3. CK Boost pelvis In the following 14 days after the external beam treatment, two high CyberKnife dose sessions will deliver a pelvic boost of 6.5 Gy each to the initial GTV or eventually to the residual GTV in case of too close vicinity of the organs at risk (OAR). This boost will be planned according to a recent paper, using a new CT scan and MRI scan for planimetric purposes. 95% of the prescribed dose will have to cover at least 90% of the PTV. The maximal CyberKnife tolerated doses to the OAR for a 6.5 Gy dose will be 5 Gy to 2cc of the bladder, rectum or sigmoid structures and 2.5 Gy to 5 cc of the small bowel. The protocol will not require a dose summation of the different steps of the treatment. The total duration of the whole treatment will have to be inferior to 55 days.