H Zhu^1,2,3*, Y Chen^1,2,3 , W Sung^1,4 , A McNamara^1,4 , T Tran⁵ , L Burigo⁶ , A Rosenfeld⁵ , J Li^2,3 , B Faddegon⁷ , J Schuemann^1,4 , H Paganetti^1,4 (1) Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, (2)Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R. China, (3)Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084, P.R. China, (4) Harvard Medical School, Boston, MA 02114, USA, (5) Centre for Medical Radiation Physics, University of Wollongong, Australia, (6) German Cancer Research Center-DKFZ, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany, (7) Department of Radiation Oncology, University of California San Francisco, CA 94143, USA

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  H Zhu

(Tuesday, 7/16/2019) 7:30 AM - 9:30 AM

Room: Stars at Night Ballroom 1

Purpose: Microdosimetric energy depositions have been recognized as a vital variable for the modeling of relative biological effectiveness (RBE) in particle therapy. To make microdosimetric simulations more readily available, a microdosimetric extension was developed for the Monte Carlo toolkit TOPAS (based on Geant4) to provide a valuable supplement to experimental microdosimetric measurements to investigate microdosimetric characteristic of different kinds of charged particles.

Methods: The extension consists of a lineal energy scorer, two RBE calculation models, a geometric extension that describes three microdosimetry detectors and several example files to demonstrate the usage of the extension. The microdosimetric extension includes geometries for spherical TEPCs (tissue equivalent proportional counters), cylindrical TEPCs and a silicon on insulator (SOI) microdosimeter. The hits of every primary or secondary particle within the sensitive volume of a detector are recorded and used to calculate microdosimetric spectra, microdosimetric quantities and RBE values with a biological weighting function approach and/or the Microdosimetric Kinetic (MK) model.

Results: With the new extension to TOPAS, users only need to set several basic geometric parameters to score microdosimetric spectra and RBE based on microdosimetric models. To validate the scorer, simulations were conducted for three types of detectors. The depth dose distributions, microdosimetric spectra, microdosimetric quantities as well as RBE values were obtained and compared with experimental results and other MC simulation data from the literature. Generally, good agreement was found between TOPAS and the experimental, MCHIT, and FLUKA results, the consistency provides a reasonable validation of TOPAS.

Conclusion: A microdosimetric extension was developed and validated in this work. The extension is applicable to spherical/cylindrical TEPCs and SOI microdosimeters. This extension provides users extended functionality for microdosimetric studies.

Funding Support, Disclosures, and Conflict of Interest: Hongyu Zhu was sponsored by China Scholarship Council for one-year study at the Massachusetts General Hospital. This work was supported by the National Cancer Institute under R01 CA187003 and U24 CA215123.

Keywords

Microdosimetry, Monte Carlo, RBE

Taxonomy

TH- External Beam- Particle therapy: Proton therapy - computational dosimetry-Monte Carlo

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