PhD ceremony Ms. C.T. Muijs: The use of PET/CT in the radiotherapy treatment planning for esophageal cancer

PhD ceremony: Ms. C.T. Muijs

Dissertation: The use of PET/CT in the radiotherapy treatment planning for esophageal cancer

Promotor(s): prof. J.A. Langendijk, prof. J.T.M. Plukker

Faculty: Medical Sciences

This thesis focused on the validation of FDG-PET/CT in the radiotherapy treatment planning for patients with esophageal cancer to determine whether the use of PET/CT results in a more adequate radiotherapy and treatment outcome.

FDG-PET/CT results in changes in radiotherapy target volumes and consequently adjusted radiotherapy treatment plans. However, it remains questionable whether the PET/CT-based target volume also represents the true tumor volume.

After CT-based neo-adjuvant (chemo)radiotherapy, microscopic tumour was found outside the margin for microscopic tumour in a substantial part of the patients at pathologic evaluation, which had an negative impact on survival. These results suggests inaccurate tumour volume delineation, inadequate margins and/or tumour growth.

The RESPECT trial was undertaken to validate the additional value of PET/CT clinically. The endpoint was the proportion of locoregional recurrences that could have been prevented if the radiotherapy treatment planning for esophageal cancer was based on PET/CT instead of CT. Locoregional recurrences were seen in 11% of the patients. Accurate recurrence analysis showed that none of these locoregional recurrences were preventable by the use of PET/CT. These results suggest a limited value of PET/CT for radiotherapy planning, in terms of preventing locoregional recurrences.

The PET/CT for radiotherapy planning can be useful for patient selection and delineation of pathologic lymph nodes. Esophageal cancer can progress rapidly, even in the time between the diagnostic PET/CT and the one for radiotherapy planning. A planning PET/CT might reveal new pathologic lymph nodes or distant metastases.