Potential pitfalls of a fiducial marker-matching technique in carbon-ion radiotherapy for lung cancer

Background/Aim: To analyze the accuracy of patient positioning and dose distribution quality using a fiducial marker-matching technique in carbon-ion radiotherapy (C-ion RT) for stage I lung cancer. Patients and Methods: Thirteen patients with 26 fiducial markers and 104 radiation fields were examined. Change in the fiducial marker position coordinates from the gross tumor volume center (Δm), and change in the water-equivalent path length of the chest wall (ΔWEL) were measured in each radiation field. Criterion for an acceptable change in dose distribution was defined as the percentage of D95 (%D95) at gross tumor volume greater than 90% of the prescribed dose. Results: Thirteen radiation fields (12.5%) were classified as unacceptable. Δm and ΔWEL had significant negative correlations with %D95 and thus were significant factors related to unacceptable irradiation fields. Conclusion: Patient positioning using a fiducial marker-matching technique resulted in 12.5% of radiation fields demonstrating unacceptable degradation due to Δm and ΔWEL.