Single- and Multifraction Stereotactic Radiosurgery Dose/Volume Tolerances of the Brain

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The risk of radionecrosis after SRS and fSRS can be modeled as a function of dose and volume treated. The use of fSRS appears to reduce risks of radionecrosis for larger treatment volumes relative to SRS.

Int J Radiat Oncol Biol Phys 2021 May 1;110(1):68-86. doi: 10.1016/j.ijrobp.2020.08.013. Epub 2020 Sep 11.

Single- and Multifraction Stereotactic Radiosurgery Dose/Volume Tolerances of the Brain

Michael T Milano 1Jimm Grimm 2Andrzej Niemierko 3Scott G Soltys 4Vitali Moiseenko 5Kristin J Redmond 6Ellen Yorke 7Arjun Sahgal 8Jinyu Xue 9Anand Mahadevan 2Alexander Muacevic 10Lawrence B Marks 11Lawrence R Kleinberg 6Affiliations expand

Abstract

Purpose: As part of the American Association of Physicists in Medicine Working Group on Stereotactic Body Radiotherapy investigating normal tissue complication probability (NTCP) after hypofractionated radiation therapy, data from published reports (PubMed indexed 1995-2018) were pooled to identify dosimetric and clinical predictors of radiation-induced brain toxicity after single-fraction stereotactic radiosurgery (SRS) or fractionated stereotactic radiosurgery (fSRS).

Methods and materials: Eligible studies provided NTCPs for the endpoints of radionecrosis, edema, or symptoms after cranial SRS/fSRS and quantitative dose-volume metrics. Studies of patients with only glioma, meningioma, vestibular schwannoma, or brainstem targets were excluded. The data summary and analyses focused on arteriovenous malformations (AVM) and brain metastases.

Results: Data from 51 reports are summarized. There was wide variability in reported rates of radionecrosis. Available data for SRS/fSRS for brain metastases were more amenable to NTCP modeling than AVM data. In the setting of brain metastases, SRS/fSRS-associated radionecrosis can be difficult to differentiate from tumor progression. For single-fraction SRS to brain metastases, tissue volumes (including target volumes) receiving 12 Gy (V12) of 5 cm3, 10 cm3, or >15 cm3 were associated with risks of symptomatic radionecrosis of approximately 10%, 15%, and 20%, respectively. SRS for AVM was associated with modestly lower rates of symptomatic radionecrosis for equivalent V12. For brain metastases, brain plus target volume V20 (3-fractions) or V24 (5-fractions) <20 cm3 was associated with <10% risk of any necrosis or edema, and <4% risk of radionecrosis requiring resection.

Conclusions: The risk of radionecrosis after SRS and fSRS can be modeled as a function of dose and volume treated. The use of fSRS appears to reduce risks of radionecrosis for larger treatment volumes relative to SRS. More standardized dosimetric and toxicity reporting is needed to facilitate future pooled analyses that can refine predictive models of brain toxicity risks.

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