[1] Univ Hosp Dusseldorf, Dept Radiat Oncol, D-40225 Dusseldorf, Germany
[2] Univ Tubingen Hosp, Dept Radiat Oncol, Tubingen, Germany
[3] Ghent Univ Hosp, Dept Radiat Oncol, Ghent, Belgium
[4] Fdn IRCCS, Ist Nazl Tumori, Dept Med Oncol, Head & Neck Unit, Milan, Italy
[5] Inst Jean Godinot Reims, Dept Radiat Oncol, Reims, France
[6] Univ Lausanne Hosp, Dept Radiat Oncol, Lausanne, Switzerland
[7] Univ Hosp N Glasgow, Dept Radiat Oncol, Glasgow, Lanark, Scotland
[8] Univ Groningen, Univ Med Ctr Groningen, Dept Radiat Oncol, Groningen, Netherlands