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Conference: Bucharest University Faculty of Physics 2015 Meeting

Section: Biophysics; Medical Physics

Title:

Dosimetry for hip phantoms irradiated with proton beams

Authors:

C. OANCEA (1,2), I. AMBROŽOVÁ (3), V. VONDRÁČEK (4), A. I. POPESCU (2), M. DAVÍDKOVÁ (3) , G. MYTSIN (1)

Affiliation:

1) Medico-Technical Complex, Dzhlepov Laboratory of Nuclear Problems, JINR, Joliot-Curie 6, 141980 Dubna, Russia

2) Faculty of Physics, University of Bucharest, 405 Atomistilor, 077125 Bucharest-Magurele, Romania

3) Department of Radiation Dosimetry, Nuclear Physics Institute ASCR, Na Truhlářce 39/64, 180 00 Prague, Czech Republic

4)Proton Therapy Center, Budínova 2437/1a, 180 00 Prague, Czech Republic

E-mail

oancea@jinr.ru

Keywords:

proton therapy, metallic implants, titanium, stainless steel, track etched detectors

Abstract:

It is estimated that between 1 % and 4 % of radiotherapy patients have prosthetic devices which could affect their therapy [1]. The scientific understanding and methodology of clinical dosimetry for patients with hip prostheses (which have high atomic number, Z) located near the area of interest is still incomplete. We performed dosimetric experiments using a scanned proton pencil beam in the Proton Therapy Center Prague, Czech Republic, in order to measure the Linear Energy Transfer (LET) in a phantom with the inclusion of metallic implants. Using two different materials, which are in standard use in worldwide hip implant production, 2, 5, 10, 15, and 20 mm thick phantoms were created. The first phantom type consists of a Titanium (Ti) alloy (density of 6.45 g/cm3), while the second is composed of a stainless steel (AK) alloy (density of 7.96 g/cm3). The implant samples were placed behind a plastic equivalent tissue with a thickness of 80 mm. In order to study the production of secondary particles, we performed four experiments using various proton beam energies. In these experiments the solid track etched detectors (TED) HARZLAS TD-1 (Nagase Landauer Ltd., Japan), 0.9 mm thick (density of 1.3 g/cm3) [2,3] have been used to determine LET spectra of primary protons and secondary particles behind the implants of different thicknesses and near their edges. The results indicate that LET spectra behind different thicknesses of each particular material do not differ. When we compare LET spectra behind the same thickness of both materials, more particles with LET below 20 keV/micron are detected behind stainless steel. On the other hand, there are less tracks corresponding to particles with higher LET in comparison to LET spectra behind Ti. Applied methodology does not allow identification of particles detected in TED. The contribution of different ionizing particles to LET spectra will be determined with help of Monte Carlo simulations using the simulation tool Geant4. The obtained microdosimetry information may possibly be used to benchmark treatment planning systems and thus include patients with orthopedic implants for proton therapy of cancer.

References:

1. C. Reft, R. Alecu, I. J. Das, B. J. Gerbi, P. Keall, E. Lief, B. J. Mijnheer, N. Papanikolaou, C. Sibata and J. Van Dyk, Dosimetric considerations for patients with HIP prostheses undergoing pelvic irradiation. Report of the AAPM Radiation Therapy Committee Task Group 63, Med. Phys. 30, 82-1162, 2003

2. D. A. Young, Etching of radiation damage in Lithium Fluoride, Nature, 182, 375-377, 1958

3. I. Jadrníčkova, F. Spurný, LET spectrometry with track etch detectors; use in high-energy radiation fields, Radiat. Meas. 43, 683-687, 2008

Acknowledgement:

We thank to Ing. Fencl Jaroslav (Beznoska s r.o. company, Kladno, Czech Republic) for providing the hip implant materials used in this work. Cristina Oancea acknowledges the PhD fellowships awarded in the frame of collaboration between the University of Bucharest, Romania and JINR, Russia and the Czech Republic and JINR, Russia.