  Let $\mu$ be a non-negative Borel measure on $R^d$ satisfying that the
measure of a cube in $R^d$ is smaller than the length of its side raised to the
$n$-th power, $0<n\leq d$. In this article we study the class of weights
related to the boundedness of radial fractional type maximal operator
associated to a Young function $B$ in the context of non-homogeneous spaces
related with the measure $\mu$. This type of maximal operators are the adequate
operators related with commutators of singular and fractional operators.
Particularly, we give an improvement of a two weighted result for certain
fractional maximal operator proved in [26].
