Dose escalation study using 4D CT planning in locally advanced pancreatic cancer

Introduction: Approximately 30% of patients diagnosed with pancreatic cancer will present with locally advanced unresectable disease (LAPC). Improved planning techniques provide the opportunity for dose escalation.

Methods: From February 2010 to September 2010, patients with LAPC suitable for CRT were planned using contrast enhanced 4D CT scanning. We compared 4D CT treatment planned according to local protocol using 50.4 Gy (4D50.4) and 55.8 Gy (4D55.8) compared with the NCRN/SCALOP protocol (50.4 Gy SCALOP50.4). Our local protocol defines gross tumour volume (GTV) outlined on all respiratory phases of image sets generated by 4D CT with a radiologist (using the SCALOP study protocol). An internal target volume (ITV) was generated as a composite of all GTVs. This ITV was grown with 1 cm circumferential margin and 1.2 cm superior–inferiorly to define a PTV. Dose constraints and PTV coverage were defined by the SCALOP protocol.

Results: We identified nine patients who had 4D CT scans from April to October 2010. We found that the mean reduction in small bowel doses for V15small bowel was 17% and the mean V45small bowel was reduced by 28% when 4D50.4 was compared with SCALOP50.4. With dose escalation to 55.8 Gy, 4D55.8 remained compliant with the organs at risk constraints and these values, including the mean small bowel doses (V15small bowel and V45small bowel) remained comparable to the SCALOP50.4. Patients set-up errors were reviewed during treatment and found to be acceptable for our PTV margins. No acute grade 3 or 4 toxicity was observed of the eight patients treated with 4D50.4 plans.

Conclusion: In this study, 4D CT planning using our protocol would allow dose escalation without a significant increase in the small bowel dose.