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We experimentally observe and theoretically analyse oscillations of a spherical bubble in a gelatin gel under ultrasound irradiation to quantify viscoelastic effects on the nonlinear bubble dynamics. A bubble nucleus is generated by focusing a laser pulse into a 6 wt% gelatin gel supersaturated with dissolved air, which enables us to control the bubble radius at mechanical equilibrium via influx of the gas air into the bubble. Linearized and finite-amplitude oscillations of the bubble are driven by 28 kHz ultrasound and recorded by a high-speed camera; the resonance curves of the oscillation amplitude as a function of the equilibrium radius are constructed for different ultrasound intensities. First, the viscosity and shear modulus of the gel are obtained by fitting the resonance curve (for the lowest ultrasound intensity) to the linearized solution of the Rayleigh–Plesset model that accounts for the gel's nonlinear elasticity of neo-Hookean type and diffusive effects on the bubble dynamics. Next, finite-amplitude oscillations of the bubble are compared with the nonlinear Rayleigh–Plesset calculations. The comparison suggests a need to include the gel's elasticity in the calculations to more accurately reproduce the nonlinear bubble dynamics. Another important finding is that the so-called spring softening feature appears in the experimentally determined resonance curve as the oscillation amplitude increases, which can be predicted by the Rayleigh–Plesset model. Furthermore, our experiment with the highest ultrasound intensity shows non-spherical oscillation of mode 1 that does not appear in the case of water but can be predicted by shape instability theory.

BackgroundMetabolomics is useful for analyzing the nutrients necessary for cancer progression, as the proliferation is regulated by available nutrients. We studied the metabolomic profile of gastric cancer (GC) tissue to elucidate the associations between metabolism and recurrence.MethodsCancer and adjacent non-cancerous tissues were obtained in a pair-wise manner from 140 patients with GC who underwent gastrectomy. Frozen tissues were homogenized and analyzed by capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). Metabolites were further assessed based on the presence or absence of recurrence.ResultsNinety-three metabolites were quantified. In cancer tissues, the lactate level was significantly higher and the adenylate energy charge was lower than in non-cancerous tissues. The Asp, β-Ala, GDP, and Gly levels were significantly lower in patients with recurrence than in those without. Based on ROC analyses to determine the cut-off values of the four metabolites, patients were categorized into groups at high risk and low risk of peritoneal recurrence. Logistic regression and Cox proportional hazard analyses identified β-Ala as an independent predictor of peritoneal recurrence (hazard ratio [HR] 5.21 [95% confidence interval 1.07–35.89], p = 0.029) and an independent prognostic factor for the overall survival (HR 3.44 [95% CI 1.65–7.14], p < 0.001).ConclusionsThe metabolomic profiles of cancer tissues differed from those of non-cancerous tissues. In addition, four metabolites were significantly associated with recurrence in GC. β-Ala was both a significant predictor of peritoneal recurrence and a prognostic factor.

BackgroundUrinary dysfunction (UD) remains a significant complication of rectal cancer surgery. In modern surgical treatment for rectal cancer, multiple operative approaches are used. Such approaches include open, laparoscopic, and robotic-assisted surgery; and multiple procedures, including anterior, intersphincteric, and abdominoperineal resection. Thus, modern surgical treatments for rectal cancer have diversified. This study aimed to identify risk factors for early UD (EUD) after total mesorectal excision (TME) and to explore the methods for decreasing postoperative EUD in diverse surgical treatments for rectal cancer.MethodsIn our retrospective cohort study, we enrolled patients with lower rectal cancer who underwent TME alone at a single high-volume cancer center between 2010 and 2017. EUD was defined as the presence of ≥ 50 mL residual urine volume. Multivariate analysis was performed to determine clinicopathological factors significantly associated with postoperative EUD.ResultsOf a total of 337 eligible patients, 32 patients (10%) had postoperative EUD. Multivariate analysis revealed that only the operative approach (laparoscopic surgery: odds ratio [OR], 8.93; 95% confidence interval [CI], 2.94–27.14, open surgery: OR, 11.55; 95% CI 2.10–63.83) was significantly associated with an increase in postoperative EUD. Robotic-assisted surgery was associated with significant reduction in postoperative EUD.ConclusionOnly robotic-assisted surgery was inversely correlated with postoperative EUD. Robotic-assisted surgery may be a useful approach to protect urinary function in lower rectal cancer surgery.

PurposesSeveral retrospective studies have demonstrated the safety and technical feasibility of robotic-assisted laparoscopic surgery (RALS). The aim of the present study was to clarify the advantages of RALS for rectal cancer by comparing its short-term outcomes with those of conventional laparoscopic surgery (CLS).MethodsBetween April, 2010 and April, 2015, a total of 974 patients underwent proctectomy for rectal cancer. After the exclusion of those who underwent open surgery, high anterior resection, lateral lymph node dissection, or multiple resection, 442 patients were enrolled in this study, including 203 who underwent RALS and 239 who underwent CLS. We compared the short-term outcomes of these two groups.ResultsThere was no case of conversion to open surgery in the RALS group, but 8 (3.3 %) cases in the CLS group (p = 0.009). Operative time was not significantly different, but blood loss was significantly less in the RALS group than in the CLS group (p < 0.001). The postoperative hospital stay was shorter in the RALS group than in the CLS group (p < 0.001). The rate of urinary retention was significantly lower in the RALS group than in the CLS group (p = 0.018).ConclusionThe short-term outcomes in this series provide further evidence that RALS may be superior to CLS for rectal cancer.

BackgroundThe long-term outcomes of robotic-assisted laparoscopic lateral lymph node dissection (RALLD) have not been fully investigated. This study aimed to assess the oncological and long-term outcomes of RALLD for rectal cancer through comparison with those of open lateral lymph node dissection (OLLD) in a retrospective study.MethodsBetween September 2002 and October 2014, the medical data of 426 patients who underwent total mesorectal excision with lateral lymph node dissection for primary rectal cancer were collected. Of these, 115 patients were excluded after data collection (stage IV, n = 61; total pelvic exenteration, n = 31; multiple cancer, n = 20; conventional laparoscopic surgery, n = 3). Before matching, 311 patients with clinical stage II/III were analyzed. Using exact matching, patients were stratified into RALLD (n = 78) and OLLD (n = 78) groups. Pathological findings and long-term outcomes were compared between the groups.ResultsThe pathological stage and number of harvested lymph nodes showed no significant differences between the groups. The rate of positive resection margin in the RALLD group tended to be lower compared with that of the OLLD group (p = 0.059). The median follow-up duration was 54.0 months in 156 patients. The 5-year overall survival rate was 95.4 and 87.8% in the RALLD and OLLD groups, respectively (p = 0.106). The 5-year relapse-free survival rate was 79.1 and 69.9% in the RALLD and OLLD groups, respectively (p = 0.157). The 5-year local relapse-free survival rate was 98.6 and 90.9% in the RALLD and OLLD groups, respectively (p = 0.029).ConclusionsThe short- and long-term outcomes indicated that RALLD may be a useful modality for locally advanced low rectal cancer.

Background Few data are available to assess the learning curve for robotic-assisted surgery for rectal cancer. The aim of the present study was to evaluate the learning curve for robotic-assisted surgery for rectal cancer by a surgeon at a single institute. Methods From December 2011 to August 2013, a total of 80 consecutive patients who underwent robotic-assisted surgery for rectal cancer performed by the same surgeon were included in this study. The learning curve was analyzed using the cumulative sum method. This method was used for all 80 cases, taking into account operative time. Results Operative procedures included anterior resections in 6 patients, low anterior resections in 46 patients, intersphincteric resections in 22 patients, and abdominoperineal resections in 6 patients. Lateral lymph node dissection was performed in 28 patients. Median operative time was 280 min (range 135–683 min), and median blood loss was 17 mL (range 0–690 mL). No postoperative complications of Clavien–Dindo classification Grade III or IV were encountered. We arranged operative times and calculated cumulative sum values, allowing differentiation of three phases: phase I, Cases 1–25; phase II, Cases 26–50; and phase III, Cases 51–80. Conclusions Our data suggested three phases of the learning curve in robotic-assisted surgery for rectal cancer. The first 25 cases formed the learning phase.

Purpose The purpose of this study was to evaluate the advantages of robot-assisted laparoscopic surgery (RALS) for lower rectal cancer and for visceral obesity cases, which have been regarded as challenging situations in rectal cancer surgery, comparing their surgical outcomes with those of conventional laparoscopic surgery (CLS). Methods Patients who underwent robotic or laparoscopic total mesorectal excision for rectal cancer were included in this retrospective study. Surgical outcomes including perioperative, postoperative, and pathological data were compared between the RALS and CLS groups. Patients were stratified into obese and non-obese groups according to visceral fat area (VFA). Obesity was defined by VFA ≥130 cm 2 . Results Two hundred thirty-six patients were enrolled, including 127 cases in the RALS group and 109 cases in the CLA group. A total of 82 (34.7 %) cases were categorized as VFA obese, including 52 cases in the RALS and 30 cases in the CLS groups. RALS for lower rectal cancer was associated with less blood loss ( p  = 0.007), a lower overall complication rate (9.4 % in RALS vs 23.9 % in CLS, p  = 0.003), and shorter postoperative stay ( p  < 0.01) than CLS, with similar operative time and pathological results. The overall complication rate was significantly lower in the RALS group with VFA obesity; blood loss was significantly less and the postoperative stay was shorter in the RALS group with visceral obesity. Conclusions The present study demonstrated that RALS has some advantages in terms of surgical outcomes over CLS in challenging situations of rectal cancer surgery, such as lower rectal cancer cases and visceral obesity cases.

BackgroundVarious predictors of the difficulty of total mesorectal excision for rectal cancer have been described. Although a bulky mesorectum was considered to pose technical difficulties in total mesorectal excision, no studies have evaluated the influence of mesorectum morphology on the difficulty of total mesorectal excision. Mesorectal fat area at the level of the tip of the ischial spines on magnetic resonance imaging was described as a parameter characterizing mesorectum morphology. This study aimed to evaluate the influence of clinical and anatomical factors, including mesorectal fat area, on the difficulty of total mesorectal excision for rectal cancer.MethodsThis study enrolled 98 patients who underwent robotic-assisted laparoscopic low anterior resection with total mesorectal excision for primary rectal cancer, performed by a single expert surgeon, between 2010 and 2015. Magnetic resonance imaging-based pelvimetry data were collected. Linear regression was performed to determine clinical and anatomical factors significantly associated with operative time of the pelvic phase, which was defined as the time interval from the start of rectal mobilization to the division of the rectum.ResultsThe median operative time of the pelvic phase was 68 min (range 33–178 min). On univariate analysis, the following variables were significantly associated with longer operative time of the pelvic phase: male sex, larger tumor size, larger visceral fat area, larger mesorectal fat area, shorter pelvic outlet length, longer sacral length, shorter interspinous distance, larger pelvic inlet angle, and smaller angle between the lines connecting the coccyx to S3 and to the inferior middle aspect of the pubic symphysis. On multiple linear regression analysis, only larger mesorectal fat area remained significantly associated with longer operative time of the pelvic phase (p = 0.009).ConclusionsMesorectal fat area may serve as a useful predictor of the difficulty of total mesorectal excision for rectal cancer.

Background The goal of this study was to evaluate the short-term outcomes of robotic-assisted lateral lymph node dissection for patients with advanced lower rectal cancer. Methods Between 2012 and 2013, 50 consecutive patients underwent robotic-assisted lateral lymph node dissection for rectal cancer in Shizuoka Cancer Center Hospital. Perioperative outcomes including operative time, operative blood loss, length of stay, postoperative complications, and histopathological data were collected prospectively. Results Median patient age was 62 years (range 36–74 years). Operative procedures included low anterior resections ( n  = 27), intersphincteric resections ( n  = 16), and abdominoperineal resections ( n  = 7). Bilateral lymph node dissection was performed in 44 patients. The median operative time was 476 min (range 320–683 min), and the median time required for lateral lymph node dissection was 165 min (range 85–257 min). The median blood loss was 27 mL (range 5–690 mL). There were no cases of open surgery or laparoscopic conversion. The median duration of postoperative hospital stay was 8 days (range 6–13 days). Clavien–Dindo classification Grade III–IV complications occurred in only one patient (2.0 %). There were no cases of anastomotic leak. There was no perioperative mortality. The median number of harvested lateral lymph nodes was 19 (range 5–47). Conclusions Robotic-assisted lateral lymph node dissection is a safe, feasible, and useful approach for patients with advanced lower rectal cancer.

Purpose Scientific evidence supporting robotic-assisted laparoscopic surgery (RALS) for rectal cancer remains inconclusive because most previous reports were retrospective case series or case-control studies, with few reports focusing on long-term oncological outcomes with a large volume of patients. The aim of this study was to clarify the short- and long-term outcomes of a large number of consecutive patients with rectal cancer who underwent RALS in a single high-volume center. Methods The records of 551 consecutive patients who underwent RALS for rectal adenocarcinoma between December 2011 and March 2017 were examined to reveal the short-term outcomes. The oncological outcomes of the 204 patients who underwent surgery between December 2011 and March 2014 were evaluated. Results Most patients had tumors located in the lower or mid-rectum (86.0%). Only 7.6% of patients underwent neoadjuvant chemoradiotherapy. Lateral lymph node dissection was performed for 191 patients (34.7%). The median operative time was 257 min, median blood loss was 10 mL, and no transfusions were needed. No conversion to open surgery was necessary. Eighteen patients (3.3%) had Clavien-Dindo grade III postoperative complications. Six patients (1.1%) had positive resection margins. The mean follow-up duration of the 204 patients was 43.6 ± 9.8 (months). The 5-year cancer-specific survival rate for stage I/II/III/IV was 100%/100%/100%/not reached, respectively. The 5-year relapse-free survival rate for stage I/II/III/IV was 93.6%/75.0%/77.6%/ not reached, respectively. The rate of local recurrence was 0.5%. Conclusions Our results suggest that RALS is technically feasible for rectal cancer and has good short- and long-term outcomes.