Microdosimetry Study of Advanced Radiotherpy (Iii)

The use of densely ionizing particles in radiotherapy becomes popular in Taiwan. Linko Chang Gung Memorial Hospital is installing the first proton therapy facility in Taiwan. Several other hospitals indicated their interest in practicing the proton or carbon ion therapy. In collaboration with National Tsing Hua University, the Taipei General Veterans Hospital is conducting clinical trials in boron neutron capture therapy (using alpha particles and lithium ions). In Europe, Japan and U.S., the targeted nuclide therapy applying Auger electrons is under intensive study. One of the advantages employing densely ionizing particles in radiotherapy is the high specific energy depositions in tumor cells. Another words, the induction of DNA double strand breaks (DSBs) by densely ionizing particles is larger than that by photons and electrons. For radiotherapy of densely ionizing particles, radiation dose should be prescribed with lineal energy weighted biological dose (in units of GyE) rather than physical dose (in units of Gy) only. Since RBE values depend on cellular microdosimetry and DNA nanodosimetry, a study of the densely ionizing particle radiotherapy is important in both clinical applications and academic research. In this project, a study of microdosimetry and nanodosimetry is proposed for therapeutic protons, carbon ions, and Auger electrons. Theoretical methods and experimental techniques will be developed for cellular and DNA dosimetry. The dose-weighted lineal energy distribution, D(y), at various locations in a phantom for tumor and normal cells will be evaluated. Combining with the biological weighting function, R(y), the effective RBE will be determined. Thus the biological doses in the treatment planning will be obtained. These studies will include: (1) the use of Monte Carlo (MC) transport code to simulate the therapeutic beams for calculations of the absorbed dose from primary and secondary particles, (2) the development of a MC program to simulate the cellular dose from densely ionizing particles, (3) the development of a MC program to simulate the DNA dose from densely ionizing particles, (4) the make of a mini tissue equivalent proportional counter (TEPC) for measurements of the dose-weighted lineal energy distribution, D(y), (5) the make of an SOI (silicon on insulator) for measurements of the dose-weighted lineal energy distribution, D(y), (6) the study of biological weighting functions, R(y), for different biological systems, and (7) the study of DNA DSB yields induced by Auger electrons emitted from radionuclides or generated by photon activations. A three-year project was previously submitted. The first-year project (2010.8-2011.7) to study proton therapy was completed with accomplishments: (1) RBE determinations for the induction of DSBs at different depths in a water phantom by therapeutic proton beams. Results were presented in the MC2010 International Conference held in Stockholm, Sweden, Nov 9-12, 2010, where the PI served as Session Chairman. This work was later accepted for publication in International Journal of Radiation Biology. (2) Measurements and dosimetry of ambient neutrons produced by the therapeutic protons using Bonner sphere spectrometer and MC simulations. Results were presented in the SSD International Conference held in Sydney, Australia, Sep 19-24, 2010, where the PI also served as Session Chairman. The work was later published in Radiation Measurements. (3) Collaboration between Chang Gung University and Beijing Tsinghua University for the study of microdosimetry. As a result of this collaboration, a joint paper on tritium microdosimetry was published in International Journal of Radiation Biology. The second-year project (2011.8-2012.7), with the study on heavy-ion therapy, is in good progress. Simulation models and microdosimeter calibrations have been completed. It is now ready to measure heavy ion lineal energies in the water phantom. These measurements will be made using heavy ions produced in the Accelerator Center, National Tsing Hua University. Also, MC simulations are on-going. The present proposal, applying for a third year project (2012.8-2013.7), is to study the targeted nuclide therapy using Auger electrons produced by photon activations and electron captures/internal conversions. This study will focus on the DNA nanodosimetry. Since collaborations with National Tsing Hua University and Beijing Tsinghua University have been established, external facilities and manpower will be incorporated in the study.

Project ID:PC10108-0814
External Project ID:NSC101-2314-B182-058