%0 Journal Article
%T What is the optimal isodose line for stereotactic radiotherapy for single brain metastases using HyperArc?
%A Sagawa T
%A Ikawa T
%A Ohira S
%A Kanayama N
%A Ueda Y
%A Inui S
%A Miyazaki M
%A Konishi K
%J J Appl Clin Med Phys
%V 0
%N 0
%D 2024 Jun 11
%M 38863310
%F 2.243
%R 10.1002/acm2.14408
%X <B>OBJECTIVE: </B>The study aimed to investigate the optimal isodose line (IDL) in linear accelerator-based stereotactic radiotherapy for single brain metastasis, using HyperArc. We compared the dosimetric parameters for target and normal brain tissue among six plans with different IDLs.<BR><B>METHODS: </B>This study included 30 patients with single brain metastasis. We retrospectively generated six plans for each tumor with different IDLs (80%, 70%, 60%, 50%, 40%, and 33%) using HyperArc. All treatment plans were normalized to the prescription dose of 35 Gy in five fractions which was covered by 95% of the planning target volume (PTV), defined by adding a 1.0 mm margin to the gross tumor volume (GTV). The dosimetric parameters were compared among the six plans.<BR><B>RESULTS: </B>For GTV > 0.1 cm3, the ratio of brain-GTV volumes receiving 25 Gy to PTV (V25Gy/PTV) was significantly lower at IDL 40%-70% than at IDL 80% and 33% (p < 0.01, retrospectively). For GTV < 0.1 cm3, V25Gy/PTV decreased continuously as IDL decreased. The values of D99% and D80% for GTV increased with decreasing IDL. An IDL of 50% or less was required to achieve D99% of greater than 43 Gy and D80% of greater than 50 Gy. The mean values of D99% and D80% for IDL 50% were 44.3 and 51.9 Gy.<BR><B>CONCLUSIONS: </B>The optimal IDL is 40%-50% for GTV > 0.1 cm3. These lower IDLs could increase D99% and D80% of GTV while lowering V25Gy of normal brain tissue, which may help reduce the risk of radiation necrosis and improve local control.