To content

Field design in pencil-beam scanning mode combined with collimating apertures for small lesions and mobile tumors

Combining the pencil-beam scanning (PBS) delivery mode with collimators represents a viable approach to reduce the burden of normal tissue with high dose, which is complementary to the adaptive workflow described above. This technique increases the lateral dose gradient, which is often inferior to the one of hard X-ray fields in conventional radiation therapy. PBS-with-apertures is the subject of Research Project 1.3: Field design in pencil-beam scanning mode combined with collimating apertures for small lesions and mobile tumors, aiming for a comprehensive optimization of all plan parameters regarding absorbed dose, radiobiological dose and out-of-field dose.

The optimization parameters comprise lateral spot positioning relative to the aperture, which in turn affects the lateral penumbra and the out-of-field dose, and the position of an optional range shifter. As a second step, moving targets will be included. Targets which are affected by the interplay of the respiratory motion and the dynamic PBS delivery could benefit from broader pencil beams, which could be realized by wider beam tunes or retracted range shifters. These measures result in a loss of conformity, which can be compensated for by patient-specific apertures.

Brain tumor from a CT scan © Abdelkhalek Hammi​/​TU Dortmund