Biology of high dose-high precision radiotherapy - experience from brachytherapy of cervix cancer

摘要

Brachytherapy treatments deliver high doses in only few fractions to target volumes and healthy tissues. These high dose values to target cells might be the reason for very successful brachytherapy concepts. With the integration of 3D based treatment planning into brachytherapy the spatial dose distribution in relation to topography can be investigated and taken into account during treatment plan optimization. An analysis of cervix cancer patients treated at the Department of Radiotherapy, Medical University of Vienna, with intracavita-ry brachytherapy for cervix cancer illustrate dose and volume relations focused to high dose regions. In particular, a D_(2CC) of the rectum or sigmoid >75 Gy EQD2 was associated with a significantly higher incidence of late toxicity compared to a Pj,.,. ≥75 Gy (EQD2). No clear cut off point for bladder late effects could be demonstrated. Clinically, the dose D_(2CC) ≤90 Gy EQD2 can be recommended for clinical use to minimize side effects for bladder. The current clinical experiences in cervix cancer brachytherapy are based on forward planning. The integration of DVH parameters for treatment planning of image guided brachytherapy results in the wish to include inverse planning optimization concepts. Other current research activities aim at non-rigid image registration and voxel tracing in order to refine existing radiobiological knowledge and data, respectively, on dose volume relations for targets and organs at risk.