You've probably done a 'net search on this name already and found that various websites only give the definition: "Son of Lord Buddha". Although Gautama Buddha did have a son named "Rahul", this isn't the literal meaning of the name but rather a historic reference.
According to *The Penguin Book of Hindu Names* by Maneka Gandhi, the entry for the name "Radula" (a form of "Radul") gives the following:
1. "able"; "efficient"; "given by Rahu"
2. "Fetter"
3. "the son of Suddhodana"; "a son of Guatama Buddha"
--
Nanaea