Applications of Accelerators and Detectors to Cancer Treatment

Abstract:

Objective.Spatially-fractionated radiotherapy (SFRT) delivered with a very-high-energy electron (VHEE) beam and a mini-GRID collimator was investigated to achieve synergistic normal tissue-sparing through spatial fractionation and the FLASH effect.Approach.A tungsten mini-GRID collimator for delivering VHEE SFRT was optimized using Monte Carlo (MC) simulations. Peak-to-valley dose ratios (PVDRs), depths of convergence (DoCs, PVDR ≤ 1.1), and peak and valley doses in a water phantom from a simulated 150 MeV VHEE source were evaluated. Collimator thickness, hole width, and septal width were varied to determine an optimal value for each parameter that maximized PVDR and DoC. The optimized collimator (20 mm thick rectangular prism with a 15 mm × 15 mm face with a 7 × 7 array of 0.5 mm holes separated by 1.1 mm septa) was 3D-printed and used for VHEE irradiations with the CERN linear electron accelerator for research beam. Open beam and mini-GRID irradiations were performed at 140, 175, and 200 MeV and dose was recorded with radiochromic films in a water tank. PVDR, central-axis (CAX) and valley dose rates and DoCs were evaluated.Main results.Films demonstrated peak and valley dose rates on the order of 100 s of MGy/s, which could promote FLASH-sparing effects. Across the three energies, PVDRs of 2-4 at 13 mm depth and DoCs between 39 and 47 mm were achieved. Open beam and mini-GRID MC simulations were run to replicate the film results at 200 MeV. For the mini-GRID irradiations, the film CAX dose was on average 15% higher, the film valley dose was 28% higher, and the film PVDR was 15% lower than calculated by MC.Significance.Ultimately, the PVDRs and DoCs were determined to be too low for a significant potential for SFRT tissue-sparing effects to be present, particularly at depth. Further beam delivery optimization and investigations of new means of spatial fractionation are warranted.

Abstract:

Given the present availability of high-gradient accelerator technology for compact and cost-effective electron linacs in the 100-200 MeV energy range, the interest for Very High Energy Electron (VHEE) radiotherapy (RT) for cancer treatment recently reached an all-time high. Particular significance is assumed by the Ultra-High Dose Rate (UHDR) regime where the so-called FLASH biological effect takes place, in which cancer cells are damaged while healthy tissue is largely spared. VHEE beams from linacs are especially well adapted for FLASH RT, given their penetration depth and the high beam current needed to treat large deep-seated tumours. In recent years, several multidisciplinary user groups carried out a number of studies on VHEE and FLASH RT issues using the CERN Linear Accelerator for Research (CLEAR) user facility, in close collaboration with the local operation team. In this paper, we give an overview of such activities and describe the main results of chemical and biological tests aimed at clarifying the damage mechanisms at the root of the FLASH effect and the relevant beam parameters needed to achieve it. We also describe the dedicated systems and methods developed and used in CLEAR for these activities, focusing on recent advances in the crucial aspects of uniform beam delivery and high dose rate real-time dosimetry.

Abstract:

Background

Access to high quality radiotherapy (RT) continues to be a major issue across Africa with Africa having just 34% of its optimal capacity.

Methods

We co-developed a survey with clinical, academic and policy stakeholders designed to provide a structured assessment of the barriers and enablers to RT capacity building in Africa. The survey covered nine key themes including funding, procurement, education and training. The survey was sent to RT professionals in 28 countries and the responses underwent qualitative and quantitative assessment.

Results

We received completed questionnaires from 26 African countries. Funding was considered a major issue, specifically the lack of a ring fenced funds from the Ministry of Health for radiotherapy and the consistency of revenue streams which relates to a lack of prioritisation for RT. In addition to a significant shortfall in RT workforce disciplines, there is a general lack of formal education and training programmes. 13/26 countries reported having some IAEA support for RT for education and training. Solutions identified to improve access to RT include a) increasing public awareness of its essential role in cancer treatment; b) encouraging governments to simplify procurement and provide adequate funding for equipment; c) increasing training opportunities for all radiotherapy disciplines and d) incentivizing staff retention.

Conclusion

This survey provides unique information on challenges to delivering and expanding radiotherapy services in Africa. The reasons are heterogonous across countries but one key recommendation would be for national Cancer Control plans to directly consider radiotherapy and specifically issues of funding, equipment procurement, servicing and training.

Policy summary

The study demonstrates the importance of mixed methods research to inform policy and overcome barriers to radiotherapy capacity and capability in LMICs.