[Magnetic-resonance-guided radiotherapy : The beginning of a new era in radiation oncology?]

Multicentric characterisation of lateral beam profiles generated by 6FFF beam of three 0.35 T MR-linac systems

BACKGROUND

The physical characterisation of FFF-beam profiles in the presence of a magnetic field requires a new standardization procedure and formulation.

PURPOSE

The aim of this multicentric experience is to propose new normalisation factors to allow for the calculation of standard parameters typical of flattened beams, such as dosimetric field size and penumbra, for a 6 MV FFF beam from an MR-linac.

METHODS

The measurements were carried out on three ViewRay-MRIdiansystems. An equal set of measurements was acquired using the same equipment. Transverse beam profiles were acquired at seven different depthsand for six beam dimensions.The inflection point was estimated as the position of the maximum of a Gaussian fit obtained from the first derivative of the profiles. The position of the minimum and maximum points of the second derivative of the above Gaussian described the fall-off region, and the external peaks of the third derivative were considered as the in-field and out-field points. The profile normalisation was determined by imposing a 55% dose level at the inflection point and the renormalisation factors were calculated.

RESULTS

The position of the inflection point, and the second and third derivatives peaks were analysed,and the renormalisation factors as a function of field size and depth were determined. The values of the unflatness and the slope have been calculated for different depths and field sizes.

CONCLUSION

This study represents the first multi-centric evaluation of the profiles on different low-field MR-Linac systems and theset of renormalisation parameters to analyse the FFF-beam on that system was effectively proposed.

Clinical application of MR-Linac in tumor radiotherapy: a systematic review

Recent years have seen both a fresh knowledge of cancer and impressive advancements in its treatment. However, the clinical treatment paradigm of cancer is still difficult to implement in the twenty-first century due to the rise in its prevalence. Radiotherapy (RT) is a crucial component of cancer treatment that is helpful for almost all cancer types. The accuracy of RT dosage delivery is increasing as a result of the quick development of computer and imaging technology. The use of image-guided radiation (IGRT) has improved cancer outcomes and decreased toxicity. Online adaptive radiotherapy will be made possible by magnetic resonance imaging-guided radiotherapy (MRgRT) using a magnetic resonance linear accelerator (MR-Linac), which will enhance the visibility of malignancies. This review's objectives are to examine the benefits of MR-Linac as a treatment approach from the perspective of various cancer patients' prognoses and to suggest prospective development areas for additional study.

[Primary treatment of prostate cancer using 1.5 T MR-linear accelerator]

Hintergrund

Der potenzielle Nutzen des verbesserten Weichteilkontrastes von MR-Sequenzen gegenüber der Computertomographie (CT) für die Radiotherapie des Prostatakarzinoms ist bekannt und führt zu konsistenteren und kleineren Zielvolumina sowie verbesserter Risikoorganschonung. Hybridgeräte aus Magnetresonanztomographie (MRT) und Linearbeschleuniger (MR-Linac) stellen eine neue vielversprechende Erweiterung der radioonkologischen Therapieoptionen dar.

Material und Methoden

Dieser Artikel gibt eine Übersicht über bisherige Erfahrungen, Indikationen, Vorteile und Herausforderungen für die Radiotherapie des primären Prostatakarzinoms mit dem 1,5-T-MR-Linac.

Ergebnisse

Alle strahlentherapeutischen Therapieindikationen für das primäre Prostatakarzinom können mit dem 1,5-T-MR-Linac abgedeckt werden. Die potenziellen Vorteile umfassen die tägliche MR-basierte Lagekontrolle in Bestrahlungsposition und die Möglichkeit der täglichen Echtzeitanpassung des Bestrahlungsplans an die aktuelle Anatomie der Beckenorgane (adaptive Strahlentherapie). Zusätzlich werden am 1,5-T-MR-Linac funktionelle MRT-Sequenzen für individuelles Response-Assessment für die Therapieanpassung untersucht. Dadurch soll das therapeutische Fenster weiter optimiert werden. Herausforderungen stellen u. a. die technische Komplexität und die Dauer der Behandlungssitzung dar.

Schlussfolgerung

Der 1,5-T-MR-Linac erweitert das radioonkologische Spektrum in der Therapie des Prostatakarzinoms und bietet Vorteile durch tagesaktuelle MRT-basierte Zielvolumendefinition und Planadaptation. Weitere klinische Untersuchungen sind notwendig, um die Patienten zu identifizieren, die von der Behandlung am MR-Linac gegenüber anderen strahlentherapeutischen Methoden besonders profitieren.