[Conformal irradiation technique for the peri- and retrobulbar space in endocrine orbitopathy].

The clinical target volume (CTV) for the irradiation of the endocrine orbitopathy (Graves ophthalmopathy) includes the peri- und retrobulbar space with the extraocular muscles. We present here a conformal irradiation technique aimed at optimal coverage of the CTV. The irradiation technique consists of two rotation fields with a central lens block and two lateral fixed fields with dorsal blocking. In each Gantry position, the lenses are faded out through the central lens block. The isocenter of the two rotation fields is located in the lenses. For quality assurance of this irradiation technique, verification of the dose distribution was performed by film dosimetry using the humanoid Aldersone phantom. The use of this irradiation technique yielded a dose distribution with conformal CTV coverage of the peri- and retrobulbar space and of the extraocular muscles. The film dosimetry of the Aldersone phantom showed a maximal deviation of 5% between the measured and the calculated dose distribution. The radiation load to the eye lenses was 25% of the applied total dose.