Serial CT Scans in Fractionated Stereotactic Radiotherapy

• CT scanning with a stereotactic lokalizer will take place once a week with a double scan (for 2 fixations) without contrast.
  

• No secondary measures.
  

Stereotactic conformal radiotherapy (SCRT) combines the precision of the stereotactically guided tumor localisation and the radiobiological advantages of the fractionation. This implies an highly accurate repositioning of the isocenter of the cerebral target at the isocenter of the linac gantry and couch + 30 times. In the use of stereotactic conformal radiotherapy (SCRT) accuracy is the mainstay for the treatment of brain tumours. The reason are reduced safety margins around the tumour (or no margins) in order to reduce normal tissue dose.

This study aims at providing a quantitative evaluation of the accuracy of two different fixation systems, where one system is also evaluated with two different set-ups. The first approach will be based on the BrainLAB thermoplastic masque (the masque with (= standard fixation) and without a custom made bite-block), the second will use the BrianLAB relocatable frame with the bite- block and a home made fixation system.

Repositioning accuracy will be evaluated in a randomized manner patient-dependent and independent with the two fixation systems mentioned above.

The rationale is to determine the margins to define the planning target volume (PTV), it is necessary to know the set-up accuracy of the immobilization system. An overestimation of the PTV would lead to possible toxicity and an underestimation could lead to a geographical miss.

The main endpoint of this trial will be the accurate reproducibility of the fixation system evaluated by repeated CT scan.