NACP 2014 and the Turku PET symposium: The interaction between therapy and imaging

In the field of radiotherapy (RT) in particular, and oncology in general, developments in imaging and therapy go hand in hand [1]. Key achievements in tomographic imaging during the past decades, in particular the development of computer tomography (CT), laid the foundation for modern individualised RT. Further improvements in therapy, however, called for new modalities for both structural and functional imaging, such as magnetic resonance imaging (MRI) and positron emission tomography (PET), to fully exploit the improved dose-sculpting potential of new RT delivery techniques. Medical physics spans across all these areas, both in terms of clinical application fields as well as regarding research, with the aim of contributing to improved treatment outcome of the cancer patients of today as well as of the future.

The present issue of Acta Oncologica contains a collection of publications presented at two recently organised joint events, the 2014 symposium of the Nordic Association for Clinical Physics (NACP) and the Turku PET symposium, held in Turku, Finland (24–27 May 2014). Such a joint set-up follows from previous NACP events held in Aarhus (in 2008) and Uppsala (in 2011), both leading to a series of papers presented in dedicated issues of Acta Oncologica [2,3]. After the Aarhus meeting, Acta Oncologica has been an official journal of NACP. Over these years, the journal has seen a steady increase in the medical physics submissions/publications [3]. This has been a mutually beneficial collaboration, with the journal providing Nordic medical physicists their own scientific publication channel while these submissions has contributed to a steady growth in the journal ‘performance parameters’ (number of submissions, citations, impact factor, etc) [4].

The Turku PET symposium is held every three years, originating from a meeting in 1977 when a group of leading PET-related scientists from different disciplines gathered in Turku under the topic of ‘Medical application of cyclotrons’. In the PET symposia in the following years the programmes have covered all areas from targetry and radiochemistry to instrumentation and modelling as well as clinical applications of PET. The present version of the PET symposium (the 13th in the sequence) gathered around 400 participants from various disciplines.

In harmony with the joint set-up with the PET symposium, the theme of the NACP 2014 symposium was ‘Imaging in Oncology’, with the aim of linking medical physicists of different disciplines. Across the Nordic countries, most medical physicists are operating in the field of RT, and this was also reflected in the work presented at the meeting, as well as the papers appearing in this issue [5–13]. These papers together illustrate the typical research areas of medical physicists, usually being instrumental for development and clinical implementation of new treatment modalities. Medical physics development also provides a better understanding of the physical principles underlying RT, with models for both dose deposition in tissue as well as for how these dose distributions translate into clinical outcomes. In the present RT papers, both old and new ‘Nordic specialities’ were represented, including developments in adaptive RT, gynaecological brachytherapy, biological modelling and proton therapy.

The theme of ‘Imaging in Oncology’ can be understood as two different areas that partly overlap, namely the functional imaging developments in oncology in general as well as the interaction between therapy and imaging.

MRI has become a well-established diagnostic imaging modality, in particular due to its high-resolution anatomy representation [14]. Also in oncology and RT, MRI is used for a number of indications [15]. Along with the focus on biological image guidance in RT, MRI-based functional imaging has received a lot of attention also in the present journal, e.g. for characterisation of prostate tumours [16–18] and for visualisation of normal tissue structures in the brain [19]. Also in the present issue medical imaging physics studies are presented, in the setting of gynaecological cancer, addressing topical issues related to the challenge of quantification of the ‘biological’ endpoints that can be derived from contrast-enhanced and diffusion-weighted MRI [20,21].

PET has always had a strong relation with oncology, both with respect to clinical application and research [22,23]. Although [18F]-FDG is still the main radiotracer [24] there are several areas where it is far from optimal. In brain lesion detection the normal brain accumulation is high and therefore more specific tracers are needed. An example from this is the study of Kiviniemi et al. of several new F-18 and generator-based Ga-68 labelled tracers on glioma with animal models [25]. Another area is imaging of hypoxic cells that do not accumulate [18F]-FDG [26,27]. Also for [18F]-FDG new imaging strategies are developed. Dynamic imaging gives more information on the FDG accumulation [28] and motion management during scanning [29] are also being developed.

The interaction between therapy and imaging has progressed greatly during the past years. The renaissance started with the introduction of PET/CT images [30] as the basis of treatment planning. Today PET/CT is routinely used for deriving methods for more accurate staging, treatment planning and treatment response assessment [31–39]. MR-based planning for better delineation of abdominal organs has been used for adaptive cervical cancer RT [40,41]. Also studies of implementing PET/MR multimodal image registration and therapy planning have been presented [42–44]. The integration of imaging and therapy is also central to other key areas of RT, including adaptive therapy [1, 45–47] as well as in different strategies for motion-management [48–52].

The Nordic medical physics societies will gather next time in the setting of NACP in 2017 (in Oslo, Norway), under the theme ‘Bridging imaging and treatment’. Again this theme will underline the distinct role and considerable potential of medical physics at this exciting interface.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.