Hi Maha,
Not exactly answering to your questions but in a similar problem I used the photon mapping method [mkpmap] (forward raytracing). You can find information here and here.
It needs some time to understand the physics and fiddle a bit around with parameters to get results but it works well for light tubes and light redirecting materials. Below is an example for a light redirecting profile I had to assess. BSDF materials work well with this method.
Maybe it is worth having a look at it.