Contribution of PET/CT In the Design of the Involved Node Radiotherapy (INRT) Concept for Patients with Localized Hodgkin Lymphoma: Preliminary Results on 117 Patients.

The INRT concept, that limit delineates irradiated volume to lymphoma-infiltrated node, requires an extremely precise determination of the number and volume of initially involved nodes. In the study, we tried to assess the additional value of a PET/CT performed before treatment.

Early-stage lymphoma patients entered in the EORTC-GELA-IIL.

Data imaging comprising PET/CT prior to treatment and CT simulation prior to radiotherapy were retrieved using the DICOM/DICOM-RT imaging network connecting all French cancer centers participating in the H10 trial. A lymph node was considered to be involved if it fulfilled 3 requirements: FDG uptake was greater than the background, was clearly identifiable on CT, and either decreased or disappeared after chemotherapy. Involved lymph nodes were delineated on CT first before adding the information provided by PET. Differences between the number of involved lymph nodes and areas were compared before and after PET/CT assessment.

From March 2007 to February 2010, 117 patients from 18 French Cancer Centers and hospitals were included in the study. PET/CT identified at least one additional FDG-avid lymph node in 82/117 patients (70%; CI 95%: 61–78%). Additional lymph nodes were observed significantly (p = 0.008) more frequently when PET/CT was performed without IV contrast (in 79% of the patients versus 56%). At least one additional lymph node area was detected by PET in 49/117 patients (42%; CI 95%: 33–51%). There was a 15% (CI 95%: 9–22%) increase in the gross target volume (GTV) due to the additional information provided by PET (a 20% increase in 10% of the patients). On the other hand, after chemotherapy, there was a 10% (CI 95%: 5–18%) increase in the clinical target volume (CTV) in the 96 assessable patients (a 20% increase in 10% of the patients).

PET/CT with IV contrast may be an important imaging procedure for implementing the INRT concept.

Ribrag:LFB: Honoraria, Research Funding; servier: Research Funding; celgene: Research Funding; pfizer: Honoraria; novartis: Honoraria.