The dose accumulation and the impact of deformable image registration on dose reporting parameters in a moving patient undergoing proton radiotherapy.

INTRODUCTION: Potential changes in patient anatomy during proton radiotherapy may lead to a deviation of the delivered dose. A dose estimate can be computed through a deformable image registration (DIR) driven dose accumulation. The present study evaluates the accumulated dose uncertainties in a patient subject to an inadvertent breathing associated motion. MATERIALS AND METHODS: A virtual lung tumour was inserted into a pair of single participant landmark annotated computed tomography images depicting opposite breathing phases, with the deep inspiration breath-hold the planning reference and the exhale the off-reference geometry. A novel Monte Carlo N-Particle, Version 6 (MCNP6) dose engine was developed, validated and used in treatment plan optimization. Three DIR methods were compared and used to transfer the exhale simulated dose to the reference geometry. Dose conformity and homogeneity measures from International Committee on Radioactivity Units and Measurements (ICRU) reports 78 and 83 were evaluated on simulated dose distributions registered with different DIR algorithms. RESULTS: The MCNP6 dose engine handled patient-like geometries in reasonable dose calculation times. All registration methods were able to align image associated landmarks to distances, comparable to voxel sizes. A moderate deterioration of ICRU measures was encountered in comparing doses in on and off-reference anatomy. There were statistically significant DIR driven differences in ICRU measures, particularly a 10% difference in the relative D98% for planning tumour volume and in the 3 mm/3% gamma passing rate. CONCLUSIONS: T he dose accumulation over two anatomies resulted in a DIR driven uncertainty, important in reporting the associated ICRU measures for quality assurance.

Simulation study to improve the performance of a whole-body PbF2 Cherenkov TOF-PET scanner.

Using Cherenkov radiation in positron emission tomography (PET) has the potential to improve the time of flight (TOF) resolution and reduce the cost of detectors. In previous studies promising TOF results were achieved when lead fluoride (PbF2) crystals were used instead of a scintillator. In this work, a whole-body PbF2 Cherenkov TOF-PET scanner was simulated and optimized. Different configurations of the PbF2 crystals and their surface treatment were considered. Also evaluated was the influence of the crystal-photodetector coupling and of the detection efficiency of the photodetectors. Of special interest is a whole-body PbF2 Cherenkov TOF-PET scanner with a multi-layer detector, which improves the time resolution and reduces the parallax error, without compromising the detection efficiency. Images of a phantom were reconstructed for different configurations of the simulated whole-body PbF2 Cherenkov TOF-PET scanner and the quality of images was compared to that of a whole-body TOF-PET scanner with standard LSO scintillators. The TOF resolution of the whole-body PbF2 Cherenkov TOF-PET scanner with a multi-layer detector was 143 ps FWHM, out of which the fundamental limitation due to light production and transportation was only 22 ps FWHM.