Patients eligible for the trial and having signed their consent to participate will undergo a scan to verify the possibility of implantation of the balloon. Before and after implantation of the balloon, a dosimetric scan will be performed. Radiotherapy will be administered according to the habits of each centre : Intensity modulated radiotherapy : 2 Gy / session, 5 weekly sessions, total dose of 74-80 Gy (+/- associated with an hormone therapy).
Patients will have a clinical examination :
* prior to the start of treatment
* once a week during the radiotherapy
* at the end of the radiotherapy
* and at the end of the study.
They will also complete quality of life questionnaires :
* prior to the start of treatment
* at mid-treatment
* at the end of the radiotherapy
* and at 3, 6, 12 and 24 months after the end of the radiotherapy.
Finally, patients will undergo a laboratory examination :
* prior to the start of treatment
* 3 months after the end of the radiotherapy
* and then every 6 months.
