[Imaging protocols for the management of respiratory motions in the radiotherapy planning for early stage lung cancer patients].

The aim of our work is to present the imaging techniques used at the National Institute of Oncology for taking into consideration the breathing motion at radiation therapy treatment planning. Internationally recommended imaging techniques, such as 4D CT, respiratory gating and ITV (Internal Target Volume) definition were examined. The different imaging techniques were analysed regarding the delivered dose during imaging, the required time to adapt the technique, and the necessary equipment. The differences in size of PTVs (Planning Target Volume) due to diverse volume defining methods were compared in 5 cases. For 4D CT breath monitoring is crucial, which requires special equipment. To decrease the relatively high exposure of 4D CT it is possible to scan only a few predefined breathing phases. The possible positions of the tumour can be well approximated with CT scans taken in the inhale maximum, the exhale maximum and in intermediate phase. The intermediate phase can be exchanged with an ordinary CT image set, and the extreme phase CT images can be ensured by given verbal instructions for the patient. This way special gating equipment is not required. Based on these 3 breathing phases an ITV can be defined. Using this ITV definition method the margin between the CTV (Clinical Target Volume) and the PTV can be reduced by 1 cm. Using this imaging protocol PTV can be reduced by 30%. A further 10% PTV reduction can be achieved with respiratory gating. In the routine clinical practice respiratory motion management with a 3-phase CT-imaging protocol the PTV for early-stage lung cancer can be significantly reduced without the use of 4D CT and/or respiratory gating. For special, high precision treatment techniques 4D CT is recommended.