TH-TMO 2006 Problem 4

Let $P$ be a point outside a circle centered at $O$ . From $P$ , tangent lines are drawn to the circle, touching the circle at points $A$ and $B$ . Ray $\overrightarrow{BO}$ is drawn intersecting the circle again at $C$ and intersecting ray $\overrightarrow{PA}$ at $Q$ . If $3QA = 2AP$ , what is the value of $\sin \angle CAQ$ ?