SRS dose based on size
<2cm: 24Gy
2-3cm: 18Gy
3-4 cm: 15Gy
RTOG 90-05
Remember as May 1990
Q: To determine the maximum tolerated dose of single fraction radiosurgery in patients with recurrent previously irradiated primary brain tumors and brain metastases.
A:The maximum tolerated doses of single fraction radiosurgery were defined for this population of patients as 24 Gy, 18 Gy, and 15 Gy for tumors </= 20 mm, 21-30 mm, and 31-40 mm in maximum diameter.
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Unacceptable CNS toxicity was more likely in patients with larger tumors,
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Eligibility criteria:
1) non brainstem tumors
2) Size <4cm
3) recurrents disease were eligible
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SRS vs WBRT
SRS had better cognitive outcomes and no difference in local control
SRS vs observation
SRS better local control no difference in OS
GK Parameters
CI: Conformity index= ideal value is 1
Prescription isodose volume/ tumor volume
reflects how conformal prescription is
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HI: Heterogeneity index = ideal value<2
Max tumor dose/prescription dose
reflects how heterogeneous the dose distribution is
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GI: Gradient Index = ideal value is 3
Volume receiving 50% of prescription dose/volume receiving 100% of the prescription dose
reflects* how rapid and steep the dose fall off is*
Post-op SRS
- Within in 4 weeks
- Associated with decrease in local recurrence
- > 4 weeks 23.6 % vs < 4 weeks 2.3%
- But no impact on Overall survival
