Microdosimetric Assessment of Nice Therapeutic Proton Beam Biological Quality

Laura De Nardo^1,2, Valentina Cesari³, Nicole Iborra⁴, Valeria Conte³, Paolo Colautti³, Joël Hérault⁴, Giorgio Tornielli^1,2, Pierre Chauvel⁴

1. University of Padova, Physics Department, Via Marzolo 8, I 35131 Padova (Italy)
2. INFN - Sezione di Padova, Via Marzolo 8, I 35131 Padova (Italy)
3. INFN - Laboratori Nazionali di Legnaro, Viale dell’Università 2, I 35020 Legnaro (Italy)
4. Centre Antoine-Lacassagne Biomedical Cyclotron, 227 Avenue de la Lanterne, F 06200 Nice (France)

Manuscript received: September 1, 2003; revised: Febraury 10, 2004 Accepted for publication: May 10, 2004.

Abstract

A cylindrical slim tepc (Tissue-Equivalent Proportional Counter) of 0.9 mm sensitive volume and 2.7 mm of total encumbrance has been constructed. With such a mini counter we have measured the physical quality of the therapeutic proton beam of the Centre Antoine-Lacassagne of Nice (France). Microdosimetric Relative Biological Effectiveness values (rbeµ) have been calculated by using different weighting functions for early effects in mouse intestinal crypt cells. rbeµ, calculated by using the weighting function for 8 Gy, fits very well in-vitro radiobiological data (human melanoma surviving at 8 Gy and human tongue cell carcinoma surviving at 2 Gy) all along the Spread-Out Bragg peak (sobp). The sobp lateral penumbra physical quality has been as well measured. At the sobp end, the biological effective dose is shifted of about 0.5 mm with respect to the absorbed dose, both longitudinally and laterally.

keywords: tepc, Microdosimetry, Proton therapy, Proton rbe.

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