23rd Annual NASA Space Radiation Investigators' Workshop (2012)
8072.pdf
Out-of-field dose studies with an anthropomorphic phantom: comparison of X-rays and particle therapy
treatments
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C. La Tessa , T. Berger , R. Kaderka , D. Schardt1, C. Körner2, U. Ramm3, J. Licher3, N. Matsufuji4, C.
Vallhagen-Dahlgren5, T. Lomax6, G. Reitz2 and M. Durante1,7
1GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstrasse 1, 64291 Darmstadt, Germany
(c.latessa@gsi.de), 2German Aerospace Center, DLR, Cologne, Germany, 3Klinikum Goethe Universität KGU,
Frankfurt, Germany, 4National Institute of Radiological Science (NIRS) Chiba, Japan,5Uppsala University
Hospital, Uppsala, Sweden, 6Paul Scherrer Institute (PSI), Villigen, Switzerland and 7TU Darmstadt, Darmstadt,
Germany.
The extension of the life expectancy following malignant tumor posed a growing concern on the effects of radiation
on normal tissues and in particular on the risk of developing secondary radiation-induced cancer. It is well known
that short- and long-term side effects following cancer treatment with radiation are strongly related to the dose
delivered outside the tumour. In fact, primary ions interact along the irradiation path towards the target volume and
can both be scattered and undergo nuclear fragmentation. The secondary ions, especially light particles as protons
and neutrons, might have enough range to deposit a non negligible amount of energy even far away from the target,
causing relevant damage to organs or tissues particularly sensitive to radiation.
An extensive investigation of the dose profile following radiotherapy was conducted for several common emerging
modalities, studying the influence of both the type of radiation and the delivery techniques. The following facilities
were involved in the measurements: Klinikum Goethe University (KGU) in Frankfurt, Germany, for the irradiation
with IMRT (Intensity Modulated Radiation Therapy) photons; The Svedberg Laboratory (TSL) in Uppsala, Sweden,
for the irradiation with passively modulated protons; the Paul Scherrer Institute (PSI) in Villigen, Switzerland, for
the irradiation with scanned protons; the National Institute of Radiological Sciences NIRS (HIMAC) in Chiba,
Japan, for the irradiation with passively modulated carbon ions; the Helmholtzzentrum für Schwerionenforschung
GmbH (GSI) in Darmstadt, Germany, for the irradiation with scanned carbon ions. In all experiments, an
anthropomorphic RANDO phantom was irradiated according to a 3-D treatment plan designed for a 5 x 2 x 5 cm3
target located in the center of the head. The phantom was equipped with a diamond detector and
thermoluminescence detectors of the types 6LiF:Mg, Ti (TLD-600) and 7LiF:Mg, Ti (TLD-700) to estimate the
surface and internal dose coming from charged particles, photons and thermal neutrons. Furthermore, during the
exposure to passively delivered and scanned carbon ions, the quality of the radiation field outside the tumor volume
was assessed with a Tissue Equivalent Proportional Counter (TEPC). The contribution to the dose of secondary
neutrons with energy between 0.8 and 10 MeV was measured during the treatment with scanned carbon ions using a
Silicon Scintillation Detector (SSD). For the irradiation with photons, the yield of photoneutrons with energies
between 10 keV and 20 MeV was detected with a Bubble Detector Spectrometer (BDS).
The dose equivalent deposited by photoneutrons out-of-field during IMRT treatment is of the same order of
magnitude (mSv*treatment-Gy) as photons and appears to be constant independently of the distance from the field,
due to their heavy leakage from the linac head.
Further results showed that the highest out-of-field dose values both on the skin and inside the phantom were
measured with IMRT photon treatment. The irradiation with photons and particles delivered with passive techniques
is accompanied by a heavy leakage of the primary beam and secondary particles through the accelerator head, which
is visible on the dose distribution at the surface and is translated into an almost isotropic irradiation of the patient
outside the target.
The combination of the results collected in this work together with data from literature indicate that the dose
contribution of secondary neutrons produced by fragmentation reactions in the beam line and tissue appears to be
small, even considering their enhanced biological effectiveness.
Overall, scanned carbon ions seem to represent the best compromise for sparing the tissue situated both nearby the
tumor and in the far-out-of-field region.
ACKNOWLEDGEMENTS
This study was supported by the European project ALLEGRO (grant agreement No. 231965).