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Tumor Control in Ion Beam Radiotherapy with Different Ions in Presence of Hypoxia

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A Attili

A Attili1*, F Torriani2 , G Russo3 , F Dalmasso1,4 , S Giordanengo1 , F Bourhaleb3 , G Battistoni5 , A Kraan6,7 , R Cirio1,4 , (1) Istituto Nazionale di Fisica Nucleare, Sez. Torino, Torino, Italy , (2) Politecnico di Torino, Torino, Italy , (3) Internet-Simulation Evaluation, Envision, Torino, Italy , (4) Universita degli Studi di Torino, Torino, Italy , (5) Istituto Nazionale di Fisica Nucleare, Sez. Milano, Milano, Italy , (6) Istituto Nazionale di Fisica Nucleare, Sez. Pisa, Pisa, Italy , (7) Universita degli Studi di Pisa, Pisa, Italy


SU-E-T-770 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The reduced concentration of oxygen in cells (hypoxia) results in a lower cell death rate after irradiation that can lead to treatment failure. The effect can be expressed by the oxygen enhancement ratio (OER). So far, only few attempts to include OER in treatment planning for ion beam therapy were made, which are based on the dose averaged LET estimates and do not distinguish among ion species and fractionation schemes. To overcome these limitations, we implemented a new OER model and used it to estimate tumor control in clinical cases.

Methods: The model, based on the microdosimetric kinetic model, was benchmarked with in-vitro data from different ions irradiation. It was included in the simulation of treatments of a set of clinical cases (glioblastoma) using p, Li, He, C and O ion beams. Tumor Control Probability (TCP) was estimated as a function of oxygen partial pressure, dose per fraction and primary ion type.

Results: The modelized OER was found to be strongly dependent on both LET and ion type, and showed a decreasing OER for increasing dose per fraction with a slope that depends on the LET and ion type, in good agreement with the experimental data. In the clinical cases studied, an increase in TCP by increasing ion charge and dose per fraction (more than 30% variation from p to O for moderate hypoxia) was found. Higher OER decrease rates as function of dose per fraction were found for lighter ions (up to 20% varying from 2 to 8 Gy(RBE)).

Conclusions: A novel modeling of the OER that explicitly includes the dependence on ion type and dose per fraction was implemented. The model was exploited to evaluate the impact of hypoxia in ion beam radiotherapy, facilitating the identification of the treatment condition optimality, including fractionation scheme and ion type.

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