[en] The absorbed dose standard for high dose rate (HDR) ¹⁹²Ir brachytherapy sources at the UK National Physical Laboratory (NPL) is a graphite calorimeter. Calorimetry offers a more direct method to measure absorbed dose compared to ionometry and usually results in lower overall measurement uncertainties. Radiation energy imparted in the annular calorimeter core with a mean radius of 2.5 cm is converted to the quantity of interest, absorbed dose rate to water at 1 cm distance from the centre of the source, 𝐷 ̇ _{w, 1 cm}. The required graphite-to-water conversion and perturbation correction factors for absorbed dose measurements of the HDR ¹⁹²Ir Isodose Control Flexisource have been calculated with Monte Carlo (MC) techniques. 𝐷 ̇ _{w, 1 cm} of the HDR ¹⁹²Ir Flexisource was measured with the calorimeter and the reference air kerma rate (RAKR) was measured with NPL’s HDR ¹⁹²Ir air kerma primary standard. The dose rate constant of the Flexisource was measured by taking the ratio of the two quantities and was compared against the published consensus value.

[en] Purpose: Elekta recently developed a solution for in-vivo EPID dosimetry (iViewDose, Elekta AB, Stockholm, Sweden) in conjunction with the Netherlands Cancer Institute (NKI). This uses a simplified commissioning approach via Template Commissioning Models (TCMs), consisting of a subset of linac-independent pre-defined parameters. This work compares the performance of iViewDose using a TCM commissioning approach with that corresponding to full commissioning. Additionally, the dose reconstruction based on the simplified commissioning approach is validated via independent dose measurements. Methods: Measurements were performed at the NKI on a VersaHD™ (Elekta AB, Stockholm, Sweden). Treatment plans were generated with Pinnacle 9.8 (Philips Medical Systems, Eindhoven, The Netherlands). A farmer chamber dose measurement and two EPID images were used to create a linac-specific commissioning model based on a TCM. A complete set of commissioning measurements was collected and a full commissioning model was created.The performance of iViewDose based on the two commissioning approaches was compared via a series of set-to-work tests in a slab phantom. In these tests, iViewDose reconstructs and compares EPID to TPS dose for square fields, IMRT and VMAT plans via global gamma analysis and isocentre dose difference. A clinical VMAT plan was delivered to a homogeneous Octavius 4D phantom (PTW, Freiburg, Germany). Dose was measured with the Octavius 1500 array and VeriSoft software was used for 3D dose reconstruction. EPID images were acquired. TCM-based iViewDose and 3D Octavius dose distributions were compared against the TPS. Results: For both the TCM-based and the full commissioning approaches, the pass rate, mean γ and dose difference were >97%, <0.5 and <2.5%, respectively. Equivalent gamma analysis results were obtained for iViewDose (TCM approach) and Octavius for a VMAT plan. Conclusion: iViewDose produces similar results with the simplified and full commissioning approaches. Good agreement is obtained between iViewDose (simplified approach) and the independent measurement tool. This research is funded by Elekta Limited

[en] The need for standardization and improved dosimetry for pre-clinical studies has become a priority for clinical and translational radiotherapy working groups. At UCL Cancer Institute, a small animal irradiator SARRP (Xstrahl) is used for both: in vivo and in vitro (cells) irradiations. The geometrical conditions for cell irradiations don’t allow for the use of Muriplan treatment planning system. Full backscatter conditions required by dosimetry protocols are also not possible. Therefore, an accurate dosimetry of the beam in those delivering conditions is required. The current study presents a dosimetric characterization of the SARRP for cell irradiations.

[en] Inorganic scintillation detectors (ISDs) are a source of interest for relative measurements in a wide range of X-ray beams. Their small dimensions and the possibility to produce real-time readings, makes them attractive for measurements in small fields. A commercially available detector for in vivo dosimetry, DoseWire (DoseVue N.V, Belgium), was characterized with medium energy X-rays. The present study evaluates the possibilities of its use for relative measurements in small animal irradiators.

[en] Electron beams from laser-plasma wakefield accelerators have low transverse emittance, comparable to those from conventional radio frequency accelerators, which highlights their potential for applications, many of which will require the use of quadrupole magnets for optimal electron beam transport. We report on characterizing electron bunches where double bunches are observed under certain conditions. In particular, we present pepper-pot measurements of the transverse emittance of 120–200 MeV laser wakefield electron bunches after propagation through a triplet of permanent quadrupole magnets. It is shown that the normalized emittance at source can be as low as 1 π mm mrad (resolution limited), growing by about five times after propagation through the quadrupoles due to beam energy spread. The inherent energy-dependence of the magnets also enables detection of double electron bunches that could otherwise remain unresolved, providing insight into the self-injection of multiple bunches. The combination of quadrupoles and pepper-pot, in addition, acts as a diagnostic for the alignment of the magnetic triplet. (paper)

[en] The lack of suitable dosimetry protocols, coupled with the increasing complexity of pre-clinical irradiation platforms, undermines confidence in preclinical studies and represents a serious obstacle in the translation to clinical practice. To accurately measure output of a pre-clinical radiotherapy unit, appropriate Codes of Practice (CoP) for medium energy X-rays need to be used. However, determination of absorbed dose to water (D_w) relies on application of backscatter factor (B_w) employing in-air method or carrying out in-phantom measurement at the reference depth of 2 cm in a full scatter condition. The full scatter conditions require the size of the phantom extending outside the beam edges and have been recommended to be at least 30 × 30 × 30 cm³. In most of the instances in pre-clinical irradiators the full scatter conditions cannot be fulfilled and, moreover, are not adequate to geometries used in pre-clinical practice. Therefore, additional recommendations to the existing CoP are required to accurately determine the dose rate (beam output) relevant to irradiation configurations in pre-clinical radiation research.

[en] Recent Monte Carlo (MC) studies have shown that the use of Very high Energy Electrons (VHEEs), with energies up-to 250 MeV, can provide more favourable dose distributions in comparison to current photon and electron therapy. Ionisation chamber response and correction factors, in particular for ion recombination, are typically small at clinical energies and can be accounted for with high precision according to an electron beam dosimetry Code of Practice. In high dose-per-pulse beams, ion recombination is a larger concern with a correction of approximately 20% being observed for Intraoperative Radiotherapy (IORT) beams. For the case of ultra-short VHEEs the dose-per-pulse can be orders of magnitude higher than that of IORT. Therefore, the ability to correct accurately for ion recombination will play a crucial role in dose determination using ionisation chambers. Current recombination models are quoted to be accurate for the high saturation region where more than 70% of the charge is being collected by the chamber. Those models are expected to be invalid for the ultra-short VHEEs and a new ion recombination correction procedure may be required.

[en] Very high energy electrons (VHEE) in the range from 100–250 MeV have the potential of becoming an alternative modality in radiotherapy because of their improved dosimetry properties compared with MV photons from contemporary medical linear accelerators. Due to the need for accurate dosimetry of small field size VHEE beams we have performed dose measurements using EBT2 Gafchromic® film. Calibration of the film has been carried out for beams of two different energy ranges: 20 MeV and 165 MeV from conventional radio frequency linear accelerators. In addition, EBT2 film has been used for dose measurements with 135 MeV electron beams produced by a laser-plasma wakefield accelerator. The dose response measurements and percentage depth dose profiles have been compared with calculations carried out using the general-purpose FLUKA Monte Carlo (MC) radiation transport code. The impact of induced radioactivity on film response for VHEEs has been evaluated using the MC simulations. A neutron yield of the order of 10"−"5 neutrons cm"−"2 per incident electron has been estimated and induced activity due to radionuclide production is found to have a negligible effect on total dose deposition and film response. Neutron and proton contribution to the equivalent doses are negligible for VHEE. The study demonstrates that EBT2 Gafchromic film is a reliable dosimeter that can be used for dosimetry of VHEE. The results indicate an energy-independent response of the dosimeter for 20 MeV and 165 MeV electron beams and has been found to be suitable for dosimetry of VHEE. (paper)