Radiofrequency ablation: effect of surrounding tissue composition on coagulation necrosis in a canine tumor model

PURPOSE: To determine the effect of surrounding tissue type on coagulation necrosis from radiofrequency (RF) ablation in a homogeneous animal tumor model. MATERIALS AND METHODS: Thirty canine venereal sarcomas were implanted in three tissue sites (subcutaneous, kidney, and lung) in 13 mildly immunosuppressed dogs. Five of 25 tumors, which were 19 mm +/- 3 (mean +/- SD) in diameter, were allocated to each of five groups: (a) subcutaneous tumors, (b) kidney tumors, (c) lung tumors with blood flow, and (d) subcutaneous and (e) renal tumors without blood flow, which was achieved by sacrificing the animal to eliminate tumor perfusion. A sixth group comprised larger subcutaneous tumors (mean diameter, 46 mm +/- 4) that were also treated. RF ablation was performed with a 1-cm tip and 5 minutes of ablation at 90 degrees C +/- 1. Impedance, temperature, and resultant coagulation diameter were recorded and compared. Data were analyzed statistically, including one-way analysis of variance to determine the effect of tissue conductivity (ie, systemic impedance) on necrosis size and tissue temperatures. Linear regression analysis was used to compare changes in impedance between the control and experimental groups. RESULTS: Increasing linear correlation was observed between tumor coagulation diameter and overall baseline system impedance (R(2) = 0.65). RF ablation of lung tumors resulted in the greatest coagulation diameter (13.0 mm +/- 3.5) compared with that in the other groups (P <.01). The smallest coagulation diameter was observed in kidney tumors in the presence of blood flow (7.3 mm +/- 0.6) compared with that in the other groups (P <.01). Elimination of blood flow in kidney tumors increased coagulation diameter to 10.3 mm +/- 0.6 (P <.01). After RF ablation, coagulation diameter in the subcutaneous tumor groups was the same (mean, 9.8 mm +/- 1.0) (difference not significant), regardless of tumor size or presence of blood flow. CONCLUSION: The characteristics of tissue that surrounds tumor, including vascularity and electric conductivity, affect ablation outcome. Predominance of tissue-specific characteristics will likely result in site-specific differences in RF-induced coagulation necrosis.     

Radiofrequency ablation: Effect of pharmacologic modulation of hepatic and renal blood flow on coagulation diameter in a VX2 tumor model

PURPOSE: To determine whether pharmacologic agents can be used to modulate blood flow in hepatic and renal tumors sufficiently to alter the extent of radiofrequency (RF)-induced coagulation. MATERIALS AND METHODS: VX2 tumors (8-15 mm) were implanted in the liver (n = 25) or kidney (n = 8) of 33 New Zealand White rabbits. RF was applied to tumors for 6 minutes with use of conventional electrodes (125 mA +/- 35; 90 degrees C +/- 2 degrees C tip temperature). In the hepatic model, blood flow was modulated with use of halothane, epinephrine, or arsenic trioxide (2-6 mg/kg). Laser Doppler flowmetry was used to quantify changes in hepatic blood flow. Correlation of blood flow with induced coagulation diameter was performed. RF ablation was then performed in a renal model with and without arsenic trioxide. RESULTS: For liver tumors, halothane and arsenic trioxide reduced blood flow to 40.3% +/- 17.8% and 29% +/- 15% of normal, respectively, whereas epinephrine increased blood flow to 207.8% +/- 97.9%. Correlation of blood flow to coagulation diameter was demonstrated (R(2) = 0.40). Coagulation measured 7 mm +/- 1 with epinephrine, 10 mm +/- 1 with normal blood flow, 12 mm +/- 3 with halothane, and 13 mm +/- 3 with arsenic trioxide (P <.04 compared with controls). In the renal model, arsenic trioxide decreased blood flow (44% +/- 16%) and increased coagulation diameter (10.9 mm +/- 1) compared with controls (84% +/- 11% and 7.6 mm +/- 1; P <.01, both comparisons). CONCLUSIONS: RF-induced coagulation necrosis in rabbit hepatic and renal tumors is affected by tumor blood flow. Pharmacologic modulation of tumor blood flow may provide a noninvasive way to decrease blood flow during thermally mediated ablation therapy, potentially enabling the creation of larger zones of coagulation necrosis.     

Outcomes of Laparoscopic Sleeve Gastrectomy in Patients Older than 60 Years

Background

Morbidity and mortality following laparoscopic sleeve gastrectomy (LSG) occur at acceptable rates, but its safety and efficacy in the elderly are unknown.

Methods

A retrospective review was performed of all patients aged >60 years who underwent LSG from 2008 to 2012. These patients were 1:2 matched, by gender and body mass index (BMI) to young patients, 18?<?age?<?50. Data analyzed included demographics, preoperative and postoperative BMI, postoperative complications, and improvement or resolution of obesity-related comorbidities.

Results

Fifty-two morbid obese patients older than 60 years underwent LSG (mean age, 62.9?±?0.3 years). These were matched to 104 young patients, age 18–50 years (mean age, 35.7?±?0.8 years). Groups did not differ in male gender (44 vs. 43 %, p?=?0.9), preoperative BMI (42.6?±?0.7 vs. 42.6?±?0.6, p?=?0.97), and length of follow-up (17?±?2 vs. 22?±?1.4 months, p?=?0.06). Obesity-related comorbidities were significantly higher in the older group (96 vs. 65 %, p?<?0.001). Excess weight loss (EWL) was higher in the younger group (75?±?2.4 vs. 62?±?3 %, p?=?0.001). Older patients had a significantly higher rate of a concurrent hiatal hernia repair (23 vs. 1.9 %, p?<?0.001). Overall postoperative minor complication rate was higher in the older group (25 vs. 4.8 %, p?<?0.001). This included atrial fibrillation (9.5 %), urinary tract infection (7 %), trocar site hernia (4 %), dysphagia, surgical site infection, bleeding, bowel obstruction, colitis, and nutritional deficiency (2 %, each). No perioperative mortality occurred. Comorbidity resolution or improvement was comparable between groups (88 vs. 80 %, p?=?0.13).

Conclusions

LSG is safe and very efficient in patients aged >60, despite higher rates of perioperative comorbidities.     

Escalation and Intensification of Radiotherapy for Stage III Non-small Cell Lung Cancer: Opportunities for Treatment Improvement

In this overview we review and model how radiotherapy tumour control and complication rates vary with dose, fractionation, schedule duration, irradiated volume and use of chemotherapy for stage III non-small cell lung cancer (NSCLC), and use the modelling to study the effectiveness of different NSCLC dose-escalation approaches being developed in the UK. Data have been collated for pneumonitis, lung fibrosis, early and late oesophagitis, cord and cardiac complications, and local progression-free survival at 30 months. Dependences of the various end points on treatment-related factors are catalogued and analysed using the linear-quadratic incomplete repair model to account for dose and fractionation effects, making linear corrections for differences in schedule duration, and loosely characterising volume effects using parallel- and series-type concepts. Tolerance limits are calculated for the different end points and distilled into ranges of prescribed dose likely to be tolerable when delivered in 2.5 and 4 week radiation and 6 week chemoirradiation schedules using conformal techniques. Worthwhile (～20%) gains in 30 month local progression-free survival should be achievable at safely deliverable levels of dose escalation. The analysis suggests that longer schedules may be more beneficial than shorter ones, but this finding is governed by the relative rates of tumour and oesophageal accelerated proliferation, which are quite imprecisely known. Consequently escalated 2.5, 4 and 6 week schedules are being developed; each should lead to useful improvements in local control but it is not yet known which schedule will be most effective.     

Converting absorbed dose to medium to absorbed dose to water for Monte Carlo based photon beam dose calculations

Current clinical experience in radiation therapy is based upon dose computations that report the absorbed dose to water, even though the patient is not made of water but of many different types of tissue. While Monte Carlo dose calculation algorithms have the potential for higher dose accuracy, they usually transport particles in and compute the absorbed dose to the patient media such as soft tissue, lung or bone. Therefore, for dose calculation algorithm comparisons, or to report dose to water or tissue contained within a bone matrix for example, a method to convert dose to the medium to dose to water is required. This conversion has been developed here by applying Bragg-Gray cavity theory. The dose ratio for 6 and 18 MV photon beams was determined by computing the average stopping power ratio for the primary electron spectrum in the transport media. For soft tissue, the difference between dose to medium and dose to water is approximately 1.0%, while for cortical bone the dose difference exceeds 10%. The variation in the dose ratio as a function of depth and position in the field indicates that for photon beams a single correction factor can be used for each particular material throughout the field for a given photon beam energy. The only exception to this would be for the clinically non-relevant dose to air. Pre-computed energy spectra for 60Co to 24 MV are used to compute the dose ratios for these photon beams and to determine an effective energy for evaluation of the dose ratio.     

Correlation between first- and early third-trimester glucose screening test results

One hundred twenty-four normal gravidas had paired first- and early third-trimester (26-32 weeks) 1-hour oral glucose screening tests performed. First-trimester oral glucose screening test values correlated significantly with third-trimester glucose screening test results for the entire population, for whites and non-whites, and for normal-weight and obese patients. First-trimester oral glucose screening test values at or below 110 mg/dL were seldom associated with third-trimester oral glucose screening test results at or above 135 mg/dL and were not associated with abnormal 3-hour glucose tolerance test (GTT) results. Nine of the gravidas (7.3%) were diagnosed with gestational diabetes mellitus during the third trimester, all of whom had first-trimester glucose screening test results above 110 mg/dL. The difference in incidence of gestational diabetes mellitus between gravidas having first-trimester glucose screening test results at or below 110 mg/dL (0%) and those having values above 110 mg/dL (16.4%) was highly significant (P less than .0001). For patients with first-trimester glucose screening test values at or below 110 mg/dL, third-trimester glucose screening may be unnecessary. In contrast, for gravidas having first-trimester glucose screening test results at or above 135 mg/dL, there is a high positive predictive value for elevated repeat glucose screening test results during the early third trimester. Patients having elevated first-trimester glucose screening values at or above 140 mg/dL are at particularly high risk for elevated glucose screening test results later in pregnancy and should forego repeat 1-hour third-trimester glucose screening in favor of a direct third-trimester 3-hour GTT.     

Wilmss' tumor: The northern israel oncology institute experience

Between 1971 and 1992, 42 children (median age = 2 years) with histologically proven Wilms' tumor were evaluated at the Northern Israel Oncology Institute. Most patients were staged according to National Wilms' Tumor Study (NWTS) criteria by which 18 were clinical stage I-II and 24 were III-IV. Combined therapy (surgery, chemotherapy, and radiotherapy) was given with a change to lower dose radiotherapy (<2,000cG) after 1981. The pre-1981 group (13 patients) suffered six relapses, most of which were pulmonary, whereas the 1981-1992 group (29 patients) had three relapses. The actuarial 5-year survival rate using Kaplan-Meier tables was 79% for the entire group but 100% for the 1981-1992 group and 38% for the 1971-1980 group. One case of immediate hepatic toxicity and one sudden death, unknown cause, of a patient in remission occurred in the group. Late deleterious effects were seen in five other patients; four had scoliosis and one developed osteoid osteoma of a rib. Despite these encouraging results, the necessity of ongoing monitoring for further longterm toxicities is apparent.