gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Relative biological effectiveness of the modulated protons beams used at the Institute Curie-Protontherapy Center in Orsay (ICPO)

Meeting Abstract

  • V. Calugaru - Radiotherapy, Institut Curie, ICPO, Orsay, France
  • C. Nauraye - Physics, Institut Curie, ICPO, Orsay, France
  • F. Megnin-Chanet - INSERM U612, Institut Curie-Recherche, Orsay, France
  • G. Noel - Radiotherapy, Centre de Lutte contre le Cancer Paul Strauss, Strasbourg, France
  • V. Favaudon - INSERM U612, Institut Curie-Recherche, Orsay, France

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog034

DOI: 10.3205/09ptcog034, URN: urn:nbn:de:0183-09ptcog0347

Published: September 24, 2009

© 2009 Calugaru et al.
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Outline

Text

Background: The relative biological effectiveness (RBE) in the modulated proton beams used in different protontherapy facilities has been determined at 1.0–1.4 from in vitro studies (Paganetti, et al. Int J Radiat Oncol Biol Phys. 2002;53:407-21) and estimated at 1.10 (relative to 60Co photons) from in vivo studies (Gueulette, et al. Radiother Oncol. 2004;73 Suppl 2:148-54). However, authors reported RBE values for cell killing between 1.4 and 2.1 at the distal edge of the spread-out Bragg peak (SOBP) generated from protons beams with nominal energy in the range 65-70 MeV (Courdi, et al. Br J Radiol. 1994;67:800-4; Wouters, et al. Radiat Res 1996;146:159-70; Paganetti, et al. Int J Radiat Oncol Biol Phys. 1997;37:719-29; Tang, et al. Br J Cancer 1997;76:220-5; Bettega, et al. Int J Radiat Biol. 2000;76:1297-303). These results support the conclusion that proton RBE values could be high only at the most distal and descending part of the SOBP but little attention has been paid to the variation of RBE with depth in the SOBP as a function of the nominal energy of the primary proton beam. This problem is important because a higher value of the RBE would increase the risk of an overdosage and necrosis in the distal part of the SOBP.

Materials and methods: We analyzed in human cell lines the effect of the modulated 73 and 200 MeV proton beams used for treatment of uveal melanoma and intracranial tumors at the ICPO for two endpoints : the incidence of DNA double-strand breaks (DSB) as a function of the position of cells in the SOBP measured by pulse-field electrophoresis, and the efficiency of cell killing by clonogenic assays. 137Cs γ-rays (RBE=1.07) were taken as a reference.

Results and conclusion: The RBE for cell killing was close to 1.1 at entrance and in the mid-SOBP but increased rapidly in the distal part of the 73 MeV SOBP only to reach a value of 2.1–2.3. In contrast the RBE for DSB formation was found to be 1.16±0.08 and did not vary appreciably with the incident proton energy and position in the SOBP.

The results correlate with the predictions made from nanodosimetry studies developed by Ottolenghi and coll. (Biaggi, et al. Nucl Instrum Meth Phys Res B. 1999;159:89-100.) who correlated this with complex DNA damage within chromatin, the nature of which we are currently investigating.