Local excision for rectal carcinoma

[Transanal Tumor Resection: Indication, Surgical Technique and Management of Complications]

Transanal resection procedures are special operations for the minimally invasive treatment of rectal tumours. Apart from benign tumours, this procedure is suitable for the excision of low-risk T1 rectal carcinomas, if these can be completely removed (R0 resection). With stringent patient selection, very good oncological results are achieved. Various international trials are currently evaluating whether local resection procedures are oncologically sufficient if there is a complete or near complete response after neoadjuvant radio-/chemotherapy. Numerous studies have shown that the functional results and the postoperative quality of life after local resection are excellent, especially considering the well-known functional deficits of alternative operations, such as low anterior or abdominoperineal resection.Severe complications are very rare. Most complications, such as urinary retention or subfebrile temperatures, are minor in nature. Suture line dehiscences are usually clinically unremarkable. Major complications comprise significant haemorrhage and the opening of the peritoneal cavity. The latter must be recognized intraoperatively and can usually be managed by primary suture. Infection, abscess formation, rectovaginal fistula, injury of the prostate or even urethra are extremely rare complications.

A model based on endorectal ultrasonography predicts lateral lymph node metastasis in low and middle rectal cancer

PURPOSE

To investigate the risk factors for lymph node (LN) metastasis in low and middle rectal tumors, construct a predictive model and test the model's diagnostic efficacy.

METHODS

The clinical and pathological data of 172 patients with rectal cancer confirmed by surgery were retrospectively evaluated, among whom 61 patients were finally included in this study. Patients were divided into positive groups and negative groups based on LN metastasis, and risk factors that might affect LN metastasis were analyzed. Finally, a risk predictive model was constructed based on the weights of each risk factor.

RESULTS

Compared with pathology, the efficacy of diagnosing LN metastasis only according to conventional endorectal ultrasonography (ERUS) features of LN was not high, with sensitivity 67%, specificity 86%, positive predictive value 76%, negative predictive value 80%, and accuracy 79%. Univariate analysis showed that circumferential angle of the tumor, ultrasonic T- stage (UT stage), conventional ultrasound features diagnosis of LN metastasis, strain ratio (SR) of tumor were risk factors for LN metastasis, while vascular resistance index of rectal tumor was protective factor. Multivariate analysis showed that UT stage (OR = 7.188, p = 0.049), conventional ultrasound features diagnosis of LN metastasis (OR = 8.010, p = 0.025) and SR (OR = 5.022, p = 0.031) were independent risk factors for LN metastasis. These risk factors were included in logistic regression analysis and the model was established, Y = -7.3 + 1.9 X10 + 2.1 X11 + 1.6 X13 (Y = Logit[P], P: LN metastasis rate, X10: UT stage, X11: conventional ultrasound features diagnosis of LN metastasis, X13: SR). The receiver operating characteristic (ROC) curve was used to test the model's predictive efficacy, the area under the curve was 0.95, sensitivity: 95%, specificity: 87%. Hosmer-Lemeshow goodness of fit test showed X2 = 6.015, p = 0.65 (p > 0.05), indicating that the model had a high predictive value.

CONCLUSION

Evaluation of perirectal LN metastasis only based on conventional ERUS features of LN was not effective enough. UT stage of tumor, conventional ultrasound features diagnosis of LN metastasis and SR were independent risk factors for LN metastasis. The predictive model had good assessment efficacy and had certain clinical application value.

Rectal cancer: Maximizing local control and minimizing toxicity

Adoption of multimodality treatment approach for rectal cancer has resulted in significant improvements in oncologic outcomes. The roles of chemotherapy, radiation, and surgery in rectal cancer treatment are continuously evolving with the goal of achieving the best possible oncologic and functional outcome while minimizing treatment toxicity. The aim of this review is to summarize the most recent trials focusing on organ-sparing treatment strategies and the optimal selection of patients for neoadjuvant radiation therapy.

Robotic Transanal Minimally Invasive Surgery for the Excision of Rectal Neoplasia: Clinical Experience With 58 Consecutive Patients

BACKGROUND

Given the significant perioperative risks and costs of total mesorectal excision, minimally invasive transanal surgical approaches have grown in popularity for early rectal cancer and rectal polyps. This article discusses a transanal robotic surgery technique to perform full-thickness resections of benign and malignant rectal neoplasms.

OBJECTIVE

The purpose of this study was to describe an initial experience with robotic transanal minimally invasive surgery.

DESIGN

This was a retrospective cohort study of consecutive patients who underwent robotic transanal minimally invasive surgery.

SETTINGS

The study was conducted at a high-volume colorectal surgery practice with a large health maintenance organization.

PATIENTS

Patients at Southern California Kaiser Permanente with early rectal cancer and rectal polyps amenable to transanal excision were included.

INTERVENTIONS

Transanal resection of rectal tumors were removed using robotic transanal minimally invasive surgery.

MAIN OUTCOME MEASURES

Local recurrence of rectal pathology was measured.

RESULTS

A total of 58 patients underwent robotic transanal minimally invasive surgery with full-thickness rectal resection by 4 surgeons for the following indications: rectal cancer (n = 28), rectal polyp (n = 18), rectal carcinoid (n = 11), and rectal GI stromal tumor (n = 1). Mean operative time was 66.2 minutes (range, 17-180 min). The mean tumor height from the anal verge was 8.8 cm (range, 4-14 cm), and the mean specimen size was 3.3 cm (range, 1.3-8.2 cm). A total of 57 (98.3%) of 58 specimens were intact, and 55 (94.8%) of 58 specimens had negative surgical margins. At a mean follow-up of 11.5 months (range, 0.3-33.3 mo), 3 patients (5.5%) developed local recurrences, and all underwent successful salvage surgery.

LIMITATIONS

The study was limited by being a retrospective, nonrandomized trial with short follow-up.

CONCLUSIONS

Robotic transanal minimally invasive surgery is a safe, oncologically effective surgical approach for rectal polyps and early rectal cancers. It offers the oncologic benefits and perioperative complication profile of other transanal minimally invasive surgical approaches but also enhances surgeon ergonomics and provides an efficient transanal rectal platform. See Video Abstract at http://links.lww.com/DCR/A759.

Local Excision of Rectal Cancer

Local excision (LE) of early-stage rectal cancer avoids the morbidity associated with radical surgery but has historically been associated with inferior oncologic outcomes. Newer techniques, including transanal endoscopic microsurgery (TEM) and transanal minimally invasive surgery (TAMIS), have been developed to improve the quality of LE and extend the benefits of LE to tumors in the more proximal rectum. This article provides an overview of conventional LE, TEM, and TAMIS techniques, including indications for their use and pertinent literature on their associated outcomes for rectal cancer.

Analysis of tumor-infiltrating gamma delta T cells in rectal cancer

AIM: To investigate the regulatory effect of Vδ1 T cells and the antitumor activity of Vδ2 T cells in rectal cancer.

METHODS: Peripheral blood, tumor tissues and para-carcinoma tissues from 20 rectal cancer patients were collected. Naïve CD4 T cells from the peripheral blood of rectal cancer patients were purified by negative selection using a Naive CD4⁺ T Cell Isolation Kit II (Miltenyi Biotec). Tumor tissues and para-carcinoma tissues were minced into small pieces and digested in a triple enzyme mixture containing collagenase type IV, hyaluronidase, and deoxyribonuclease for 2 h at room temperature. After digestion, the cells were washed twice in RPMI1640 and cultured in RPMI1640 containing 10% human serum supplemented with L-glutamine and 2-mercaptoethanol and 1000 U/mL of IL-2 for the generation of T cells. Vδ1 T cells and Vδ2 T cells from tumor tissues and para-carcinoma tissues were expanded by anti-TCR γδ antibodies. The inhibitory effects of Vδ1 T cells on naïve CD4 T cells were analyzed using the CFSE method. The cytotoxicity of Vδ2 T cells on rectal cancer lines was determined by the LDH method.

RESULTS: The percentage of Vδ1 T cells in rectal tumor tissues from rectal cancer patients was significantly increased, and positively correlated with the T stage. The percentage of Vδ2 T cells in rectal tumor tissues from rectal cancer patients was significantly decreased, and negatively correlated with the T stage. After culture for 14 d with 1 μg/mL anti-TCR γδ antibodies, the percentage of Vδ1 T cells from para-carcinoma tissues was 21.45% ± 4.64%, and the percentage of Vδ2 T cells was 38.64% ± 8.05%. After culture for 14 d, the percentage of Vδ1 T cells from rectal cancer tissues was 67.45% ± 11.75% and the percentage of Vδ2 T cells was 8.94% ± 2.85%. Tumor-infiltrating Vδ1 T cells had strong inhibitory effects, and tumor-infiltrating Vδ2 T cells showed strong cytolytic activity. The inhibitory effects of Vδ1 T cells from para-carcinoma tissues and from rectal cancer tissue were not significantly different. In addition, the cytolytic activities of Vδ2 T cells from para-carcinoma tissues and from rectal cancer tissues were not significantly different.

CONCLUSION: A percentage imbalance in Vδ1 and Vδ2 T cells in rectal cancer patients may contribute to the development of rectal cancer.

Survival after local excision or radical resection for early-stage colorectal cancer

AIM: To compare the overall survival after local excision or radical resection for early-stage colorectal cancer.

METHODS: Patients who met the criteria were screened from the SEER database between 1998 and 2008, and they were divided into a local excision group and a radical resection group according to the mode of surgery. Each group was further divided into colon or rectal cancer subgroup according to the location of tumor. Kaplan-Meier analysis was performed to determine the overall survival between the two groups and independent prognostic factors.

RESULTS: A total of 13975 cases were included in the study. Of 13647 cases receiving radical resection, 10389 had colon cancer and 3258 had rectal cancer. Of 148 cases receiving local excision, 62 had colon cancer and 86 had rectal cancer. Tumors at T1 stage tended to receive local excision, while tumors at T2 stage were more inclined to accept radical resection (P < 0.001). Univariate survival analysis showed that there were statistical differences between the two groups in 5-year and 10-year survival rates of patients with stage T1 colon cancer, althougn no significant differences were noted in patients with stage T2 colon cancer and those with both stages T1 and T2 rectal cancer. Multivariate survival factor analysis showed that gender, age, race, tumor size, tumor differentiation and mode of surgery were independent prognostic factors, but both colon cancer and rectal cancer had their own characteristics.

CONCLUSION: Local excision can obtain the same survival rate as radical surgery in patients with stages T1 and T2 rectal cancer. Compared to local excision, radical resection can offer better overall survival in patients with stage T1 colon cancer, while more cases are needed to analyze the difference in patients with stage T2 colon cancer.

[Management of complications in anal and transanal tumor surgery]

Anal and transanal tumor operations are safe and are associated with a very low morbidity. Perianal and anal lesions as well as low rectal tumors can be excised by direct exposure using an anal retractor. For lesions situated in the middle or upper third of the rectum, special instrumentation, such as transanal endoscopic microsurgery (TEM) and transanal endoscopic operation (TEO) should be used to avoid unnecessary R1 resections. Fatal complications are extremely rare and most complications, such as urinary retention or temporary subfebrile temperatures, are minor. Suture line dehiscences are usually clinically unremarkable. Major complications comprise significant hemorrhage and opening of the peritoneal cavity. The latter must be recognized intraoperatively and can usually be managed by primary suturing. Infections, abscess formation, rectovaginal fistula, injury of the prostate or even urethra are extremely rare complications.

High frequency of CD8 positive lymphocyte infiltration correlates with lack of lymph node involvement in early rectal cancer

AIMS

A trend towards local excision of early rectal cancers has prompted us to investigate if immunoprofiling might help in predicting lymph node involvement in this subgroup.

METHODS

A tissue microarray of 126 biopsies of early rectal cancer (T1 and T2) was stained for several immunomarkers of the innate and the adaptive immune response. Patients' survival and nodal status were analyzed and correlated with infiltration of the different immune cells.

RESULTS

Of all tested markers, only CD8 (P = 0.005) and TIA-1 (P = 0.05) were significantly more frequently detectable in early rectal cancer biopsies of node negative as compared to node positive patients. Although these two immunomarkers did not display prognostic effect "per se," CD8+ and, marginally, TIA-1 T cell infiltration could predict nodal involvement in univariate logistic regression analysis (OR 0.994; 95% CI 0.992-0.996; P = 0.009 and OR 0.988; 95% CI 0.984-0.994; P = 0.05, resp.). An algorithm significantly predicting the nodal status in early rectal cancer based on CD8 together with vascular invasion and tumor border configuration could be calculated (P < 0.00001).

CONCLUSION

Our data indicate that in early rectal cancers absence of CD8+ T-cell infiltration helps in predicting patients' nodal involvement.

Depth and lateral spread of microscopic residual rectal cancer after neoadjuvant chemoradiation: implications for treatment decisions

AIM

The aim of this study was to determine the distribution of residual tumour within the bowel wall in relation to residual mucosal abnormalities (RMAs) and surrounding normal mucosa in patients with rectal cancer who underwent neoadjuvant chemoradiation followed by curative surgery.

METHOD

Archived pathological slides from a cohort of 60 patients with residual tumour were retrieved. The incidence, distance and depth of tumour spread (ypT) under RMAs and adjacent normal mucosa were reviewed and recorded.

RESULTS

Histological sections containing both RMA and adjacent normal mucosa were available for 45 of 60 patients with ypT1 (n = 6), ypT2 (n = 18) and ypT3 (n = 21) disease. The maximal depth of invasion, as measured by ypT stage, was found underneath the RMA in 44 of 45 (98%) patients. Microscopic tumour spread lateral to the RMA and under adjacent normal mucosa was found in 32 of 45 (71%) patients. The median and maximum distances of lateral spread for ypT1 tumours were 0 and 4 mm; for ypT2 were 2.5 and 9 mm; and for ypT3 were 4 and 9 mm respectively.

CONCLUSION

Lateral tumour spread under normal mucosa adjacent to RMAs is a common finding and extended up to 9 mm in this study. The epicentre for maximum depth of invasion was directly underneath the RMAs in nearly all cases. These data have clinical and technical implications if local excision is to be considered.

Clinical competence in the surgery of rectal cancer: the Italian Consensus Conference

BACKGROUND AND AIM

The literature continues to emphasize the advantages of treating patients in "high volume" units by "expert" surgeons, but there is no agreed definition of what is meant by either term. In September 2012, a Consensus Conference on Clinical Competence was organized in Rome as part of the meeting of the National Congress of Italian Surgery (I Congresso Nazionale della Chirurgia Italiana: Unità e valore della chirurgia italiana). The aims were to provide a definition of "expert surgeon" and "high-volume facility" in rectal cancer surgery and to assess their influence on patient outcome.

METHOD

An Organizing Committee (OC), a Scientific Committee (SC), a Group of Experts (E) and a Panel/Jury (P) were set up for the conduct of the Consensus Conference. Review of the literature focused on three main questions including training, "measuring" of quality and to what extent hospital and surgeon volume affects sphincter-preserving procedures, local recurrence, 30-day morbidity and mortality, survival, function, choice of laparoscopic approach and the choice of transanal endoscopic microsurgery (TEM).

RESULTS AND CONCLUSION

The difficulties encountered in defining competence in rectal surgery arise from the great heterogeneity of the parameters described in the literature to quantify it. Acquisition of data is difficult as many articles were published many years ago. Even with a focus on surgeon and hospital volume, it is difficult to define their role owing to the variability and the quality of the relevant studies.

When is local excision appropriate for "early" rectal cancer?

Local excision is increasingly performed for “early stage” rectal cancer in the US; however, local recurrence after local excision has become a controversial issue in Western countries. Local recurrence is considered to originate based on the type of tumor and procedure performed, and in surgical margin-positive cases. This review focuses on the inclusion criteria of “early” rectal cancers for local excision from the Western and Japanese points of view. “Early” rectal cancer is defined as T1 cancer in the rectum. Only the tumor grade and depth of invasion are the “high risk” factors which can be evaluated before treatment. T1 cancers with sm1 or submucosal invasion <1,000 μm are considered to be “low risk” tumors with less than 3.2 % nodal involvement, and are considered to be candidates for local excision as the sole curative surgery. Tumors with a poor tumor grade should be excluded from local excision. Digital examination, endoscopy or proctoscopy with biopsy, a barium enema study and endorectal ultrasonography are useful for identifying “low risk” or excluding “high risk” factors preoperatively for a comprehensive diagnosis. The selection of an initial local treatment modality is also considered to be important according to the analysis of the nodal involvement rate after initial local treatment and after radical surgery.

Local excision of rectal cancer followed by radical surgery because of poor prognostic features does not compromise the long term oncologic outcome

AIM

The outcome of patients undergoing full-thickness local excision (LE) of rectal cancers may be compromised if poor prognostic features are found in the LE specimen. Our aim was to evaluate the long-term results of radical surgery performed after LE because poor prognostic factors are identified.

METHOD

Patients with biopsy-proven rectal cancer who had undergone full-thickness LE followed by radical surgery because of a positive margin, T stage ≥3, lymphovascular invasion, poor differentiation or mucinous histology were identified from a prospective database. Their records were retrospectively reviewed and follow up was updated.

RESULTS

Between 1995 and 2003, 17 patients underwent LE followed by radical surgery because of poor prognostic features. Combined chemotherapy and radiotherapy was given to 11 (65%) patients before radical surgery. Patients underwent radical surgery after a median of 14 (range: 0-40) weeks from LE. Nine underwent a low anterior resection and eight an abdominoperineal resection. At the time of radical surgery, residual disease was found in six (35%) patients (in lymph nodes in three; intramural in two; and both lymph nodes and intramural in one). Four of the patients with residual disease had undergone neoadjuvant therapy before radical surgery. The mean follow up was 110 (95% CI: 92-129) months. Recurrence-free survival at 10 years was 88%. There was no case of local recurrence, and two patients died of metastatic disease.

CONCLUSION

In this series patients who underwent early radical surgery because of poor prognostic features found at LE had good overall and cancer-specific long-term survival. Even after neoadjuvant therapy, more than a third of patients had residual disease at the time of radical surgery. We therefore recommend radical surgery with neoadjuvant therapy when poor prognostic features are found at LE.

Transanal minimally invasive surgery (TAMIS) using a new disposable device: our initial experience

Disposable single-port surgery devices have been used for transanal minimally invasive surgery (TAMIS). Their advantage, compared to transanal endoscopic microsurgery, is that they do not require special equipment or training. The aim of this study was to assess our initial experience using the single-site laparoscopic (SSL™) access system (Ethicon Endo-Surgery, Cincinnati, OH, USA) for TAMIS. Five patients eligible for local excision of rectal tumors, four males and one female, mean age 58 years (range 50-78), underwent surgery using the SSL™ device. The average distance from anal verge was 4 cm (range 1-6). Four patients had an initial diagnosis of adenoma, and one had a previous endoscopic excision of a T1 adenocarcinoma with positive margins. In one patient, due to the lack of exposure, the procedure was converted to a low anterior resection. In the remaining four patients, average setup time was 7 minutes (range 4-15) and average operative time was 52 minutes (range 38-72). All resection margins were tumor free. There were no postoperative complications. Two of the presumed adenomas were intramucosal adenocarcinomas, while one patient had a T2 tumor and underwent radical surgery. Although at the present time the appropriate use of local excision is still under debate, TAMIS is a technique with great potential. Because of its simplicity and similarity with conventional laparoscopic surgery, it can be learned easily by surgeons not trained in transanal endoscopic microsurgery.

Approach to rectal cancer surgery

Rectal cancer is a distinct subset of colorectal cancer where specialized disease-specific management of the primary tumor is required. There have been significant developments in rectal cancer surgery at all stages of disease in particular the introduction of local excision strategies for preinvasive and early cancers, standardized total mesorectal excision for resectable cancers incorporating preoperative short- or long-course chemoradiation to the multimodality sequencing of treatment. Laparoscopic surgery is also increasingly being adopted as the standard rectal cancer surgery approach following expertise of colorectal surgeons in minimally invasive surgery gained from laparoscopic colon resections. In locally advanced and metastatic disease, combining chemoradiation with radical surgery may achieve total eradication of disease and disease control in the pelvis. Evidence for resection of metastases to the liver and lung have been extensively reported in the literature. The role of cytoreductive surgery and hyperthermic intraperitoneal chemotherapy for peritoneal metastases is showing promise in achieving locoregional control of peritoneal dissemination. This paper summarizes the recent developments in approaches to rectal cancer surgery at all these time points of the disease natural history.

The surgical significance of residual mucosal abnormalities in rectal cancer following neoadjuvant chemoradiotherapy

BACKGROUND

Local excision of rectal cancer after neoadjuvant chemoradiotherapy (CRT) has been proposed as an alternative to radical surgery in selected patients. However, little is known about the significance of the morphological and histological features of residual tumour.

METHODS

Patients who had undergone CRT at the authors' institution between 1997 and 2010 were identified. Multiple features were assessed as putative markers of pathological response. These included: gross residual disease, diameter of residual mucosal abnormalities, tumour differentiation, presence of lymphovascular/perineural invasion and lymph node ratio.

RESULTS

Data from 220 of 276 patients were suitable for analysis. Diameter of residual mucosal abnormalities correlated strongly with pathological tumour category after CRT (ypT) (P < 0·001). Forty of 42 tumours downstaged to ypT0/1 had residual mucosal abnormalities of 2·99 cm or less after CRT. Importantly, 19 of 31 patients with a complete pathological response had evidence of a residual mucosal abnormality consistent with an incomplete clinical response. The ypT category was associated with both pathological node status after CRT (P < 0·001) and lymph node ratio (P < 0·001). Positive nodes were found in only one of 42 patients downstaged to ypT0/1. The risk of nodal metastases was associated with poor differentiation (P = 0·027) and lymphovascular invasion (P < 0·001).

CONCLUSION

In this series, the majority of patients with a complete pathological response did not have a complete clinical response. In tumours downstaged to ypT0/1 after CRT, residual mucosal abnormalities were predominantly small and had a 2 per cent risk of positive nodes, thus potentially facilitating transanal excision. The presence of adverse histological characteristics risk stratified tumours for nodal metastases.

Does a learning curve exist in endorectal two-dimensional ultrasound accuracy?

BACKGROUND

Aim of the study was to assess adequacy of Colorectal Surgical Society of Australia and New Zealand (CSSANZ) endorectal ultrasound (ERUS) training and whether a subsequent learning curve exists.

METHODS

A prospective audit of ERUS for staging rectal cancer by a single surgeon from commencement of consultant practice was performed. Data were recorded in a prospectively maintained database. The audit commenced on completion of CSSANZ training. T- and N-stage were assessed clinically, then by ERUS prior to treatment and finally by histology over 8 years.

RESULTS

The results were compared over three time periods: the first a single year, then two three-year periods. Two hundred and seventy-two patients were examined. Two hundred and thirty-three were assessable for T-stage (13 no tumour excision, 26 long course pre-operative radiotherapy) and 142 for N-stage (74 endoanal excision, 17 proximal mesorectum un-assessable). Overall accuracy was 82% for T-stage and 73% for N-stage. Accuracy for T- and N-staging did not change significantly over the three time periods (T: 82.1, 82.3, 81.6%, P = 0.14; N: 83.3, 67.9, 74.2%, P = 0.31). The utility of ERUS was demonstrated by clinical assessment not being possible in 32% of cases and where the two modalities disagreed was correct 82% of the time.

CONCLUSIONS

Endorectal ultrasound rectal cancer staging is accurate for T-stage. Competency in ERUS can be achieved in the CSSANZ fellowship and accuracy does not improve with further experience. An ERUS accreditation scheme should be established for future trainees.

The indication and surgical results of local excision following radiotherapy for low rectal cancer

AIM

Radical surgery of rectal cancer is associated with significant morbidity, and some patients with low-lying lesions must accept a permanent colostomy. The objective of this study was to evaluate the outcome of local excision followed by adjuvant radiotherapy for rectal cancer for curative purposes.

METHOD

One hundred and seven patients with rectal carcinoma performed with local excision were analysed retrospectively.

RESULTS

The procedures of local excision were trans-anal resection in 83 patients, trans-sacral resection in 16, trans-sphincteric local resection in five, and trans-vaginal resection in three. The overall disease-free survival rate was 80.4% (86/107), including 90.0% (54/60) for T1 and 72.3% (34/47) for T2 tumours, respectively. Eighty-two of 107 patients underwent adjuvant postoperative radiotherapy after local excision, and 25 did not, and the DFS rates between radiation and nonradiation group were significantly different for T2 [81.6% (31/38) vs 33.3% (3/9), P < 0.05], but not for T1 tumours (90.9%vs 87.5%, P > 0.05). The rates of local recurrence and distant metastasis were 13.1% (14/107) and 4.7% (5/106), respectively, and the median time to relapse was 15 months (range: 10-53) for local recurrence and 30 months (21-65) for distant recurrence. The risk factors for local recurrence were large tumour (≥3 cm), poorly differentiated adenocarcinoma and T2 tumour.

CONCLUSIONS

Local excision followed adjuvant radiotherapy is an alternative and feasible technique for small T1 rectal cancer in selected cases.

Endocavitary thermal therapy by MRI-guided phased-array contact ultrasound: experimental and numerical studies on the multi-input single-output PID temperature controller's convergence and stability

PURPOSE

Endocavitary high intensity contact ultrasound (HICU) may offer interesting therapeutic potential for fighting localized cancer in esophageal or rectal wall. On-line MR guidance of the thermotherapy permits both excellent targeting of the pathological volume and accurate preoperatory monitoring of the temperature elevation. In this article, the authors address the issue of the automatic temperature control for endocavitary phased-array HICU and propose a tailor-made thermal model for this specific application. The convergence and stability of the feedback loop were investigated against tuning errors in the controller's parameters and against input noise, through ex vivo experimental studies and through numerical simulations in which nonlinear response of tissue was considered as expected in vivo.

METHODS

An MR-compatible, 64-element, cooled-tip, endorectal cylindrical phased-array applicator of contact ultrasound was integrated with fast MR thermometry to provide automatic feedback control of the temperature evolution. An appropriate phase law was applied per set of eight adjacent transducers to generate a quasiplanar wave, or a slightly convergent one (over the circular dimension). A 2D physical model, compatible with on-line numerical implementation, took into account (1) the ultrasound-mediated energy deposition, (2) the heat diffusion in tissue, and (3) the heat sink effect in the tissue adjacent to the tip-cooling balloon. This linear model was coupled to a PID compensation algorithm to obtain a multi-input single-output static-tuning temperature controller. Either the temperature at one static point in space (situated on the symmetry axis of the beam) or the maximum temperature in a user-defined ROI was tracked according to a predefined target curve. The convergence domain in the space of controller's parameters was experimentally explored ex vivo. The behavior of the static-tuning PID controller was numerically simulated based on a discrete-time iterative solution of the bioheat transfer equation in 3D and considering temperature-dependent ultrasound absorption and blood perfusion.

RESULTS

The intrinsic accuracy of the implemented controller was approximately 1% in ex vivo trials when providing correct estimates for energy deposition and heat diffusivity. Moreover, the feedback loop demonstrated excellent convergence and stability over a wide range of the controller's parameters, deliberately set to erroneous values. In the extreme case of strong underestimation of the ultrasound energy deposition in tissue, the temperature tracking curve alone, at the initial stage of the MR-controlled HICU treatment, was not a sufficient indicator for a globally stable behavior of the feedback loop. Our simulations predicted that the controller would be able to compensate for tissue perfusion and for temperature-dependent ultrasound absorption, although these effects were not included in the controller's equation. The explicit pattern of acoustic field was not required as input information for the controller, avoiding time-consuming numerical operations.

CONCLUSIONS

The study demonstrated the potential advantages of PID-based automatic temperature control adapted to phased-array MR-guided HICU therapy. Further studies will address the integration of this ultrasound device with a miniature RF coil for high resolution MRI and, subsequently, the experimental behavior of the controller in vivo.