ESTRO 2021 Abstract Book

S1466

ESTRO 2021

Conclusion The presented treatment and intrafraction movement control protocol have allowed the implementation of the SRS technique while maintaining the precision and accuracy of 0.3mm, 0.3 °.

PO-1744 An Italian project for dosimetry audits in radiotherapy P. Martucci 1,2 , M. Pimpinella 1 , S. Russo 3 , C. Fiandra 4 , M. D'Arienzo 1 , V. De Coste 1 , C. Pugliatti 5 , P. De Felice 1 , M. Stasi 6 1 ENEA, National Institute of Ionizing Radiation Metrology, Rome, Italy; 2 Tor Vergata University, Department of Biomedicine and Prevention, Graduate School of Medical Physics, Rome, Italy; 3 AUSL Toscana Centro, Health Physics Unit, Florence, Italy; 4 University of Turin, Department of Oncology, Turin, Italy; 5 Tecnologie Avanzate, Research and Development, Turin, Italy; 6 AO Ordine Mauriziano, Health Physics Unit, Turin, Italy Purpose or Objective In Italy, a multi-step project started in 2019 with the aim to develop, organize and perform national dosimetry remote audits in radiotherapy in order to certify the reference output of high energy photon beams. Materials and Methods Photon beams in the range 6 MV-18 MV including flattening filter free (FFF) beams and non-standard treatment units (CyberKnife, TomoTherapy) are considered. Thermoluminescent (TL) dosimeters, calibrated in terms of absorbed dose to water (D w ) in a reference 60 Co gamma beam, are used for the reference output measurement. Each dosimeter consists of 20 TL detectors (TLD-100; chips 3.2x3.2x0.89 mm 3 ) assembled in a waterproof PMMA holder mimicking the shape of a Farmer type ionization chamber. The average value of the individual TLD readings represents the dosimeter signal. Correction factors accounting for energy dependence and volume averaging (mainly for the FFF beams) are applied to the dosimeter signal. In addition, long-term variations in the TL dosimetry system response are taken into account by means of readouts of irradiated reference TL dosimeters.