Beam characterisation of the 1.5 T MRI-linac.

As a prerequisite for clinical treatments it was necessary to characterize the Elekta 1.5 T MRI-linac 7 MV FFF radiation beam. Following acceptance testing, beam characterization data were acquired with Semiflex 3D (PTW 31021), microDiamond (PTW 60019), and Farmer-type (PTW 30013 and IBA FC65-G) detectors in an Elekta 3D scanning water phantom and a PTW 1D water phantom. EBT3 Gafchromic film and ion chamber measurements in a buildup cap were also used. Special consideration was given to scan offsets, detector effective points of measurement and avoiding air gaps. Machine performance has been verified and the system satisfied the relevant beam requirements of IEC60976. Beam data were acquired for field sizes between 1 × 1 and 57 × 22 cm2. New techniques were developed to measure percentage depth dose (PDD) curves including the electron return effect at beam exit, which exhibits an electron-type practical range of 1.2 ± 0.1 cm. The Lorentz force acting on the secondary charged particles creates an asymmetry in the crossline profiles with an average shift of +0.24 cm. For a 10 × 10 cm2 beam, scatter from the cryostat contributes 1% of the dose at isocentre. This affects the relative output factors, scatter factors and beam profiles, both in-field and out-of-field. The average 20%-80% penumbral width measured for small fields with a microDiamond detector at 10 cm depth is 0.50 cm. MRI-linac penumbral widths are very similar to that of the Elekta Agility linac MLC, as is the near-surface dose PDD(0.2 cm) = 57%. The entrance surface dose is ∼36% of Dmax. Cryostat transmission is quantified for inclusion within the treatment planning system. As a result, the 1.5 T MRI-linac 7 MV FFF beam has been characterised for the first time and is suitable for clinical use. This was a key step towards the first clinical treatments with the MRI-linac, which were delivered at University Medical Center Utrecht in May 2017 (Raaymakers et al 2017 Phys. Med. Biol. 62 L41-50).

Biochemical evaluation of the vitamin and iron status of an apparently healthy Dutch free-living elderly population. Comparison with younger adults.

In order to obtain information on "normal" values, the vitamin and iron status have been investigated of an apparently healthy Dutch elderly population, living in their own homes in the centre of the Netherlands. In total 99 women and 99 men (overall mean age 72 yrs) volunteered in the study. By omitting the elderly suffering from one or more diseases as well as those using vitamin supplements, 131 aged people were selected for the biochemical evaluation of the vitamin and iron status of healthy elderly. Results have been compared with those obtained for healthy adults below 50 years of age. The "normal" values obtained appear to deviate significantly from those of the group of apparently healthy younger adults for several vitamins. Especially, lower values were observed for the vitamin A, total carotenoids, vitamin D, B6, B12 and folic acid status. Furthermore, lower serum iron and iron saturation as well as creatinine excretion with the urine were found as compared to healthy younger adults. Apparently, only in the case of vitamin B6, there is serious doubt about the adequacy of the status of the elderly, which needs further investigation. As far as has been investigated, it appeared that reference values derived from a population of apparently healthy adults below 50 years of age are not applicable to apparently healthy elderly.