In the morning...
The second day started with a very busy morning in which two different sessions followed one another. Chairmen Thomas Beyer and Ulli Köster opened up the second part of the discussion about nuclear medicine that had started yesterday evening. Michael Lassmann, from the University of Wurzburg (Germany), took the stage to give an overview of “theranostics” in nuclear medicine.
Michael Lassmann during his talk. (Picture: Salvatore Fiore)
The word “theranostics”, coined in 2005 for describing the use of imaging for therapy planning in radiation oncology, is used in nuclear medicine to refer to the use of short-lived tracers for predicting the absorbed doses in molecular radiotherapy and, thus, helping to evaluate the safety and efficacy of a treatment. It is a very active field of research and nowadays many new radiopharmaceuticals are available for imaging and molecular radiotherapy. Nevertheless, it is still a challenge to establish reliable dose-response relationships.
The following speakers gave an overview of different isotopes and biomarkers used for a variety of nuclear medicine applications and, more specifically, as tracers able to offer insight into treatment efficacy.
Nigel Stevenson, from the US enterprise R-NAV, in particular, presented new positive results about the use of the isotope Sn-117m, which is a prime candidate for several personalized nuclear medicine applications, thanks to its unique characteristics. It emits a primary photon that can be used for imaging, as it is easily detectable with a SPECT camera system, along with mono-energetic conversion electrons that have a therapeutic effect.
The second part of the morning was dedicated to detectors and imaging. The session, chaired by Denis Dauvergne and Alberto Del Guerra, started with an intriguing talk by Thomas Bortfeld, from the Massachusetts General Hospital and Harvard Medical School, who focused the attention on an issue that is very critical for hadron-therapy effectiveness: beam spatial control. The biggest advantage of particle beam therapy, which is the finite range of the beam, can be a double-edged sword, because the over- or under-shoot of the beam requires extra margins (in order to spare the healthy tissue), but this can compromise the dose distribution and the efficacy of the therapy. That is why big effort is being put in developing imaging techniques for beam range assessment.
A number of possibilities are being studied, but according to Bortfeld at the moment prompt gamma imaging appears to be the most promising; it is based on the detection of secondary gamma radiation emitted from nuclear reactions of protons with tissue. It would allow detecting in real time the position of the beam in the body of the patient (during treatment) with an accuracy of about 1mm. With such a precision the range margins could be reduced, resulting in significant improvements of treatment quality.
Another interesting alternative technique for real-time range control is thermo-acoustic imaging: the proton beam produces a sound wave that can be detected in order to infer the position of the beam in the body. Actually this is not a new idea, but lately it is being reconsidered, because the technique seems able to provide a very high precision measurement of beam position.
Thomas Bortfeld talking about imaging for online beam range control. (Picture: Salvatore Fiore)
Several talks in the morning session were dedicated to positron emission tomography (PET). Reducing PET scanning times and radiation exposure, while improving image quality and accuracy, requires detectors characterized by high efficiency, and very high spatial and time resolutions. Dennis Schaart, from the Delft University of Technology, showed the encouraging results of studies on monolithic scintillators, whose signal is collected with a dual-sided readout, instead of a conventional back-side readout.
The construction of a cost-effective whole-body scanner that would allow simultaneous PET/CT and PET/MRI imaging was discussed by Pawel Moskal, from the Jagiellonian University, Poland. This J-PET apparatus, named after the Jagiellonian University where this research started, is built out of axially arranged plastic (instead of crystal) scintillator strips, forming a cylinder. The light signals produced in the scintillators are converted to electrical pulses by photomultipliers placed at the two ends of each strip. The hit position and time are reconstructed on the base of the time of arrival of light signals to the extremes of the scintillator strips.
The morning was closed up by Riccardo Faccini, from INFN and Università Sapienza, Rome, who presented a novel technique for radio-guided surgery (RGS). RGS is based on the principle of introducing in the tumor specific radiolabelled tracers and then perform a complete resection of the lesion under the guide of the radiation emitted by the tracers. While established methods employ gamma emitting tracers and gamma-ray detection probes, the Italian team of which Faccini is a member is developing an innovative technique exploiting beta radiation. The advantages are that it penetrates only a few millimeters, resulting both in a lower required radio-pharmaceutical activity and the possibility to adopt this technique for tumors located nearby healthy organs. In addition, the use of beta particles emitters would reduce the exposition to radiation of the medical personal.
A few more talks in the afternoon closed the session dedicated to detectors and imaging. Sebastian Lehrack, from the Ludwig Maximilians Universität of Munich, and Kevin Jones, from the University of Pennsylvania, went back to beam range control based on the measurement of the acoustic signals generated by proton or ion beams. Finally, Bjarne Stugu, from the University of Bergen, Norway, presented the last results accomplished by the 3DMiMic collaboration, which designed and fabricated very thin silicon strip detectors for microbeam monitoring.
In the afternoon...
New technologies are key weapons in the fight against cancer and several sessions of the conference cover this field with high-level presentations and speakers.
Among them, Jan Lagendijk, from the Universitair Medisch Centrum Utrecht focussed his presentation on the use of magnetic resonance imaging for external beam radiotherapy guidance. Lagendijk explained that although for certain tumours it is possible to have a good visualization of the cancerous structures with cone beam CT-linac radiotherapy systems, that’s not the case for all the tumours. Indeed, for most other tumour locations, such as rectum, oesophagus, pancreas, kidney or individual lymph nodes, the limited visualization using cone beam CT and the lack of dynamic information hinder a better targeting.
After Lagendijk’s talk, we saw another aspect of MRI guidance thanks to Shady Kotb, from the Université Claude Bernard Lyon 1. Like his colleague, Kotb confirmed that effective treatment with radiation therapy is often limited by non-optimal tumour visualization as well as by effects produced by collateral damage of healthy tissues. But in his study, Kotb’s presented a different approach: he showed that one possibility to overcome the problem is to combine radiation with nanoparticles containing high-Z elements, which are known to locally boost the effectiveness of radiation as cancer killer. In order to test this hypothesis, Kotb’s team developed gadolinium-based nanoparticles named AGuIX (Activation-Guided Irradiation by X-ray) for MRI-guided radiotherapy. After a radiosensitization – the action of making tumour cells more sensitive to radiation therapy – they observed a significant effect when AGuIX were combined with X-rays exposure in vitro. Next step: a clinical trial phase I on patients with multiple brain metastases will be launched in France in winter 2016.
Immaculada Martínez-Rovira, from the Laboratoire d’Imagerie et Modélisation en Neurobiologie et Cancérologie d’Orsay, and the Universitat Autònoma de Barcelona, tackled another topic: hadron minibeam radiation therapy. Hadron therapy, which has remarkable effectiveness, still could benefit from a lower impact on non-targeted tissues to allow its administration at higher doses, and hadron minibeam radiation therapy (MBRT) may be an answer. MBRT consists in combining spatially fractionated radiation therapy with submillimetric-width beams (hundreds of μm). This novel strategy benefits from the advantages of high dose conformability and remarkable biological effectiveness of hadron therapy and might guarantee tissue recovery and reduce the side effects of radiation in healthy tissues.
After the coffee break, we joined the IT side of the force with Klaus Maier-Hein, from the University of Heidelberg. He showed that radiomics – the extraction and analysis of large amounts of advanced quantitative imaging features with high throughput – can be used for image-based personalized medicine. Maier-Hein captivated the audience with a very interesting example on computing models: together with his team, he developed a method to anticipate the development and progression of tumours – a work still in progress but already very promising!
The afternoon concluded in music with a public lecture of Domenico Vicinanza and Genevieve Williams on sound as tool for scientific investigation (that you can watch here). A relaxing way of digesting the rich scientific plate that the ICTR-PHE participants enjoyed today!