engleski

National audit on dose delivery in radiation oncology

Purpose: Dosimetry audits are an important tool for verification of treatment planning system (TPS) modelling and treatment delivery. Comprehensive on-site audit methodology was developed, and national audit performed under the International Atomic Energy Agency project CRO6019. Material and methods: Implementation of advanced radiation oncology techniques in Croatia began during past decade. Currently six out of seven sites are performing advanced techniques. This requires rigorous absorbed dose distribution verification prior dose delivery. On-site audit was performed using 2D methodology due to its feasibility for transportation. Main part of the methodology development was to correlate 3D and 2D verification methodologies. Additionally, radiochromic films were used. Audit had two parts: absorbed dose measurements in reference conditions and 2D verification of absorbed dose distributions (reference field, five fields pyramid, clinical dose distributions: head and neck and prostate). Calculation and experimental verification of dose distributions using audited sites’ devices where prerequisite for audit. Sites were obliged to calculated absorbed dose distributions prior experimental part of the audit. Results: Results can be divided in three categories: in-house development of comprehensive methodology to be applied for on-site audit, questionnaire on application of advanced radiation oncology techniques and validation of data acquired during the audit. Thorough methodology development multiple comparisons were performed e.g., 3D true and perpendicular composites, 2D perpendicular composites at 0°and 90°, ionization chamber true and perpendicular composites. Experimental results confirmed feasibility of 2D dosimetry for the audit. Answers on the questionnaire shown that there is single linear accelerator dedicated to application of advanced techniques at each site. Two sites perform VMAT only, two both VMAT and IMRT, and two IMRT only. Three sites use 6 MV X-ray beams and three 6MV and 10 MV. Five sites use advanced calculation algorithms (Monte Carlo and Acuros XB). Pre-treatment verifications are performed regularly at each site. Half of sites perform it using portal dosimetry. Tolerance criteria used are as follows: 3%/2mm (4), 2%/2mm (1), and 3%/1mm (1). Gamma passing rate higher than 95% is criterium at all sites. Despite complex processing methodology required, radiochromic film dosimetry had proved dosimetric potentials to supplement audit methodology in non-reference conditions. Comprehensive analyses of acquired data have shown acceptable results of majority of audited sites. Conclusions: National audit had proved that pre- treatment dosimetry at national level is performed in suitable way. Nevertheless, there is a room for improvements and optimization is required.

dosimetry audit, absorbed dose measurements, 2D dosimetry, VMAT, IMRT

nije evidentirano