In this study, we compared RATS and VATS for patients with lung cancer who were deemed suitable for lobectomy. The results showed that the long-term outcomes, including three-year survival rates, were comparable between the RATS and VATS groups. This finding is consistent with those of previous meta-analyses and reports from single institutions [2, 4, 6, 7, 9,10,11,12,13,14]. Similar to previous reports, there was no marked difference in the upstaging rate from cN0 to pN1/2 between the two groups, suggesting that RATS can achieve radicality comparable to VATS [15, 16].

Compared to VATS, RATS has a longer operative time but less blood loss. This suggests that superior maneuverability and high-definition vision of RATS may contribute to more precise surgical manipulation and better bleeding control. However, RATS lacks tactile feedback, necessitating meticulous dissection of the blood vessels and careful handling of the lungs, which may contribute to the longer operative time observed in RATS. In the future, advancements in robotic technology that enable tactile feedback during RATS may prove beneficial in reducing the operative time and further enhancing bleeding control.

The conversion rate from RATS to open thoracotomy varies considerably across reports [1,2,3,4,5,6,7]. In our study, RATS had a significantly lower conversion rate to open thoracotomy than VATS. This result is consistent with findings from other studies [1, 4, 5, 7]. There are two possible reasons for this. First, the incidence of pulmonary artery injury was higher in the VATS group than in the RATS group. In our study, the reasons for conversion to open thoracotomy in VATS were emergency thoracotomy due to pulmonary artery injury in 4 out of 10 cases (40%) and maneuverability issues in the others. Conversely, the incidence of pulmonary artery injuries in RATS was low (n = 4), with only 1 case requiring conversion to open thoracotomy due to high urgency. Furthermore, there were no instances in which conversion to open thoracotomy was necessary due to maneuverability issues.

The advantages of high-definition vision and the free maneuverability of forceps with articulated joints in RATS may have resolved various difficult situations and problems that could not be addressed with VATS. Lymph nodes adhering to vessels pose a technical challenge and increase the risk of conversion to emergency or prophylactic open thoracotomy due to vascular injury. RATS, with its enhanced dexterity, precision, and magnified vision, allows for meticulous dissection. For example, even if a lymph node cannot be dissected from a vessel, it is easier with RATS than with VATS to dissect the lung parenchyma, expose the vessel more peripherally, and divide it at a location that avoids the adhered lymph node. Our experience suggests that, at least in our institution, the advantages of magnified vision in RATS outweigh the disadvantages of the lack of tactile feedback when handling vessels, resulting in a reduced conversion rate. Second, the decision to convert to thoracotomy in RATS is significantly influenced by not only the surgeon's experience but also the assistant’s proficiency. At our institution, multiple robotic surgeons during the study period also participated as assistants in other RATS procedures. This means that the assistants were highly skilled and possessed an advanced understanding of the unique movements and blind spots associated with robotic surgery, as they themselves were experienced robotic surgeons. Furthermore, in RATS, in which the surgeon cannot immediately intervene, the assistant's experience is crucial for proceeding with the operation without anxiety about conversion to open thoracotomy. The assistant must be capable of effectively managing emergencies. This may have contributed to the low conversion rate of RATS in our institution.

In our study, while RATS demonstrated a trend toward a lower rate of intraoperative pulmonary artery injury than VATS, the difference was not statistically significant (4 [2.9%] vs. 11 [8.0%], p = 0.069). However, once pulmonary artery injury occurred, the conversion rate to open thoracotomy was similar between the approaches: 25% (1 of 4 cases) for RATS and 36% (4 of 11 cases) for VATS. This suggests that if pulmonary artery hemorrhaging occurs, conversion to open thoracotomy may be necessary with a comparable frequency in both RATS and VATS to ensure safe completion of the operation. This result is consistent with previous studies reporting higher in-hospital mortality in patients undergoing lung surgery who required emergent conversion to open thoracotomy than in those who underwent complete minimally invasive surgery [5]. Therefore, to minimize the need for emergency conversion due to bleeding, it may be necessary in the future to establish clear criteria for conversion, such as a time limit for dissecting lymph nodes adhered to vessels.

As previously reported [17], the incidence of prolonged postoperative air leaks was higher in the RATS group than in the VATS group. Although the reason for the increased incidence of prolonged air leak after RATS could not be elucidated in a previous study, the incidence of prolonged postoperative air leak after VATS at our institution was lower than that in other reports, whereas the incidence of prolonged air leak after RATS was comparable to other published data. A significantly higher incidence of unexpected postoperative air leaks was observed in the RATS group than in the VATS group. This finding suggests that missed air leaks during the intraoperative sealing test may have contributed to this finding. Many of these patients underwent pleurodesis with OK-432 intrapleural administration, which was the main cause of Clavien-Dindo classification grade ≥ III complications in RATS. There were no marked differences in the length of hospital stay, 30-day re-operation rate, or 30-day re-admission rate. Based on our findings and those of previous reports, RATS appears to offer postoperative and long-term outcomes comparable to those of VATS. A future challenge to be addressed is the comparison of the postoperative quality of life between the two groups. Cheng et al. used the QoR-15 scale to show that RATS has better postoperative recovery than VATS [18]. Lan et al. showed that RATS was associated with a lower rate of postoperative dysfunction in the first seven days after surgery than VATS [19]. In our study, we were unable to compare these items because patient pain and recovery data were unavailable.

The median follow-up period was 44.5 months, and the 3-year OS and DFS rates were calculated. There were no significant differences in either the OS or DFS between the two groups, although the RATS group tended to show a lower 3-year DFS than the VATS group. This may be attributed to the significantly higher proportion of pStage III patients in the RATS group. Although further investigation with a larger sample size is necessary, these findings suggest that the surgical approach does not significantly affect the long-term outcomes.

Several limitations associated with the present study warrant mention. First, this was a single-center retrospective cohort study with a limited number of cases. However, the use of propensity score matching to adjust for imbalances in patient backgrounds is believed to yield more reliable results. Second, in both the RATS and VATS groups, the surgeons were not fixed, and differences in skill levels may have been reflected in the results. Because of the Japanese system, in which RATS surgeons are limited to board-certified members of the Japanese Association for Thoracic Surgery, RATS surgeons in this study had significantly more surgical experience than VATS surgeons. Attempts to match years of experience resulted in a drastically reduced sample size and an uneven distribution of cases among specific surgeons, precluding adjustment for this difference between the two groups. Finally, segmentectomy was covered by insurance in 2020 during the study period. Furthermore, because the results of the JCOG0802/WJOG4607L trial [20] were announced around the same time, segmentectomy is now actively performed for lung cancers with a maximum diameter of ≤ 20 mm. Therefore, some of the patients enrolled in this study may now be eligible for segmentectomy, and the patient population may differ somewhat from the current clinical practice. The accumulation of more cases and further investigations are necessary.

In conclusion, at our institution, RATS lobectomy for lung cancer demonstrated long-term outcomes comparable to those of VATS lobectomy. Although RATS was associated with a longer operative time than VATS, its potential benefits included reduced blood loss and a lower conversion rate to open thoracotomy than VATS.