Computed tomography (CT) has revolutionized external radiotherapy by making it possible to visualize and segment the tumors and the organs at risk in a three-dimensional way. However, if CT is a now a standard, it presents some limitations, notably concerning tumor characterization and delineation. Its association with functional and anatomical images, that are positron emission tomography (PET) and magnetic resonance imaging (MRI), surpasses its limits. This association can be in the form of a trimodality PET/CT/MRI. The objective of this mini-review is to describe the process of performing this PET/CT/MRI trimodality for radiotherapy and its potential clinical applications. Trimodality can be performed in two ways, either a PET/MRI fused to a planning CT (possibly with a pseudo-CT generated from the MRI for the planning), or a PET/CT fused to an MRI and then registered to a planning CT (possibly the CT of PET/CT if calibrated for radiotherapy). These examinations should be performed in the treatment position, and in the second case, a patient transfer system can be used between the PET/CT and MRI to limit movement. If trimodality requires adapted equipment, notably compatible MRI equipment with high-performance dedicated coils, it allows the advantages of the three techniques to be combined with a synergistic effect while limiting their disadvantages when carried out separately. Trimodality is already possible in clinical routine and can have a high clinical impact and good inter-observer agreement, notably for head and neck cancers, brain tumor, prostate cancer, cervical cancer.

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Modern radiation therapy techniques are characterized by high conformality to tumor volumes and steep dose gradients to spare normal organs. These techniques require accurate clinical target volume definitions and rigorous assessment of set up uncertainties using image guidance, a concept called image-guided radiation therapy. Due to alteration of patient anatomy, changes in tissue density/volumes and tumor shrinkage over the course of treatment, treatment accuracy may be challenged. This may result in excessive irradiation of organs at risk/healthy tissues and undercoverage of target volumes with a significant risk of locoregional failure. Adaptive radiation therapy (ART) is a concept allowing the clinician to reconsider the planned dose based on potential changes to accurately delivering the remaining radiation dose to the tumor while optimally minimizing irradiation of healthy tissues. There is little consensus on how to apply this concept in clinical practice. The current review investigates the current ART issues, including patient selection, clinical/dosimetric criteria and timing for re-planning, and practical technical issues. A practical algorithm is proposed for patient management in cases where ART is required.

Highlights: Sarcopenia is frequent in patients treated with radiation therapy (RT) or radiochemotherapy (RTCT) for head and neck squamous cell carcinomas. Sarcopenia is associated with poor disease-free survival and overall survival outcomes. Sarcopenia is not associated with a higher rate of treatment-related toxicity. Background: Sarcopenia occurs frequently with the diagnosis of head and neck squamous cell carcinoma (HNSCC). We aimed to assess the impact of sarcopenia on survival among HNSCC patients treated with radiotherapy (RT) or radiochemotherapy (RTCT). Methods: Patients treated between 2014 and 2018 by RT or RTCT with curative intent were prospectively included (NCT02900963). Optimal nutritional support follow-up, including weekly consultation with a dietician and an oncologist and daily weight monitoring, was performed. Sarcopenia was determined by measuring the skeletal muscles at the L3 vertebra on the planning CT scan for radiotherapy. For each treatment group (RT or RTCT), we assessed the prognostic value of sarcopenia for disease-free survival (DFS) and overall survival (OS) and its impact on treatment-related toxicity. Results: Two hundred forty-three HNSCC patients were included: 116 were treated by RT and 127 were treated by RTCT. Before radiotherapy, eight (3.3%) patients were considered malnourished according to albumin, whereas 88 (36.7%) patients were sarcopenic. Overall, sarcopenia was associated with OS and DFS in a multivariate analysis (HR 1.9 [1.1–3.25] and 1.7 [1.06–2.71], respectively). It was similar for patients treated with RT (HR 2.49 [1.26–4.9] for DFS and 2.24 [1.03–4.86] for OS), whereas for patients treated with RTCT sarcopenia was significantly associated with OS and DFS in univariate analysis only. Sarcopenia was not related to higher treatment-related toxicity. Conclusions: Pretherapeutic sarcopenia remains frequent and predicts OS and DFS for non-frail patients treated with curative intent and adequate nutritional support.

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