[1] Eberhard Karls Univ Tubingen, Univ Hosp, Dept Radiat Oncol, Tubingen, Germany
[2] Eberhard Karls Univ Tubingen, Med Fac, Tubingen, Germany
[3] Eberhard Karls Univ Tubingen, Univ Hosp, Dept Radiat Oncol, Sect Biomed Phys, Tubingen, Germany
[4] Univ Hosp Zurich, Dept Radiat Oncol, Zurich, Switzerland