Dosimetric inter-institutional comparison in European radiotherapy centres: Results of IAEA supported treatment planning system audit

BACKGROUND AND PURPOSE

One of the newer audit modalities operated by the International Atomic Energy Agency (IAEA) involves audits of treatment planning systems (TPS) in radiotherapy. The main focus of the audit is the dosimetry verification of the delivery of a radiation treatment plan for three-dimensional (3D) conformal radiotherapy using high energy photon beams. The audit has been carried out in eight European countries - Estonia, Hungary, Latvia, Lithuania, Serbia, Slovakia, Poland and Portugal. The corresponding results are presented.

MATERIAL AND METHODS

The TPS audit reviews the dosimetry, treatment planning and radiotherapy delivery processes using the 'end-to-end' approach, i.e. following the pathway similar to that of the patient, through imaging, treatment planning and dose delivery. The audit is implemented at the national level with IAEA assistance. The national counterparts conduct the TPS audit at local radiotherapy centres through on-site visits. TPS calculated doses are compared with ion chamber measurements performed in an anthropomorphic phantom for eight test cases per algorithm/beam. A set of pre-defined agreement criteria is used to analyse the performance of TPSs.

RESULTS

TPS audit was carried out in 60 radiotherapy centres. In total, 190 data sets (combination of algorithm and beam quality) have been collected and reviewed. Dosimetry problems requiring interventions were discovered in about 10% of datasets. In addition, suboptimal beam modelling in TPSs was discovered in a number of cases.

CONCLUSIONS

The TPS audit project using the IAEA methodology has verified the treatment planning system calculations for 3D conformal radiotherapy in a group of radiotherapy centres in Europe. It contributed to achieving better understanding of the performance of TPSs and helped to resolve issues related to imaging, dosimetry and treatment planning.

Quality assurance for clinical trials

Cooperative groups, of which the Radiation Therapy Oncology Group is one example, conduct national clinical trials that often involve the use of radiation therapy. In preparation for such a trial, the cooperative group prepares a protocol to define the goals of the trial, the rationale for its design, and the details of the treatment procedure to be followed. The Radiological Physics Center (RPC) is one of several quality assurance (QA) offices that is charged with assuring that participating institutions deliver doses that are clinically consistent and comparable. The RPC does this by conducting a variety of independent audits and credentialing processes. The RPC has compiled data showing that credentialing can help institutions comply with the requirements of a cooperative group clinical protocol. Phantom irradiations have been demonstrated to exercise an institution's procedures for planning and delivering advanced external beam techniques (1-3). Similarly, RPC data indicate that a rapid review of patient treatment records or planning procedures can improve compliance with clinical trials (4). The experiences of the RPC are presented as examples of the contributions that a national clinical trials QA center can make to cooperative group trials. These experiences illustrate the critical need for comprehensive QA to assure that clinical trials are successful and cost-effective. The RPC is supported by grants CA 10953 and CA 81647 from the National Cancer Institute, NIH, DHHS.