Validation and analysis of dose distributions in a new and entirely redesigned cobalt-60 stereotactic radiosurgery units.

The objective of this study was to evaluate the reproducibility of dose distributions in stereotactic treatment planning throughout Gamma Knife (GK) stereotactic radiosurgery (SRS) procedures in both GK model C and Perfexion (PFX). An originally-developed phantom and a radiochromic film were used for obtaining actual dose distributions. The phantom, with inserted films, was placed on a Leksell skull frame. Computed tomography (CT) was then acquired with a stereotactic localizer box attached to the frame, dose planning was made using the Leksell GammaPlan treatment planning system, and the phantom was ended up as beam delivery on an equal with clinical radiosurgery process. The reproducibility of the dose plan was provided by distance to agreement (DTA) values between planned and irradiated dose distributions calculated by dedicated film analysis software. The DTA values were determined for the isodose lines at 30%, 50%, 70%, and 90% of the maximum dose. In our study, the reproducibility of dose distributions in GK PFX was lower than in GK model C. As the results common to both units, the mean values of middle dose area (50% isodose) were about half the values of high (90% isodose) and low (30% isodose) dose area. Therefore validation of dose distributions is absolutely essential in commissioning of GK PFX. In addition, when risk organs are close to the target, dose prescription should be normalized for middle isodose line.

[Effect of source positional discrepancy on dose and dose distributions in cobalt-60 stereotactic radiosurgery units].

We assessed the impact of source positional discrepancy on dose and dose distributions in Gamma Knife (GK) Perfexion (PFX) stereotactic radiosurgery. A spherical phantom dedicated in GK machine was used and irradiated by 2 Gy in each position moved at an interval of 0.1 mm from its original position using three types of collimators (4, 8, 16 mm) to evaluate the changes of dose. In addition, to obtain the dose distributions, radiochromic film was inserted in the phantom and irradiated by 6 Gy in each position moved at an interval of 1 mm from its original position using three types of collimators. A distance-to-agreement analysis (DTA) was performed to compare isodose lines from 10% to 90% of dose distributions between the original and deviated position. As a result, when the source moved toward the discrepancy from the center of the collimator, the dose and dose distributions discrepancies increased according to the degree of discrepancy. Especially in 4-mm collimator, 0.5 mm discrepancy caused dose reduction of 5%. On the other hand, 0.5 mm discrepancy showed merely dose differences less than 0.5% in 8 mm and 16 mm collimators. Regarding dose distributions, 1 mm discrepancy in all collimators showed little changes in DTA within 1 mm on average.

Geometric accuracy of 3D coordinates of the Leksell stereotactic skull frame in 1.5 Tesla- and 3.0 Tesla-magnetic resonance imaging: a comparison of three different fixation screw materials.

We assessed the geometric distortion of 1.5-Tesla (T) and 3.0-T magnetic resonance (MR) images with the Leksell skull frame system using three types of cranial quick fixation screws (QFSs) of different materials-aluminum, aluminum with tungsten tip, and titanium-for skull frame fixation. Two kinds of acrylic phantoms were placed on a Leksell skull frame using the three types of screws, and were scanned with computed tomography (CT), 1.5-T MR imaging and 3.0-T MR imaging. The 3D coordinates for both strengths of MR imaging were compared with those for CT. The deviations of the measured coordinates at selected points (x = 50, 100 and 150; y = 50, 100 and 150) were indicated on different axial planes (z = 50, 75, 100, 125 and 150). The errors of coordinates with QFSs of aluminum, tungsten-tipped aluminum, and titanium were <1.0, 1.0 and 2.0 mm in the entire treatable area, respectively, with 1.5 T. In the 3.0-T field, the errors with aluminum QFSs were <1.0 mm only around the center, while the errors with tungsten-tipped aluminum and titanium were >2.0 mm in most positions. The geometric accuracy of the Leksell skull frame system with 1.5-T MR imaging was high and valid for clinical use. However, the geometric errors with 3.0-T MR imaging were larger than those of 1.5-T MR imaging and were acceptable only with aluminum QFSs, and then only around the central region.

Assessment of spatial uncertainty in computed tomography-based Gamma Knife stereotactic radiosurgery process with automated positioning system.

BACKGROUND: In this study, we assessed the geometric accuracy of an automated positioning system in Gamma Knife (GK) surgery. Specifically, we looked at the total spatial uncertainty over the entire treatment range of GK stereotactic radiosurgery (SRS) procedures in both the GK model C and the Perfexion (PFX). METHODS: An originally-developed phantom and a radiochromic film were used for obtaining actual dose distributions. The phantom, with inserted films on different axial planes (z = 60, 75, 100, 125, 140 mm), sagittal planes (x = 60, 75, 100, 125, 140 mm), and coronal planes (y = 60, 75, 100, 125, 140 mm), was placed on a Leksell skull frame. Computed tomography (CT) was then performed with a stereotactic localizer box attached to the frame, and dose planning was made using the Leksell GammaPlan treatment planning system. The phantom finally received beam delivery using a single shot of a 4-mm collimator helmet. The discrepancy between the planned shot position and the irradiated center position was evaluated by a dedicated film analysis software. RESULTS: The total uncertainty of CT-based GK SRS was less than 1 mm for almost all measured points over the stereotactic space in both the model C and the PFX. In addition, the geometric accuracy of the automated positioning system was estimated to be less than 0.1 mm and equal to 0.5 mm in the central and peripheral areas, respectively. CONCLUSIONS: We confirmed that the total spatial uncertainties of both the GK model C and the PFX are acceptable for clinical use.

[Image distortion and artifacts caused by the use of a titanium aneurism clip in 1.5 tesla- and 3 tesla-magnetic resonance imaging: effect on 60cobalt stereotactic radiosurgery treatment planning].

In gamma knife stereotactic radiosurgery (GKSRS) treatment planning, 1.5 tesla (T)-magnetic resonance imaging (MRI) is normally used to identify the target lesion. Image artifacts and distortion arise in MRI if a titanium clip is surgically implanted in the brain to treat cerebral aneurysm. 3-T MRI scanners, which are increasingly being adopted, provide imaging of anatomic structures with better clinical usefulness than 1.5-T MRI machines. We investigated signal defects and image distortions both close to and more distant from the titanium clip in 1.5-T and 3-T MRI. Two kinds of phantoms were scanned using 1.5-T and 3-T MRI. Acquisitions with and without the clip were performed under the same scan parameters. No difference was observed between 1.5 T and 3 T in local decrease of signal intensity; however, image distortion was observed at 20 mm from the clip in 3 T. Over the whole region, the distortions caused by the clip were less than 0.3 mm and 1.6 mm under 1.5-T and 3-T MRI, respectively. The geometric accuracy of 1.5-T MRI was better than 3-T MRI and thus better for GKSRS treatment planning. 3-T MRI, however, appears less suitable for use in treatment planning.

[Assessment of overall spatial accuracy in image guided stereotactic body radiotherapy using a spine registration method].

Stereotactic body radiotherapy (SBRT) for lung and liver tumors is always performed under image guidance, a technique used to confirm the accuracy of setup positioning by fusing planning digitally reconstructed radiographs with X-ray, fluoroscopic, or computed tomography (CT) images, using bony structures, tumor shadows, or metallic markers as landmarks. The Japanese SBRT guidelines state that bony spinal structures should be used as the main landmarks for patient setup. In this study, we used the Novalis system as a linear accelerator for SBRT of lung and liver tumors. The current study compared the differences between spine registration and target registration and calculated total spatial accuracy including setup uncertainty derived from our image registration results and the geometric uncertainty of the Novalis system. We were able to evaluate clearly whether overall spatial accuracy is achieved within a setup margin (SM) for planning target volume (PTV) in treatment planning. After being granted approval by the Hospital and University Ethics Committee, we retrospectively analyzed eleven patients with lung tumor and seven patients with liver tumor. The results showed the total spatial accuracy to be within a tolerable range for SM of treatment planning. We therefore regard our method to be suitable for image fusion involving 2-dimensional X-ray images during the treatment planning stage of SBRT for lung and liver tumors.

[Effect on treatment planning based on properties of cobalt-60 stereotactic radiosurgery units].

The brand-new version of gamma knife, Perfexion, is equipped with an automatic collimator arrangement system that does not require manual collimator exchange and a couch-traveling system that is approximately ten times faster than Model C, so treatment time with multiple shots is assumed to remain within a clinically acceptable range. In this study, the treatment plans for Model C and Perfexion were compared from the viewpoint of number of shots, coverage, selectivity, conformity, and gradient in planning target volume (PTV) coverage. We enrolled 187 and 89 patients with vestibular schwannomas treated by Model C and Perfexion in the study. Treatment planning was created on a Leksell GammaPlan workstation. The mean PTV was 5.2 ml (range 0.1-18.4 ml) in Model C and 4.1 ml (range 0.1-32.1 ml) in Perfexion. The mean shot number for Model C and Perfexion was 11 (range 2-27) and 16 (range 1-41) at the isodose contour of 40-60%, respectively. The mean PTV coverage was 94% (range 73-100%) and 98% (range 91-100%), and the mean PTV selectivity was 83% (range 46-98%) and 87% (range 63-97%) for Model C and Perfexion, respectively. The mean conformity index was 1.15 (range 0.81-2.02) and 1.14 (range 0.97-1.57), and the mean gradient index was 2.82 (range 2.37-3.35) and 2.91 (range 2.55-4.48) for Model C and Perfexion, respectively. In Perfexion, better PTV coverage and selectivity were achieved by using an excessively large number of shots. In addition, the use of a small collimator in Perfexion produced a steeper dose gradient. Our comparative research demonstrated the greater clinical usefulness of Perfexion.

Simulational study of a dosimetric comparison between a Gamma Knife treatment plan and an intensity-modulated radiotherapy plan for skull base tumors.

Fractionated stereotactic radiotherapy (SRT) is performed with a linear accelerator-based system such as Novalis. Recently, Gamma Knife Perfexion (PFX) featured the Extend system with relocatable fixation devices available for SRT. In this study, the dosimetric results of these two modalities were compared from the viewpoint of conformity, heterogeneity and gradient in target covering. A total of 14 patients with skull base tumors were treated with Novalis intensity-modulated (IM)-SRT. Treatment was planned on an iPlan workstation. Five- to seven-beam IM-SRT was performed in 14-18 fractions with a fraction dose of 2.5 or 3 Gy. With these patients' data, additional treatment planning was simulated using a GammaPlan workstation for PFX-SRT. Reference CT images with planning structure contour sets on iPlan, including the planning target volume (PTV, 1.1-102.2 ml) and organs at risk, were exported to GammaPlan in DICOM-RT format. Dosimetric results for Novalis IM-SRT and PFX-SRT were evaluated in the same prescription doses. The isocenter number of PFX was between 12 and 50 at the isodose contour of 50-60%. The PTV coverage was 95-99% for Novalis and 94-98% for PFX. The conformity index (CI) was 1.11-1.61 and 1.04-1.15, the homogeneity index (HI) was 1.1-3.62 and 2.3-3.25, and the gradient index (GI) was 3.72-7.97 and 2.54-3.39 for Novalis and PFX, respectively. PTV coverage by Novalis and PFX was almost equivalent. PFX was superior in CI and GI, and Novalis was better in HI. Better conformality would be achieved by PFX, when the homogeneity inside tumors is less important.

[Setup accuracy of stereotactic body radiation therapy (SBRT) using virtual isocenter in image-guided radiation therapy (IGRT)].

We use Novalis Body system for stereotactic body radiation therapy (SBRT) in lung and liver tumors. Novalis system is dedicated to SBRT with image-guided patient setup system ExacTrac. The spinal bone is the main landmark in patient setup during SBRT using ExacTrac kV X-ray system. When the target tumor is located laterally distant from the spinal bone at the midline, it is difficult to ensure the accuracy of the setup, especially if there are rotational gaps (yaw, pitch and roll) in the setup. For this, we resolve the problem by using a virtual isocenter (VIC) different from isocenter (IC) .We evaluated the setup accuracy in a rand phantom by using VIC and checked the setup errors using rand phantom and patient cases by our original method during the setup for IC. The accuracy of setup using VIC was less than 1.0 mm. Our original method was useful for checking patient setup when VIC used.

Assessment of spatial uncertainties in the radiotherapy process with the Novalis system.

PURPOSE: The purpose of this study was to evaluate the accuracy of a new version of the ExacTrac X-ray (ETX) system with statistical analysis retrospectively in order to determine the tolerance of systematic components of spatial uncertainties with the Novalis system. METHODS AND MATERIALS: Three factors of geometrical accuracy related to the ETX system were evaluated by phantom studies. First, location dependency of the detection ability of the infrared system was evaluated. Second, accuracy of the automated calculation by the image fusion algorithm in the patient registration software was evaluated. Third, deviation of the coordinate scale between the ETX isocenter and the mechanical isocenter was evaluated. From the values of these examinations and clinical experiences, the total spatial uncertainty with the Novalis system was evaluated. RESULTS: As to the location dependency of the detection ability of the infrared system, the detection errors between the actual position and the detected position were 1% in translation shift and 0.1 degrees in rotational angle, respectively. As to the accuracy of patient verification software, the repeatability and the coincidence of the calculation value by image fusion were good when the contrast of the X-ray image was high. The deviation of coordinates between the ETX isocenter and the mechanical isocenter was 0.313 +/- 0.024 mm, in a suitable procedure. CONCLUSIONS: The spatial uncertainty will be less than 2 mm when suitable treatment planning, optimal patient setup, and daily quality assurance for the Novalis system are achieved in the routine workload.

Stereotactic imaging for radiosurgery: localization accuracy of magnetic resonance imaging and positron emission tomography compared with computed tomography.

Computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) provide complementary information for treatment planning in stereotactic radiosurgery. We evaluated the localization accuracy of MRI and PET compared with CT. Two kinds of phantoms applicable to the Leksell G stereotactic skull frame (Elekta, Tokyo) were developed. Deviations of measured coordinates at target points (x = 50, 100, 150; y = 50, 100, 150) were determined on different axial planes (z = 30-140 for MRI and CT study and Z = 50-120 for PET and CT study). For MRI, the deviations were no more than 0.8 mm in each direction. For PET, the deviations were no more than 2.7 mm. For both imaging modalities studied, accuracy was at or below the imaging resolution (pixel size) and should be considered useful for clinical stereotactic planning purposes.

[Survey of patients' impressions of radiotherapy and their need for additional medical information: Japanese domestic survey of 1,529 patients in 2002].

PURPOSE: We clarified the images, impressions, and information about radiotherapy in standard Japanese patients and, at the same time, investigated their need for information about radiotherapy, in order to identify what we, as radiation oncologists, should do to decrease patient anxiety and create good physician-patient relationships. MATERIALS AND METHODS: We handed out 10 questionnaires to 1529 patients from April 2002 through July 2002 in 22 Japanese institutions that were equipped with radiotherapy machines. Questionnaires contained 10 items asking about patients' background, their impression of radiotherapy, frequency of exposure to information about radiotherapy, need to obtain information about radiotherapy, and ideal additional medical informational resources or their content. RESULTS: About 60% of patients had had the opportunity to obtain information about radiotherapy "sometimes" or "often," but 80% of them were not satisfied with the availability of information and answered that it was inadequate. Ten percent responded that they had no idea about radiotherapy. Thirty percent felt unspecified anxiety concerning radiotherapy, and those who had less chance to be exposed to information about radiotherapy felt more anxiety than the others (33.2% vs. 25.2%, p=0.0008). The need for "explanation and information about adverse effects" was the top priority, followed by "explanation of outcome." Although they generally obtained information from their physician (radiation oncologist), they also wanted additional information via written media (662 patients, 43%). However, patients who were over 60 years old most wanted to obtain additional medical information directly from their own radiation oncologist (37.7%). CONCLUSION: Information about radiotherapy given to patients and the general public is still insufficient in Japan. To fully utilize radiotherapy, which is a very effective treatment option against cancer, and to reduce anxiety about radiotherapy among cancer patients, more information is necessary.

Long-term results of gamma knife surgery for growth hormone-producing pituitary adenoma: is the disease difficult to cure?

OBJECT: The authors conducted a study to determine the long-term results of gamma knife surgery for residual or recurrent growth hormine (GH)-producing pituitary adenomas and to compare the results with those after treatment of other pituitary adenomas. METHODS: The series consisted of 67 patients. The mean tumor diameter was 19.2 mm and volume was 5.4 cm3. The mean maximum dose was 35.3 Gy and the mean margin dose was 18.9 Gy. The mean follow-up duration was 63.3 months (range 13-142 months). The tumor resolution rate was 2%, the response rate 68.3%, and the control rate 100%. Growth hormone normalization (GH < 1.0 ng/ml) was found in 4.8%, nearly normal (< 2.0 ng/ml) in 11.9%, significantly decreased (< 5.0 ng/ml) in 23.8%, decreased in 21.4%, unchanged in 21.4%, and increased in 16.7%. Serum insulin-like growth factor (IGF)-1 was significantly decreased (IGF-1 < 400 ng/ml) in 40.7%, decreased in 29.6%, unchanged in 18.5%, and increased in 11.1%, which was almost parallel to the GH changes. CONCLUSIONS: Gamma knife surgery was effective and safe for the control of tumors; however, normalization of GH and IGF-1 secretion was difficult to achieve in cases with large tumors and low-dose radiation. Gamma knife radiosurgery is thus indicated for small tumors after surgery or medication therapy when a relatively high-dose radiation is required.

[Three-dimensional conformal radiotherapy with multi-leaf collimator]

In radiation therapy, it is very important to concentrate the high dose to the clinical target volume. For this purpose, S. Takahashi developed the dynamic conformal radiotherapy in 1960. In the first half of 1990' this conformal technique with multi-leaf collimator (MLC) was gradually becoming popular, because the three dimensional extent of the clinical target volume and the surrounding normal tissues was accurately recognized by the use of the serial CT-images, and the 3D-treatment planning was considerably easily obtained by the development of computer-technique. The 3D-CRT (conformal radiation therapy) based on the 3D-treatment planning in a broad sense means the coplanar or non-coplanar irradiation with multi-leaf collimator, and at present it is one of the most reasonable treatment techniques. In order to correspond the high dose region to the clinical target volume as possible, IM (intensity modulation) technique was introduced to the 3D-CRT using MLC in the second half of 1990'. Therefore, the static CRT is routinely used not only in Europe/ USA but also in Japan. But, it is often very difficult to obtain the concave high dose region in static CRT with MLC, even though the IM-technique is applied. At this occasion, the concave high dose region is easily obtained by the use of dynamic CRT such as the hollowed -out technique developed by S. Takahashi in Japan. The dynamic CRT technique is also useful with the static IM-CRT technique. There are two main aims of conformal radiotherapy: First, the protection of the surrounding normal tissues, and second, improvement of the local control rate. Usually the second aim can't be easily achieved, because the tumor control probability curves are often flat. The DVH concept is usually valuable to choose the optimal treatment planning. But, it is difficult to find the optimal dose-distribution, when two DVH-curves cross each other on the middle range of irradiated dose. On that occasion, the NTCP-concept is useful. From the standpoint of the tolerable dose, normal organs are classified into two types: parallel and serial. Therefore, two types of the NTCP-formula should be prepared to apply the NTCP-concept clinically.