Dosimetric comparison of Helical Tomotherapy and Gamma Knife Stereotactic Radiosurgery for single brain metastasis

The targeting MRI data set from the GKSRS were used for tomotherapy planning. Five patients with single brain metastasis treated with GKSRS were re-planned in the HT planning station using the same prescribed doses. There was no expansion of the GTV to create the PTV. Sub-volumes were created within the PTV and prescribed to the maximum dose seen in the GKSRS plans to imitate the hot spot normally seen in GKSRS. The PTV objective was set as a region at risk in HT planning using the same prescribed dose to the PTV periphery as seen in the corresponding GKSRS plan. The tumor volumes ranged from 437–1840 mm3.Conformality indices are inconsistent between HT and GKSRS. HT generally shows larger lower isodose line volumes, has longer treatment time than GKSRS and can treat a much larger lesion than GKSRS. Both HT and GKSRS single fraction dose-volume toxicity may be prohibitive in treating single or multiple lesions depending on the number and the sizes of the lesions.Based on the trend for larger lower dose volumes and more constricted higher dose volumes in HT as compared to GKSRS, dosimetric equivalency was not reached between HT and GKSRS.For patients with single brain metastasis, the addition of surgical resection or radiosurgery to whole brain radiation therapy improves survival [1,2]. In Gamma Knife？ stereotactic radiosurgery (GKSRS), a single fraction of radiation is used to treat metastatic lesions in the brain. There appears to be a fine line between treatment success and the predominant form of late-toxicity from GKSRS, radiation necrosis [3]. Helical tomotherapy is an emerging technology based mainly on the linkage and integration of known and widely-used technology in radiation oncology into a single system, i.e. a linear accelerator and computed tomography, allowing precise daily targeting of IMRT using megavoltage CT (MVCT) guidance.In this study we will compare dosimetric plans between GKSRS and single fraction helical tomotherapy (HT) for five patients wi