Calculate the volume of a part of a sphere inside a cylinder

Find the volume of the part of the sphere $\displaystyle r^2+z^2=a^2$ which is inside the cylinder $\displaystyle r=a \sin (\theta)$ where $\displaystyle (r,z,\theta)$ are the cylindrical coordinates.

My attempt : I'm not able to visualize the sphere nor the cylinder.

For the sphere, does $\displaystyle r^2=x^2+y^2$? If so then I can imagine the sphere. (Centered at the origin $\displaystyle (0,0,0)$ and with radius $\displaystyle a$).

For the cylinder $\displaystyle \sqrt{x^2+y^2}=a \sin (\theta)$ I don't know how to go further. I also feel it's useless to convert all in Cartesian coordinates but this way it's easier to me to visualize the volumes.