Q Chen

Pain control by image-guided radiosurgery for solitary spinal metastasis.

Precision and accuracy of image-guided spinal radiosurgery has been previously demonstrated. This study was carried out to determine the clinical efficacy of spine radiosurgery for the treatment of solitary spinal metastases with or without cord compression. A total of 49 patients with 61 separate spinal metastases were treated with radiosurgery. All patients had pathologically proven primary cancers and had either synchronous or metachronous metastasis to the spine. The majority of the patients presented with back pain. All patients received single-dose radiosurgery to the involved spine only. The radiosurgery dose ranged from 10 to 16Gy. The primary endpoint was pain control, but outcomes in neurological status and radiological tumor control also were assessed. The median time to pain relief was 14 days and the earliest time of pain relief was within 24hours. Complete pain relief was achieved in 46%, partial relief in 18.9%, and stable symptoms in 16.2%. Relapse of pain at the treated spinal segment was 6.9%. Median duration of pain relief at the treated spine was 13.3 months. Overall pain control rate for one year was 84%. This experience demonstrates that spinal radiosurgery can achieve rapid and durable pain relief. Single-dose radiosurgery has a potential to be a viable treatment option for single spinal metastasis.

2D/3D image fusion for accurate target localization and evaluation of a mask based stereotactic system in fractionated stereotactic radiotherapy of cranial lesions.

The purpose of this study was to evaluate the accuracy of a two-dimensional (2D) to three-dimensional (3D) image-fusion-guided target localization system and a mask based stereotactic system for fractionated stereotactic radiotherapy (FSRT) of cranial lesions. A commercial x-ray image guidance system originally developed for extracranial radiosurgery was used for FSRT of cranial lesions. The localization accuracy was quantitatively evaluated with an anthropomorphic head phantom implanted with eight small radiopaque markers (BBs) in different locations. The accuracy and its clinical reliability were also qualitatively evaluated for a total of 127 fractions in 12 patients with both kV x-ray images and MV portal films. The image-guided system was then used as a standard to evaluate the overall uncertainty and reproducibility of the head mask based stereotactic system in these patients. The phantom study demonstrated that the maximal random error of the image-guided target localization was +/-0.6 mm in each direction in terms of the 95% confidence interval (CI). The systematic error varied with measurement methods. It was approximately 0.4 mm, mainly in the longitudinal direction, for the kV x-ray method. There was a 0.5 mm systematic difference, primarily in the lateral direction, between the kV x-ray and the MV portal methods. The patient study suggested that the accuracy of the image-guided system in patients was comparable to that in the phantom. The overall uncertainty of the mask system was +/-4 mm, and the reproducibility was +/-2.9 mm in terms of 95% CI. The study demonstrated that the image guidance system provides accurate and precise target positioning.

Technical and Clinical Experience with Spine Radiosurgery: A New Technology for Management of Localized Spine Metastases

This study is to demonstrate the technical and clinical experience of applying image guided spinal radiosurgery for treatment of localized spinal metastasis. A dedicated shaped beam radiosurgery unit with intensity modulated radiotherapy (IMRT) and x-ray based image-guided radiotherapy (IGRT) were used for the radiosurgery procedure. A total of 196 patients with 270 lesions of spinal metastases were treated with this procedure from May 2001 to October 2005. All patients received single dose radiosurgery to the involved spine only. The radiosurgery dose was escalated from 10 to 18 Gy in 2 Gy increments. The technical experience using IMRT planning and IGRT implementation has been summarized. Clinical results reporting pain relief responses have been analyzed for the first 49 patients treated with this procedure. For IMRT treatment planning, seven posterior/oblique fields were generally used for spinal radiosurgery as the optimal setup to balance conformality versus complexity. A criterion of 10 Gy to 10% of the adjacent spinal cord volume has been met with satisfactory target dose coverage for most of the cases. When the spinal cord dose exceeded this constraint, the tumor coverage was somewhat compromised. Accurate target localization has been achieved for all patients using the x-ray image-guided system. The preliminary clinical results have demonstrated that pain response was achieved in 85% of patients, with neurological improvement in patients with spinal cord compression. Patients tolerated the treatment well without major acute toxicities. Image guided spinal radiosurgery can be successfully applied to treat patients with focal spine metastases.

Evaluation of residual patient position variation for spinal radiosurgery using the Novalis image guided system

PURPOSE The Novalis system has been demonstrated to achieve accurate target localization on anthropomorphic phantoms. However, other factors, such as rotational deviation, patient intrafraction motion, and image fusion uncertainty due to patient body deformation, could contribute additional position uncertainty for actual patients. This study evaluates such position uncertainty for spinal radiosurgery patients. MATERIALS AND METHODS Fifty-two consecutive spinal radiosurgery patients were included in the study. Rotational deviation was evaluated from 6-deg of freedom (6D) fusion results for all patients. The combined uncertainty of patient motion and image fusion was determined from fusion results of additional kV x-ray images acquired before, during, and after treatment for 25 of the 52 patients. The uncertainty of image fusion was also evaluated by performing 6D fusion ten different times with various regions of interest in the images selected for fusion. This was performed for two patients with L3 and T2 lesions, respectively, for comparison. RESULTS The mean rotational deviation was 0.7 +/- 1.8, 0.7 +/- 1.5, and 0.7 +/- 1.6 deg along the yaw, roll, and pitch directions, respectively. The combined uncertainty from patient motion and image fusion was 0.1 +/- 0.9, 0.2 +/- 1.2, and 0.2 +/- 1.0 mm in the anteroposterior (AP), longitudinal, and lateral directions, respectively. The uncertainty (standard deviation) due to image fusion was less than 0.28 mm in any direction for the L3 lesion and 0.8 mm in the AP direction for the T2 lesion. CONCLUSION Overall position uncertainty for spinal radiosurgery patients has been evaluated. Rotational deviation and patient motion were the main factors contributed to position uncertainty for actual patient treatment.

A technique of quantitatively monitoring both respiratory and nonrespiratory motion in patients using external body markers.

The purpose of this study was to develop a technique that could quantitatively monitor the nonrespiratory motion of a patient during stereotactic body radiotherapy (SBRT). Multiple infrared external markers were placed on the patients chest and abdominal surface to obtain patient motion signals. These motion signals contained both respiratory and nonrespiratory motion information. The respiratory motion usually has much larger amplitude on the abdominal surface than on the chest surface. Assuming that the nonrespiratory motion is a rigid body translation, we have developed a computer algorithm to derive both the respiratory and nonrespiratory motion signals instantly from two sets of motion signals. In first-order approximation, the respiratory motion was represented by the motion signal on the abdominal surface, and the nonrespiratory motion was represented by the motion signal on the chest surface subtracting its respiratory component. The algorithm was retrospectively tested on 24 patients whose motion signals were recorded during a gated-CT simulation procedure. The result showed that the respiratory noise in the nonrespiratory motion signal was reduced to less than 1 mm for almost all patients, demonstrating that the technique was able to detect nonrespiratory motion with a sensitivity of about 1 mm. It also showed that 50% of the patients had > or =2 mm, and 2 patients had > or =3 mm slow drift during the 15-25 min simulation procedure, suggesting that nonrespiratory motion could exist during prolonged treatment. This technique can potentially be used to control the nonrespiratory motion during SBRT. However, further validation is required for its clinical use.

Comparison of similarity measures for rigid-body CT/dual X-ray image registrations

A set of experiments were conducted to evaluate six similarity measures for intensity-based rigid-body 3D/2D image registration. Similarity measure is an index that measures the similarity between a digitally reconstructed radiograph (DRR) and an x-ray planar image. The registration is accomplished by maximizing the sum of the similarity measures between biplane x-ray images and the corresponding DRRs in an iterative fashion. We have evaluated the accuracy and attraction ranges of the registrations using six different similarity measures on phantom experiments for head, thorax, and pelvis. The images were acquired using Varian Medial System On-Board Imager. Our results indicated that normalized cross correlation and entropy of difference showed a wide attraction range (62 deg and 83 mm mean attraction range, ωmean), but the worst accuracy (4.2 mm maximum error, emax). The gradient-based similarity measures, gradient correlation and gradient difference, and the pattern intensity showed sub-millimeter accuracy, but narrow attraction ranges (ωmean=29 deg, 31 mm). Mutual information was in-between of these two groups (emax=2.5 mm, ωmean= 48 deg, 52 mm). On the data of 120 x-ray pairs from eight IRB approved prostate patients, the gradient difference showed the best accuracy. In the clinical applications, registrations starting with the mutual information followed by the gradient difference may provide the best accuracy and the most robustness.

Initial validation and clinical experience with 3D optical-surface-guided whole breast irradiation of breast cancer.

We had introduced 3D optical surface-guided radiotherapy (SGRT) of the breast cancer (BC). We then initiated the feasibility, accuracy, and precision studies of stereovision in detection of any breast displacement through the course of treatment for total thirty breasts undertaken whole breast irradiation (WBI). In the SGRT, CT-based plan data were parsed into an in-house computer program through which the reference surfaces were generated in 3D video format. When patients were positioned on treatment Tables, real-time stereovisions were rapidly acquired while the live surface tracking shown steady thorax motion. The real-time surface images were automatically aligned with the reference surface and detected shape and location changes of the breast were online corrected through the Table and beam adjustments. Accumulated dose to each patient was computed according to the frequency distribution of the measured breast locations during beam on time. Application of SGRT had diminished large skin-marking errors of >5-mm and daily breast-setup errors of >10-mm that occurred on half of cases. Accuracy (mean) and precision (two standard deviations) of the breast displacements across the tangential field edges in the (U, V) directions were improved from (−0.5 ± 8.8, 2.2 ± 10.8) mm in conventional setup to (0.4 ± 4.6, 0.7 ± 4.4) mm in the final position while intra-fractional motion contributed only (0.1 ± 2.8, 0.0 ± 2.2) mm in free breathing. Dose uniformity and coverage to targets had both been increased by up to 10% and the lung or heart intersections have been decreased by half of those volumes if they were irradiated at the initial positions. SGRT of BC appears to be feasible regardless of skin tones, as fast as a snapshot for 3D imaging, and very accurate and precise for daily setup of flexible breast targets. Importantly, the technique allows us to verify the breast shape and position during beam-on time.

TH-D-VaIB-02: Skin and Body Dose Measurements for Varian Cone-Beam CT (CBCT) During IMRT for Prostate Cancer

Purpose: With the increased use of CBCT for daily patient setup, kV dose delivered to patient should be investigated. This study is to measure skin and body dose from Varian daily CBCT for prostate patients. Methods and Materials: CBCT scans were acquired in half‐fan and pulsed‐fluoro mode with a half bow‐tie mounted. A technical setting of 125kV, 80mA and 25ms was used. Skin and body doses were first measured for a Rando pelvic and an IMRT QA phantom, set centrally, with TLD and a cylindrical chamber. Then skin dose for 7 prostate patients undergoing daily CBCT was measured. To avoid the ring artifacts centered at prostate, the treatment couch was dropped 3cm from patients tattoo. TLD capsules were placed on patients skin at 3 sites: AP, Lt Lat and Rt Lat. Phantom measurement was also made for this setup. The absorbed dose was determined by the air‐kerma‐based calibration method recommended by TG61. Results: For phantoms set centrally, measured skin dose was ∼6 cGy, ∼5.6 cGy, ∼3.7cGy at AP, Lt Lat, and Rt Lat, respectively. Body dose at the center was ∼3–4 cGy. With table dropping (TD), only AP skin dose was increased ∼12%. Patient AP skin dose varied with separation, ranging 4–6 cGy for thicker patients (AP 23 – 33 cm) and 6 – 8 cGy for thinner patients. Minimum changes were observed on lateral dose for patients with different size. Lt Lat skin (4cGy) and bone (9cGy) doses were higher than Rt Lat skin (3cGy) and bone dose (6cGy) Conclusions: Daily CBCT provides better patient setup but it increases skin and body dose. The dose can range from 120 – 330 cGy for skin and 120 – 380 cGy for body during the 42 daily fractions delivered for IMRT prostate patients.

SU‐FF‐J‐124: The Hounsfield Unit (HU) Accuracy in Varian's Cone‐Beam CT (CBCT) and Its Effect On Dosimetric Verification

Purpose: To evaluate the HU accuracy of Varians on board CBCT and its effect on the accuracy of dose calculation for dosimetric verification. Methods and Materials: A mini CT QC phantom (15cm diameter, 2cm thickness) with different inserts (2cm diameter) of known electron densities was embedded into an IMRT QA phantom to form a body phantom and scanned using CBCT. The scan was acquired in half‐fan and pulsed‐fluoro mode with a half bowtie mounted. A technical setting of 125kV, 80mA and 25ms was used. The HU for each insert was measured and the HU‐ED curve for CBCT was obtained. After that, a Rando pelvic phantom was scanned with both CBCT and SIM‐CT using nearly the same KV. The two sets of CT were fused so that SSD at any beam direction agree to 1mm. In this way, the structures drawn in SIM‐CT (to simulate prostate treatment) can be exactly transferred to CBCT. Without inhomgeneity correction; the two sets of CT generate exactly the same plan. With inhomogeneity correction, the dosimetric difference was mainly from the HU difference. Results: The average HU difference between CBCT and SIM‐CT is ∼50 but the standard deviation of HU in CBCT is 3–4 times higher. Due to higher beam hardening effect in CBCT, the HU at phantom center is 60–80 higher than that at edges. There is also a ring artifact of 20cm diameter and 1.5cm broad in which the HU is 200 lower. Even though, the dosimetric difference with inhomogeneity correction is relatively small. The minimum dose, maximum dose and mean dose etc. for any structure generally agrees within ∼2–5% between the CBCT plan and the SIM‐CT plan. The CBCT plan is ∼2% hotter at the phantom center. Conclusions: Dosimetric difference between CBCT and SIM‐CT is ∼2–5% due to the inaccurate HU in CBCT.

Cord Dose Specification and Validation for Stereotactic Body Radiosurgery of Spine

Effective dose to a portion of the spinal cord in treatment segment, rather than the maximum point dose in the cord surface, was set as the dose limit in stereotactic-body radiosurgery (SBRS) of spine. Such a cord dose specification is sensitive to the volume size and position errors. Thus, we used stereotactic image guidance to minimize phantom positioning errors and compared the results of a 0.6-cm(3) Farmer ionization chamber and a 0.01-cm(3) compact ionization chamber to determine the detector size effect on 9 SBRS cases. The experimental errors ranging from 2% to 7% were estimated by the deviation of the mean dose in plans to the chamber with spatial displacements of 0.5 mm. The mean and measured doses for the large chamber to individual cases were significantly (approximately 17%) higher than the doses with the compact chamber placed at the same point. Our experimental results shown that the mean doses to the volume of interest could represent the measured cord doses. For the 9 patients, the mean doses to 10% of the cord were about 10 Gy, while the maximum cord doses varied from 11.6 to 17.6 Gy. The mean dose, possibly correlated with the cord complication, provided us an alternative and reliable cord dose specification in SBRS of spine.