@article{oai:repo.qst.go.jp:00058550,
 author = {Mori, Shinichiro and 森 慎一郎},
 journal = {ESTRO news letter},
 month = {Apr},
 note = {What was your motivation for initiating this study?
Pencil beam scanning (PBS) is more sensitive to motion than passive scattering, hence, its use remains limited to anatomical sites not requiring respiratory gating. Tumors in the upper liver region (close to the diaphragm) can be affected substantially by respiration-induced beam range variation, caused by the replacement of liver tissue by lung tissue. Therefore, a separate study for liver tumors is required prior to the start of clinical treatment to ensure the robustness of PBS.
\nWhat were the main challenges during the work?
The main challenges were to create a simulation environment, which is reflecting our treatment delivery and the reality very well. In order to do so we have implemented in our simulation as many machine parameters as possible, for example energy variation times, spot sweep velocity and beam intensity. Further we needed artifact-less 4DCT data from real patients to obtain representative tumor motion.
\nWhat is the most important finding of your study?
Generally, by applying a gating strategy we would expect to always get improved dose homogeneity and a lower dose to the surrounding tissue, due to the reduction of the motion amplitude. But this was not always the case, because a short gate window leads to less irradiation time, and hence it required us to extend the rescanned irradiation of a layer over several gating windows. This extension can lead to unwanted interference effects and counter the beneficial effects of rescanning. By choosing an odd number of rescanning we could minimize this effect and obtain good target conformity for 5 and more rescannings.
\nWhat are the implications of this research?
This robustness study brought us closer to finally treat liver tumors more conformable by using the scanning technology. Albeit there are some assumption in this study, we think that with all other investigations we did, we are not far off to start the treatment of moving targets with the presented combination of phase controlled rescanning and gating at NIRS in the near future.},
 title = {Conformity and robustness of gated rescanned carbon ion pencil beam scanning of liver tumors at NIRS},
 volume = {93},
 year = {2014}
}