Massachusetts General Hospital

Radiation Treatment Involving Moving Targets

Dynamic radiation therapy involves variable geometries. While intensity-modulated photon therapy is based on moving leafs in a multi-leaf collimator, intensity modulated proton therapy is based on changing magnetic fields. Conventional proton therapy using a scattering system is based on time-dependent range modulator settings. In addition to time-dependent beam properties, the patient geometry may be time dependent due to respiratory or cardiac motion. Monte Carlo simulations can be applied to model electro-mechanical motion in the treatment head and to model respiratory organ motion. 4D Monte Carlo allows continuously changing geometrical setup during simulation.

At Massachusetts General Hospital we are able to simulate all clinically used treatment head configurations for proton and photon treatments. For organ motion studies, 4D dose calculation is applied using patient specific 4D CT information. To accumulate dose deposition over different respiratory patient states, the position of each voxel as a function of time has to be known. The tracking of voxel positions over time is done using deformable image registration algorithms, which generate voxel displacement maps.
These are transformation matrices to correlate different respiratory states describing positional voxel changes within a particular volume between different points in time. The local dose is calculated as a function of moving sub-volumes and not as a function of position relative to a specific coordinate system.

Biosketch:
Dr. Harald Paganetti is currently a biophysicist at Massachusetts General Hospital and an assistant professor of radiation oncology at Harvard Medical School. Dr. Paganetti is an active member of AAPM, serving on study sections for NIH and is a consultant for the ICRU. His main research areas are Monte Carlo dose calculation for quality assurance and dose calculation in proton beam therapy, four-dimensional Monte Carlo dose calculation, relative biological effectiveness of proton beams, dose rate effects in intensity modulated radiation therapy, secondary dose in radiation therapy, and PET/CT imaging in proton therapy. His Monte Carlo code is currently the only clinically used proton Monte Carlo dose calculation package worldwide.
For his innovative idea of four-dimensional Monte Carlo he received an R01 grant by NIH. Besides his dominant role in proton Monte Carlo simulations, he has published more papers on modeling proton biology than anybody else in the field. He also collaborates with Dr. George Xu at RPI on using the VIP-Man patient models for radiation treatment.

Tuesday, March 7, 2006
SAGE 3510 - 4:00 p.m. to 5:00 p.m.
Refreshments served AFTER 3:50 p.m.