def eqd2(d, alpha_beta)
      # FIXME: Perhaps better to use number of fractions instead of fraction dose?!
      raise ArgumentError, "A positive alpha_beta factor is required (got: #{alpha_beta})." unless alpha_beta.to_f > 0.0
      @value * (d.to_f + alpha_beta.to_f) / (2.0 + alpha_beta.to_f)
    end
def eqd2(d, alpha_beta)
      # FIXME: Perhaps better to use number of fractions instead of fraction dose?!
      raise ArgumentError, "A positive alpha_beta factor is required (got: #{alpha_beta})." unless alpha_beta.to_f > 0.0
      @value * (d.to_f + alpha_beta.to_f) / (2.0 + alpha_beta.to_f)
    end
Calculates the equivalent dose, given in 2 Gy fractions, EQD2. This is
 the total dose, that according to the linear-quadratic (LQ) model, if
 given in 2 Gy fractions, would yield the same biological effect as this
 total dose.

 @param [#to_f] d fraction dose
 @param [#to_f] alpha_beta the alpha/beta tissue factor to be used
 @return [Float] the equivalent dose when given in 2 Gy fractions