Microdosimetry Study of Advanced Radiotherpy (II)

The use of densely ionizing particles in radiotherapy becomes popular in Taiwan. The Linko Chang Gung Memorial Hospital is currently installing the first proton therapy facility in Taiwan. Several other hospitals also showed interest in practicing the proton or carbon ion therapy. In collaboration with National Tsing Hua University, the Taipei General Veterans Hospital is now conducting clinical trials in boron neutron capture therapy (using alpha particles and lithium ions). In Europe, Japan and United States, the photon activation therapy based on targeted platinum loaded drugs is under intensive study. One of the advantages for densely ionizing particles in radiotherapy is the high specific energy depositions in tumor cells. Another words, under equal absorbed dose the probability of DNA double strand breaks by these particles is larger than that by photons and electrons. For the radiotherapy using 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). Since RBE values depend on the cellular microdosimetry and DNA nanodosimetry, the study of densely ionizing particles in radiotherapy is important in clinical applications and academic research. In this project, a study of the cellular microdosimetry and DNA nanodosimetry is proposed for densely ionizing particles in radiotherapy, i.e. protons, carbon ions, and synchrotron photons. With this study, the biological doses for these treatment modalities will be evaluated. The proposed study will develop theoretical methods and experimental techniques for the calculations and measurements of therapeutic beamlines for the densely ionizing particles. These beamlines will be used to determine the dose-weighted lineal energy distribution, D(y), in tumor and normal cells at different locations in the phantom or the body. Combining with the biological weighting function, R(y), the effective RBE will be determined. Further, the biological doses in the prescription and treatment planning will be obtained. Methods to be developed in the study include (1) the use of Monte Carlo (MC) transport code to simulate the densely ionizing particle beamlines for calculations of the absorbed dose contributed from all secondary particles produced in the phantom or the body, (2) the development of a MC microdosimetry program to simulate the cellular dose from densely ionizing particle beamlines, (3) the development of a MC nanodosimetry program to simulate the DNA dose from densely ionizing particle beamlines, (4) the design and fabrication of a mini tissue equivalent proportional counter (TEPC) for measurements of the dose-weighted lineal energy distribution, D(y), (5) the design and fabrication of an SOI (silicon on insulator) microdosimeter for measurements of the dose-weighted lineal energy distribution, D(y), (6) the study of biological weighting functions, R(y), for different cells and biological endpoints, and (7) the study of DNA double strand break yields induced byAuger electrons emitted from the photon activation therapy. A three-year project was proposed. The first-year project (2010.8-2011.7) was aimed to deal with proton therapy. So far, research accomplishments include (1) RBEs relative to 60Co for the induction of double strand breaks (DSBs) at different depths in a water phantom for therapeutic proton beams. This work was presented by the PI in the MC2010 International Conference held in Stockholm, Sweden, November 9-12, 2010. In this conference, the PI was invited to serve as session chairman. The work was also submitted to the International Journal of Radiation Biology for publication. (2) Measurements and dosimetry of environmental neutrons produced by the therapeutic protons were studied using Bonner sphere spectrometer and Monte Carlo simulations. This work was presented by the PI in the SSD International Conference held in Sydney, Australia, September 19-24, 2010. In the conference, the PI was invited to serve as session chairman. The work was also submitted to Radiation Measurements for publication. (3) The PI was invited to visit Tsinghua University in Beijing to address a series of talks in micro- and nano-dosimtry for heavy charged particles. A collaboration was set up to develop a Monte Carlo code for DNA damages including direct and indirect actions. The second-year project (2011.8-2012.7) will study heavy-ion radiotherapy which is more important than proton therapy in clinical applications. General guidelines of study will follow the methods developed in the first-year project. However, additional microdosimetry measurements will be made using the mini TEPC and the SOI microdosimeter.

Project ID:PC10007-1132
External Project ID:NSC100-2314-B182-026