A new radiation dose minimization protocol in early chemotherapy response in lymphoma using 18F-FDG PET-CT

177 Objectives There is ever-increasing evidence of 18F-FDG-PET-CT being useful in monitoring early response to chemotherapy in lymphoma. With a concern of radiation burden this study aimed to assess if PET-CT acquisition area could be minimised in order to reduce radiation dose and acquisition time. Methods Retrospective analysis of 1000 consecutive lymphoma patients (553 male, mean 42.4years-old, 421 Hodgkin’s Lymphoma (HL), 579 Non-HL) was performed to record sites of disease on pre-chemotherapy PET-CT and the first post-chemotherapy PET-CT. The body is divided into four conventional parts (head-and-neck, thorax, abdomen and pelvis) for recording sites of disease. The potential reduction in radiation dose and time-saving achieved by limiting to the sites of known disease identified on pre-chemotherapy PET-CT was calculated. Results No FDG-uptake was seen in 744/1000 first post-chemotherapy PET-CT. FDG-uptake at known disease sites was seen in 256/1000 cases. 902/1000 of the patients had disease confined to only one or two body parts out of four. Incidental synchronous non-lymphomatous malignancy (such as colonic or lung carcinoma) was identified in 48/1000 cases in pre-chemotherapy PET-CT. Post-chemotherapy PET-CT did not reveal any unexpected sites of lymphoma or incidental interval malignancy. Limiting PET-CT to the sites of known disease would have reduced a mean radiation dose by 3.6 mSv (24.3 %), with a mean time-saving of 16 minutes (66.6%). Conclusions In order to assess early response to chemotherapy it may be sufficient to scan the sites of known disease. This leads to reduce the incidence of secondary cancers, particularly in the young patients experiencing multiple radiation exposure.