Response to Letter to the Editor for “Effect of Intraoperative Image-Guided Spinal Navigation Technologies on Endoscopic Lumbar Spine Surgery: A Systematic Review and Meta-Analysis”

We thank the authors for their thoughtful comments and the opportunity to clarify our methodology.

In the 6 studies contributing to the radiation dose outcome, 5 studies reported data directly from the radiation emitter device, calculated as cumulative air kerma (CAK), also termed reference air kerma (RAK), in units of mGy.^1-5 RAK indicates the radiation incident on the patient’s skin during fluoroscopy or interventional procedures, measured at a standardized reference point (typically 15 cm from the isocenter toward the X-ray tube). The remaining study measured radiation using a dosimeter placed on the patient’s neck, reporting peak skin dose (PSD) in μSv. ⁶ For X-rays, a radiation weighting factor of 1 applies (1 Gy = 1 Sv),^7,8 and we therefore used standardized mean difference (SMD) to harmonize these different scales in our pooled analysis.

In clinical practice, both dose–area product (DAP) and CAK are widely used for patient radiation monitoring. DAP is a useful index for estimating stochastic risk, while CAK is commonly used to approximate skin dose.^8,9 PSD, in contrast, provides a better estimate of deterministic risk (tissue reactions) but is rarely available in real time and usually requires direct dosimetry or indirect estimation from CAK with correction for backscatter and overlapping fields.^10,11 Prior validation studies have shown that CAK can serve as a reliable surrogate for PSD when accurately displayed, supporting its use as a dose indicator.^12,13

We agree that combining directly and indirectly measured PSD may introduce methodological heterogeneity. To address this concern, we conducted a sensitivity analysis excluding the study that used direct dosimetry. The results remained consistent with the primary analysis, and heterogeneity was not substantially altered (Supplemental File 1). These findings reinforce our conclusion that intraoperative navigation is associated with a meaningful reduction in radiation exposure.

Nevertheless, we acknowledge that future studies should report more standardized and comprehensive radiation metrics, including effective dose and surgeon exposure, to further strengthen the evidence base and clinical applicability of this field.

Supplemental Material

Supplemental Material - Response to Letter to the Editor for “Effect of Intraoperative Image-Guided Spinal Navigation Technologies on Endoscopic Lumbar Spine Surgery: A Systematic Review and Meta-Analysis”

Supplemental Material for Response to Letter to the Editor for “Effect of Intraoperative Image-Guided Spinal Navigation Technologies on Endoscopic Lumbar Spine Surgery: A Systematic Review and Meta-Analysis” by Yu-Che Wang, Hsu-I Chou, Ying-Fong Su, Garcia de Oliveira Rafael, Abhinav K. Sharma, Yang-Ching Chen, Anh Tuan Bui, Ching-Yu Lee, Jowy Tani, Cheng-Chun Chang, Takaki Yoshimizu, Wongthawat Liawrungrueang, Tsung-Jen Huang, Daisuke Sakai, Klaus John Schnake, Jason Pui Yin Cheung, Don Young Park, and Meng-Huang Wu in Global Spine Journal