Ivan Buzurovic

A robotic approach to 4D real-time tumor tracking for radiotherapy

Respiratory and cardiac motions induce displacement and deformation of the tumor volumes in various internal organs. To accommodate this undesired movement and other errors, physicians incorporate a large margin around the tumor to delineate the planning target volume, so that the clinical target volume receives the prescribed radiation dose under any scenario. Consequently, a large volume of healthy tissue is irradiated and sometimes it is difficult to spare critical organs adjacent to the tumor. In this study we have proposed a novel approach to the 4D active tracking and dynamic delivery incorporating the tumor motion prediction technique. This method has been applied to the two commercially available robotic treatment couches. The proposed algorithm can predict the tumor position and the robotic systems are able to continuously track the tumor during radiation dose delivery. Therefore a precise dose is given to a moving target while the dose to the nearby critical organs is reduced to improve the patient treatment outcome. The efficacy of the proposed method has been investigated by extensive computer simulation. The tumor tracking method is simulated for two couches: HexaPOD robotic couch and ELEKTA Precise Table. The comparison results have been presented in this paper. In order to assess the clinical significance, dosimetric effects of the proposed method have been analyzed.

Tumor Motion Prediction and Tracking in Adaptive Radiotherapy

Respiratory and cardiac motions induce displacement and deformation of the tumor-volume in various internal organs. To accommodate this undesired movement and other errors, physicians incorporate a large margin around the tumor to delineate Planning Target Volume (PTV), so that the Clinical Target Volume (CTV) receives the prescribed radiation dose under any scenario. Consequently, a large volume of healthy tissue is irradiated and sometimes it is difficult to spare critical organs adjacent to the tumor. In this study we have proposed a novel approach to 4D Active Tracking and Dynamic Delivery (ATDD) together with tumor motion prediction. Proposed algorithm can predict tumor position and the robotic system can continuously track the tumor during radiation dose delivery, so that a precise dose is given to a moving target while reducing dose to nearby critical organs for improved patient treatment outcome. The efficacy of the proposed method has been investigated by extensive computer simulation. The results have been presented in this article.

Redesign of process map to increase efficiency: Reducing procedure time in cervical cancer brachytherapy

PURPOSE To increase intraprocedural efficiency in the use of clinical resources and to decrease planning time for cervical cancer brachytherapy treatments through redesign of the procedures process map. METHODS AND MATERIALS A multidisciplinary team identified all tasks and associated resources involved in cervical cancer brachytherapy in our institution and arranged them in a process map. A redesign of the treatment planning component of the process map was conducted with the goal of minimizing planning time. Planning time was measured on 20 consecutive insertions, of which 10 were performed with standard procedures and 10 with the redesigned process map, and results were compared. Statistical significance (p < 0.05) was measured with a two-tailed t test. RESULTS Twelve tasks involved in cervical cancer brachytherapy treatments were identified. The process map showed that in standard procedures, the treatment planning tasks were performed sequentially. The process map was redesigned to specify that contouring and some planning tasks are performed concomitantly. Some quality assurance tasks were reorganized to minimize adverse effects of a possible error on procedure time. Test dry runs followed by live implementation confirmed the applicability of the new process map to clinical conditions. A 29% reduction in planning time (p < 0.01) was observed with the introduction of the redesigned process map. CONCLUSIONS A process map for cervical cancer brachytherapy was generated. The treatment planning component of the process map was redesigned, resulting in a 29% decrease in planning time and a streamlining of the quality assurance process.

Prediction Control for Brachytherapy Robotic System

In contemporary brachytherapy procedure, needle placement at desired location is challenging due to a variety of reasons. We have designed and fabricated an image-guided robot-assisted brachytherapy system to improve the needle placement and seed delivery. In this article we have used two different predictive control strategies in order to investigate the needle insertion efficacy and system dynamics during prostate brachytherapy. First, we used neural network predictive control (NNPC) to predict an insertion force. The NNPC uses the linearized state-space model of the robotic system to predict future system performances. Second, we used feedforward model predictive control (MPC) which allows the controller to compensate the influence of a measured disturbances impact immediately rather than waiting until the effect appears in the system. Feedback control problem for the contact force regulation is considered. The simulation results and experiments for both cases are presented and compared.

Dynamics-based decentralized control of robotic couch and multi-leaf collimators for tracking tumor motion

Tumors in thorax region incur significant amount of motion and deformation due to respiratory and cardiac cycles. To accommodate this undesired movement, physicians incorporate a large standard margin around the tumor to delineate a planning target volume (PTV), so that the clinical target volume (CTV) receives the prescribed dose under any scenario. Consequently, a large volume of healthy tissue might be irradiated and sometimes it is difficult to spare critical organs adjacent to the tumor. For compensating this tumor motion, techniques such as breath-hold, gating, and active tracking and dynamic delivery (ATDD) are used. Although, ATDD is the most effective technique, it is the most challenging one. The ATDD can be accomplished in three different ways: adjusting the multi-leaf collimator (MLC), adjusting the couch, and adjusting the MLC and couch simultaneously. The first two techniques have been explored and/or implemented in practice. However, the third approach has not been investigated extensively. In this study, we have proposed a novel approach for ATDD that exploits the advantages of both the MLC (or MLC-bank) and the HexaPODtrade robotic couch. In our proposed new approach, we have decomposed and allocated the tumor motion trajectory to the subsystems (MLC or MLC-bank and HexaPOD robotic couch) based on their natural frequency domains using wavelet technique. The efficacy of the proposed method has been investigated by extensive computer simulation and the results are presented in this paper.

Independent brachytherapy plan verification software: Improving efficacy and efficiency

BACKGROUND AND PURPOSE To compare the pre-treatment brachytherapy plan verification by a physicist assisted by custom plan verification software (SAV) with those performed manually (MV). MATERIALS AND METHODS All HDR brachytherapy plans used for treatment in 2013, verified using either SAV or MV, were retrospectively reviewed. Error rate (number of errors/number of plans) was measured and verification time calculated. All HDR brachytherapy safety events recorded between 2010 and 2013 were identified. The rate of patient-related safety events (number of events/number of fractions treated) and the impact of SAV on the underlying errors were assessed. RESULTS Three/106 errors (2.8%) were found in the SAV group and 24/273 (8.8%) in the MV group (p=0.046). The mean ±1 standard deviation plan verification time was 8.4±4.0min for SAV and 11.6±5.3 for MV (p=0.006). Seven safety events out of 4729 fractions delivered (0.15%) were identified. Four events (57%) were associated with plan verification and could have been detected by SAV. CONCLUSIONS We found a safety event rate in HDR brachytherapy of 0.15%. SAV significantly reduced the number of undetected errors in HDR treatment plans compared to MV, and reduced the time required for plan verification.

The decreased use of brachytherapy boost for intermediate and high-risk prostate cancer despite evidence supporting its effectiveness

PURPOSE The Canadian Androgen Suppression Combined with Elective Nodal and Dose Escalated Radiation Therapy (ASCENDE-RT) randomized trial showed that brachytherapy boost reduces recurrence by 50% compared to dose-escalated radiation. We examined how men with identical inclusion criteria to the ASCENDE-RT trial were being treated in the United States. METHODS AND MATERIALS We used the National Cancer Database to identify prostate cancer patients treated with radiation from 2004 through 2012 who met the inclusion criteria of the ASCENDE-RT trial (intermediate-/high-risk prostate cancer, excluding patients with prostate-specific antigen >40 or tumor stage T3b/T4). The Mantel-Haenszel test was used to investigate the trend for type of radiation modality used over the study period. RESULTS A cohort of 156,411 patients was identified. Of those, 103,188 men (66%) were treated with external beam radiation therapy (EBRT) alone, 31,129 (20%) with brachytherapy alone, and 22,094 (14%) with EBRT plus brachytherapy. EBRT plus a brachytherapy boost demonstrated a significant decrease in utilization from 2004 to 2012 in both academic and nonacademic centers, declining from 15% to 8% in academic centers and from 19% to 11% in nonacademic centers (p-Value for trend <0.0001 for both). Academic centers were significantly less likely to use brachytherapy boost than nonacademic centers (adjusted odds ratio: 0.68; 95% confidence interval: 0.66-0.70; p-Value: <0.0001). CONCLUSIONS Radiation oncology practices have demonstrated a significant reduction in the use of brachytherapy boost from 2004 to 2012, and the lowest utilization was in academic centers. In light of the superior results demonstrated for brachytherapy boost by the ASCENDE-RT trial, it is unclear whether academic centers are prepared to train the next generation of residents in this critical modality.

On finite and practical stability of time delayed systems: Lyapunov-Krassovski approach, delay dependent criteria

This paper gives sufficient conditions for the practical and finite time stability of linear continuous time delay systems of the form X(t)=A0X(t)+A1X(t−τ). When we consider finite time stability, these new, delay independent conditions are derived using the approach based on Lyapunov-Krassovski functionals. In this case these functionals need not to have: a) properties of positivity in whole state space and b) negative derivatives along system trajectories. When we consider practical stability, before mentioned concept of stability, it is combined and supported by classical Lyapunov technique to guarantee attractivity properties of system behavior.

Active tracking and dynamic dose delivery for robotic couch in radiation therapy

Precise and accurate dose delivery is critically important in external beam radiation therapy. In many cases target-volumes are stationary, but the problem arises when the tumors move significantly due to cardiac and respiratory motions. This is a case for tumors in lung, esophagus, pancreas, liver, prostate, breast, and other organs in thoracic and abdominal regions. In the article we have described the Active Tracking and Dynamic Dose Delivery (ATDD) technique for real-time tumor motion compensation. In this approach, the robotic treatment table moves while delivering the radiation beam and compensates for breathing-induced tumor motion. Many parameters of the control system, such as patient mass or breathing pattern, are initially uncertain and may vary during the treatment. To solve these problems, feedforward adaptive control was adopted to minimize irradiation to healthy tissue and spare critical organs while ensuring prescribed radiation dose coverage to the target-volume.

Partial transmission high-speed continuous tracking multi-leaf collimator for 4D adaptive radiation therapy

As a technique for compensating for tumor motion induced by respiratory and cardiac motions, various dynamic approaches are being investigated and implemented in radiation therapy. This paper presents a novel system that can continuously track the tumor during radiation dose delivery so that a precise dose is given to a moving target while reducing dose to nearby critical organs for improved patient treatment outcome. The efficacy of the proposed methodology has been investigated by extensive computer simulation using a Proportional, Integral and Derivative (PID) controller. System design and simulation results are presented in this paper.