Influence of secondary neutrons induced by proton radiotherapy for cancer patients with implantable cardioverter defibrillators

<p>Abstract</p> <p>Background</p> <p>Although proton radiotherapy is a promising new approach for cancer patients, functional interference is a concern for patients with implantable cardioverter defibrillators (ICDs). The purpose of this study was to clarify the influence of secondary neutrons induced by proton radiotherapy on ICDs.</p> <p>Methods</p> <p>The experimental set-up simulated proton radiotherapy for a patient with an ICD. Four new ICDs were placed 0.3 cm laterally and 3 cm distally outside the radiation field in order to evaluate the influence of secondary neutrons. The cumulative in-field radiation dose was 107 Gy over 10 sessions of irradiation with a dose rate of 2 Gy/min and a field size of 10 × 10 cm². After each radiation fraction, interference with the ICD by the therapy was analyzed by an ICD programmer. The dose distributions of secondary neutrons were estimated by Monte-Carlo simulation.</p> <p>Results</p> <p>The frequency of the power-on reset, the most serious soft error where the programmed pacing mode changes temporarily to a safety back-up mode, was 1 per approximately 50 Gy. The total number of soft errors logged in all devices was 29, which was a rate of 1 soft error per approximately 15 Gy. No permanent device malfunctions were detected. The calculated dose of secondary neutrons per 1 Gy proton dose in the phantom was approximately 1.3-8.9 mSv/Gy.</p> <p>Conclusions</p> <p>With the present experimental settings, the probability was approximately 1 power-on reset per 50 Gy, which was below the dose level (60-80 Gy) generally used in proton radiotherapy. Further quantitative analysis in various settings is needed to establish guidelines regarding proton radiotherapy for cancer patients with ICDs.</p

First steps towards a fast-neutron therapy planning program

<p>Abstract</p> <p>Background</p> <p>The Monte Carlo code GEANT4 was used to implement first steps towards a treatment planning program for fast-neutron therapy at the FRM II research reactor in Garching, Germany. Depth dose curves were calculated inside a water phantom using measured primary neutron and simulated primary photon spectra and compared with depth dose curves measured earlier. The calculations were performed with GEANT4 in two different ways, simulating a simple box geometry and splitting this box into millions of small voxels (this was done to validate the voxelisation procedure that was also used to voxelise the human body).</p> <p>Results</p> <p>In both cases, the dose distributions were very similar to those measured in the water phantom, up to a depth of 30 cm. In order to model the situation of patients treated at the FRM II MEDAPP therapy beamline for salivary gland tumors, a human voxel phantom was implemented in GEANT4 and irradiated with the implemented MEDAPP neutron and photon spectra. The 3D dose distribution calculated inside the head of the phantom was similar to the depth dose curves in the water phantom, with some differences that are explained by differences in elementary composition. The lateral dose distribution was studied at various depths. The calculated cumulative dose volume histograms for the voxel phantom show the exposure of organs at risk surrounding the tumor.</p> <p>Conclusions</p> <p>In order to minimize the dose to healthy tissue, a conformal treatment is necessary. This can only be accomplished with the help of an advanced treatment planning system like the one developed here. Although all calculations were done for absorbed dose only, any biological dose weighting can be implemented easily, to take into account the increased radiobiological effectiveness of neutrons compared to photons.</p

Overview of recent experimental works on high energy neutron shielding

Several experiments on high energy neutron shielding have recently been performed using medium to high energy accelerators of energies above 20 MeV. Below 100 MeV, the benchmark experiments have been done using 25 and 35 MeV p-Li quasi-monoenergetic neutrons at the Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Japan, 43 and 68 MeV p-Li quasi-monoenergetic neutrons at the Azimuthally Varying Field (AVF) cyclotron facility, TIARA of Japan Atomic Energy Research Institute (JAERI). Above 100 MeV, the neutron shielding experiments have been done using 800 MeV protons at ISIS, Rutherford Appleton laboratory (RAL), England, 400 MeV/nucleon carbon ions at the heavy ion medical accelerator facility, HIMAC of National Institute of Radiological Sciences (NIRS), Japan, 500 MeV protons at the spallation neutron source facility, KEK spallation neutron source facility (KENS) of High Energy Accelerator Research Organization (KEK), Japan, 500 MeV protons at the accelerator facility, TRIUMF, Canada, 1.6 to 24 GeV protons at the Alternating Gradient Synchrotron (AGS), Brookhaven National Laboratory (BNL), U.S.A., 28.7 GeV electrons at the Stanford Linear Accelerator Center (SLAC), U.S.A., 800 MeV protons at the Los Alamos Neutron Science Center (LANSCE), Los Alamos National Laboratory (LAND, U.S.A., 120, 205 GeV/c protons and 160 GeV/nucleon lead ions at the European Organization for Nuclear Research (CERN), Switzerland, 230 MeV protons at the Loma Linda University Medical Center, U.S.A., 200 MeV protons at the Orsay Proton Therapy Center, France. In this review paper, the outlines of these deep penetration experiments are summarized together with the neutron detection techniques