Effect of Whole Brain Radiation Therapy on the Absolute Brain Volume Loss

Abstract

number of the "success" Bernoulli trials with n Z 1,000,000,000 (ZN0) with the success probability Z Ps. The number of surviving cells after the second irradiation (ZN2) was the "success" number in the results of the Bernoulli trials for nZN1 with success probability Z Ps. The Ps was considered constant during the continuing radiotherapy with 33 irradiations, and so iterations until N33 were calculated. If N33 became 0, it was considered that all cells were dead and that local control was achieved. If N33 was not 0, it was considered to show local failure. The calculation was repeated 10,000 times. The Ps was sampled in each repeated calculation and the LCR was the number of events where all cells were dead after the radiotherapy divided by 10,000. Scenario B: The difference of Scenario B from Scenario A is that Ps is changed in each irradiation during the continuing radiotherapy, making the number of surviving cells after the second irradiation (ZN2) the summation of the "success" number in the Bernoulli trials with nZN1 and success probability Z Ps that was resampled before the second irradiation. The Ps of all irradiations is different in general in Scenario B. Other details are as in Scenario A. Results: The LCR are shown in the Table. The effect of different probability distributions appears to lessen the local control rate when the mean cell survival rate ! 0.5. Conclusion: This primitive stochastic cell survival model was able to calculate LCR.