Ix series linac

The standards laboratories provide calibration factors under standard ambient conditions. For the National Physical Laboratory, these are 20 °C, 1013.25 mbar (1013.25 hPa), and 50% humidity. All of the readings reported in this work have been corrected for nonstandard ambient conditions employing IPEM recommendations [15] . IBA CC04 (SN: 108640) ion chamber in combination with Dose1 electrometer (IBA Dosimetry, Nuremberg) have been used to study ion recombination with conventional radiotherapy electron beam and VHEE beams. CC04 is a thimble-type, waterproof ion chamber which exhibits high spatial resolution due to its small volume (0.04 cm 3 ) and is considered to be suitable for small fields measurements in high dose gradients [21] . The measurements with the CC04 chamber are recommended to be carried out at +300 V polarizing voltage. The electrometer was set up in the charge integration mode to determine the accumulated charge over the whole irradiation period. Ion recombination measurements have been carried out for 165 MeV VHEE beams at the SPARC beamline [4] and for 20 MeV electron beam generated by a Varian iX series LINAC.

For ion recombination measurements in the 20 MeV electron beam, the IBA CC04 chamber was placed in a standard grade solid water phantom (Gammex, Middleton, WI) with 5 cm of build-up and 20 cm thickness of solid water to provide adequate backscattering conditions (Fig. 1(a)). The chamber was irradiated with a 20 MeV electron beam with Varian iX series LINAC at SSD of 100 cm with a 10 Â 10 cm 2 field size.
Ion recombination measurements with VHEE beam have been carried out at the SPARC LINAC. A 3 mm thick Perspex window was used to interface the beamline with open air, in which the dosimetric setup was placed. VHEE measurements were carried out in a 30 Â 30 Â 30 cm 3 water phantom, placed 41 cm after the exit window. Ion chamber is positioned at a depth of 2.8 cm (Fig. 1(b)). The field size of the beam at the plane of measurement was 0.9 cm FWHM (full width at half maximum). The energy of the electron beam for this irradiation was set to 165 MeV with 0.5% FWHM energy spread. The root mean square (rms) electron bunch length duration was 0.87 ps.