With regards to patient selection she determined that elderly patients (≥70 years) who were carefully selected for chemoradiotherapy had similar long-term outcomes as younger patients (<70 years). Age alone should therefore not be a contraindication for this treatment. She also investigated the predictive value of tumor markers in the blood (CEA and CA19-9) before starting chemoradiotherapy. This revealed that patients with elevated levels of both tumor markers have a 10 times increased chance of early disease recurrence. Being able to predict this is important since 1 in 5 patients doesn't profit from an intensive, combined treatment with chemoradiotherapy and surgery because of early disease recurrence.
In collaboration with radiotherapists around the Netherlands Voncken also investigated the role of PET-CT in tumor delineation for the treatment plan. Although PET did influence the delineation of the tumor, there was still variation between radiotherapists in determining the tumor borders, indicating there is room for further improvement. In addition, she found that compensating for respiration movement during PET-CT did not improve the demarcation of the tumor nor the detection of suspicious lymph nodes.
Voncken also investigated several variables that could improve image-guided radiotherapy and more accurate and individualized irradiation. In order to irradiate a tumor accurately uncertainty margins are necessary. She found possible ways to reduce and individualize those margins.
One in three oesophageal cancer patients has a complete pathological response following neo-adjuvant chemoradiotherapy, that is, before surgery. Recognizing a good response is still challenging though and current techniques to measure that response (f.e. PET-CT and endoscopy) have limitations. Recent technical improvements have enabled making high resolution MRI-images of oesophageal tumors. Vonckens research into response assessment of oesophageal cancer following chemoradiotherapy by means of MRI-scans is promising and shows that the assessment could possibly be improved with those scans.
Practical information about the defense can be found on VU university's website.