For T4a bladder cancer only involving the prostatic stroma and no bladder involvement, what is your final cone-down volume?

For bladder tumors that are well localized, whether the tumor is well localized in one portion of the bladder or well localized by virtue of primarily prostatic involvement, it is appropriate to provide a tumor-focused cone-down volume assuming one can provide image guidance or otherwise ensure that the CTV is well covered during the boost treatment. It would be reasonable to apply a 1.5-2 cm expansion to create the cone-down PTV.