The MR-Linac will provide excellent soft tissue contrast for on-treatment imaging. It is well known that the electron return effect (ERE) results in areas of increased and decreased dose at air/tissue boundaries, which can be compensated for in plan optimisation. However, anatomical changes may affect the quality of this compensation. In this paper we aim to quantify the interaction of anatomical changes with ERE in head and neck (H&N) cancer patients. Twenty patients treated with either 66 Gy or 60 Gy in 30 fractions were selected. Ten had significant weight-loss during treatment requiring repeat CT (rCT) and ten had PTVs close to the sinus cavity. Plans were optimised using Monaco to meet the departmental dose constraints and copied to the rCT and re-calculated. For the sinus patients, we optimised plans with full and empty sinus at both 0 T and 1.5 T. The effect of the opposite filling state was next evaluated. No clinically relevant difference between the doses in the PTV and OARs were observed related to weight-loss in 0 T or 1.5 T fields. Variable sinus filling caused greater dosimetric differences near the walls of the sinus for plans optimised with a full cavity in 1.5 T, indicating that optimising with an empty sinus makes the plan more robust to changes in filling. These findings indicate that current off-line strategies for adaptive planning for H&N patients are also valid on an MR-linac, if care is taken with sinus filling.

Abstract. The amount of energy carried by γ-rays during the fission process is an important consideration when developing new reactor designs. Many studies of γ-ray energy and multiplicity, from a multitude of fissioning systems, were measured during the 1970s. However the data from such experiments largely underestimates the heating effect caused by γ-rays in the structure of a reactor. It is therefore essential to obtain more accurate measurements of the energy carried during γ-ray emission. As such, the OECD Nuclear Energy Agency has put out a high priority request [1] for measurements of the mean γ-ray energy and multiplicity to an accuracy better than 7.5 percent from several fissioning systems; including 235 U(n thermal ). Measurements of the γ-rays from these fissioning nuclei were performed with the SpecTrometer for Exotic Fission Fagments (STEFF).

Abstract.We have developed a new setup to measure prompt γ -rays from the 235 U(n th , f ) reaction. The setup consists of two multi-wire proportional counters (MWPCs) to detect the fission fragments, two LaBr 3 (Ce) scintillators to measure the γ -rays. The highly efficient setup was installed at the PF1B beam line of the Institut Laue Langevin (ILL). We have successfully measured the γ -ray spectrum up to about 20 MeV for the fist time in neutron-induced fission.

No abstract

The prompt fission γ-ray energy spectrum for cold-neutron induced fission of 235 U was measured in the energy range Eγ = 0.8-20 MeV, by gaining a factor of about 10 5 in statistics compared to the measurements performed so far. The spectrum exhibits local bump structures at Eγ ∼4 MeV and ∼6 MeV, and also a broad one at ∼15 MeV. In order to understand the origins of these bumps, the γ-ray spectra were calculated using a statistical Hauser-Feshbach model, taking into account the de-excitation of all the possible primary fission fragments. It is shown that the bump at ∼4 MeV is created by the transitions between the discrete levels in the fragments around 132 Sn, and the bump at ∼6 MeV mostly comes from the complementary light fragments. It is also indicated that a limited number of nuclides, which have high-spin states at low excitation energies, can contribute to the bump structure around Eγ ∼15 MeV, induced by the transition feeding into the low-lying high-spin states.