ESTRO 36 Abstract Book

S422 ESTRO 36 _______________________________________________________________________________________________

plaques with radiochromic film, and all of them use specifically machined plastic phantoms. We aimed to develop a practical experimental method for measuring the absolute absorbed dose distributions in water produced by 106 Ru/ 106 Rh plaques using the EBT3 radiochromic film. Material and Methods Two experimental setups were developed to measure dose planes (1) perpendicular to the symmetry axis of the plaque at 5 mm from the intersection of the symmetry axis with the concave plaque surface, and (2) containing the symmetry axis of the plaques (PDD planes). Both, the plaque and the film, were immersed in water. The required materials are easily affordable by a medical physics department without the need of specifically machined solid phantoms. The setups were tested measuring dose distributions from one CCA and two CCX plaques. Dose distributions were obtained from the irradiated films using the triple-channel dosimetry algorithm implemented in the FilmQA 2015 software. The measured dose distributions were compared with the results of Monte Carlo simulations run with the PENELOPE code, and with published data. Results The measured absolute dose rates agreed with the values quoted in the calibration certificates of the plaques within the experimental uncertainty, with typical differences below 5%. The relative standard uncertainties obtained were of 3.8% for dose distributions measured at planes perpendicular to the symmetry axis at 5 mm from the surface of the plaque, and of 7.4% for planes containing the symmetry axis. These values are comparable to those reported by other authors using plastic phantoms, but avoiding the uncertainties associated to the conversion from dose–to–plastic to dose–to–water. A good agreement was obtained between measurements and simulations, improving upon published data (see figures for data of depth-dose curves, and lateral profiles at 5 mm from the surface of the plaque, for the CCX plaques).

Conclusion We developed a practical experimental method to measure with the EBT3 radiochromic film the dose distributions in water produced by 106 Ru/ 106 Rh ophthalmic plaques. The obtained results were of similar or better quality than those obtained using solid phantoms. These setups may ease the quality assurance procedures to the users of these plaques. PO-0794 Comprehensive quality assurance test for high precision teletherapy S. Wegener 1 , A. Spiering 1 , O.A. Sauer 1 1 University Hospital, Radiation Oncology, Würzburg, Germany Purpose or Objective Modern radiation therapy aims to minimize negative side effects on healthy tissue by tailoring the dose distribution as accurately as possible to each individual tumor. This leads to a progressively increasing complexity of the treatment plans and demands a very high precision of all involved components. Even small errors can significantly compromise treatment techniques which require such an extensive precision as stereotactic radiation therapy. A suitable quality management for such techniques should include a regular end-to-end test that closely mimics the entire procedure of the actual patient treatment while being able to reliably detect a variety of possible errors