Three-dimensional conformal setup (3D-CSU) of patients using the coordinate system provided by three internal fiducial markers and two orthogonal diagnostic X-ray systems in the treatment room

PURPOSE: To test the accuracy of a system for correcting for the rotational error of the clinical target volume (CTV) without having to reposition the patient using three fiducial markers and two orthogonal fluoroscopic images. We call this system "three-dimensional conformal setup" (3D-CSU). METHODS AND MATERIALS: Three 2.0-mm gold markers are inserted into or adjacent to the CTV. On the treatment couch, the actual positions of the three markers are calculated based on two orthogonal fluoroscopies crossing at the isocenter of the linear accelerator. Discrepancy of the actual coordinates of gravity center of three markers from its planned coordinates is calculated. Translational setup error is corrected by adjustment of the treatment couch. The rotation angles (alpha, beta, gamma) of the coordinates of the actual CTV relative to the planned CTV are calculated around the lateral (x), craniocaudal (y), and anteroposterior (z) axes of the planned CTV. The angles of the gantry head, collimator, and treatment couch of the linear accelerator are adjusted according to the rotation of the actual coordinates of the tumor in relation to the planned coordinates. We have measured the accuracy of 3D-CSU using a static cubic phantom. RESULTS: The gravity center of the phantom was corrected within 0.9 +/- 0.3 mm (mean +/- SD), 0.4 +/- 0.2 mm, and 0.6 +/- 0.2 mm for the rotation of the phantom from 0-30 degrees around the x, y, and z axes, respectively, every 5 degrees. Dose distribution was shown to be consistent with the planned dose distribution every 10 degrees of the rotation from 0-30 degrees. The mean rotational error after 3D-CSU was -0.4 +/- 0.4 (mean +/- SD), -0.2 +/- 0.4, and 0.0 +/- 0.5 degrees around the x, y, and z axis, respectively, for the rotation from 0-90 degrees. CONCLUSIONS: Phantom studies showed that 3D-CSU is useful for performing rotational correction of the target volume without correcting the position of the patient on the treatment couch. The 3D-CSU will be clinically useful for tumors in structures such as paraspinal diseases and prostate cancers not subject to large internal organ motion.     

Uncertainty in treatment of head-and-neck tumors by use of intraoral mouthpiece and embedded fiducials

PURPOSE: To reduce setup error and intrafractional movement in head-and-neck treatment, a real-time tumor tracking radiotherapy (RTRT) system was used with the aid of gold markers implanted in a mouthpiece. METHODS AND MATERIALS: Three 2-mm gold markers were implanted into a mouthpiece that had been custom made for each patient before the treatment planning process. Setup errors in the conventional immobilization system using the shell (manual setup) and in the RTRT system (RTRT setup) were compared. Eight patients with pharyngeal tumors were enrolled. RESULTS: The systematic setup errors were 1.8, 1.6, and 1.1 mm in the manual setup and 0.2, 0.3, and 0.3 mm in the RTRT setup in right-left, craniocaudal, and AP directions, respectively. Statistically significant differences were observed with respect to the variances in setup error (p <0.001). The systematic and random intrafractional errors were maintained within the ranges of 0.2-0.6 mm and 1.0-2.0 mm, respectively. The rotational systematic and random intrafractional errors were estimated to be 2.2-3.2 degrees and 1.5-1.6 degrees , respectively. CONCLUSIONS: The setup error and planning target volume margin can be significantly reduced using an RTRT system with a mouthpiece and three gold markers.     

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.     

Dosimetric effect of translational and rotational errors for patients undergoing image-guided stereotactic body radiotherapy for spinal metastases

PURPOSE: To investigate the dosimetric effects of translational and rotational patient positioning errors on the treatment of spinal and paraspinal metastases using computed tomography image-guided stereotactic body radiotherapy. The results of this study provide guidance for the treatment planning process and recognition of the dosimetric consequences of daily patient treatment setup errors. METHODS AND MATERIALS: The data from 20 patients treated for metastatic spinal cancer using image-guided stereotactic body radiotherapy were investigated in this study. To simulate the dosimetric effects of residual setup uncertainties, 36 additional plans (total, 756 plans) were generated for each isocenter (total, 21 isocenters) on the planning computed tomography images, which included isocenter lateral, anteroposterior, superoinferior shifts, and patient roll, yaw, and pitch rotations. Tumor volume coverage and the maximal dose to the organs at risk were compared with those of the original plan. Six daily treatments were also investigated to determine the dosimetric effect with or without the translational and rotational corrections. RESULTS: A 2-mm error in translational patient positioning error in any direction can result in >5% tumor coverage loss and >25% maximal dose increase to the organs at risk. Rotational correction is very important for patients with multiple targets and for the setup of paraspinal patients when the isocenter is away from bony structures. Compared with the original plans, the daily treatment data indicated that translational adjustments could correct most of the setup errors to mean divergences of -1.4% for tumor volume coverage and -0.3% for the maximal dose to the organs at risk. CONCLUSION: For the best dosimetric results, spinal stereotactic treatments should have setup translational errors of < or =1 mm and rotational errors of < or =2 degrees .     

Precision required for dose-escalated treatment of spinal metastases and implications for image-guided radiation therapy (IGRT).

INTRODUCTION: To evaluate the precision required in dose-escalated IMRT treatment of spinal metastases and paraspinal tumors. METHODS: In IMRT treatment plans of nine patients with spinal metastases (n=7) and paraspinal tumors (n=2) translational patient positioning errors (0-10mm) and rotational errors (0-7.5 degrees ) were simulated. The dose to the spinal cord (D5(spine)) resulting from these simulations was evaluated and NTCP for spinal cord necrosis was calculated. All patient set-up errors observed during treatment were simulated and the influence on D5(spine) was investigated. RESULTS: To keep the dose distribution to the spinal cord within +/-5% (+/-10%) of the prescribed dose, maximum tolerable errors of 1mm (2mm) in the transversal plane, 4mm (7mm) in superior-inferior direction and maximum rotations of 3.5 degrees (5 degrees ) were calculated on average. The translational and rotational component of clinically observed set-up errors increased D5(spine) by 23+/-14% and 3+/-2% on average, respectively. CONCLUSION: Steep dose gradients of IMRT planning require very high precision. In selected patients correction of both translational and rotational errors may be beneficial.     

Cone-beam computed tomography in hypofractionated stereotactic radiotherapy for brain metastases

ABSTRACT: BACKGROUND: To assess interfraction translational and rotational setup errors, in patients treated with image-guided hypofractionated stereotactic radiotherapy, immobilized by a thermoplastic mask and a bite-block and positioned using stereotactic coordinates. METHODS: 37 patients with 47 brain metastases were treated with hypofractionated stererotactic radiotherapy. All patients were immobilized with a combination of a thermoplastic mask and a bite-block fixed to a stereotactic frame support. Daily cone-beam CT scans were acquired for every patient before the treatment session and were matched online with planning CT images, for 3D image registration. The mean value and standard deviation of all translational (X,Y,Z) and rotational errors (thetax, thetay, thetaz) were calculated for the matching results of bone matching algorithm. RESULTS: A total of 194 CBCT scans were analyzed. Mean +/- standard deviation of translational errors (X, Y, Z) were respectively 0.5 +/- 1.6 mm (range -5.7 and 5.9 mm) in X; 0.4 +/- 2.7 mm (range -8.2 and 12.1 mm) in Y; 0.4 +/- 1.9 mm (range -7.0 and 14 mm) in Z; median and 90th percentile were respectively within 0.5 mm and 2.4 mm in X, 0.3 mm and 3.2 mm in Y, 0.3 mm and 2.2 mm in Z. Mean +/- standard deviation of rotational errors (thetax, thetay, thetaz) were respectively 0.0 degrees +/- 1.3 degrees (thetax) (range -6.0 degrees and 3.1 degrees); -0.1 degrees +/- 1.1 degrees (thetay) (range -3.0 degrees and 2.4 degrees); -0.6 degrees +/- 1.4 degrees (thetaz) (range -5.0 degrees and 3.3 degrees). Median and 90th percentile of rotational errors were respectively within 0.1 degrees and 1.4 degrees (thetax), 0.0 degrees and 1.2 degrees (thetay), 0.0 degrees and 0.9 degrees (thetaz). Mean +/- SD of 3D vector was 3.1 +/- 2.1 mm (range 0.3 and 14.9 mm); median and 90th percentile of 3D vector was within 2.7 mm and 5.1 mm. CONCLUSIONS: Hypofractionated stereotactic radiotherapy have the significant limitation of uncertainty in interfraction repeatability of the patient setup; image-guided radiotherapy using cone-beam computed tomography improves the accuracy of the treatment delivery reducing setup uncertainty, giving the possibility of 3-dimensional anatomic informations in the treatment position.     

Real-time tumor-tracking radiotherapy for adrenal tumors.

PURPOSE: To investigate the three-dimensional movement of internal fiducial markers near the adrenal tumors using a real-time tumor-tracking radiotherapy (RTRT) system and to examine the feasibility of high-dose hypofractionated radiotherapy for the adrenal tumors. MATERIALS AND METHODS: The subjects considered in this study were 10 markers of the 9 patients treated with RTRT. A total of 72 days in the prone position and 61 treatment days in the supine position for nine of the 10 markers were analyzed. All but one patient were prescribed 48 Gy in eight fractions at the isocenter. RESULTS: The average absolute amplitude of the marker movement in the prone position was 6.1+/-4.4 mm (range 2.3-14.4), 11.1+/-7.1 mm (3.5-25.2), and 7.0+/-3.5 mm (3.9-12.5) in the left-right (LR), craniocaudal (CC), and anterior-posterior (AP) directions, respectively. The average absolute amplitude in the supine position was 3.4+/-2.9 mm (0.6-9.1), 9.9+/-9.8 mm (1.1-27.1), and 5.4+/-5.2 mm (1.7-26.6) in the LR, CC, and AP directions, respectively. Of the eight markers, which were examined in both the prone and supine positions, there was no significant difference in the average absolute amplitude between the two positions. No symptomatic adverse effects were observed within the median follow-up period of 16 months (range 5-21 months). The actuarial freedom-from-local-progression rate was 100% at 12 months. CONCLUSIONS: Three-dimensional motion of a fiducial marker near the adrenal tumors was detected. Hypofractionated RTRT for adrenal tumors was feasible for patients with metastatic tumors.     

Real-time tumor-tracking radiation therapy for lung carcinoma by the aid of insertion of a gold marker using bronchofiberscopy

BACKGROUND: The authors developed fluoroscopic real-time tumor-tracking radiation therapy (RTRT) by insertion of a gold marker using bronchofiberscopy to reduce uncertainties in organ motion and set-up error in external radiotherapy for moving tumors. The purpose of the current study was to evaluate RTRT's feasibility in lung carcinoma treatment. METHODS: The three-dimensional position of a 1.0-2.0 mm gold marker in or near the tumor was detected by two sets of fluoroscopies every 0.03 seconds. The treatment beam was gated to irradiate the tumor only when the position of the marker coincided with its planned position using the RTRT system. Bronchofiberscopic equipment for insertion of the marker into the lung tumor was developed and used for 20 lung tumors in 18 patients. Patients were given high dose hypofractionated focal irradiation (35-48 Gy in 4-8 fractions in 4-10 days) with a planning target volume margin of 5 mm for the tumor. RESULTS: The markers were successfully inserted and maintained at the inserted position during and after the radiotherapy in 14 (88%) of 16 peripheral-type lung tumors and in none of four central-type lung tumors, indicating that this method of RTRT was not feasible for central-type lung tumors. Tracking of the marker was successfully performed in 1 of 2 tumors with a 1.0 mm marker and in all of 12 tumors with a 1.5-2.0 mm marker. On the whole, 13 (65%) of the 20 tumors were successfully treated with RTRT. Local tumor control was achieved and maintained for all 12 patients (13 tumors), who were treated with RTRT, with a median followup of 9 months (range, 5-15). Localized radiation pneumonitis was found radiographically at the lung volume that was irradiated with about 20 Gy, without symptoms in all but one patient. CONCLUSIONS: The insertion of a gold marker into or near peripheral-type lung tumors using bronchofiberscopy is a feasible and safe technique. Excellent initial response and low incidence of clinical complications suggest that the high dose hypofractionated focal irradiation using the RTRT system can be a good local treatment for peripheral-type lung tumors.     

Assessment of residual error for online cone-beam CT-guided treatment of prostate cancer patients

PURPOSE: Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image-guidance applications in our clinic. The objective of this work was to assess the magnitude and stability of the residual setup error associated with CBCT online-guided prostate cancer patient setup. Residual error pertains to the uncertainty in image registration, the limited mechanical accuracy, and the intrafraction motion during imaging and treatment. METHODS AND MATERIALS: The residual error for CBCT online-guided correction was first determined in a phantom study. After online correction, the phantom residual error was determined by comparing megavoltage portal images acquired every 90 degrees to the corresponding digitally reconstructed radiographs. In the clinical study, 8 prostate cancer patients were implanted with three radiopaque markers made of high-winding coils. After positioning the patient using the skin marks, a CBCT scan was acquired and the setup error determined by fusing the coils on the CBCT and planning CT scans. The patient setup was then corrected by moving the couch accordingly. A second CBCT scan was acquired immediately after the correction to evaluate the residual target setup error. Intrafraction motion was evaluated by tracking the coils and the bony landmarks on kilovoltage radiographs acquired every 30 s between the two CBCT scans. Corrections based on soft-tissue registration were evaluated offline by aligning the prostate contours defined on both planning CT and CBCT images. RESULTS: For ideal rigid phantoms, CBCT image-guided treatment can usually achieve setup accuracy of 1 mm or better. For the patients, after CBCT correction, the target setup error was reduced in almost all cases and was generally within +/-1.5 mm. The image guidance process took 23-35 min, dictated by the computer speed and network configuration. The contribution of the intrafraction motion to the residual setup error was small, with a standard deviation of +/-0.9 mm. The average difference between the setup corrections obtained with coil and soft-tissue registration was greatest in the superoinferior direction and was equal to -1.1 +/- 2.9 mm. CONCLUSION: On the basis of the residual setup error measurements, the margin required after online CBCT correction for the patients enrolled in this study would be approximatively 3 mm and is considered to be a lower limit owing to the small intrafraction motion observed. The discrepancy between setup corrections derived from registration using coils or soft tissue can be due in part to the lack of complete three-dimensional information with the coils or to the difficulty in prostate delineation and requires further study.     

Intercepting radiotherapy using a real-time tumor-tracking radiotherapy system for highly selected patients with hepatocellular carcinoma unresectable with other modalities

PURPOSE: To assess the clinical outcome of intercepting radiotherapy, in which radiotherapy is delivered only when a tumor in motion enters a target area, using a real-time tumor-tracking radiotherapy (RTRT) system for patients with hepatocellular carcinoma who were untreatable with other modalities because the tumors were adjacent to crucial organs or located too deep beneath the skin surface. METHODS AND MATERIALS: Eighteen tumors, with a mean diameter of 36 mm, were studied in 15 patients. All tumors were treated on a hypofractionated schedule with a tight margin for setup and organ motion using a 2.0-mm fiducial marker in the liver and the RTRT system. The most commonly used dose of radiotherapy was 48 Gy in 8 fractions. Sixteen lesions were treated with a BED(10) of 60 Gy or more (median, 76.8 Gy). RESULTS: With a mean follow-up period of 20 months (range, 3-57 months), the overall survival rate was 39% at 2 years after RTRT. The 2-year local control rate was 83% for initial RTRT but was 92% after allowance for reirradiation using RTRT, with a Grade 3 transient gastric ulcer in 1 patient and Grade 3 transient increases of aspartate amino transaminase in 2 patients. CONCLUSIONS: Intercepting radiotherapy using RTRT provided effective focal high doses to liver tumors. Because the fiducial markers for RTRT need not be implanted into the tumor itself, RTRT can be applied to hepatocellular carcinoma in patients who are not candidates for other surgical or nonsurgical treatments.     

Magnitude and clinical relevance of translational and rotational patient setup errors: a cone-beam CT study

PURPOSE: To establish volume imaging using an on-board cone-beam CT (CB-CT) scanner for evaluation of three-dimensional patient setup errors. METHODS AND MATERIALS: The data from 24 patients were included in this study, and the setup errors using 209 CB-CT studies and 148 electronic portal images were analyzed and compared. The effect of rotational errors alone, translational errors alone, and combined rotational and translational errors on target coverage and sparing of organs at risk was investigated. RESULTS: Translational setup errors using the CB-CT scanner and an electronic portal imaging device differed <1 mm in 70.7% and <2 mm in 93.2% of the measurements. Rotational errors >2 degrees were recorded in 3.7% of pelvic tumors, 26.4% of thoracic tumors, and 12.4% of head-and-neck tumors; the corresponding maximal rotational errors were 5 degrees , 8 degrees , and 6 degrees . No correlation between the magnitude of translational and rotational setup errors was observed. For patients with elongated target volumes and sharp dose gradients to adjacent organs at risk, both translational and rotational errors resulted in considerably decreased target coverage and highly increased doses to the organs at risk compared with the initial treatment plan. CONCLUSIONS: The CB-CT scanner has been successfully established for the evaluation of patient setup errors, and its feasibility in day-to-day clinical practice has been demonstrated. Our results have indicated that rotational errors are of clinical significance for selected patients receiving high-precision radiotherapy.     

6D image guidance for spinal non-invasive stereotactic body radiation therapy: Comparison between ExacTrac X-ray 6D with kilo-voltage cone-beam CT

Purpose

To investigate setup discrepancies measured with ExacTrac X-ray 6 degree-of-freedom (6D) and cone-beam computed tomography (CBCT) for patients under treatments of stereotactic body radiation therapy (SBRT).

Materials and methods

In this work, phantom and patient studies were performed. In the phantom studies, an anthropomorphic phantom was placed with pre-defined positions, and imaged with ExacTrac X-ray 6D and CBCT to test the accuracy of the imaging systems. In the patient studies, 16 spinal SBRT patient cases were retrospectively analyzed. The patients were initially positioned in customized immobilization cradles and then aligned with ExacTrac X-ray 6D and CBCT. The setup discrepancies were computed and quantitatively analyzed.

Results

This study indicates modest discrepancies between ExacTrac X-ray 6D and CBCT with spinal SBRT. The phantom experiments showed that translational and rotational discrepancies in root-mean-square (RMS) between ExacTrac X-ray 6D and CBCT were, respectively, <1.0 mm and <1°. In the retrospective patient studies, translational and rotational discrepancies in RMS between ExacTrac X-ray 6D and CBCT were <2.0 mm and <1.5°.

Conclusions

ExacTrac X-ray 6D represents a potential alternative to CBCT; however, pre-caution should be taken when only ExacTrac X-ray 6D is used to guide SBRT with small setup margins.     

Automatic target localization and verification for on-line image-guided stereotactic body radiotherapy of the spine

To facilitate image-guided stereotactic body radiotherapy (IG-SBRT) of spinal and paraspinal tumors, the authors have developed an on-line image registration system for automated target localization and patient position verification with high precision. When rotations are present in a patient's daily setup position, a setup error of a few millimeters can be introduced in localization of the isocenter by using surrounding bony structures. This setup error not only will deteriorate the dose coverage of the tumor, more importantly it will overdose the spinal cord. To resolve this issue, the image registration program developed by the authors detects translational shifts as well as rotational shifts using 3D CT image registration. Unacceptable rotations were corrected by either repositioning the patient or adjusting the treatment couch that was capable of rotational corrections when such a couch was available for clinical use. One pair of orthogonal digitally reconstructed radiographs (DRR) were generated from the daily pretreatment CT scan to compare with the corresponding DRRs generated from the planning CT scan to confirm the target shift correction. After the patient's position was corrected a pair of orthogonal portal images were taken for final verification. The accuracy of the image registration result was found to be within 0.1 mm on a head and neck phantom. Target shifts of a fraction of a millimeter were readily visible in our DRR comparison and portal image verification. The time needed to complete the image registration and DRR comparison was about 3 minutes. An integrated system that combines a high-speed CT scanner and a linear accelerator was used for imaging and treatment delivery. Application of the program in actual IG-SBRT cases demonstrated that it was accurate, fast, and reliable. It serves as a useful tool for image-guided radiotherapy where high precision of target localization is required.     

Feasibility of insertion/implantation of 2.0-mm-diameter gold internal fiducial markers for precise setup and real-time tumor tracking in radiotherapy

PURPOSE: To examine the feasibility and reliability of insertion of internal fiducial markers into various organs for precise setup and real-time tumor tracking in radiotherapy (RT). MATERIALS AND METHODS: Equipment and techniques for the insertion of 2.0-mm-diameter gold markers into or near the tumor were developed for spinal/paraspinal lesions, prostate tumors, and liver and lung tumors. Three markers were used to adjust the center of the mass of the target volume to the planned position in spinal/paraspinal lesions and prostate tumors (the three-marker method). The feasibility of the marker insertion and the stability of the position of markers were tested using stopping rules in the clinical protocol (i.e., the procedure was abandoned if 2 of 3 or 3 of 6 patients experienced marker dropping or migration). After the evaluation of the feasibility, the stability of the marker positions was monitored in those patients who entered the dose-escalation study. RESULTS: Each of the following was shown to be feasible: bronchoscopic insertion for the peripheral lung; image-guided transcutaneous insertion for the liver; cystoscopic and image-guided percutaneous insertion for the prostate; and surgical implantation for spinal/paraspinal lesions. Transcutaneous insertion of markers for spinal/paraspinal lesions and bronchoscopic insertion for central lung lesions were abandoned. Overall, marker implantation was successful and was used for real-time tumor tracking in RT in 90 (90%) of 100 lesions. No serious complications related to the marker insertion were noted for any of the 100 lesions. Using three markers surgically implanted into the vertebral bone, the mean +/- standard deviation in distance among the three markers was within 0.2 +/- 0.6 mm (range -1.4 to 0.8) through the treatment period of 30 days. The distance between the three markers gradually decreased during RT in five of six prostate cancers, consistent with a mean rate of volume regression of 9.3% (range 0.015-13%) in 10 days. CONCLUSIONS: Internal 2.0-mm-diameter gold markers can be safely inserted into various organs for real-time tumor tracking in RT using the prescribed equipment and techniques. The three-marker method has been shown to be a useful technique for precise setup for spinal/paraspinal lesions and prostate tumors.     

Intracranial application of IMRT based radiosurgery to treat multiple or large irregular lesions and verification of infra-red frameless localization system

We have employed a frameless localization system for intracranial radiosurgery, utilizing a custom biteblock with fiducial markers and an infra-red camera for set-up and monitoring patient position. For multiple brain metastases or large irregular lesions, we use a single-isocenter intensity-modulated approach. We report our quality assurance measurements and our experience using Intensity Modulated Radiosurgery (IMRS) to treat such intracranial lesions. A phantom with integrated targets and fiducial markers was utilized to test the positional accuracy of the system. The frameless localization system was used for patient setup and target localization as well as for motion monitoring during treatment. Inverse optimization planning gave satisfactory dose coverage and critical organ sparing. Patient setup was guided by the infrared camera through fine adjustment in three translational and three rotational degrees for isocenter localization and verified by orthogonal kilovoltage (kV) images, taken before treatment to ensure the accuracy of treatment. The relative localization of the camera based system was verified to be highly accurate along three translational directions of couch motion and couch rotation. After verification, we began treating patients with this technique. About 8–12 properly selected fixed beams with a single isocenter were sufficient to achieve good dose coverage and organ sparing. Portal dosimetry with an Electronic Portal Imaging Device (EPID) and kV images provided excellent quality assurance for the IMRS plan and patient setup. The treatment time was less than 60 min to deliver doses of 16–20 Gy in a single fraction. The camera-based system was verified for positional accuracy and was deemed sufficiently accurate for stereotactic treatments. Single isocenter IMRS treatment of multiple brain metastases or large irregular lesions can be done within an acceptable treatment time and gives the benefits of dose-conformity and organ-sparing, easy plan QA, and patient setup verification.     

Registration accuracy and possible migration of internal fiducial gold marker implanted in prostate and liver treated with real-time tumor-tracking radiation therapy (RTRT).

BACKGROUND AND PURPOSE: We have developed a linear accelerator synchronized with a fluoroscopic real-time tumor-tracking system to reduce errors due to setup and organ motion. In the real-time tumor-tracking radiation therapy (RTRT) system, the accuracy of tumor tracking depends on the registration of the marker's coordinates. The registration accuracy and possible migration of the internal fiducial gold marker implanted into prostate and liver was investigated.MATERIALS AND METHODS: Internal fiducial gold markers were implanted in 14 patients with prostate cancer and four patients with liver tumors. Computed tomography (CT) was carried out as a part of treatment planning in the 18 patients. A total of 72 follow-up CT scans were taken. We calculated the relative relationship between the coordinates of the center of mass (CM) of the organs and those of the marker. The discrepancy in the CM coordinates during a follow-up CT compared to those recorded during the planning CT was used to study possible marker migration.RESULTS: The standard deviation (SD) of interobserver variations in the CM coordinates was within 2.0 and 0.4 mm for the organ and the marker, respectively, in seven observers. Assuming that organs do not shrink, grow, or rotate, the maximum SD of migration error in each direction was estimated to be less than 2.5 and 2.0 mm for liver and prostate, respectively. There was no correlation between the marker position and the time after implantation.CONCLUSION: The degree of possible migration of the internal fiducial marker was within the limits of accuracy of the CT measurement. Most of the marker movement can be attributed to the measurement uncertainty, which also influences registration in actual treatment planning. Thus, even with the gold marker and RTRT system, a planning target volume margin should be used to account for registration uncertainty.     

Serum S100beta: a noninvasive marker of blood-brain barrier function and brain lesions

BACKGROUND: S100beta protein is expressed constitutively by brain astrocytes. Elevated S100beta levels in cerebrospinal fluid and serum reported after head trauma, subarachnoid hemorrhage, and stroke were correlated with the extent of brain damage. Because elevated serum S100beta also was shown to indicate blood-brain barrier (BBB) dysfunction in the absence of apparent brain injury, it remains unclear whether elevation of serum levels of S100beta reflect BBB dysfunction, parenchymal damage, or both. METHODS: The authors conducted a prospective study of serum S100beta levels in six patients who underwent hyperosmotic BBB disruption (BBBD) with intraarterial chemotherapy for primary central nervous system lymphoma. In addition, 53 serum S100beta samples were measured in 51 patients who had a variety of primary or metastatic brain lesions at the time of neuroimaging. RESULTS: S100beta was correlated directly with the degree of clinical and radiologic signs of BBBD in patients who were enrolled in the hyperosmotic study. In patients with neoplastic brain lesions, gadolinium enhancement on a magnetic resonance image was correlated with elevated S100beta levels (n = 45 patients; 0.16 +/- 0.1 microg/L; mean +/- standard error of the mean) versus nonenhancing scans (n = 8 patients; 0.069 +/- 0.04 microg/L). Primary brain tumors (n = 8 patients; 0.12 +/- 0.08) or central nervous system metastases also presented with elevated serum S100beta levels (n = 27 patients; 0.14 +/- 0.34). Tumor volume was correlated with serum S100beta levels only in patients with vestibular schwannoma (n = 6 patients; 0.13 +/- 0.10 microg/L) but not in patients with other brain lesions. CONCLUSIONS: S100beta was correlated directly with the extent and temporal sequence of hyperosmotic BBBD, further suggesting that S100beta is a marker of BBB function. Elevated S100beta levels may indicate the presence of radiologically detectable BBB leakage. Larger prospective studies may better determine the true specificity of S100beta as a marker for BBB function and as an early detection or follow-up marker of brain tumors.     

Pitch, roll, and yaw variations in patient positioning

PURPOSE: To use pretreatment megavoltage-computed tomography (MVCT) scans to evaluate positioning variations in pitch, roll, and yaw for patients treated with helical tomotherapy. METHODS AND MATERIALS: Twenty prostate and 15 head-and-neck cancer patients were selected. Pretreatment MVCT scans were performed before every treatment fraction and automatically registered to planning kilovoltage CT (KVCT) scans by bony landmarks. Image registration data were used to adjust patient setups before treatment. Corrections for pitch, roll, and yaw were recorded after bone registration, and data from fractions 1-5 and 16-20 were used to analyze mean rotational corrections. RESULTS: For prostate patients, the means and standard deviations (in degrees) for pitch, roll, and yaw corrections were -0.60 +/- 1.42, 0.66 +/- 1.22, and -0.33 +/- 0.83. In head-and-neck patients, the means and standard deviations (in degrees) were -0.24 +/- 1.19, -0.12 +/- 1.53, and 0.25 +/- 1.42 for pitch, roll, and yaw, respectively. No significant difference in rotational variations was observed between Weeks 1 and 4 of treatment. Head-and-neck patients had significantly smaller pitch variation, but significantly larger yaw variation, than prostate patients. No difference was found in roll corrections between the two groups. Overall, 96.6% of the rotational corrections were less than 4 degrees. CONCLUSIONS: The initial rotational setup errors for prostate and head-and-neck patients were all small in magnitude, statistically significant, but did not vary considerably during the course of radiotherapy. The data are relevant to couch hardware design for correcting rotational setup variations. There should be no theoretical difference between these data and data collected using cone beam KVCT on conventional linacs.     

Organ motion in image-guided radiotherapy: lessons from real-time tumor-tracking radiotherapy

External radiotherapy using imaging technology for patient setup is often called image-guided radiotherapy (IGRT). The most important problem to solve in IGRT is organ motion. Four-dimensional radiotherapy (4DRT), in which the accuracy of localization is improved – not only in space but also in time – in comparison to 3DRT, is required in IGRT. Real-time tumor-tracking radiotherapy (RTRT) has been shown to be feasible for performing 4DRT with the aid of a fiducial marker near the tumor. Lung, liver, prostate, spinal/paraspinal, gynecological, head and neck, esophagus, and pancreas tumors are now ready for dose escalation studies using RTRT.