Real-time Tracking Radiotherapy Research Articles

Investigation of fiducial marker recognition possibility by water equivalent length in real-time tracking radiotherapy.

Real-time tumor tracking radiotherapy (RTRT) systems typically use fiducial markers implanted near the tumor to track the target using X-ray fluoroscopy. Template pattern matching, used in tracking, is often used to automatically localize the fiducial markers. In radiotherapy of the liver, the thickness of the body that can recognize the fiducial markers must be clinically assessed. The purpose of this study was to quantify the recognition of fiducial markers according to body thickness in stereotactic body radiotherapy of the liver using clinical images obtained using SyncTraX FX4. The recognition scores of fiducial markers were examined in relation to water equivalent length (WEL), tube current, and each flat panel detector. The relationship between the contrast ratio of the fiducial marker and the background and the WEL was also investigated. The average recognition score was found to be less than 20 when the WEL was greater than 25cm. The probability of successful tracking of image recognition was mostly smaller than 0.8 when the WEL was over 30cm. The relationship between WEL and tube current did not significantly differ between 100 and 140mA, but there was a significant difference (p < 0.05) for all other combinations. To ensure tracking of fiducial markers during SBRT, if the WEL representing body thickness is longer than 25cm, the X-ray fluoroscopy arrangement should be determined based on the WEL.

Safe Distance Limit between the Target and Intestinal Tract in Real-Time Tracking Radiotherapy for Liver Tumors

Safe Distance Limit between the Target and Intestinal Tract in Real-Time Tracking Radiotherapy for Liver Tumors

Clinical commissioning of a new patient positioning system, SyncTraX FX4, for intracranial stereotactic radiotherapy.

Background & AimsA new real‐time tracking radiotherapy (RTRT) system, the SyncTraX FX4 (Shimadzu, Kyoto, Japan), consisting of four X‐ray tubes and four ceiling‐mounted flat panel detectors (FPDs) combined with a linear accelerator, was installed at Uonuma Kikan Hospital (Niigata, Japan) for the first time worldwide. In addition to RTRT, the SyncTraX FX4 system enables bony structure‐based patient verification. Here we provide the first report of this system's clinical commissioning for intracranial stereotactic radiotherapy (SRT).Materials & MethodsA total of five tests were performed for the commissioning: evaluations of (1) the system's image quality; (2) the imaging and treatment coordinate coincidence; and (3) the localization accuracy of cone‐beam computed tomography (CBCT) and SyncTraX FX4; (4) the measurement of air kerma; (5) an end‐to‐end test.Results & DiscussionThe tests revealed the following. (1) All image quality evaluation items satisfied each acceptable criterion in all FPDs. (2) The maximum offsets among the centers were ≤0.40 mm in all combinations of the FPD and X‐ray tubes (preset). (3) The isocenter localization discrepancies between CBCT and preset #3 in the SyncTraX FX4 system were 0.29 ± 0.084 mm for anterior‐posterior, −0.19 ± 0.13 mm for superior‐inferior, 0.076 ± 0.11 mm for left‐right, −0.11 ± 0.066° for rotation, −0.14 ± 0.064° for pitch, and 0.072±0.058° for roll direction. the Pearson's product‐moment correlation coefficient between the two systems was >0.98 in all directions. (4) The mean air kerma value for preset #3 was 0.11 ± 0.0002 mGy in predefined settings (80 kV, 200 mA, 50 msec). (5) For 16 combinations of gantry and couch angles, median offset value in all presets was 0.31 mm (range 0.14–0.57 mm).ConclusionOur results demonstrate a competent performance of the SyncTraX FX4 system in terms of the localization accuracy for intracranial SRT.

Study on Predicting Tumor Motion via Memory-Based Learning

Prediction is necessary to compensate system latency in real-time tracking radiotherapy for thoracic and abdominal cancers. The paper proposes a memory-based learning method to predict respiratory tumor motion. The method first stores the training data in memory and then finds relevant data to answer a particular query. By fitting relatively simple models to local patches instead of fitting one single global model, it is able to capture highly nonlinear and complex relations between the internal tumor motion and external surrogates accurately and immediately. Furthermore, due to the local nature of weighting functions, it is inherently robust to outliers in the training data.

Real-time 4-D radiotherapy for lung cancer.

Respiratory motion considerably influences dose distribution, and thus clinical outcomes in radiotherapy for lung cancer. Breath holding, breath coaching, respiratory gating with external surrogates, and mathematical predicting models all have inevitable uncertainty due to the unpredictable variations of internal tumor motion. The amplitude of the same tumor can vary with standard deviations > 5 mm occurring in 23% of T1-2N0M0 non-small cell lung cancers. Residual motion varied 1-6 mm (95th percentile) for the 40% duty cycle of respiratory gating with external surrogates. The 4-D computed tomography is vulnerable to problems relating to the external surrogates. Real-time 4-D radiotherapy (4DRT), where the temporal changes in anatomy during the delivery of radiotherapy are explicitly considered in real time, is emerging as a new method to reduce these known sources of uncertainty. Fluoroscopic, real-time tumor-tracking technology using internal fiducial markers near the tumor has ± 2 mm accuracy, and has achieved promising clinical results when used with X-ray therapy. Instantaneous irradiation based on real-time verification of internal fiducial markers is considered the minimal requisite for real-time 4DRT of lung cancers at present. Real-time tracking radiotherapy using gamma rays from positron emitters in tumors is in the preclinical research stage, but has been successful in experiments in small animals. Real-time tumor tracking via spot-scanning proton beam therapy has the capability to cure large lung cancers in motion, and is expected to be the next-generation real-time 4DRT.

Use of Implanted Markers and Interportal Adjustment With Real-Time Tracking Radiotherapy System to Reduce Intrafraction Prostate Motion

Interportal adjustment was applied to patients with prostate cancer using three fiducial markers and two sets of fluoroscopy in a real-time tumor-tracking radiotherapy (RTRT) system. The incidence of table position adjustment required to keep intrafractional uncertainty within 2.0 mm was investigated in this study. The coordinates of the center of gravity of the three fiducial markers were measured at the start of every portal irradiation in intensity-modulated radiotherapy (IMRT) with seven ports. The table position was adjusted to the planned position if the discrepancy was larger than 2.0 mm in the anterior-posterior (AP), cranial-caudal (CC), or left-right (LR) directions. In total, we analyzed 4,541 observations in 20 patients who received 70 Gy in 30 fractions (7.6 times a day on average). The incidence of table position adjustment at 10 minutes from the initial setup of each treatment was 14.2%, 12.3%, and 5.0% of the observations in the AP, CC, and LR directions, respectively. The accumulated incidence of the table position adjustment was significantly higher at 10 minutes than at 2 minutes for AP (p = 0.0033) and CC (p = 0.0110) but not LR (p = 0.4296). An adjustment greater than 5 mm was required at least once in the treatment period in 11 (55%) patients. Interportal adjustment of table position was required in more than 10% of portal irradiations during the 10-minute period after initial setup to maintain treatment accuracy within 2.0 mm.

Alternative approach in the treatment of adrenal metastasis with a real‐time tracking radiotherapy in patients with hormone refractory prostate cancer

Patients with an adrenal tumor usually undergo laparoscopic adrenalectomy. However, an alternative treatment approach might be needed in some patients with adrenal metastasis from malignancy or with severe complications. Real-time tracking radiotherapy (RTRT) with a gold marker is considered one of the feasible treatment options because this system can reduce the adverse effects of organ movement such as that in the adrenal gland or kidney. A 64-year-old patient with hormone refractory prostate cancer presented with clinically isolated adrenal metastasis. The patient underwent RTRT treatment with an implanted gold marker in the right adrenal metastasis. There were no adverse events. Although disease progression with elevated prostate-specific antigen occurred 8 months later, there was no further growth of the right adrenal metastasis before he died. From our experience, RTRT with an implanted gold marker might be feasible for the treatment of isolated adrenal metastasis from malignancies including prostate cancer.

RTRT-based Evaluation of the Effectiveness of the Stereotactic Body Frame in Reducing Intrafraction Organ Motion

The effectiveness of the stereotactic body frame (SBF) in reducing intra-fractional organ motion due to respiration in gated irradiation is investigated here. Reduced range of organ motion is desired in order to shorten irradiation time and lower the exposure to fluoroscopic X-rays during a real-time tracking radiotherapy (RTRT) irradiation.

Three-Dimensional Intrafractional Motion of Breast During Tangential Breast Irradiation Monitored With High-Sampling Frequency Using a Real-Time Tumor-Tracking Radiotherapy System

To evaluate the three-dimensional intrafraction motion of the breast during tangential breast irradiation using a real-time tracking radiotherapy (RT) system with a high-sampling frequency. A total of 17 patients with breast cancer who had received breast conservation RT were included in this study. A 2.0-mm gold marker was placed on the skin near the nipple of the breast for RT. A fluoroscopic real-time tumor-tracking RT system was used to monitor the marker. The range of motion of each patient was calculated in three directions. The mean +/- standard deviation of the range of respiratory motion was 1.0 +/- 0.6 mm (median, 0.9; 95% confidence interval [CI] of the marker position, 0.4-2.6), 1.3 +/- 0.5 mm (median, 1.1; 95% CI, 0.5-2.5), and 2.6 +/- 1.4 (median, 2.3; 95% CI, 1.0-6.9) for the right-left, craniocaudal, and anteroposterior direction, respectively. No correlation was found between the range of motion and the body mass index or respiratory function. The mean +/- standard deviation of the absolute value of the baseline shift in the right-left, craniocaudal, and anteroposterior direction was 0.2 +/- 0.2 mm (range, 0.0-0.8 mm), 0.3 +/- 0.2 mm (range, 0.0-0.7 mm), and 0.8 +/- 0.7 mm (range, 0.1-1.8 mm), respectively. Both the range of motion and the baseline shift were within a few millimeters in each direction. As long as the conventional wedge-pair technique and the proper immobilization are used, the intrafraction three-dimensional change in the breast surface did not much influence the dose distribution.

The effect of tumor location and respiratory function on tumor movement estimated by real-time tracking radiotherapy (RTRT) system

The effects of tumor location and pulmonary function on the motion of fiducial markers near lung tumors were evaluated to deduce simple guidelines for determining the internal margin in radiotherapy without fiducial markers. Pooled data collected by a real-time tumor-tracking radiotherapy system on 42 markers in 39 patients were analyzed. The pulmonary functions of all patients were assessed before radiotherapy. Using chest X-ray film, the position of the marker was expressed relative to the geometry of the unilateral lung. Posterior location meant the area of the posterior half of the lung in a lateral chest X-ray film, and caudal location meant the caudal half of the chest X-ray film; these categories were determined by measuring the distance between the marker and anatomic landmarks, including the apex, costophrenic angle, midline of spinal canal, lateral, anterior, and posterior boundary of the lung. Before the radiotherapy, 18 patients had obstructive respiratory dysfunction (ratio of forced expiratory volume in 1 s to forced vital capacity [FEV1.0/FVC] <70), 5 patients had constrictive dysfunction (percent vital capacity [%VC] <80), and 3 had mixed dysfunction. Means of FEV1.0/FVC and %VC were 97.0% and 66.5%, respectively. Median tumor movements in the x (left-right), y (anteroposterior), and z (craniocaudal) directions were 1.1 mm, 2.3 mm, and 5.4 mm, respectively. There was no significant correlation between respiratory function and magnitude of marker movement in any direction. Median marker movement in the z direction was 2.6 mm for the cranial location and 11.8 mm for the caudal location, respectively (p < 0.001). Median movement in the z direction was 11.8 mm for posterior location and 3.4 mm for anterior location, respectively (p < 0.01). Simple measurement of the relative location on plain chest X-ray film was related, but respiratory function test was not related, to the craniocaudal amplitude of the motion of the fiducial marker near lung tumors.

An innovative image-guided radiotherapy system with a quasi-nonisocenteric feature

An innovative image-guided radiotherapy system with a quasi-nonisocenteric feature

Use of an implanted marker and real-time tracking of the marker for the positioning of prostate and bladder cancers

Purpose: A real-time tracking radiotherapy was investigated to assess its usefulness in precise localization and verification of prostate and bladder cancers. Methods and Materials: The real-time tracking radiation therapy (RTRT) system consists of implantation of a 2.0-mm gold marker into a clinical target volume (CTV), three-dimensional radiation treatment planning (3DRTP) system, and the use of two sets of diagnostic x-ray television systems in the linear accelerator room, image processing units, and an image display unit. The position of the patient can be corrected by adjusting the actual marker position to the planned marker position, which has been transferred from the 3DRTP and superimposed on the fluoroscopic image on the display unit of the RTRT system. The position of the markers can be visualized during irradiation and after treatment delivery to verify the accuracy of the localization. Ten patients with prostate cancer and 5 patients with bladder cancer were examined using this system for the treatment setup on 91 occasions. Results: After manual setup using skin markers, the median of absolute value of discrepancies between the actual position of the marker and the planned position of the marker for prostate cancer was 3.4 (0.1–8.9) mm, 4.1 (0.2–18.1) mm, and 2.3 (0.0–10.6) mm for the lateral, anteroposterior, and craniocaudal directions, respectively. The 3D median distance between the actual and planned positions of the marker was 6.9 (1.1–18.2) mm for prostate cancer and 6.9 (1.7–18.6) mm for bladder cancer. After relocation using RTRT, the 3D distance between the actual and planned position of the marker was 0.9 ± 0.9 mm. Median 3D distances between actual positions after treatment delivery and planned positions were 1.6 (0.0–6.3) mm and 2.0 (0.5–8.0) mm during daily radiotherapy for the marker in patients with prostate cancer and bladder cancer, respectively. Conclusion: We believe the new positioning system can reduce uncertainty due to setup error and internal organ motion, although further improvement is needed for the system to account for the rotational and elastic changes of the affected tissues.