The histological features of microwave coagulation therapy: an assessment of a new applicator design

Radiobiological effects and medical applications of non-ionizing radiation

Radiation is used in medicine to diagnose and treat diseases but it can also cause harm to the body by burning or mutation. This depends on whether the radiation is ionizing or nonionizing. Despite its vast applications in surgery, dermatology and cosmetics, little is taught and thus known about non-ionizing radiation. This review article discusses the fundamentals of non-ionizing electromagnetic radiations. The main aim is to extensively explain the different types of non-ionizing radiation. This will equip students and medical personnel with knowledge on different medical applications and expose them to a variety of specializations in medicine that utilize non-ionizing radiation. The article discusses the physics, hazard, means of protection and medical application of each type of radiation: ultraviolet radiation, light (both visible light and LASER), infrared radiation, microwaves and extremely low frequency radiation separately. It presents these terms in a simple manner that avoids rigors mathematics and physics, which makes them comprehensible for medical students. The development of new diagnostic and therapeutic approaches could also lead to increased hazards to the body unless they are treated with precaution. If not adequately monitored, a significant health risk may be posed to potentially exposed employees. Hence proper dosage should be used for non-ionizing radiation. This is only possible through understanding of the risks/benefits of these radiations by studying the physics and radiobiological effects of each individual radiation.

Microwave ablation for the removal of pharyngeal benign lesions: A prospective pilot case series

OBJECTIVE

We evaluated microwave ablation (MWA) for treatment of isolated pharyngeal benign lesions, in terms of technical feasibility, efficacy, and safety.

METHODS

The patients with pharyngeal benign lesions were treated with endoscopic MWA with a 2450-MHz single cooled-shaft microwave antenna and sent for histological examination. Postoperative pain intensity was measured via visual analogue scale (VAS) on the 12th hour and the third postoperative days.

RESULTS

Of the 137 patients with pharyngeal benign lesions who met the inclusion criteria. The most commonly involved site was the uvula (n = 66, 48.2%), followed by the lateral pharyngeal wall (n = 37, 27.0%), the nasopharyngeal posterior wall (n = 23, 16.8%) and the soft palate (n = 11, 8.0%). All of the procedures were completed using local anesthesia and were well-tolerated by the patients. The ablation time was 5-10 min, with an average duration of 6.3 ± 1.8 min. The most common pathology was papilloma (n = 96, 70.1%), followed by nasopharyngeal cysts (n = 21, 15.3%), polyp (n = 10, 7.3%), epidermoid cysts (n = 8, 5.8%) and Thornwaldt cysts (n = 2, 1.5%). The mean VAS pain score was 2.36 ± 1.08 on postoperative 12th hour and 1.21 ± 0.54 on postoperative third day. At the 6-month follow-up examination, there were no severe complications, such as recurrence, bleeding, or synechiae of the nasal cavity, eustachian tube injury, in any of the patients.

CONCLUSIONS

The MWA for the treatment of isolated pharyngeal benign lesion is feasible and alternative to conventional surgical methods, it allows excision of the lesion while providing hemostasis, involves only a short ablation time and has a very low risk of complications. Most of our patients well-tolerate the procedure, which may be performed under local anesthesia in the outpatient setting.

Microwave Ablation for the Removal of Benign Lesion of Nasal Cavity: "How I Do It"

Background

Isolated benign lesions of the nasal cavity are commonly seen in the rhinology clinic; their treatment using various therapies has been explored in several studies.

Methods

In this retrospective study, isolated lesions of the nasal cavity were removed from 47 patients using microwave ablation (MWA) with a 2450-MHz cooled MWA antenna and sent for histological examination.

Results

The most commonly involved site was the nasal septum (n = 21, 44.7%), followed by the inferior turbinate (n = 12, 25.5%), bulla ethmoidalis (n = 9, 19.1%), and uncinate process (n = 5, 10.6%). The most common pathology was hemangioma (n = 36, 76.6%), followed by nasal polyp (n = 9, 19.1%) and squamous papilloma (n = 2, 4.3%). All lesions were removed endoscopically using MWA in patients administered local anesthesia. The total duration of ablation was 5 to 10 minutes, with an average duration of 7.3 ± 2.6 minutes. Follow-up at 6 months revealed no severe complications, including no cases of recurrent epistaxis, septal perforation, or synechiae of the nasal cavity.

Conclusions

The advantages of MWA are its short ablation time and minimal complications. This was demonstrated in our study in which a single session of MWA was sufficient to excise the isolated lesion while providing hemostasis. Most of the patients well tolerated the procedure, which could be performed using local anesthesia in the outpatient setting.

Evaluation of liver lesions by use of shear wave elastography and computed tomography perfusion imaging after radiofrequency ablation in clinically normal dogs

OBJECTIVE To evaluate acute changes of the liver by use of shear wave elastography (SWE) and CT perfusion after radiofrequency ablation (RFA). ANIMALS 7 healthy Beagles. PROCEDURES RFA was performed on the liver (day 0). Stiffness of the ablation lesion, transitional zone, and normal parenchyma were evaluated by use of SWE, and blood flow, blood volume, and arterial liver perfusion of those regions were evaluated by use of CT perfusion on days 0 and 4. All RFA lesions were histologically examined on day 4. RESULTS Examination of the SWE color-coded map distinctly revealed stiffness of the liver tissue, which increased from the normal parenchyma to the transitional zone and then to the ablation zone. For CT perfusion, blood flow, blood volume, and arterial liver perfusion decreased from the transitional zone to the normal parenchyma and then to the ablation zone. Tissue stiffness and CT perfusion variables did not differ significantly between days 0 and 4. Histologic examination revealed central diffuse necrosis and peripheral hyperemia with infiltration of lymphoid cells and macrophages. CONCLUSIONS AND CLINICAL RELEVANCE Coagulation necrosis induced a loss of blood perfusion and caused tissue hardening (stiffness) in the ablation zone. Hyperemic and inflammatory changes of the transitional zone resulted in increased blood perfusion. Acute changes in stiffness and perfusion of liver tissue after RFA could be determined by use of SWE and CT perfusion. These results can be used to predict the clinical efficacy of RFA and to support further studies, including those involving hepatic neoplasia.

Microwave ablation of the liver: a description of lesion evolution over time and an investigation of the heat sink effect

AIM

Microwave ablation has been successfully used to treat unresectable liver tumours for many years. However, despite its widespread use, there seems to be a relative paucity of experimental data regarding lesion evolution and the effects of any surrounding vasculature on ablation morphology. The aim of this study was to investigate the principal pathological changes in the liver following microwave ablation, in particular the heat sink effect. In addition we carefully reviewed the available literature to provide an overview of all relevant pathological studies.

METHODS

Microwave ablation was carried out on male rats at various distances from the hilum. Histological (H&E) and immunocytochemical (caspase 3) analyses of the lesion were performed at various time points; 0, 4, 24, 48  hours, 2 weeks and 1 month. A literature review was carried out using Medline, Embase and the Cochrane database to identify all relevant histological studies.

RESULTS

The lesion underwent complete coagulative necrosis and was extremely regular at the ablation edge with no evidence of any influence from surrounding blood vessels at all time points. H&E and caspase 3 results were consistent and microwave caused little collateral damage outside the intended ablation zone.

CONCLUSION

This study suggests that microwave ablation is extremely concise and is minimally affected by the heat sink effect. Comparative investigations with other treatment modalities are required.

Microwave ablation for unresectable hepatic tumours: clinical results using a novel microwave probe and generator

BACKGROUND

Microwave ablation is an in situ method of tumour destruction used to treat patients with unresectable liver tumours. A new microwave generator and probe, designed to deliver high energy into solid tumours quickly has been developed at our institution. We report the results of its use in patients with unresectable liver tumours treated by a single surgeon in a single institution.

METHODS

Thirty-one patients with 89 unresectable liver tumours were recruited into the study and underwent microwave ablation in a single procedure.

RESULTS

There were no post-operative complications. At a median of 24 months post ablation, 15 patients were alive with 7 patients disease free. At a median of 26 months, 8 patients were alive with tumour recurrence but only 1 with local recurrence. The remaining 7 patients with recurrence were found to have new disease at locations remote from the ablation site. Fourteen patients died of disease progression at a median survival of 15 months, with only 1 patient with local and remote tumour recurrence. Of the total numbers of tumours treated (n=89), a local tumour recurrence rate of 2% was observed. Overall median survival was 29 months with 3 year survival of 40%.

DISCUSSION

Microwave tissue ablation using this novel generator and probe has a low local recurrence and complication rate. Overall survival is comparable to alternative ablation modalities and its ability to treat, even large tumours, with a single insertion of the probe makes it an extremely attractive treatment option.

Liver ablation techniques: a review

BACKGROUND

Ablation techniques for unresectable liver carcinomas have evolved immensely since their introduction. Results of studies involving these techniques are restricted to reports of patient case series, which are often not presented in a standardised manner. This review aims to summarise the major studies in ablation technologies and present them in a way that may make comparison between the major modalities easier.

METHODS

All major databases (Medline, Cochrane, Embase and Pubmed) were searched for studies using microwave, radiofrequency or cryoablation to treat unresectable liver tumours. Only studies with at least 30 patients and 3-year follow-up were included. Complication, recurrence and survival rates of all studies are summarised and presented.

RESULTS AND CONCLUSION

It is difficult to compare ablation modalities, as probe design and energy sources have evolved rapidly over the last decade. Ablation offers an invaluable palliative option and in some cases it may offer rates of cure approaching that of surgical resection with lower morbidity and mortality. Perhaps the time has come, therefore, for prospective large-scale randomised control trials to take place comparing ablation modalities to each other and surgical resection.

Microwave ablation in a hepatic porcine model: correlation of CT and histopathologic findings

BACKGROUND

Thermal ablative techniques have gained increasing popularity in recent years as safe and effective options for patients with unresectable solid malignancies. Microwave ablation has emerged as a relatively new technique with the promise of larger and faster burns without some of the limitations of radiofrequency ablation (RFA). Here we study a new microwave ablation device in a living porcine model using gross, histologic, and radiographic analysis.

MATERIALS AND METHODS

The size and shape of ablated lesions were assessed using six pigs in a non-survival study. Liver tissue was ablated using 2, 4, and 8 min burns, in both peripheral and central locations, with and without vascular inflow occlusion. To characterize the post-ablation appearance, three additional pigs underwent several 4 min ablations each followed by serial computed tomography (CT) imaging at 7, 14, and 28 days postoperatively.

RESULTS

The 2 and 4 min ablations resulted in lesions that were similar in size, 33.5 cm(3) and 37.5 cm(3), respectively. Ablations lasting 8 min produced lesions that were significantly larger, 92.0 cm(3) on average. Proximity to hepatic vasculature and inflow occlusion did not significantly change lesion size or shape. In follow-up studies, CT imaging showed a gradual reduction in lesion volume over 28 days to 25-50% of the original volume.

DISCUSSION

Microwave ablation with a novel device results in consistently sized and shaped lesions. Importantly, we did not observe any significant heat-sink effect using this device, a major difference from RFA techniques. This system offers a viable alternative for creating fast, large ablation volumes for treatment in liver cancer.

Characteristics of Microstrip Muscle-Loaded Single-Arm Archimedean Spiral Antennas as Investigated by FDTD Numerical Computations

The radiation characteristics and mode of operation of single-arm, groundplane backed, Archimedean spiral antennas are investigated by means of conformal finite difference time domain numerical analysis. It is shown that this antenna type may be categorized as a well-matched, broadband, circularly polarized traveling wave structure that can be fed directly by nonbalanced coaxial networks. The study further concentrates on relevant design and description features parameterized in terms of measures like radiation efficiency, sensing depth, directivity, and axial ratio of complementary polarizations. We document that an antenna of only 30-mm transverse size produces circularly polarized waves in a two-octave frequency span (2-8 GHz) with acceptable radiation efficiency (76%-94%) when loaded by muscle-like tissue.