ESTRO 36 Abstract Book

S176 ESTRO 36 2017 _______________________________________________________________________________________________

1 Université Catholique de Louvain- Institute of Experimental & Clinical Research, Molecular Imaging- Radiotherapy & Oncology, Brussels, Belgium 2 Centre Antoine Lacassagne, Medical Physics, Nice, France 3 EBG MedAustron GmbH, Medical Physics, Wiener Neustadt, Austria 4 National Physical Laboratory, Acoustics and Ionising Radiation Division, Teddington, United Kingdom 5 Cliniques Universitaire St-Luc, Radiotherapy and Oncology Dep., Brussels, Belgium 6 IBA Dosimetry GmbH, Schwarzenbruck, Germany Purpose or Objective The main application of calorimeters in standards laboratories is as primary standard of absorbed dose to water against which ionisation chambers (ICs) are calibrated. At present, no calorimeter is established as a primary standard instrument in proton beams. Based on the absorbed dose-formalism of IAEA TRS-398, this work describes a direct comparison between a water calorimeter (WCal) and plane-parallel ICs in clinical pulsed pencil beam scanning (PBS) proton beams, delivered by a synchrocyclotron. The temporal beam characteristics and the absence of a dosimetry protocol for such beams create significant challenges in absorbed dose determination. The aim of this work is to demonstrate the feasibility a water calorimetry in pulsed PBS beams. Material and Methods The method consisted in comparing the response of WCal and ICs (PPC40 and PPC05) in the same reference conditions. Measurements have been performed at a depth of 3.1 cm using two mono-layers maps of proton beams (10 x 10 cm²), with incident beam energies of 96.17 MeV (range in water = 6.8 g/cm²) and 226.08 MeV (range in water = 31.7 g/cm²), respectively. The response of the WCal is corrected for heat transfer (calculated using numerical simulations based on finite element method) and non-water material inside the WCal (using experimentally derived factors). Using hydrogen- saturated high-purity water in the WCal, the chemical heat defect is assumed to be zero. Classical correction factors are applied to the response of ICs: temperature and pressure, polarity and recombination (k s ). k s was studied in detail due to the very high beam dose rate used with the delivery method. Results Table 1 shows preliminary relative differences of D w measured with WCal and IC, during two independent experimental campaigns, for both energies. A small positioning uncertainty could explain that the ratios obtained during campaign B are higher for the low energy beam. For campaign A, however, ratios are higher for the high energy beam, which cannot be explained by a positioning uncertainty. A new campaign is planned to repeat the measurement of correction factors to improve the statistics of the results.

SP-0337 “From the ground up” – tackling challenges at the country level M.L. Yap 1 1 Liverpool Cancer Therapy Centre, Ingham Institute for Applied Medical Research, Liverpool, Australia The global incidence of cancer is rising rapidly, particularly in low and middle-income countries (LMICs). Radiotherapy is a core component of cancer care and has been demonstrated to be cost effective. Despite this, there is a significant shortfall of services in LMICs, with 65% of low-income countries having no radiotherapy services available. Recently, an evidence-based case for investment in radiotherapy services in LMICs has been developed. The Collaboration for Cancer Outcomes, Research and Evaluation (CCORE) group have demonstrated that if the gap in radiotherapy services in LMICs were closed by 2035, millions of patients would derive local control and/or survival benefits as a result of radiotherapy. In addition, the Global Task Force for Radiotherapy in Cancer Control (GTFRCC)'s Lancet Oncology Commission paper demonstrated that although initial outlays are required to start up a radiotherapy service, economic net gains can be achieved in LMICs over a 20-year period. IT has been estimated that >5500 megavoltage machines would be required to meet the gap in radiotherapy services in LMICs. However the challenges pertaining to radiotherapy in LMICs are not just limited to the supply of radiotherapy machines, but also concern the safe and effective running of new and established radiotherapy departments. The breakdown of the solitary radiotherapy machine in Uganda was publicised in the mainstream media last year, as a stark image of the challenges facing LMIC radiotherapy departments. There is a severe shortage of trained radiotherapy and oncology staff in LMICs, with the GTFRCC report estimating that over 30 000 radiation oncologists, 22 000 medical physicists and 78 000 radiation therapists will need to be trained in LMICs by 2035 in order to meet the projected radiotherapy demand. Regional organisations such as RANZCR-FRO’s Asia Pacific Radiation Oncology Special Interest Group (APROSIG) aim to support LMIC radiotherapy departments in this endeavour, alongside international initiatives such as the International Cancer Experts Corp, and Medical Physicists without Borders. As well as regional/international support, the key factors on a local level imperative to success will be discussed, with examples such as Cambodia and Botswana used to illustrate these. With regards to technology use in these countries, the approach has been stratified to the needs and expertise on a local level. Collaboration between these local, regional and international initiatives, as well as the IAEA, PACT, ESTRO, ASTRO and other organisations is crucial to the safe and effective delivery of radiotherapy in LMICs. SP-0338 Access to radiotherapy: cancer-specific approaches to a global problem D.Rodin 1Princess Margaret Centre, Department of Radiation Oncologym Toronto, Canada

Abstract not received

Conclusion The preliminary results are very encouraging and demonstrate that water calorimetry is feasible in a clinical pulsed PBS proton beam. The absolute relative differences between D w derived from WCal and IC are inferior to 2%, which is within the tolerance of the IAEA TRS-398 protocol. Due to the depth-dose distribution, a depth inferior to 3.1 cm (e.g. 2 cm where the gradient is lower) would be more suitable to minimise the uncertainty in positioning. Further numerical and experimental investigations are

Proffered Papers: Dose measurement and dose calculation for proton beams

OC-0339 Water calorimetry in a pulsed PBS proton beam S. Rossomme 1 , R. Trimaud 2 , V. Floquet 2 , M. Vidal 2 , A. Gerard 2 , J. Herault 2 , H. Palmans 3,4 , J.M. Denis 5 , D. Rodriguez Garcia 5 , S. Deloule 6 , S. Vynckier 1,5