Three-fraction CyberKnife radiotherapy for brain metastases in critical areas: referring to the risk evaluating radiation necrosis and the surrounding brain volumes circumscribed with a single dose equivalence of 14 Gy (V14)

Abstract

The efficacy and toxicity of three-fraction CyberKnife radiotherapy were evaluated in patients with brain metastases in critical areas. One hundred and fifty-nine metastases in 145 patients including tumors >10 cm3 were treated with three-fraction CyberKnife radiotherapy with a median marginal dose of 27 Gy at a median prescribed isodose of 60%. Changes in the neurological manifestations, local tumor control and adverse effects were investigated after treatment. The surrounding brain volumes circumscribed with 23.1 Gy (single dose equivalence of 14 Gy: V14) were measured to evaluate the risk of adverse effects. Neurological manifestations, such as motor weakness, visual disturbances and aphasia improved in 26 of 97 patients (26.8%). Local tumor control was obtained in 137 of 143 metastases (95.8%) during a median follow-up of 7 months. Nine patients had symptomatic edema and three of them (2.1%) required surgical resection because of radiation necrosis. The V14 of these patients was 4.6–31.5 cm3. There were 35 lesions with a V14 of 7 cm3 or more and three of them developed extensive brain edema due to radiation necrosis. None of the patients with a V14 of <7 cm3 exhibited edema requiring an operation. We therefore conclude that a high rate of local tumor control and low rates of complications are obtained after three-fraction CyberKnife radiotherapy for metastases in critical areas. The V14 of the surrounding brain therefore seems to be a useful indicator for the risk evaluation of radiation necrosis in patients with larger metastases.

Dose-volume prediction of radiation-related complications after hypofractionated conformal radiotherapy for brain metastases in critical areas

“…[11][12]. In the present study based on data for 470 lesions, the statistical analyses of risk factors for complications showed the V14 to be a significant factor according to the univariate and multivariate analyses.…”

“…Morbidity, and even mortality, has been reported after fractionated radiosurgery for large brain metastases [9][10]. We previously reported the efficacy and toxicity of three-fraction and five-fraction radiotherapy for brain metastases in critical areas and recommended that larger fraction numbers should be selected for large brain metastases based on the dose-volume effects on the surrounding brain circumscribed with a single dose equivalent (SDE) of 14 Gy (V14: defined based on experiences of radiosurgery) to avoid radiation necrosis [11][12].…”

Five-fraction CyberKnife radiotherapy for large brain metastases in critical areas: impact on the surrounding brain volumes circumscribed with a single dose equivalent of 14 Gy (V14) to avoid radiation necrosis

“…The V14 was calculated in all 85 lesions to evaluate the risk of radiation necrosis, as in three-fraction radiotherapy. The results using 28.8 Gy seemed to be better than those using 30 Gy for estimating the complication risk in five-fraction treatment, and also appeared to be compatible with the results using 23.1 Gy in three-fraction radiotherapy [8]. The exact calculation method that should be used to obtain the proper single dose equivalent of 14 Gy in five-fraction radiotherapy has not yet been established [24].…”

The impact of CyberKnife's prescription isodose percentage on intracranial target planning

“…For CK dosimetric planning, some authors used median PIPs of about 79%, (2) while others believed values near 73% may be more appropriate (3) . Inoue et al (4) used 60% PIP for a three‐fractioned course of 27 Gy. Our current data evaluated a wider range of PIPs compared to these published studies.…”