Medical image computing and computer-aided medical interventions applied to soft tissues. Work in progress in urology

Until recently, Computer-Aided Medical Interventions (CAMI) and Medical Robotics have focused on rigid and non deformable anatomical structures. Nowadays, special attention is paid to soft tissues, raising complex issues due to their mobility and deformation. Mini-invasive digestive surgery was probably one of the first fields where soft tissues were handled through the development of simulators, tracking of anatomical structures and specific assistance robots. However, other clinical domains, for instance urology, are concerned. Indeed, laparoscopic surgery, new tumour destruction techniques (e.g. HIFU, radiofrequency, or cryoablation), increasingly early detection of cancer, and use of interventional and diagnostic imaging modalities, recently opened new challenges to the urologist and scientists involved in CAMI. This resulted in the last five years in a very significant increase of research and developments of computer-aided urology systems. In this paper, we propose a description of the main problems related to computer-aided diagnostic and therapy of soft tissues and give a survey of the different types of assistance offered to the urologist: robotization, image fusion, surgical navigation. Both research projects and operational industrial systems are discussed

Comparison of transabdominal ultrasound and electromagnetic transponders for prostate localization.

The aim of this study is to compare two methodologies of prostate localization in a large cohort of patients. Daily prostate localization using B-mode ultrasound has been performed at the Nebraska Medical Center since 2000. More recently, a technology using electromagnetic transponders implanted within the prostate was introduced into our clinic (Calypso(R)). With each technology, patients were localized initially using skin marks. Localization error distributions were determined from offsets between the initial setup positions and those determined by ultrasound or Calypso. Ultrasound localization data was summarized from 16619 imaging sessions spanning 7 years; Calypso localization data consists of 1524 fractions in 41 prostate patients treated in the course of a clinical trial at five institutions and 640 localizations from the first 16 patients treated with our clinical system. Ultrasound and Calypso patients treated between March and September 2007 at the Nebraska Medical Center were analyzed and compared, allowing a single institutional comparison of the two technologies. In this group of patients, the isocenter determined by ultrasound-based localization is on average 5.3 mm posterior to that determined by Calypso, while the systematic and random errors and PTV margins calculated from the ultrasound localizations were 3 - 4 times smaller than those calculated from the Calypso localizations. Our study finds that there are systematic differences between Calypso and ultrasound for prostate localization

Computer- and robot-assisted Medical Intervention

Medical robotics includes assistive devices used by the physician in order to make his/her diagnostic or therapeutic practices easier and more efficient. This chapter focuses on such systems. It introduces the general field of Computer-Assisted Medical Interventions, its aims, its different components and describes the place of robots in that context. The evolutions in terms of general design and control paradigms in the development of medical robots are presented and issues specific to that application domain are discussed. A view of existing systems, on-going developments and future trends is given. A case-study is detailed. Other types of robotic help in the medical environment (such as for assisting a handicapped person, for rehabilitation of a patient or for replacement of some damaged/suppressed limbs or organs) are out of the scope of this chapter.Comment: Handbook of Automation, Shimon Nof (Ed.) (2009) 000-00

Use of radiobiological modeling in treatment plan evaluation and optimization of prostate cancer radiotherapy

There are many tools available that are used to evaluate a radiotherapy treatment plan, such as isodose distribution charts, dose volume histograms (DVH), maximum, minimum and mean doses of the dose distributions as well as DVH point dose constraints. All the already mentioned evaluation tools are dosimetric only without taking into account the radiobiological characteristics of tumors or OARs. It has been demonstrated that although competing treatment plans might have similar mean, maximum or minimum doses they may have significantly different clinical outcomes (Mavroidis et al. 2001). For performing a more complete treatment plan evaluation and comparison the complication-free tumor control probability (P+) and the biologically effective uniform dose (D ) have been proposed (Källman et al. 1992a, Mavroidis et al. 2000). The D concept denotes that any two dose distributions within a target or OAR are equivalent if they produce the same probability for tumor control or normal tissue complication, respectively (Mavroidis et al. 2001)..

Real-Time Ultrasound Image-Guidance and Tracking in External Beam Radiotherapy

Background and Purpose - To evaluate the accuracy of Clarity (clinical version) system by using ultrasound phantom and some probe position. - To evaluate the intrafraction motion of prostate by collecting and analyzing ultrasound monitoring data from some patients. - To evaluate the accuracy of Clarity (Anticosti) system by using 3D phantom programmed with sinusoidal and breathing movement patterns to simulate computer-controlled based breath-hold phases interspersed with spontaneous breathing. - To evaluate the clinical applicability of Clarity (Anticosti) system for liver cases in healthy volunteers. The tracking results of healthy volunteers were compared to surface marker. - To evaluate the intrafraction motion during breath-hold in liver case by collecting and analyzing US monitoring data from some patients. Material and Methods The accuracy of Clarity (clinical version) system was evaluated using ultrasound phantom and some probe position. Two different probes were used: transabdominal ultrasound (TAUS) and transperineal ultrasound (TPUS) probe. Two positions of the phantom were used for TPUS, the vertical and the horizontal position. Intrafraction motion assessment of the prostate was based on continuous position monitoring with a 4D US system along the three directions; left(+)-right (LR), anterior(+)-posterior (AP), and inferior(+)-superior (SI). 770 US monitoring sessions in 38 prostate cancer patients’ normo-fractionated VMAT treatment series were retrospectively evaluated. The overall mean values and standard deviations (SD) along with random and systematic SDs were computed. The tracking accuracy of the research 4D US system was evaluated using two motion phantoms programmed with sinusoidal and breathing patterns to simulate free breathing and DIBH. The clinical performance was evaluated with 5 healthy volunteers. US datasets were acquired in computer-controlled DIBH with varying angular scanning angles. Tracked structures were renal pelvis (spherical structure) and portal/liver vein branches (non-spherical structure). An external marker was attached to the surface of both phantoms and volunteers as a secondary tracked object by an infrared camera for comparison. Residual intrafractional motion of DIBH tracking target relative to beginning position in each breath-hold plateau region was analysed along three directions; superior-inferior (SI), left-right (LR) and anterior-posterior (AP). 12 PTVs of 11 patients with primary/secondary liver tumours or adrenal gland/spleen metastases of diverse primaries were irradiated with SBRT in DIBH. Real time tracking of target or neighbouring surrogate structures was performed additionally using 4D US system during CBCT acquisition after permission of local IRB. Results The geometric positioning tolerance for Clarity-Sim and Clarity-Guide is 1 mm according to the manufacturer’s specifications. The results showed that all phantom and probe combinations met this criterion. The mean duration of each prostate monitoring session was 254s. The mean (μ), the systematic error () and the random error (σ) of intrafraction prostate motion were μ=(0.01, -0.08, 0.15)mm, =(0.30, 0.34, 0.23)mm and σ=(0.59, 0.73, 0.64)mm in LR, AP and SI direction, respectively. The percentage of treatments for which prostate motion was 2mm was present in about 0.67% of the data. The percentage increased to 2.42%, 6.14%, and 9.35% at 120s, 180s and 240s, respectively. The phantom measurements using Clarity (Anticosti) system showed increasing accuracy of US tracking with decreasing scanning range. The probability of lost tracking was higher for small scanning ranges (43.09% (10°) and 13.54% (20°)).The tracking success rates in healthy volunteers during DIBH were 93.24% and 89.86% for renal pelvis and portal vein branches, respectively. There was a strong correlation between the motion of the marker and the US tracking for the majority of analyzed breath-holds. 84.06% and 88.41% of renal pelvis target results and 82.26% and 91.94% of liver vein target results in AP and SI direction, the Pearson correlation coefficient was between 0.71 and 0.99. For evaluation of the intrafraction motion during breath-hold, 680 individual BHs during 93 treatment fractions were analysed. On visual control of tracking movies, target was lost in 27.9% of tracking, leaving a total of 490 BHs with optimal tracking. During these BHs, mean(+SD) target displacement were 1.7(+0.8)mm, 0.9(+0.4)mm, 2.2(+1.0)mm and 3.2(+1.0)mm for SI, LR, AP and 3D vector, respectively. Most of target displacement was below 2mm with percentage of 64.6%, 88.1% and 60.5% for SI, LR and AP, respectively. Data percentage of large target displacement increased with added BH time. At 5s, 3D vector of target displacement >10mm could be observed in 0.1% of data. Percentage values increased to 0.2%, 0.6%, and 1.1% at 10s, 15s and 20s, respectively. Conclusions The 4D US system offers a non-invasive method for online organ motion monitoring without additional ionizing radiation dose to the patient. The magnitudes of intrafraction prostate motion along the SI and AP directions were comparable. On average, the smallest motion was in the LR direction and the largest in AP direction. Most of the prostate displacements were within a few millimeters. However, with increased treatment time, larger 3D vector prostate displacements up to 18.30 mm could be observed. Shortening the treatment time can reduce the intrafractional motion and its effects and US monitoring can help to maximize treatment precision particularly in hypofractionated treatment regimens. For organ monitoring during BH application, the 4D US system showed a good performance and tracking accuracy in a 4D motion phantom when tracking a target that moves in accordance to a simulating breathing pattern. A 30°scanning range turned out to be an optimal parameter to track along with respiratory motion considering the accuracy of tracking and the possible loss of the tracked structure. The ultrasound tracking system is also applicable to a clinical setup with the tested hardware solution. The tracking capability of surrogate structures for upper abdominal lesions in DIBH is promising but needs further investigation in a larger cohort of patients. Ultrasound motion data show a strong correlation with surface motion data for most of individual breath-holds. Further improvement of the tracking algorithm is suggested to improve accuracy along with respiratory motion if using larger scanning angles for detection of high-amplitude motion and non-linear transformations of the tracking target. The exact quantification of residual motion impact requires an in-depth analysis of time spent at every position, nevertheless mean residual motion during DIBH is low and predominant direction is SI and AP. Only infrequently larger displacements of 3D vector >1 cm were observed, for short periods. Beam interruption at predefined thresholds could take DIBH treatments close to perfection. Key words: Medical Physics, 4D ultrasound, IGRT (image-guided radiotherapy), prostate motion, stereotactic body radiotherapy (SBRT), deep inspiratory breath-hold (DIBH)

A comparative assessment of prostate positioning guided by three-dimensional ultrasound and cone beam CT

Background: The accuracy of the Elekta Clarity (TM) three-dimensional ultrasound system (3DUS) was assessed for prostate positioning and compared to seed-and bone-based positioning in kilo-voltage cone-beam computed tomography (CBCT) during a definitive radiotherapy. Methods: The prostate positioning of 6 patients, with fiducial markers implanted into the prostate, was controlled by 3DUS and CBCT. In total, 78 ultrasound scans were performed trans-abdominally and compared to bone-matches and seed-matches in CBCT scans. Setup errors detected by the different modalities were compared. Systematic and random errors were analysed, and optimal setup margins were calculated. Results: The discrepancy between 3DUS and seed-match in CBCT was -0.2 +/- 2.7 mm laterally,-1.9 +/- 2.3 mm longitudinally and 0.0 +/- 3.0 mm vertically and significant only in longitudinal direction. Using seed-match as reference, systematic errors of 3DUS were 1.3 mm laterally, 0.8 mm longitudinally and 1.4 mm vertically, and random errors were 2.5 mm laterally, 2.3 mm longitudinally, and 2.7 mm vertically. No significant difference could be detected for 3DUS in comparison to bone-match in CBCT. Conclusions: 3DUS is feasible for image guidance for patients with prostate cancer and appears comparable to CBCT based image guidance in the retrospective study. While 3DUS offers some distinct advantages such as no need of invasive fiducial implantation and avoidance of extra radiation, its disadvantages include the operator dependence of the technique and dependence on sufficient bladder filling. Further study of 3DUS for image guidance in a large patient cohort is warranted

Improving 3D ultrasound prostate localisation in radiotherapy through increased automation of interfraction matching.

Background and purpose Daily image guidance is standard care for prostate radiotherapy. Innovations which improve the accuracy and efficiency of ultrasound guidance are needed, particularly with respect to reducing interobserver variation. This study explores automation tools for this purpose, demonstrated on the Elekta Clarity Autoscan®. The study was conducted as part of the Clarity-Pro trial (NCT02388308). Materials and methods Ultrasound scan volumes were collected from 32 patients. Prostate matches were performed using two proposed workflows and the results compared with Clarity's proprietary software. Gold standard matches derived from manually localised landmarks provided a reference. The two workflows incorporated a custom 3D image registration algorithm, which was benchmarked against a third-party application (Elastix). Results Significant reductions in match errors were reported from both workflows compared to standard protocol. Median (IQR) absolute errors in the left-right, anteroposterior and craniocaudal axes were lowest for the Manually Initiated workflow: 0.7(1.0) mm, 0.7(0.9) mm, 0.6(0.9) mm compared to 1.0(1.7) mm, 0.9(1.4) mm, 0.9(1.2) mm for Clarity. Median interobserver variation was ≪0.01 mm in all axes for both workflows compared to 2.2 mm, 1.7 mm, 1.5 mm for Clarity in left-right, anteroposterior and craniocaudal axes. Mean matching times was also reduced to 43 s from 152 s for Clarity. Inexperienced users of the proposed workflows attained better match precision than experienced users on Clarity. Conclusion Automated image registration with effective input and verification steps should increase the efficacy of interfraction ultrasound guidance compared to the current commercially available tools

Comparative evaluation of a novel, moderately hypofractionated radiation protocol in 56 dogs with symptomatic intracranial neoplasia

BACKGROUND: Use of strongly hypofractionated radiation treatments in dogs with intracranial neoplasia did not improve outcomes and yielded increased rates of toxicosis. OBJECTIVES: To evaluate safety and efficacy of a new, moderately hypofractionated radiation protocol of 10 × 4 Gy compared to a standard protocol. ANIMALS: Convenience sample of 56 client-owned dogs with primary symptomatic brain tumors. METHODS: Retrospective observational study. Twenty-six dogs were assigned to the control standard protocol of 20 × 2.5 Gy (group A) and 30 dogs to the new protocol of 10 × 4 Gy (group B), assigned on owners' informed consent. Statistical analysis was conducted under the "as treated" regime, using Kaplan-Meier and Cox-regression analysis. Treatment was delivered with technically advanced image-guided radiation therapy. The 2 treatment groups were compared in terms of outcome and signs of toxicosis. RESULTS: Overall progression-free interval (PFI) and overall survival (OS) time were favorable, with 663 (95%CI: 497;828) and 637 (95%CI: 403;870) days, respectively. We found no significant difference between the two groups: PFI for dogs in group A vs B was 608 (95%CI: 437;779) days and mean (median not reached) 863 (95%CI: 644;1083) days, respectively (P = .89), and OS for dogs in group A vs B 610 (95%CI: 404;816) and mean (median not reached) 796 (95%CI: 586;1007) days (P = .83). CONCLUSION AND CLINICAL IMPORTANCE: In conclusion, 10 × 4 Gy is a safe and efficient protocol for treatment of primary intracranial neoplasia and future dose escalation can be considered