# Presentations

PO-BPC-Virtual-13 (Saturday, 4/17/2021)   [Eastern Time (GMT-4)]

Purpose: To calculate all the required parameters for avoiding necrosis using quality metrics in order to restrict 12 Gy volume below 10cc.

Methods: The dose is generally determined by the function of volume and maximum diameter of the metastatic lesion rather than the histology alone. The quality metric parameters CI, SI, GI are used to calculate normal brain volume more than 12 Gy. The fall off percentage dose is used to develop analytical formula to avoid necrosis.

Results: Fractionation can be given according to tumor volume using (1+Quotient(Vol(cc)/4)). The analytical fit of fractionated normal brain 12 Gy equivalent with ????value of 3 Gy is 12*x0.44, where x is fractionation The accuracy is within 0.5Gy with respect to LQ model. TV*((GI/sel)-1) is normal brain volume of half of prescribed dose, where TV~=TTV, where TV is Tumor Volume, TTV is Treated Tumor, GI is gradient index, sel is selectivity. Volume Accuracy calculated-Measured in %/% 7+-6, Where TV tumor volume, GI- gradient Index, sel-selectivity.Analysis from the isodose fall off resulting from the arrangement of filling cones a. Large:small as 50:50 during optimizationThe analytical formula for TMR10 algorithm is fit in the form A.k-x for calculating any required iso volume outside the tumor, where A is initial volume, k is Required iso percentage and x is constant -1.5. Similarly done for the arrangements with size of the cones 80:20, 20:80.The initial value A is a function of tumor volume given byA= 450*PIV-450, Provided Gradient Index<3, where PIV(PIV=TV/sel) is prescribed iso volume in cc, given by TV/sel. A is representative of Lower IsoVolume nearing zero IsoVolume. Experimentally max of 5% difference is obtained and selectivity is less than 0.7.

Conclusion: The above mentioned analytical formulas can be used for quick check on parameters and protecting normal brain.

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