[Quality assurance in protontherapy: a systematic approach in progress at Orsay]

The degree of accuracy and reliability required in proton therapy can only be guaranteed if a comprehensive quality assurance (QA) programme is established. Such a programme obviously has common features with general QA in radiotherapy, but some aspects are specific to the use of protons and particularly to the characteristics of each facility. A study is in progress at Orsay to convert a series of quality controls into a systematic quality assurance programme. It includes some basic steps on organisation, setting up a QA committee and QA task groups, organising meetings, policies, procedures, records, qualifications, and determining some examples of tolerance in controls. Among some critical and specific points identified in this process are the combined treatment with photons at different institutions, the specificity of a non-hospital-based and complex facility, the high degree of precision required for the patient setup, and the need to develop in-house basic tools such as the treatment planning system. The inclusion of all the patients in prospective well-defined clinical trials, the comparison with alternative techniques and the radiobiological studies are considered as fundamentals for the QA programme. Present dosimetric and radiobiological intercomparisons between protontherapy centres are considered as partial audits. A study is in progress to establish common dosimetric and clinical protocols, radiobiological models and dose and volume specifications. In spite of the differences between the existing facilities, it should also be possible to obtain international consensus on general guidelines for a QA programme in proton therapy.