Dr Michael Jameson, PhD
Research and Development Physicist
New South Wales Cancer Institute Early Career Fellow, Liverpool and Macarthur Cancer Therapy Centres
Ingham Institute for Applied Medical Research, University of New South Wales, Sydney, Australia
Diagnostic medical imaging has become more routinely used in radiotherapy, from planning to response assessment. The tools to register (geometrically align) and fuse (view multiple images at the same time) medical images have become standard in radiotherapy treatment planning systems.
The inclusion of deformable image registration (DIR) represented a new challenge for medical physicists as the results can be non-intuitive and the algorithms are somewhat “black box” in commercial systems. Therefore, a group of NSW medical physicists working on these radiotherapy planning issues, began to meet circa 2016.
A number of face-to-face and virtual meetings were held to discuss some of these problems. Discussions were particularly focused on the draft American Association of Medical Physicists’ (AAPM) TG-132 report which dealt with the use of image registration and fusion algorithms used in radiotherapy techniques. The report expertly dealt with DIR applications and QA but, by design, did not cover deforming radiotherapy dose distributions.
When TG-132 was eventually released and we began further discussions on its implementation, we realised we weren’t the only ones grappling with these issues, other physicists in NSW were also trying to commission DIR. So, we decided to arrange a workshop on this topic with the catchy name the ‘Society for Medical Image Registration and Fusion’ (SMIRF) for the group attending. Members would be affectionately known as SMIRFs! The ACPSEM, NSW Branch Chairman (Jeff Barber and a SMIRF) volunteered to coordinate the workshop. So….
Inaugural Workshop on Image Registration
In June of 2018, the NSW/ACT branch of ACPSEM, organised a workshop on DIR be held at the University of Sydney. The target audience for the workshop were Physicists, Therapists, Radiation Oncologists and Computer Scientists. The workshop was held over two days covering a range of theoretical and practical topics on DIR.
Day 1.
A survey report of national and international centres using DIR in the clinic, was presented. Important lectures that followed were:
• the theory and various applications of DIR;
• atlas segmentation; and
• a comprehensive review of TG-132.
A multidisciplinary panel discussion followed which addressed case studies and controversial topics and then attention was focused on deforming dose and adaptive radiotherapy.
All this excitement was topped with canapes, drinks and networking in the Holme building on campus!
Day 2.
The practical issues related to implementing DIR and the related technologies in a clinical setting, were discussed in-depth. The audience was polled extensively using their smartphones to form consensus on topics including:
• commissioning;
• dose accumulation;
• re-treat;
• sharing atlas data;
• response assessment;
• DIR in brachytherapy;
• standard nomenclature; and
• frameworks for sharing data and adaptation.
There was an overview of available research platforms and the meeting discussed TROG related concerns about image registration in clinical trials.
The overall response to attend was both overwhelming and encouraging. Registration was closed well before the event. In fact, we ran out of space in the room (>120 people)!
Follow-up Melbourne Workshop
Following the success of the Sydney workshop and, with support from the Victorian Department of Health and Human Services, a condensed version of the NSW workshop was re-run in Melbourne. It was hosted by Peter MacCallum Hospital. Once again, the attendance and enthusiastic engagement was encouragingly strong. There were plenty of lively discussions on potential DIR use for clinical cases.
Proposed Special Interest Group
Given the success of the workshops, the SMIRFs consulted the ACPSEM with the possibility of forming a special interest group. With such a strong engagement from the other radiotherapy disciplines as co-organisers, speakers and attendees, we decided that any special interest group formed should be multidisciplinary and the first of its kind as an ACPSEM focus group.
Now that the SMIRFs were growing up, a more serious and less likely to attract legal action name was needed.
The ACPSEM accepted the formation of MIRSIG as a focus group with the objectives:
- Provide a strong and unified driving force for the management of medical image registration in Australasia
- Provide professional standards and solutions for safe and effective use of medical image registration for the benefit of the public.
The first formal meeting of MIRSIG was held on the 28 October at the Engineering and Physical Sciences in Medicine Conference (EPSM 2019) held in Perth.
Current activities planned for MIRSIG include:
• running workshops;
• publishing manuscripts on current and best practice in medical image registration; and;
• DIR challenges.
There are number of upcoming workshops. This includes “Practical Image Registration: Accounting for previous treatments and replans”, to be held in conjunction with the TROG ASM in March 2020. The TROG workshop will focus on:
• multi-modal target delineation;
• assessment of registration quality;
• composite dose distributions;
• tolerances;
and will involve a number of practical DIR sessions.
Future Activities
Future joint activities planned with professional organisations include ESTRO. MIRSIG has also a number of publications forthcoming. These include:
• An international practice pattern survey led by Johnson Yuen detailing the current state of rigid and deformable image registration in Australasia and internationally.
• A workshop report and recommendations for the clinical use of DIR, prepared by Jeffrey Barber, will be completed in 2020.
The annual initiative of a world planning competition, creating and comparing the ‘best’ plan, has become common practice in radiotherapy. It’s now a regular feature of the Trans-Tasman Radiation Oncology Group Annual Scientific Meeting (TROG ASM). These planning challenges have gained in popularity as they enable planners in different departments, centres or even countries to compare and compete with their colleagues to create the ‘best’ possible plan.
The facility to compare plans is also a valuable tool to establish a measure of quality and variability that may exist in the planning practice throughout the radiotherapy community.
Encouraged by the success of the radiation knowledge website, MIRSIG is developing a DIR version. Users will have the opportunity to download imaging data from a number of cases and perform DIR as they would clinically. The results of this study will be compared to the ground truth (known correct registration) and ranked.
In summary,
The MIRSIG is a newly established special interest group of ACPSEM. But it is open to multidisciplinary participation. The group is open to all healthcare disciplines and we are actively seeking interested members to join.
MIRSIG is undertaking a number of activities focused on improving the science and practice of medical imaging registration. We warmly welcome you to join MIRSIG and become an active member subscribing to betterhealthcaretechnology.org also.
Further enquiries can be directed to: mirsig@acpsem.org.au
Dr Michael Jameson PhD, 12 February 2020
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