Techniques from the field of nuclear medicine have been used for diagnostic and therapeutic purposes for over 50 years already, and for many years now, positron emission tomography (PET) has been an integral part of tumor diagnostics. PET/CT is an ideal combination of structural imaging (CT) and functional/metabolic imaging (PET) using an integrated scanner to make use of the advantages of both techniques: While a PET scan is very sensitive in detecting changes e.g. in malignant cells, which are visualized by means of a slightly radioactive tracer substance, the image resolution and anatomical information it provides are limited. CT imaging, on the other hand, offers a very high spatial resolution, permitting to allocate the recorded abnormal metabolic process to the corresponding anatomical structures or pathological masses. Constant technical improvements of this method now permit a complete body scan in only about 15 minutes with less and less exposure to radiation.
PET is a diagnostic procedure with therapeutic consequences and is becoming increasingly important in Hodgkin lymphoma, where it is used in particular to differentiate between vital tumor tissue and scarred residual tissue. PET/CT results play a role in treatment decisions in various situations, both during chemotherapy and after its completion when it has to be decided whether a patient needs additional radiotherapy.
PET/CT in Hodgkin lymphoma
PET/CT diagnostics in Hodgkin lymphoma are performed by means of the tracer [18F]FDG, which enables to measure the metabolized glucose (sugar) in the tissue. Vital lymphoma tissue has an increased glucose metabolism while the metabolic processes in scarred tissue are reduced.
Since the beginning of the GHSG’s 5th trial generation (HD15 for advanced stages of Hodgkin lymphoma), PET/CT has been used as an examination technique. Patients with residual tumor tissue received an [18F]FDG-PET/CT. Due to the high negative predictive value of the PET/CT scan, PET-negative patients (no tracer accumulation in the residual tumor tissue) were not irradiated. Radiotherapy was only performed on those patients with PET-positive residual tumor tissue after chemotherapy. With this approach the negative predictive value of FDG-PET could be tested in a large number of patients and, moreover, for PET-negative patients the toxicity of therapy could be reduced. The GHSG’s HD15 trial for advanced stages of Hodgkin lymphoma proved PET to possess a very high negative predictive value after chemotherapy (94%). The GHSG’s results of the HD15 trial, which were published in “Blood” and “Lancet”, led the German Joint Government Committee (G-BA) to accept [18F]FDG-PET/CT as a regular examination covered by public health insurance.
For the assessment of the PET and the activity in the residual lymphoma tissue, the Deauville criteria are applied.
This key for describing the glucose metabolism is used internationally and was developed and agreed upon on two international conferences by study groups and experts (on the International Workshop on Interim PET in Lymphoma, which took place in Deauville/France in 2009 and in Menton/France in 2010, 2011 and 2012).
Tasks of the nuclear-medical review center
- To consult nuclear-medical examiners and oncologists by reassessing PET/CT examinations
- To organize the expert panel meetings for all active trials