Comparison of manual and semi-automatic registration in augmented reality image-guided liver surgery: a clinical feasibility study

BACKGROUND

The laparoscopic approach to liver resection may reduce morbidity and hospital stay. However, uptake has been slow due to concerns about patient safety and oncological radicality. Image guidance systems may improve patient safety by enabling 3D visualisation of critical intra- and extrahepatic structures. Current systems suffer from non-intuitive visualisation and a complicated setup process. A novel image guidance system (SmartLiver), offering augmented reality visualisation and semi-automatic registration has been developed to address these issues. A clinical feasibility study evaluated the performance and usability of SmartLiver with either manual or semi-automatic registration.

METHODS

Intraoperative image guidance data were recorded and analysed in patients undergoing laparoscopic liver resection or cancer staging. Stereoscopic surface reconstruction and iterative closest point matching facilitated semi-automatic registration. The primary endpoint was defined as successful registration as determined by the operating surgeon. Secondary endpoints were system usability as assessed by a surgeon questionnaire and comparison of manual vs. semi-automatic registration accuracy. Since SmartLiver is still in development no attempt was made to evaluate its impact on perioperative outcomes.

RESULTS

The primary endpoint was achieved in 16 out of 18 patients. Initially semi-automatic registration failed because the IGS could not distinguish the liver surface from surrounding structures. Implementation of a deep learning algorithm enabled the IGS to overcome this issue and facilitate semi-automatic registration. Mean registration accuracy was 10.9 ± 4.2 mm (manual) vs. 13.9 ± 4.4 mm (semi-automatic) (Mean difference - 3 mm; p = 0.158). Surgeon feedback was positive about IGS handling and improved intraoperative orientation but also highlighted the need for a simpler setup process and better integration with laparoscopic ultrasound.

CONCLUSION

The technical feasibility of using SmartLiver intraoperatively has been demonstrated. With further improvements semi-automatic registration may enhance user friendliness and workflow of SmartLiver. Manual and semi-automatic registration accuracy were comparable but evaluation on a larger patient cohort is required to confirm these findings.

Beam distortion due to gold fiducial markers during salvage high-intensity focused ultrasound in the prostate

PURPOSE

High intensity focused ultrasound (HIFU) provides a non-invasive salvage treatment option for patients with recurrence after external beam radiation therapy (EBRT). As part of EBRT the prostate is frequently implanted with permanent fiducial markers. To date, the impact of these markers on subsequent HIFU treatment is unknown. The objective of this work was to systematically investigate, using computational simulations, how these fiducial markers affect the delivery of HIFU treatment.

METHODS

A series of simulations was performed modelling the propagation of ultrasound pressure waves in the prostate with a single spherical or cylindrical gold marker at different positions and orientations. For each marker configuration, a set of metrics (spatial-peak temporal-average intensity, focus shift, focal volume) was evaluated to quantify the distortion introduced at the focus. An analytical model was also developed describing the marker effect on the intensity at the focus. The model was used to examine the marker's impact in a clinical setting through case studies.

RESULTS

The simulations show that the presence of the marker in the pre-focal region causes reflections which induce a decrease in the focal intensity and focal volume, and a shift of the maximum pressure point away from the transducer's focus. These effects depend on the shape and orientation of the marker and become more pronounced as its distance from the transducer's focus decreases, with the distortion introduced by the marker greatly increasing when placed within 5 mm of the focus. The analytical model approximates the marker's effect and can be used as an alternative method to the computationally intensive and time consuming simulations for quickly estimating the intensity at the focus. A retrospective review of a small patient cohort selected for focal HIFU after failed EBRT indicates that the presence of the marker may affect HIFU treatment delivery.

CONCLUSIONS

The distortion introduced by the marker to the HIFU beam when positioned close to the focus may result in an undertreated region beyond the marker due to less energy arriving at the focus, and an overtreated region due to reflections. Further work is necessary to investigate whether the results presented here justify the revision of the patient selection criteria or the markers' placement protocol.

Abstract PD1-8: Acquired resistance to rapamycin and mTOR kinase inhibitors is mediated by non-overlapping mutations in distinct sites in the mTOR protein

The mammalian target of rapamycin (mTOR) protein kinase regulates protein translation and proliferation by integrating the availability of energy, nutrients and the presence of growth factors. Dysregulation of mTOR is a common event in human tumors and results from mutational activation of receptor tyrosine kinases, PI3K signaling or inactivating mutations of the Tuberous Sclerosis or GATOR complexes as well as the LKB/AMP kinase pathway.

The prevalence of mTOR activation in cancer has led to the development of two classes of inhibitors of the protein as therapeutics: the natural product rapamycin and its analogs as well as direct inhibitors of mTOR kinase. mTOR exists in at least two multi-protein complexes. The mTORC1 complex phosphorylates S6K and 4EBP and stimulates protein translation, metabolism as well as other processes. The mTORC2 complex phosphorylates and activates AKT and other AGC kinases. Rapamycin binds to the immunophilin FKBP12. Drug-bound FKBP12 complex binds to mTOR FRB domain and selectively inhibits the activity of mTORC1. However, rapalogs preferentially inhibit S6K phosphorylation compared to 4EBP phosphorylation. Rapalogs have undergone extensive clinical testing and have significant antitumor activity in renal cell and pancreatic neuroendocrine tumors and, in combination with aromatase inhibitors, in resistant, ER positive breast cancers. In contrast, mTOR kinase inhibitors suppress both mTORC1 and mTORC2 functions and potently inhibit S6K, 4EBP and AKT S473 phosphorylation. These drugs are in early clinical testing.

In order to better understand the mechanism of action of these drugs and potential mechanisms of tumor escape from mTOR inhibition, we selected breast tumor cells for resistance to growth inhibition in cell culture by treatment with either rapamycin or an mTOR kinase inhibitor. In rapamycin resistant cells, phosphorylation of S6K and S6 were insensitive to the drug, but remained sensitive to mTOR kinase inhibitors. Conversely, in clones resistant to mTOR kinase inhibitors, mTORC1 and mTORC2 substrates were insensitive to the drugs, but S6K and S6 phosphorylation remained sensitive to rapamycin. Deep sequencing results explained these findings: rapamycin resistant clones harbored mutations in the FRB domain of mTOR, in the sites shown to interact with the FKBP12-rapamycin complex; mTOR kinase resistant clones harbored mutations in the mTOR catalytic domain. These mutations were not observed in the parental cells. It is likely that the mutations identified in each domain prevent binding of the drug.

Consistent with these data, growth of rapamycin resistant cells retain sensitivity to mTOR kinase inhibitors and mTOR kinase resistant cells retain sensitivity to rapalogs, both in tissue culture and in vivo. The results suggest that tumor cells with acquired resistance to mTOR inhibitors retain a requirement for mTOR signaling for proliferation. Furthermore, tumors resistant to either class of drug may not be cross-resistant to the other and combined therapy with both might delay the onset of resistance. Further studies on the genetics of human tumors with acquired resistance to these agents will determine the clinical importance of these findings.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD1-8.

Tissue deformation and shape models in image-guided interventions: a discussion paper

This paper promotes the concept of active models in image-guided interventions. We outline the limitations of the rigid body assumption in image-guided interventions and describe how intraoperative imaging provides a rich source of information on spatial location of anatomical structures and therapy devices, allowing a preoperative plan to be updated during an intervention. Soft tissue deformation and variation from an atlas to a particular individual can both be determined using non-rigid registration. Established methods using free-form deformations have a very large number of degrees of freedom. Three examples of deformable models--motion models, biomechanical models and statistical shape models--are used to illustrate how prior information can be used to restrict the number of degrees of freedom of the registration algorithm and thus provide active models for image-guided interventions. We provide preliminary results from applications for each type of model.

The value of taking an 'ethics history'

OBJECTIVES

To study the value of taking an ethics history as a means of assessing patients' preferences for decision making and for their relatives' involvement.

DESIGN

Questionnaire administered by six junior doctors to 56 mentally competent patients, admitted into general and geriatric medical beds.

SETTING

A large district general hospital in the United Kingdom.

MAIN MEASURES

To establish whether patients were adequately informed about their illness and whether they minded the information being communicated to their relatives. To establish their preference regarding truthful disclosure and participation in decision making with risk attached. To establish whether they wished to be involved in CPR decision making, and if not, who should make the decision. To establish whether they knew of living wills and whether they had any advance directives.

RESULTS

Twenty-four (43%) were inadequately informed of their illness. Forty-six (82%) said they would want to know were something serious to be found. Twenty-eight (50%) wanted to make their own decision if requiring risky treatment and 11 (20%) wanted family members involved. Thirty-one (55%) wanted to make a cardiopulmonary resuscitation (CPR) decision and five of these decisions differed from those made by the doctors. Twenty-five (45%) preferred the doctors to decide. Eleven (20%) of the patients had heard of living wills but only one had executed such a will. Seven (13%) of the patients wished to provide advance directives. Three (5%) did not find the history taking helpful but none were discomforted.

CONCLUSION

Taking an ethics history is a simple means of obtaining useful information about patients' preferences.

Monocyte chemoattractant protein-1: receptor interactions and calcium signaling mechanisms

Monocyte chemoattractant protein-1 (MCP-1) is a member of the Cys-Cys chemokine family. Two related MCP-1 receptors have been identified (CC-CKR2A and CC-CKR2B), although the precise kinetics of ligand binding and calcium signaling of these receptors has yet to be investigated. To examine this more closely, the human MCP-1 receptors were cloned and expressed in Chinese hamster ovary (CHO) cells. Membranes prepared from cells expressing CC-CKR2B bind MCP-1 selectively and with high affinity (Kd = 120 pM). MCP-1 stimulation of recombinant CHO cells expressing CC-CKR2B induces a rapid increase in intracellular Ca2+ through both receptor-operated Ca2+ channels and mobilization of Ca2+ from intracellular stores, and leads to a rapid temperature-dependent internalization of the ligand/receptor complexes. In contrast, recombinant CHO cells expressing CC-CKR2A, and membranes prepared from these cells, fail to bind detectable levels of MCP-1. However, MCP-1 stimulation of cells expressing CC-CKR2A induces a small but significant increase in intracellular Ca2+. Repeated stimulation of these cells with MCP-1 leads to a potentiation of the response to a level comparable to that seen in cells expressing CC-CKR2B. These observations suggest that the levels of cell surface CC-CKR2A are controlled by novel mechanisms.

High level expression of human MCP-1 using the LCR/MEL expression system

We have expressed human monocyte chemoattractant protein-1 (hMCP-1) in preerythroid mouse erythroleukemia (MEL) C88 cells using the locus control region/MEL expression system and studied the biological activity of the purified protein in a range of in vitro experimental systems. The recombinant hMCP-1 is expressed at high levels (approximately 10 mg/liter) in this system and is modified in a manner which is very similar to native hMCP-1. We have developed a simple high-yielding two-step purification route employing dye ligand and ion exchange chromatographies which enables us to separate glycosylated and unglycosylated hMCP-1. The purified glycosylated and unglycosylated forms of hMCP-1 have equivalent biological activities in all of the assay systems tested.

Locations and immunoreactivities of phosphorylation sites on bovine and porcine tau proteins and a PHF-tau fragment

Tau protein is a phosphorylated neuronal microtubule-associated protein. Tau protein is also present in the major pathological lesions of Alzheimer's disease in an insoluble hyperphosphorylated state as paired helical filaments (PHFs). We have investigated the phosphorylation state of control taus and a fragment of PHF-tau. Tau samples were digested with protease, separated by reversed-phase high-performance liquid chromatography, and analyzed by mass spectrometry and Edman microsequencing. The serine homologous with S404 of human tau 441 was phosphorylated on bovine and porcine tau and up to two phosphates were present on a peptide of amino acids 182-240 of bovine tau (193-251 of human tau 441). The serine within the KSPV motif was not phosphorylated on bovine or porcine tau. PHF-tau fragments, isolated from pronase-treated PHFs encompassed a 93-amino acid region within the microtubule binding domain. Enzymatic digestion and mass spectrometric analysis showed no phosphate was present and a second carboxyl terminus was identified at E380. Antibodies T3P and SMI34, which recognize PHF-tau and peptides phosphorylated at the sequence KSPV, both reacted with bovine and porcine tau even though the KSPV sequence was not phosphorylated. These data indicate that the 93-amino acid sequence of F5.5 tau from PHFs is not phosphorylated, and the serine equivalent to S404 of human tau is phosphorylated in bovine and porcine tau. Antibodies T3P and SMI34 react with phosphorylated epitopes that are not unique to PHF-tau and that are not necessarily at the KSPV site.

Pharmacokinetics and efficacy of structurally related spirohydantoin and spirosuccinimide aldose reductase inhibitors

1. Six potent aldose reductase inhibitors (ARI), three spirohydantoin (I to III) and three spirosuccinimide (IV to VI) compounds, showed similar IC50 activities in vitro for the inhibition of rat lens aldose reductase, but their ED50 values in diabetic rats varied as much as 20-fold in the lens and 50-fold in the sciatic nerve tissue. Pharmacokinetic studies were undertaken to investigate these findings. Structure-pharmacokinetic relationships were studied following i.v. administration to cynomolgus monkeys. 2. The clearance (CL) of each spirosuccinimide ARI was faster (greater than 5 times) than that of the corresponding spirohydantoin compound. In both series the CL values of the C(4) methyl and methoxy analogues were 4-fold greater than those for the unsubstituted compounds, although the CL values of the methoxy and methyl derivatives in the same series were not significantly different. 3. The volumes of distribution (Vss) of the spirohydantoins were about one-half those of the corresponding spirosuccinimides, and the Vss values of the parent compounds of both ARI series did not differ dramatically from those of their methyl and methoxy analogues. 4. All six compounds were eliminated from plasma in a biexponential fashion. The half-lives (lambda 1 and lambda 2) of the spirohydantoin compounds were much longer than those of the corresponding spirosuccinimide compounds, and the unsubstituted compounds had longer half-lives than their methyl and methoxy derivatives. The longest lambda 1 and lambda 2 half-lives were observed for imirestat, while two of the spirosuccinimides had the shortest half-lives. 5. These results indicate that the relationships observed between the in vitro and in vivo activities of the six ARI can be attributed to structurally dependent differences in metabolic clearance.