Robustness of patient positioning for interfractional error in carbon ion radiotherapy for stage I lung cancer: Bone matching versus tumor matching

Publication date: Available online 31 October 2017
Source:Radiotherapy and Oncology
Author(s): Makoto Sakai, Yoshiki Kubota, Jun-ichi Saitoh, Daisuke Irie, Katsuyuki Shirai, Ryosuke Okada, Masami Torikoshi, Tatsuya Ohno, Takashi Nakano
Background and purposePatient positioning was compared by tumor matching (TM) and conventional bony structure matching (BM) in carbon ion radiotherapy for stage I non-small cell lung cancer to evaluate the robustness of TM and BM in determining interfractional error.Material and methodsSixty irradiation fields were analyzed. Computed tomography (CT) images acquired before treatment initiation for confirmation (Conf-CT) were obtained under the same settings as the treatment planning CT images and used to evaluate both positioning methods. The dose distributions were recalculated for Conf-CT using both BM and TM, and the dose–volume histogram parameters [V95% of clinical target volume, V5Gy(RBE) of normal lung, and acceptance ratio (ratio of cases with V95% > 95%)] were evaluated. The required margin, which in 90% of cases achieved the acceptable condition, was also examined.ResultsUsing BM and TM, the median V95% was 98.93% and 100% (p < 0.001) and the mean V5Gy(RBE) was 135.9 and 125.8 (p = 0.694), respectively. The estimated required margins were 7.9 and 3.3 mm and increased by 53.9% and 2.5% of V5Gy(RBE), respectively, compared with planning.ConclusionsTM ensured a better dose distribution than did BM. To enable TM, volumetric imaging is crucial and should replace 2D radiographs for carbon therapy of stage I lung cancer.



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