6. Given that $P$ is a point inside the circle $\odot O$ with a radius of $15 \mathrm{~cm}$, and among all the chords passing through $P$, there are 25 chords whose lengths are integer centimeters. Then the range of $O P$ is ( ).
(A) $\left(12, \frac{\sqrt{611}}{2}\right)$
(B) $\left(12, \frac{\sqrt{613}}{2}\right)$
(C) $\left(12, \frac{\sqrt{611}}{2}\right]$
(D) $\left(12, \frac{\sqrt{613}}{3}\right]$
6.A.

In circle $\odot O$ with a radius of $15 \mathrm{~cm}$, the diameter is the longest chord. Among the chords passing through point $P$, the longest chord (diameter) is unique, and there are 24 other chords with integer lengths of $29 \mathrm{~cm}, 28 \mathrm{~cm}, \cdots, 18 \mathrm{~cm}$, each occurring twice. In $\odot O$, the distances from the center $O$ to the chords of lengths $18 \mathrm{~cm}$ and $17 \mathrm{~cm}$ are $12 \mathrm{~cm}$ and $\frac{\sqrt{611}}{2} \mathrm{~cm}$, respectively.

Since the shortest chord among all chords passing through point $P$ in $\odot O$ is the one perpendicular to $OP$, we have
$$
12<O P<\frac{\sqrt{611}}{2} \text {. }
$$