Treatment planning systems dosimetry auditing project in Portugal

Abstract

a b s t r a c tBackground and purpose: The Medical Physics Division of the Portuguese Physics Society (DFM_SPF) in collaboration with the IAEA, carried out a national auditing project in radiotherapy, between September 2011 and April 2012. The objective of this audit was to ensure the optimal usage of treatment planning systems. The national results are presented in this paper. Material and methods: The audit methodology simulated all steps of external beam radiotherapy workflow, from image acquisition to treatment planning and dose delivery. A thorax CIRS phantom lend by IAEA was used in 8 planning test-cases for photon beams corresponding to 15 measuring points (33 point dose results, including individual fields in multi-field test cases and 5 sum results) in different phantom materials covering a set of typical clinical delivery techniques in 3D Conformal Radiotherapy. Results: All 24 radiotherapy centers in Portugal have participated. 50 photon beams with energies 4 e18 MV have been audited using 25 linear accelerators and 32 calculation algorithms. In general a very good consistency was observed for the same type of algorithm in all centres and for each beam quality. Conclusions: The overall results confirmed that the national status of TPS calculations and dose delivery for 3D conformal radiotherapy is generally acceptable with no major causes for concern. This project contributed to the strengthening of the cooperation between the centres and professionals, paving the way to further national collaborations.

National dosimetric audit network finds discrepancies in AAA lung inhomogeneity corrections

“…Furthermore, their study also found similar discrepancies for the Varian AAA algorithm however the results were attributed to input beam data and beam modelling. Similar European and South American audits have also been reported and shown to be effective [34,35].…”

Dosimetry audit simulation of treatment planning system in multicenters radiotherapy

“…These results showed that dose calculation algorithm more accurate in calculating the dose in the homogeneous material (point 1, 3 and 5) than inhomogeneous material (point 9 and 10). This result corresponds to the previous study where measurement of point dose in the bone has a global trend toward overdose [11]. Calculated dose in TPS lower than the measured dose in high density material for high energy x-ray beam because of the fact that the general dose calculation algorithm can not accurately modeling the increase interaction coefficient in the bone but just take into account the reduced transmission when photon beam passed the high-density medium [11].…”

“…Deviation out of agreement criteria was found at point 10 at posterior beam direction. The previous study deviation out of agreement criteria was also found at point 10 at posterior beam direction, where 22 of 68 measurements are out of agreement criteria [11]. While, other study showed that deviation out of agreement criteria was found at point 6 and 10 for correction based algorithm, whereas for model-based algorithms taking into account lateral electron transport are within agreement criteria [12].…”

A multi-centre analytical study of small field output factor calculations in radiotherapy

“…This is caused both by the relatively large penumbra size, as well as by the changes in the energy spectrum [1][2][3][4][5] . The significant role of external dosimetry audits [6][7][8], including small field tests, in radiation therapy clinical trials, is often evoked [9]. Methodologies of audits of small field output performance were formerly proposed [8,10,11].…”