Calculation of isoeffective doses and the alpha/beta value by comparing results following radiosurgery and radiotherapy for arteriovenous malformations of the brain.

OBJECT

The authors sought to assess the relationship between obliteration rate and different dose parameters following fractionated radiotherapy for arteriovenous malformations (AVMs). A comparison of the results of radiosurgery and radiotherapy for AVMs was made to calculate the best fit alpha/beta value, which would then be used as a model for predicting the treatment outcome, independent of the number of fractions applied.

METHODS

Data from 1453 patients were analyzed: 1154 treated with radiosurgery and 300 with fractionated radiotherapy. The relationships between dose and obliteration rate after 3 years were calculated, and the best fit curve to the empirical results was defined. The higher the dose per fraction, biologically effective dose, and the lower the total dose, the higher the obliteration rate. The isoeffective doses when comparing radiotherapy and radiosurgery independent of the alpha/beta value could not be defined. The dose per fraction had the best predictive value, independent of the number of fractions.

CONCLUSIONS

Dose per fraction seems to be the decisive parameter for the treatment response following both radiotherapy and radiosurgery. A larger number of fractions did not increase the obliteration rate. The data indicate that higher doses per fraction should be used when irradiating AVMs.