Synchrony--cyberknife respiratory compensation technology

Vision-based variable impedance control with oscillation observer for respiratory motion compensation during robotic needle insertion: a preliminary test

BACKGROUND

To reduce the radiation exposure of patients and physicians during needle-based procedures, robotic needle insertion systems have been widely developed. However, during robotic needle insertion, the respiratory motion of the patient can cause serious injury.

METHODS

A vision-based variable impedance control algorithm was introduced to compensate for the respiratory motion. The algorithm controls the robot so that the applied forces and moments on the needle are zero. Also, an oscillation observer was introduced to ensure patient safety. A preliminary test was performed using a seven degrees of freedom (7-DOF) robot and a phantom.

RESULT

It was found that the proposed algorithm greatly decreases damage to the phantom due to respiratory motion. Also, the proposed oscillation observer was able to ensure robot stability.

CONCLUSIONS

The proposed control scheme allows the robot to compensate for the respiratory motion to ensure patient safety during a needle-based procedure.

The potential of positron emission tomography for intratreatment dynamic lung tumor tracking: a phantom study

PURPOSE

This study aims to evaluate the potential and feasibility of positron emission tomography for dynamic lung tumor tracking during radiation treatment. The authors propose a center of mass (CoM) tumor tracking algorithm using gated-PET images combined with a respiratory monitor and investigate the geometric accuracy of the proposed algorithm.

METHODS

The proposed PET dynamic lung tumor tracking algorithm estimated the target position information through the CoM of the segmented target volume on gated PET images reconstructed from accumulated coincidence events. The information was continuously updated throughout a scan based on the assumption that real-time processing was supported (actual processing time at each frame ≈ 10 s). External respiratory motion and list-mode PET data were acquired from a phantom programmed to move with measured respiratory traces (external respiratory motion and internal target motion) from human subjects, for which the ground truth target position was known as a function of time. The phantom was cylindrical with six hollow sphere targets (10, 13, 17, 22, 28, and 37 mm in diameter). The measured respiratory traces consisted of two sets: (1) 1D-measured motion from ten healthy volunteers and (2) 3D-measured motion from four lung cancer patients. The authors evaluated the geometric accuracy of the proposed algorithm by quantifying estimation errors (Euclidean distance) between the actual motion of targets (1D-motion and 3D-motion traces) and CoM trajectories estimated by the proposed algorithm as a function of time.

RESULTS

The time-averaged error of 1D-motion traces over all trajectories of all targets was 1.6 mm. The error trajectories decreased with time as coincidence events were accumulated. The overall error trajectory of 1D-motion traces converged to within 2 mm in approximately 90 s. As expected, more accurate results were obtained for larger targets. For example, for the 37 mm target, the average error over all 1D-motion traces was 1.1 mm; and for the 10 mm target, the average error over all 1D-motion traces was 2.8 mm. The overall time-averaged error of 3D-motion traces was 1.6 mm, which was comparable to that of the 1D-motion traces. There were small variations in the errors between the 3D-motion traces, although the motion trajectories were very different. The accuracy of the estimates was consistent for all targets except for the smallest.

CONCLUSIONS

The authors developed an algorithm for dynamic lung tumor tracking using list-mode PET data and a respiratory motion signal, and demonstrated proof-of-principle for PET-guided lung tumor tracking. The overall tracking error in phantom studies is less than 2 mm.

Short-term effects of cyberknife combined with TACE for treatment of primary liver cancer

AIM: To evaluate the short-term clinical effects and adverse reactions of cyberknife combined with transarterial chemoembolization (TACE) for the treatment of primary liver cancer.

METHODS: The medical records for 108 patients with primary liver cancer who received cyberknife and TACE between January 2012 and May 2013 were retrospectively reviewed. Patient demographics, tumor characteristics, treatment details and post-treatment complications were recorded for each patient.

RESULTS: There were 96 males and 12 females. Intra-arterial chemoembolization and cyberknife (DT 35-60 Gy/3-6 fraction/3-7 d) were performed successfully, resulting in a substantial reduction or complete disappearance of tumors in nearly all patients, with a total effective rate (CR + PR + SD) of 100%. No major complications were encountered.

CONCLUSION: Cyberknife combined with TACE for the treatment of primary liver cancer is effective with mild adverse reactions.

Role of stereotactic radiosurgery in gynecologic cancer

PURPOSE OF REVIEW

This current work offers an opinion on the evidence accumulated in humans regarding stereotactic ablative radiation (SABR) therapy, a favorable option for the treatment of persistent or recurrent metastatic gynecologic cancers.

RECENT FINDINGS

SABR precisely and accurately kills cancer cells, making durable disease control possible. This article evaluates SABR's clinical performance and the variations in the main components of SABR technology, such as target localization and radiation beam collimation coupled with respiratory motion tracking, in the context of their contribution to the banked clinical successes in gynecologic radiation oncology.

SUMMARY

In an era of patient requests for short radiotherapy courses, SABR now provides well tolerated and efficacious treatment for women with gynecologic cancers.

Toward correcting drift in target position during radiotherapy via computer-controlled couch adjustments on a programmable Linac

PURPOSE

Real-time tracking of respiratory target motion during radiation therapy is technically challenging, owing to rapid and possibly irregular breathing variations. The authors report on a method to predict and correct respiration-averaged drift in target position by means of couch adjustments on an accelerator equipped with such capability.

METHODS

Dose delivery is broken up into a sequence of 10 s field segments, each followed by a couch adjustment based on analysis of breathing motion from an external monitor as a surrogate of internal target motion. Signal averaging over three respiratory cycles yields a baseline representing target drift. A Kalman filter predicts the baseline position 5 s in advance, for determination of the couch correction. The method's feasibility is tested with a motion phantom programmed according to previously recorded patient signals. Computed couch corrections are preprogrammed into a research mode of an accelerator capable of computer-controlled couch translations synchronized with the motion phantom. The method's performance is evaluated with five cases recorded during hypofractionated treatment and five from respiration-correlated CT simulation, using a root-mean-squared deviation (RMSD) of the baseline from the treatment planned position.

RESULTS

RMSD is reduced in all 10 cases, from a mean of 4.9 mm (range 2.7-9.4 mm) before correction to 1.7 mm (range 0.7-2.3 mm) after correction. Treatment time is increased ∼5% relative to that for no corrections.

CONCLUSIONS

This work illustrates the potential for reduction in baseline respiratory drift with periodic adjustments in couch position during treatment. Future treatment machine capabilities will enable the use of "on-the-fly" couch adjustments during treatment.

Optimization of normalized prescription isodose selection for stereotactic body radiation therapy: conventional vs robotic linac

PURPOSE

Although modern technology has allowed for target dose escalation by minimizing normal tissue dose, the dose delivered to a tumor and surrounding tissues still depends largely on the inherent characteristics of the radiation delivery platform. This work aims to determine the optimal prescription isodose line that minimizes normal tissue irradiation for stereotactic body radiation therapy (SBRT) for a conventional linear accelerator and a robotic delivery platform.

METHODS

Spherical targets with diameters of 10, 20, and 30 mm were constructed in the lungs and liver of a computer based digital torso phantom which simulates respiratory and cardiac motion. Normal tissue contours included normal lung, normal liver, and a concentric 10 mm shell of normal tissue extending from the spherical target surface. For linac planning, noncoplanar, nonopposing three dimensional (3D) conformal beams were designed, and variable prescription isodose lines were achieved by varying the MLC block margin. For CyberKnife planning, variable prescription isodose lines were achieved by inverse planning. True 4D dose calculations were used for the moving target and surrounding tissue based on each of ten phases of a 4D CT dataset. Doses of 60 Gy in three fractions were prescribed to cover 95% of the target tumor. Commonly used conformality, dosimetric, and radiobiological indices for lung and liver SBRT were used to compare different plans and determine the optimally prescribed isodose line for each treatment platform.

RESULTS

For linac plans, the average optimal prescription isodose line based on all indices evaluated occurred between 59% and 69% for lung tumors and between 67% and 77% for liver tumors depending on the tumor size. CyberKnife plans had average optimal prescription isodose lines occurring between 40% and 48% for lung tumors and between 41% and 42% depending on the tumor size. However, prescription isodose lines under 50% are not advised to prevent large heterogeneous dose distributions within the target.

CONCLUSIONS

The choice of prescription isodose line was shown to have a significant impact on parameters commonly used as constraints for lung and liver SBRT treatment planning for both linac-based and CyberKnife delivery platforms. By methodically choosing the prescription isodose line, normal tissue toxicities from SBRT may be reduced.

Stereotactic radiosurgery for gynecologic cancer

Stereotactic body radiotherapy (SBRT) distinguishes itself by necessitating more rigid patient immobilization, accounting for respiratory motion, intricate treatment planning, on-board imaging, and reduced number of ablative radiation doses to cancer targets usually refractory to chemotherapy and conventional radiation. Steep SBRT radiation dose drop-off permits narrow 'pencil beam' treatment fields to be used for ablative radiation treatment condensed into 1 to 3 treatments. Treating physicians must appreciate that SBRT comes at a bigger danger of normal tissue injury and chance of geographic tumor miss. Both must be tackled by immobilization of cancer targets and by high-precision treatment delivery. Cancer target immobilization has been achieved through use of indexed customized Styrofoam casts, evacuated bean bags, or body-fix molds with patient-independent abdominal compression.(1-3) Intrafraction motion of cancer targets due to breathing now can be reduced by patient-responsive breath hold techniques,(4) patient mouthpiece active breathing coordination,(5) respiration-correlated computed tomography,(6) or image-guided tracking of fiducials implanted within and around a moving tumor.(7-9) The Cyberknife system (Accuray [Sunnyvale, CA]) utilizes a radiation linear accelerator mounted on a industrial robotic arm that accurately follows patient respiratory motion by a camera-tracked set of light-emitting diodes (LED) impregnated on a vest fitted to a patient.(10) Substantial reductions in radiation therapy margins can be achieved by motion tracking, ultimately rendering a smaller planning target volumes that are irradiated with submillimeter accuracy.(11-13) Cancer targets treated by SBRT are irradiated by converging, tightly collimated beams. Resultant radiation dose to cancer target volume histograms have a more pronounced radiation "shoulder" indicating high percentage target coverage and a small high-dose radiation "tail." Thus, increased target conformality comes at the expense of decreased dose uniformity in the SBRT cancer target. This may have implications for both subsequent tumor control in the SBRT target and normal tissue tolerance of organs at-risk. Due to the sharp dose falloff in SBRT, the possibility of occult disease escaping ablative radiation dose occurs when cancer targets are not fully recognized and inadequate SBRT dose margins are applied. Clinical target volume (CTV) expansion by 0.5 cm, resulting in a larger planning target volume (PTV), is associated with increased target control without undue normal tissue injury.(7,8) Further reduction in the probability of geographic miss may be achieved by incorporation of 2-[(18)F]fluoro-2-deoxy-D-glucose ((18)F-FDG) positron emission tomography (PET).(8) Use of (18)F-FDG PET/CT in SBRT treatment planning is only the beginning of attempts to discover new imaging target molecular signatures for gynecologic cancers.

Stereotactic body radiotherapy for colorectal liver metastases: a pooled analysis

BACKGROUND

This study was undertaken to determine outcomes of stereotactic body radiotherapy for colorectal liver metastases in a pooled patient cohort.

METHODS

Patients with colorectal liver metastases from 3 institutions were included if they had 1 to 4 lesions, received 1 to 6 fractions of stereotactic body radiotherapy, and had radiologic imaging ≥ 3 months post-treatment. Sixty-five patients with 102 lesions treated from August 2003 to May 2009 were retrospectively analyzed. A tumor control probability (TCP) model was used to estimate the 3-fraction dose required for > 90% local control after converting the schedule into biologically equivalent dose (BED), single-fraction equivalent dose, or linear quadratic model-based single-fraction dose.

RESULTS

Forty-seven (72%) patients had ≥ 1 chemotherapy regimen before stereotactic body radiotherapy, and 27 (42%) patients had ≥ 2 regimens. The median follow-up was 1.2 years (range, 0.3-5.2 years). The median dose was 42 gray (Gy; range, 22-60 Gy). When evaluated separately by multivariate analysis, total dose (P = .0015), dose/fraction (P = .003), and BED (P = .004) all correlated with local control by lesion. On multivariate analysis, nonactive extrahepatic disease was associated with overall survival (OS; P = .046), and sustained local control was closely correlated (P = .06). By using single-fraction equivalent dose, BED, or linear quadratic model-based single-fraction dose in the TCP model, the estimated dose range needed for 1-year local control > 90% is 46 to 52 Gy in 3 fractions.

CONCLUSIONS

Liver stereotactic body radiotherapy is well tolerated and effective for colorectal liver metastases. The strong correlation between local control and OS supports controlling hepatic disease even for heavily pretreated patients. For a 3-fraction regimen of stereotactic body radiotherapy, a prescription dose of ≥ 48 Gy should be considered, if normal tissue constraints allow.

Real time 4D IMRT treatment planning based on a dynamic virtual patient model: proof of concept

PURPOSE

To develop a novel four-dimensional (4D) intensity modulated radiation therapy (IMRT) treatment planning methodology based on dynamic virtual patient models.

METHODS

The 4D model-based planning (4DMP) is a predictive tracking method which consists of two main steps: (1) predicting the 3D deformable motion of the target and critical structures as a function of time during treatment delivery; (2) adjusting the delivery beam apertures formed by the dynamic multi-leaf collimators (DMLC) to account for the motion. The key feature of 4DMP is the application of a dynamic virtual patient model in motion prediction, treatment beam adjustment, and dose calculation. A lung case was chosen to demonstrate the feasibility of the 4DMP. For the lung case, a dynamic virtual patient model (4D model) was first developed based on the patient's 4DCT images. The 4D model was capable of simulating respiratory motion of different patterns. A model-based registration method was then applied to convert the 4D model into a set of deformation maps and 4DCT images for dosimetric purposes. Based on the 4D model, 4DMP treatment plans with different respiratory motion scenarios were developed. The quality of 4DMP plans was then compared with two other commonly used 4D planning methods: maximum intensity projection (MIP) and planning on individual phases (IP).

RESULTS

Under regular periodic motion, 4DMP offered similar target coverage as MIP with much better normal tissue sparing. At breathing amplitude of 2 cm, the lung V20 was 23.9% for a MIP plan and 16.7% for a 4DMP plan. The plan quality was comparable between 4DMP and IP: PTV V97 was 93.8% for the IP plan and 93.6% for the 4DMP plan. Lung V20 of the 4DMP plan was 2.1% lower than that of the IP plan and Dmax to cord was 2.2 Gy higher. Under a real time irregular breathing pattern, 4DMP had the best plan quality. PTV V97 was 90.4% for a MIP plan, 88.6% for an IP plan and 94.1% for a 4DMP plan. Lung V20 was 20.1% for the MIP plan, 17.8% for the IP plan and 17.5% for the 4DMP plan. The deliverability of the real time 4DMP plan was proved by calculating the maximum leaf speed of the DMLC.

CONCLUSIONS

The 4D model-based planning, which applies dynamic virtual patient models in IMRT treatment planning, can account for the real time deformable motion of the tumor under different breathing conditions. Under regular motion, the quality of 4DMP plans was comparable with IP and superior to MIP. Under realistic motion in which breathing amplitude and period change, 4DMP gave the best plan quality of the three 4D treatment planning techniques.

A dosimetric comparison of stereotactic body radiation therapy techniques for lung cancer: robotic versus conventional linac-based systems

The aim of this study is to compare the dosimetric characteristics of robotic and conventional linac‐based SBRT techniques for lung cancer, and to provide planning guidance for each modality. Eight patients who received linac‐based SBRT were retrospectively included in this study. A dose of 60 Gy given in three fractions was prescribed to each target. The Synchrony Respiratory Tracking System and a 4D dose calculation methodology were used for CyberKnife and linac‐based SBRT, respectively, to minimize respiratory impact on dose calculation. Identical image and contour sets were used for both modalities. While both modalities can provide satisfactory target dose coverage, the dose to GTV was more heterogeneous for CyberKnife than for linac planning/delivery in all cases. The dose to 1000 cc lung was well below institutional constraints for both modalities. In the high dose region, the lung dose depended on tumor size, and was similar between both modalities. In the low dose region, however, the quality of CyberKnife plans was dependent on tumor location. With anteriorly‐located tumors, the CyberKnife may deliver less dose to normal lung than linac techniques. Conversely, for posteriorly‐located tumors, CyberKnife delivery may result in higher doses to normal lung. In all cases studied, more monitor units were required for CyberKnife delivery for given prescription. Both conventional linacs and CyberKnife provide acceptable target dose coverage while sparing normal tissues. The results of this study provide a general guideline for patient and treatment modality selection based on dosimetric, tumor and normal tissue sparing considerations.

PACS numbers: 87.53.Ly, 87.55.dk.

Cardiac embolization of an implanted fiducial marker for hepatic stereotactic body radiotherapy: a case report

Introduction

In liver stereotactic body radiotherapy, reduction of normal tissue irradiation requires daily image guidance. This is typically accomplished by imaging a surrogate to the tumor. The surrogate is often an implanted metal fiducial marker. There are few reports addressing the specific risks of hepatic fiducial marker implantation. These risks are assumed to be similar to percutaneous liver biopsies which are associated with a 1-4% complication rate - almost always pain or bleeding. To the best of our knowledge, we present the first case of such a fiducial marker migrating to the heart.

Case presentation

An 81-year-old Caucasian man (5 years post-gastrectomy for a gastric adenocarcinoma) was referred post-second line palliative chemotherapy for radiotherapy of an isolated liver metastasis. It was decided to proceed with treatment and platinum fiducials were chosen for radiation targeting. Under local anesthesia, three Nester embolization coils (Cook Medical Inc., Bloomington, IN, USA) were implanted under computed tomography guidance. Before the placement of each coil, the location of the tip of the delivery needle was confirmed by computed tomography imaging. During the procedure, the third coil unexpectedly migrated through the hepatic vein to the inferior vena cava and lodged at the junction of the vena cava and the right atrium. The patient remained asymptomatic. He was immediately referred to angiography for extraction of the coil. Using fluoroscopic guidance, an EN Snare Retrieval System (Hatch Medical L.L.C., Snellville, GA, USA) was introduced through a jugular catheter; it successfully grasped the coil and the coil was removed. The patient was kept overnight for observation and no immediate or delayed complications were encountered due to the migration or retrieval of the coil. He subsequently went on to be treated using the remaining fiducials.

Conclusion

Implanted fiducial markers are increasingly used for stereotactic radiotherapy. There is sparse literature on the risks of such procedures. Although uncommon, the risk of migration does exist and therefore physicians (surgeons, oncologists and radiologists) and patients should be aware of this possibility.