 Gy in 1 fraction. All CT data and structure sets were imported to BrachyCare treatment planning system to calculate IORT dose based on atlas plans. Based on two approaches, critical structure’s dose, gradient indices and NTCP values for Brain-PTV were analyzed to evaluate IORT in terms of radiation dosimetry. Results: The mean Dmax of brainstem is (4.43 ± 3.13) Gy in ncVMAT plans, and the dose by IORT delivery is (3.27 ± 2.80) Gy. For eyes, lenses and optic nerves, IORT delivery dose is maximum 65% less than ncVMAT delivery dose and this difference is statistically significant for these structures (p≤0.05). The GI value is 2.65 and 2.24 in ncVMAT and IORT techniques respectively. In both approaches NTCP value meet the criterion which is ≤1.0. Conclusion: Based on results, low energy Xoft Axxent eBX system is better to reduce OARs dose especially when the target is in close proximity to critical structures. Moreover, this system provides better control in low dose region at outside of the target and it results better GI and less probability to radiation necrosis. Considering the dosimetric assessments, IORT is safe to treat single target high grade primary central nervous system (CNS) tumors and intracranial metastatic disease.