Dosimetric performance of cone beam CT-guided adaptive carbon-ion radiotherapy with daily replanning for pancreatic cancer.

PURPOSE: We investigated whether an ultra-hypofractionated carbon-ion radiotherapy (CIRT) protocol for pancreatic cancer (PC) could produce satisfactory dosimetric results with or without cone-beam CT-guided adaptive replanning and explored the potential dosimetric advantages of the adapted protocol.

METHODS

Eleven PC patients who underwent CBCT-guided online adaptive photon radiotherapy were selected. Data were imported into a CIRT treatment planning software to develop new plans for an ultra-hypofractionated CIRT protocol. Prescriptions and constraints were recalculated for a five-fraction schedule using a linear quadratic model for organs-at-risk (OARs) and targets, respectively. The biologically effective dose-equivalent prescribed dose was set at 43.2 Gy (relative biological effectiveness [RBE]). Each day, a synthetic CT (SCT) was generated from the planning CT (PCT) with the daily CBCT. A reference plan based on the PCT was compared to an adapted plan based on the SCT. Deformable image registration was used to allow summation of the daily doses.

RESULTS

The adapted plans met the clinical goals, whereas the reference plans exceeded the constraints in 27 % (stomach), 53 % (duodenum), and 31 % (small bowel) of the fractions. The adapted plans notably decreased V35.5 Gy[RBE] for all gastrointestinal OARs, while significantly enhancing the gross tumor volume (GTV) D95% and planning target volume (PTV) D90%. The accumulated doses showed significant improvements in the duodenum V35.5 Gy[RBE], GTV D95%, and PTV D90%.

CONCLUSION

CBCT-guided adaptive CIRT for PC demonstrated favorable dosimetric results, notably enhancing the sparing of OARs and ensuring superior target coverage compared with non-adaptive CIRT protocols.