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Consistency of RBE Assessment in Carbon Ion Radiotherapy

S Hartzell1*, F Guan2 , O Vassiliev3 , P Taylor4 , C Peterson5 , S Kry6 , The University of Texas, MD Anderson Cancer Center, Houston, TX


(Wednesday, 7/17/2019) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 7

Purpose: This study investigates the consistencies in the relative biological effectiveness (RBE) and biological dose as seen across various models applicable to carbon ion radiotherapy. The calculation of RBE values using each model (Microdosimetric Kinetic Model (MKM), the Local Effect Model 1 (LEM1), and the Repair Misrepair Fixation (RMF) model) is necessary to provide the basis of clinical uniformity across models and therefore across institutions. This will allow direct comparison of RBE values and provide a means of assessing the consistency across carbon centers, a critical parameter in the proper implementation of clinical trials within this modality.

Methods: Monte Carlo was used to generate microdosimetric and kinetic energy spectra of monoenergetic carbon beams of five different clinical energies ranging from 146 to 424 MeV. Microdosimetric spectra were then used to calculate lineal energy values that were used as inputs to generate alpha and beta values from the MKM and RMF models. Kinetic energy spectra were used along with alpha and beta tables for calculation of RBE using LEM1. The calculated carbon alpha and beta values were used along with alpha and beta values of reference radiation (x-rays) to determine RBE based on the linear quadratic method for each model.

Results: The alpha and beta values followed very different trends for each model, causing the RBE to vary correspondingly. The largest variance in RBE is seen in the Bragg peak, as two of the models (MKM and LEM1) peak towards the distal edge while the RMF model peak is centered with the Bragg peak. The biological dose, however, follows similar trends across each model but varies in magnitude at the entrance and the Bragg peak.

Conclusion: While no conclusions may be drawn with regard to the accuracy of any one model, these results display the variations seen under identical simulated conditions.


Not Applicable / None Entered.


TH- External Beam- Particle therapy: Carbon ion therapy - computational dosimetry-Monte Carlo

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