Tanja Alderliesten

Radioactive Seed Localization of Breast Lesions: An Adequate Localization Method without Seed Migration

Abstract:  Preoperative localization is important to optimize the surgical treatment of breast lesions, especially in nonpalpable lesions. Radioactive seed localization (RSL) using iodine‐125 is a relatively new approach. To provide accurate guidance to surgery, it is important that the seeds do not migrate after placement. The aim of this study was to assess short‐term and long‐term seed migration after RSL of breast lesions. In 45 patients, 48 RSL procedures were performed under ultrasound or stereotactic guidance. In the first 12 patients, the lesion was localized with two markers: an iodine‐125 seed and a reference marker. In 33 patients, 36 RSL procedures were performed using a single iodine‐125 seed. All patients received control mammograms after seed placement and prior to surgery. In the patients with two markers, migration was defined as the difference in the largest distance between the markers observed in the mammograms. For single‐marked lesions, migration was assessed by comparing distances between anatomical landmarks in the mammograms. RSL was successful in all patients. Seeds were in‐situ for 59.5 days on average (3–136 days). The detection rate during surgery was 100%. Overall, an average seed migration of 0.9 mm (standard deviation 1.0 mm) was observed. Neither differences in lesion type, nor days in situ, type of surgery or radiologic localization method were found to have impact on seed migration. RSL is an accurate preoperative localization method for breast lesions with negligible seed migration, independent of time in‐situ.

Marking the axilla with radioactive iodine seeds (MARI procedure) may reduce the need for axillary dissection after neoadjuvant chemotherapy for breast cancer

An important benefit of neoadjuvant chemotherapy is the increased potential for breast‐conserving surgery. At present the response of axillary lymph node metastases to chemotherapy is not easily assessed, rendering axilla‐conserving treatment difficult. The aim was to assess a new surgical method for evaluating the axillary response to chemotherapy.

Modeling Friction, Intrinsic Curvature, and Rotation of Guide Wires for Simulation of Minimally Invasive Vascular Interventions

Obtaining the expertise to perform minimally invasive vascular interventions requires thorough training. In this paper, an algorithm for simulating minimally invasive vascular interventions for training purposes is presented and evaluated. The algorithm enables the simulation of completely straight guide wires as well as intrinsically curved ones based on applied translations and rotations. Friction between the guide wire and the vasculature is incorporated in the model. Quantitative validation is performed by comparing the simulated guide-wire position with the actual position as assessed by 3-D rotational X-ray imaging in physical experiments on a variety of vascular phantoms that truthfully represent human anatomy. The results show that for proper settings of the models parameters, accurate simulations of guide-wire motion can be obtained, with an average precision of the guide-wire position of around 1.0 mm

Simulation of minimally invasive vascular interventions for training purposes

Objective: To master the skills required to perform minimally invasive vascular interventions, proper training is essential. A computer simulation environment has been developed to provide such training. The simulation is based on an algorithm specifically developed to simulate the motion of a guide wire—the main instrument used during these interventions—in the human vasculature. In this paper, the design and model of the computer simulation environment is described and first results obtained with phantom and patient data are presented. Materials and methods: To simulate minimally invasive vascular interventions, a discrete representation of a guide wire is used which allows modeling of guide wires with different physical properties. An algorithm for simulating the propagation of a guide wire within a vascular system, on the basis of the principle of minimization of energy, has been developed. Both longitudinal translation and rotation are incorporated as possibilities for manipulating the guide wire. The simulation is based on quasi-static mechanics. Two types of energy are introduced: internal energy related to the bending of the guide wire, and external energy resulting from the elastic deformation of the vessel wall. Results: A series of experiments were performed on phantom and patient data. Simulation results are qualitatively compared with 3D rotational angiography data. Conclusions: The results indicate plausible behavior of the simulation.

Analytical guide wire motion algorithm for simulation of endovascular interventions

Performing minimally invasive vascular interventions requires proper training, as a guide wire needs to be manipulated, by the tail, under fluoroscopic guidance. To provide a training environment, the motion of the guide wire inside the human vasculature can be simulated by computer. Such a simulation needs to be based on an algorithm that is both realistic and fast. To meet these two demands, an analytical solution to the problem of guide wire motion has been derived, using a new parametrisation of guide wire shape. The algorithm is highly generic, is entirely based on elementary physics and has good convergence properties (accuracy of 22 micron after two iterations). In an experimental validation of the algorithm in a planar model, the RMS of the spatial discrepancy between the real and simulated catheter positions was about 10% of the lumen size. Comparison of the simulated guide wire motion with 3D rotational angiography data of a real guide wire advanced in a plastic phantom of the cerebral vasculature showed that the new algorithm produced realistic results.

Assessment of set-up variability during deep inspiration breath hold radiotherapy for breast cancer patients by 3D-surface imaging.

PURPOSE To quantify set-up uncertainties during voluntary deep inspiration breath hold (DIBH) radiotherapy using 3D-surface imaging in patients with left sided breast cancer. MATERIAL AND METHODS Nineteen patients were included. Cone-beam CT-scan (CBCT) was used for online set-up correction while patients were instructed to perform a voluntary DIBH. The reproducibility of the DIBH during treatment was monitored with 2D-fluoroscopy and portal imaging. Simultaneously, a surface imaging system was used to capture 3D-surfaces throughout CBCT acquisition and delivery of treatment beams. Retrospectively, all captured surfaces were registered to the planning-CT surface. Interfraction, intra-fraction and intra-beam set-up variability were quantified in left-right, cranio-caudal and anterior-posterior direction. RESULTS Inter-fraction systematic (Σ) and random (σ) translational errors (1SD) before and after set-up correction were between 0.20-0.50 cm and 0.09-0.22 cm, respectively, whereas rotational Σ and σ errors were between 0.08 and 1.56°. The intra-fraction Σ and σ errors were ≤ 0.14 cm and ≤ 0.47°. The intra-beam SD variability was ≤ 0.08 cm and ≤ 0.28° in all directions. CONCLUSION Quantification of 3D set-up variability in DIBH RT showed that patients are able to perform a very stable and reproducible DIBH within a treatment fraction. However, relatively large inter-fraction variability requires online image guided set-up corrections.

Using histopathology breast cancer data to reduce clinical target volume margins at radiotherapy

PURPOSE This study aimed to quantify the incidence and extension of microscopic disease around primary breast tumors in patients undergoing breast-conserving therapy (BCT), focusing on a potential application to reduce radiotherapy boost volumes. METHODS AND MATERIALS An extensive pathology tumor-distribution study was performed using 38 wide local excision specimens of BCT patients. Specimen orientation was recorded and microscopic findings reconstructed to assess the incidence of microscopic disease around the macroscopic tumor. A model of disease spread was built, showing probability of disease extension outside a treated volume (P(out,vol)). The model was applied in 10 new BCT patients. Taking asymmetry of tumor excision into account, new asymmetric margins for the clinical target volume of the boost (CTV(boost)) were evaluated that minimize the volume without increasing P(out,TTV) (TTV being total treated volume: V(surgery) + CTV(boost)). Potential reductions in CTV(boost) and TTV were evaluated. RESULTS Microscopic disease beyond the tumor boundary occurred isotropically at distances > 1 cm (intended surgical margin) and > 1.5 cm (intended TTV margin) in 53% and 36% of the excision specimens, respectively. In the 10 prospective patients, the average P(out,TTV) was, however, only 16% due to larger surgical margins than intended in some directions. Asymmetric CTV(boost) margins reduced the CTV(boost) and TTV by 27% (20 cc) and 12% (21 cc) on average, without compromising tumor coverage. CONCLUSIONS Microscopic disease extension may occur beyond the current CTV(boost) in approximately one sixth of patients. An asymmetric CTV(boost) that corrects for asymmetry of the surgical excision has the potential to reduce boost volumes while maintaining tumor coverage.

Accuracy Evaluation of a 3-Dimensional Surface Imaging System for Guidance in Deep-Inspiration Breath-Hold Radiation Therapy

PURPOSE To investigate the applicability of 3-dimensional (3D) surface imaging for image guidance in deep-inspiration breath-hold radiation therapy (DIBH-RT) for patients with left-sided breast cancer. For this purpose, setup data based on captured 3D surfaces was compared with setup data based on cone beam computed tomography (CBCT). METHODS AND MATERIALS Twenty patients treated with DIBH-RT after breast-conserving surgery (BCS) were included. Before the start of treatment, each patient underwent a breath-hold CT scan for planning purposes. During treatment, dose delivery was preceded by setup verification using CBCT of the left breast. 3D surfaces were captured by a surface imaging system concurrently with the CBCT scan. Retrospectively, surface registrations were performed for CBCT to CT and for a captured 3D surface to CT. The resulting setup errors were compared with linear regression analysis. For the differences between setup errors, group mean, systematic error, random error, and 95% limits of agreement were calculated. Furthermore, receiver operating characteristic (ROC) analysis was performed. RESULTS Good correlation between setup errors was found: R(2)=0.70, 0.90, 0.82 in left-right, craniocaudal, and anterior-posterior directions, respectively. Systematic errors were ≤0.17 cm in all directions. Random errors were ≤0.15 cm. The limits of agreement were -0.34-0.48, -0.42-0.39, and -0.52-0.23 cm in left-right, craniocaudal, and anterior-posterior directions, respectively. ROC analysis showed that a threshold between 0.4 and 0.8 cm corresponds to promising true positive rates (0.78-0.95) and false positive rates (0.12-0.28). CONCLUSIONS The results support the application of 3D surface imaging for image guidance in DIBH-RT after BCS.

On the feasibility of MRI‐guided navigation to demarcate breast cancer for breast‐conserving surgery

PURPOSE The aim of this study was to investigate the feasibility of image-guided navigation approaches to demarcate breast cancer on the basis of preacquired magnetic resonance (MR) imaging in supine patient orientation. METHODS Strategies were examined to minimize the uncertainty in the instrument-tip position, based on the hypothesis that the release of instrument pressure returns the breast tissue to its predeformed state. For this purpose, four sources of uncertainty were taken into account: (1) Uligaments: Uncertainty in the reproducibility of the internal mammary gland geometry during repeat patient setup in supine orientation; (2) Ur_breathing: Residual uncertainty in registration of the breast after compensation for breathing motion using an external marker; (3) Ureconstruction: Uncertainty in the reconstructed location of the tip of the needle using an optical image-navigation system (phantom experiments, n=50); and (4) Udeformation: Uncertainty in displacement of breast tumors due to needle-induced tissue deformations (patients, n=21). A Monte Carlo study was performed to establish the 95% confidence interval (CI) of the combined uncertainties. This region of uncertainty was subsequently visualized around the reconstructed needle tip as an additional navigational aid in the preacquired MR images. Validation of the system was performed in five healthy volunteers (localization of skin markers only) and in two patients. In the patients, the navigation system was used to monitor ultrasound-guided radioactive seed localization of breast cancer. Nearest distances between the needle tip and the tumor boundary in the ultrasound images were compared to those in the concurrently reconstructed MR images. RESULTS Both Ureconstruction and Udeformation were normally distributed with 0.1±1.2mm (mean±1SD) and 0.1±0.8mm, respectively. Taking prior estimates for Uligaments (0.0±1.5mm) and Ur_breathing (-0.1±0.6mm) into account, the combined impact resulted in 3.9 mm uncertainty in the position of the needle tip (95% CI) after release of pressure. The volunteer study showed a targeting accuracy comparable to that in the phantom experiments: 2.9±1.3 versus 2.7±1.1mm, respectively. In the patient feasibility study, the deviations were within the 3.9 mm CI. CONCLUSIONS Image-guided navigation to demarcate breast cancer on the basis of preacquired MR images in supine orientation appears feasible if patient breathing is tracked during the navigation procedure, positional uncertainty is visualized and pressure on the localization instrument is released prior to verification of its position.

Towards a Real-Time Minimally-Invasive Vascular Intervention Simulation System

Recently, foundations rooted in physics have been laid down for the goal of simulating the propagation of a guide wire inside the vasculature. At the heart of the simulation lies the fundamental task of energy minimization. The energy comes from interaction with the vessel wall and the bending of the guide wire. For the simulation to be useful in actual training, obtaining the smallest possible optimization time is key. In this paper, we, therefore, study the influence of using different optimization techniques: a semianalytical approximation algorithm, the conjugate-gradients algorithm, and an evolutionary algorithm (EA), specifically the GLIDE algorithm. Simulation performance has been measured on phantom data. The results show that a substantial reduction in time can be obtained while the error is increased only slightly if conjugate gradients or GLIDE is used