Recent advances of PET imaging in clinical radiation oncology

Abstract

Radiotherapy and radiation oncology play a key role in the clinical management of patients suffering from oncological diseases. In clinical routine, anatomic imaging such as contrast-enhanced CT and MRI are widely available and are usually used to improve the target volume delineation for subsequent radiotherapy. Moreover, these modalities are also used for treatment monitoring after radiotherapy. However, some diagnostic questions cannot be sufficiently addressed by the mere use standard morphological imaging. Therefore, positron emission tomography (PET) imaging gains increasing clinical significance in the management of oncological patients undergoing radiotherapy, as PET allows the visualization and quantification of tumoral features on a molecular level beyond the mere morphological extent shown by conventional imaging, such as tumor metabolism or receptor expression. The tumor metabolism or receptor expression information derived from PET can be used as tool for visualization of tumor extent, for assessing response during and after therapy, for prediction of patterns of failure and for definition of the volume in need of dose-escalation. This review focuses on recent and current advances of PET imaging within the field of clinical radiotherapy / radiation oncology in several oncological entities (neuro-oncology, head & neck cancer, lung cancer, gastrointestinal tumors and prostate cancer) with particular emphasis on radiotherapy planning, response assessment after radiotherapy and prognostication.

Keywords: GI malignancies; Head & neck cancer; Lung cancer; Neuro-oncology; PET; Prostate cancer; Radiation oncology.

Fig. 1

A 54 years-old female patient with extensive edema on T2 MRI (a) and new contrast enhancing lesions at the temporal and occipital lobe (b) after undergoing stereotactic radiosurgery for brain metastases from malignant melanoma at both sites. MRI findings were suggestive for tumor recurrence, whereas only a faint uptake on ¹⁸F-FET PET (c) and fused PET/MRI (d) was seen in both lesions, a finding typical for radiation necrosis. Radiation necrosis was subsequently confirmed by histopathology

Fig. 2

Patient with HPV-positive squamous cell carcinoma of the right tonsil (T1 cN3 M0), who underwent ¹⁸F-FDG-PET/CT for staging prior to radiotherapy and subsequent inclusion of PET-positive tumor masses and lymph nodes in radiotherapy planning

Fig. 3

A patient with newly diagnosed NSCLC (cT2b N3 M1b) and ¹⁸F-FDG PET/CT for staging (a) and inclusion in radiotherapy planning (b)

Fig. 4

A 68-years old male patient with newly diagnosed anal cancer Stage IIIC (cT4 cN1 cM0) and ¹⁸F-FDG PET/CT with ¹⁸F-FDG avid primary tumor and inguinal lymph node (a). ¹⁸F-FDG PET/CT was then used for radiotherapy planning with boost to the right inguinal lymph nodes and primary tumor (b)

Fig. 5

A 69-years old patient with biochemical recurrence of prostate cancer (pT2c pN0 R0 Gleason score 9, preoperative PSA 11.7 ng/ml) and evidence of PET-positive lymph node metastases (a) and radiotherapy-plan with dose-escalation to the PET-positive lymph nodes (b)