A thesis submitted September 2017 for the degree of Doctor of Philosophy and defended November, 2017.
The PhD School of Science
Faculty of Science, Center for Proton Therapy, Paul Scherrer Institute, Switzerland, Department of Oncology, Section of Radiotherapy, Rigshospitalet University Hospital of Copenhagen, Niels Bohr Institute, University of Copenhagen
Per M. Rosenschöld, PhD
Antony J. Lomax, PhD
Gitte F. Persson, MD PhD
Rosalind Perrin, PhD
Damien C. Weber, MD
Svend Aage Engelholm, MD DMsc
Evaluation of the breath-hold approach in proton therapy of lung tumors
Proton therapy has the potential to improve the local control rates and reduce the risk of toxicity for lung cancer patients. However, the delivery of proton therapy is prone to uncertainties caused by anatomical changes and motion during the treatment and between the treatment fractions which may compromise its effectiveness. The dosimetric uncertainty of lung cancer proton therapy can be minimized through the use of motion mitigation techniques; increased margins, beam gating and breath-hold, tumor tracking and rescanning. Most of these techniques have been extensively investigated in the literature showing good results, but the breath-hold technique has remained relatively unexplored. The breath-hold technique has shown promising stability and reproducibility, together with good patient compliance, from photon radiation therapy treatment. The aim of this thesis was to investigate the robustness of the breath-hold approach for pencil beam scanned (PBS) proton therapy. More specifically, the residual motion as seen on repeated breath-hold computed tomography (CT) scans and fluoroscopy acquisitions were investigated using simulation and experimental studies. The work was carried out at Paul Scherrer Institute (PSI), Switzerland with clinical data from the Rigshospitalet, Copenhagen University Hospital, Denmark. All treatment plans were constructed in the in-house treatment planning system (TPS) PSIplan at PSI. Four dimensional (4D) dose simulations have been carried out using our in-house developed 4D dose calculation software based on the PSIplan and Plastimatch image registration. Experimental studies were performed at PSI using a dynamic anthropomorphic breathing phantom whose artificial lungs can be deflated and inflated according to pre-programmed motion patterns e.g. from patients.