Relative biological effectiveness of the 60-MeV therapeutic proton beam at the Institute of Nuclear Physics (IFJ PAN) in Kraków, Poland.

Dorota Słonina,Jan Swakoń,Leszek Grzanka,Urszula Sowa,Marta Ptaszkiewicz,Damian Kabat,Beata Biesaga

doi:10.1007/s00411-014-0559-0

Abstract

The aim of the study was to determine the relative biological effectiveness (RBE) of a 60-MeV proton radiotherapy beam at the Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN) in Kraków, the first one to operate in Poland. RBE was assessed at the surviving fractions (SFs) of 0.01, 0.1, and 0.37, for normal human fibroblasts from three cancer patients. The cells were irradiated near the Bragg peak of the pristine beam and at three depths within a 28.4-mm spread-out Bragg peak (SOBP). Reference radiation was provided by 6-MV X-rays. The mean RBE value at SF = 0.01 for fibroblasts irradiated near the Bragg peak of pristine beam ranged between 1.06 and 1.15. The mean RBE values at SF = 0.01 for these cells exposed at depths of 2, 15, and 27 mm of the SOBP ranged between 0.95–1.00, 0.97–1.02, and 1.05–1.11, respectively. A trend was observed for RBE values to increase with survival level and with depth in the SOBP: at SF = 0.37 and at the depth of 27 mm, RBE values attained their maximum (1.19–1.24). The RBE values estimated at SF = 0.01 using normal human fibroblasts for the 60-MeV proton radiotherapy beam at the IFJ PAN in Kraków are close to values of 1.0 and 1.1, used in clinical practice.

Highlights

To date, some 94,000 patients have received proton therapy in 36 proton therapy centres worldwide (Particle Therapy Co-Operative Group 2012)
The relative biological effectiveness (RBE) values estimated at surviving fractions (SFs) = 0.01 using normal human fibroblasts for the 60-MeV proton radiotherapy beam at the IFJ PAN in Krakow are close to values of 1.0 and 1.1, used in clinical practice
Regarding the RBE–dose relationship, at each depth of the spread-out Bragg peak (SOBP), the RBE value gradually increased with survival level; the growth was significant only for HFIB30 cells irradiated at the depth of 27 mm (p = 0.0370)

Summary

Introduction

Some 94,000 patients have received proton therapy in 36 proton therapy centres worldwide (Particle Therapy Co-Operative Group 2012). In 2011, a 60-MeV proton radiotherapy facility, the first one to operate in Poland, began to treat patients with eye tumours (mainly uveal melanoma) at the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Krakow, Poland. Protons and heavier ions show an increasing energy loss with depth in tissue that they penetrate, leading to maximum dose deposition, known as the Bragg peak, at the distal range of the proton beam. No significant dose is deposited at depths exceeding that of the Bragg peak. Such physical properties of ions are desirable in radiotherapy because they allow targeting the therapeutic dose within the tumour volume with high accuracy, sparing normal tissues and critical organs located beyond the beam’s range. For the purposes of radiotherapy, the Bragg peak in a pristine beam is too narrow to homogeneously cover the Radiat Environ Biophys (2014) 53:745–754 tumour volume; beam energy modulation is required to produce a spread-out Bragg peak (SOBP; Paganetti and Bortfeld 2006)

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Conclusion