Radiosurgical dose selection for brain metastasis.
ABSTRACT Dose selection for brain metastasis radiosurgery is based largely upon clinical data obtained over a half century of radiosurgical treatments for various benign and malignant conditions. It is expected that within the entire radiosurgical process, the step of dose selection will occur within a framework of accurate calibration of dose delivery and accurate and detailed imaging for planning the radiosurgical treatment. Brain metastasis radiosurgery should seek lifelong, uncomplicated control. A low radiosurgery dose that will not control the tumor will not achieve this therapeutic goal, and neither will a radiosurgery dose that controls the tumor but causes symptomatic brain radiation necrosis. The volume of the metastasis being targeted and the volume of normal tissues receiving substantial radiosurgical doses are of paramount importance in dose selection. A high degree of conformality of the high-dose radiosurgical treatment volume to the metastasis has been shown to decrease complications, as does a steep dose gradient between the metastasis and adjacent normal brain tissue. A dose-escalation trial conducted by the Radiation Therapy Oncology Group that differentially dose-escalated radiosurgical doses for tumors of different sizes established that single-fraction doses between 15 and 24 Gy are relatively safe in patients who have received prior fractionated radiation therapy to the brain. Corresponding data do not exist for patients who are treated with primary radiosurgery and no whole brain radiation therapy. A dose-escalation trial for three-fraction radiosurgical treatment of brain metastases is being conducted at Stanford. Knowledge of prior whole brain radiation therapy treatment details, including the dose delivered and the time interval since that treatment was given may affect the choice of radiosurgical dose, as may recent administration of systemic, radiation-potentiating chemotherapy. Physician knowledge and careful judgment, together with careful treatment planning and delivery can minimize the risks associated with brain metastasis radiosurgery.
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ABSTRACT: Purpose: To characterize the influence of perfusion on the measurement of diffusion changes over time when ADC is computed using standard two-point methods. Materials and methods: Functional diffusion maps (FDMs), which depict changes in diffusion over time, were compared with rCBV changes in patients with brain tumors. The FDMs were created by coregistering and subtracting ADC maps from two time points and categorizing voxels where ADC significantly increased (iADC), decreased (dADC), or did not change (ncADC). Traditional FDMs (tFDMs) were computed using b = 0,1000 s/mm(2). Flow-compensated FDMs (fcFDMs) were calculated using b = 500,1000 s/mm(2). Perfusion's influence on FDMs was determined by evaluating changes in rCBV in areas where the ADC change significantly differed between the two FDMs. Results: The mean ΔrCBV in voxels that changed from iADC (dADC) on the tFDM to ncADC on the fcFDM was significantly greater (less) than zero. In addition, mean ΔrCBV in iADC (dADC) voxels on the tFDM was significantly higher (lower) than in iADC (dADC) voxels on the fcFDM. Conclusion: The ability to accurately identify changes in diffusion on traditional FDMs is confounded in areas where perfusion and diffusion changes are colocalized. Flow-compensated FDMs, which use only non-zero b-values, should therefore be the standard approach.Journal of Magnetic Resonance Imaging 10/2013; 38(4). DOI:10.1002/jmri.24042 · 3.21 Impact Factor