Measurement of Dosimetric Parameters and Dose Verification in Stereotactic Radiosurgery (SRS) (original) (raw)
Related papers
International Journal of Radiation Oncology*Biology*Physics, 1999
Purpose: Linac-based stereotactic radiosurgery (SRS) was introduced in our department in 1992, and since then, more than 200 patients have been treated with this method. An in-house-developed algorithm for target localization and dose calculation has recently been replaced with a commercially available system. In this study, both systems have been compared, and positional accuracy, as well as dose calculation, have been verified experimentally. Methods and Materials: The in-house-developed software for target localization and dose calculation is an extension to George Sherouse's GRATIS® software for radiotherapy treatment planning, and has been replaced by a commercial (BrainSCAN version 3.1; BrainLAB, Germany) treatment planning system (TPS) for SRS. The positional accuracy for the entire SRS procedure (from image acquisition to treatment) has been investigated by treatment of simulated targets in the form of 0.
" Measurement of Dosimetric Parameters and Dose Verification in Stereotactic
The purpose of this study was to measure the dosimetric parameters for small photon beams to be used as input data for treatment planning computer system (TPS) and to verify dose calculated by TPS in Stereotactic Radiosurgery (SRS) procedure. The beam data required were Percentage Depth Dose (PDD), Off-axis Ratio (OAR), and Scatter Factor or Relative Output Factor. Small beams of 5mm to 45 mm diameter circular cone collimators used in SRS were utilized for beam data measurements. Two type of detectors were used which are pinpoint 3D ionization chamber (0.016cc) and EDR2 film dosimetry. The ionization chamber and EDR2 film give slightly similar results on PDD curve but for OAR measurement, the film gives more accurate results especially in penumbra length compared to ionization chamber due to characteristic of the film which has higher spatial resolution. For second part of this study, we reported the important quality assurance (QA) procedures before SRS treatment that influenced the dose delivery. These QA procedures consist of measurements on the accuracy in target localization and room laser’s alignment. The dose calculated to be delivered for treatment was verified using pinpoint ionization 3D chamber and TLD 100H. The mean deviation of measured dose using TLD 100H compared to calculated dose was 3.37%. Beside that, pinpoint ionization 3D chamber give more accurate results of dose compared to TLD 100H. The measured dose using pinpoint ionization 3D chamber are good agreement with calculated dose by TPS with deviation of 2.17%.The results are acceptable such as recommended by International Commission on Radiation Units and Measurements (ICRU) Report No. 50 that dose delivered to the target volume must be within ±5% error.
Use of a 1 mm collimator to test the accuracy of stereotactic radiotherapy
International Journal of Radiation Oncology*Biology*Physics, 1996
Purpose: To develop a method of measuring locations of the center of dose in stereotactic radiotherapy relative to ~ center of the target, and thereby obtain a test of the accuracy of stereotactic radiotherapy (SRT). Methods and Materials: An insert was mounted in an SRT collimator on a 6 MV linear accelerator to provide a photon beam-1 mm in diameter at isocenter, and a method of measuring radiation center coordinates of arced SRT beams. To simulate a small intracranial target, two halves of a Barium paste column were embedded in two adjacent slabs of a humanoid phantom. A film was placed between the slabs to image the radiation relative to the target center. A surgical head ring and computerized tomography (CT) iocalizer were attached to the phantom and CT scans were obtained. The scans were entered in a three-dimensional computerized treatment-planning system and radiation isocenter coordinates determined by iteratively moving the 90% isodose surface center of arced beam dose distributions to coincide with the target center. The phantom was bolted to an SRT floorstand with isocenter coordinates obtained from the treatment plan, and then irradiated in two sets of experiments. The first set applied five 1 mm noncoplanar arced beams with and without offsets of the planned coordinates in the transverse plane. The second set applied one large transverse arc coplanar to the film with and without offsets in the craniocaudal direction. Irradiations with coordinate offsets tested the sensitivity of the method. Films were developed and digitized with a high resolution film scanner to measure the location of the radiation relative to the target center. Results and Conclusion: The radiation center was found from 0.0 to 0.3 mm of the target center, within requirements of our clinical quality assurance program. The measurement and evaluation of coincidence of radiation and target centers are, thus, proposed as elements of radiosurgery facility acceptance and annual quality assurance.
Comparison of different radiation types and irradiation geometries in stereotactic radiosurgery
International Journal of Radiation Oncology*Biology*Physics, 1990
Recent interest in stereotactic radiosurgery of intracranial lesions, and the development of stereotactic irradiation techniques has led to the need for a systematic and complete comparison of these methods. A method for conducting these comparisons is proposed and is applied to a set of currently-used stereotactic radiosurgical techniques. Threedimensional treatment planning calculations are used to compare dose distributions for several different radiation types and irradiation geometries. Calculations were performed using charged particles (H, He, C, and Ne ions) and the irradiation geometry currently used at Lawrence Berkeley Laboratory. Photons in the Gamma Knife configuration and the Heidelberg Linac arc method are used. The 3-dimensional dose distributions were evaluated by means of dose-volume histograms and integral doses to the target volume and to normal brain. The effects of target volume, shape and location are studied. The charged particle dose distributions are more favorable than those of the photon methods. The differences between charged particles and photons increase with increasing target volume. The differences between different charged particle species are small, as are the effects of target shape and location.
Dosimetric comparison of linear accelerator-based stereotactic radiosurgery systems
Journal of Medical Physics, 2007
Stereotactic radiosurgery (SRS) is a special radiotherapy technique used to irradiate intracranial lesions by 3-D arrangements of narrow photon beams eliminating the needs of invasive surgery. Three different tertiary collimators, namely BrainLab and Radionics circular cones and BrainLab micro multileaf collimator (mMLC), are used for linear accelerator-based SRS systems (X-Knife). Output factor (S t ), tissue maximum ratio (TMR) and off axis ratio (OAR) of these three SRS systems were measured using CC01 (Scanditronix/ Welhofer) and Pinpoint (PTW) cylindrical and Markus plane parallel ionization chambers as well as TLD and radiochromic film. Measurement results of CC01 and Pinpoint chambers were very close to each other which indicate that further reduction in volume and physical dimensions of cylindrical ionization chamber is not necessary for SRS/SRT dosimetry. Output factors of BrainLab and Radionics SRS cones were very close to each other while output factors of equivalent diameter mMLC field were different from SRS circular cones. TMR of the three SRS systems compared were very close to one another. OAR of Radionics cone and BrainLab mMLC were very close to each other, within 2%. However, OARs of BrainLab cone were found comparable to OARs of Radionics cone and BrainLab mMLC within maximum variation of 4%. In addition, user-measured similar data of other three mMLC X-Knives were compared with the mMLC X-Knife data measured in this work and found comparable. The concept of switching over to mMLC-based SRS/SRT is thus validated from dosimetric characteristics
Dosimetry of stereotactic radiosurgery using lithium formate EPR dosimeters
Physics in Medicine and Biology, 2010
Small lithium formate EPR (electron paramagnetic resonance) dosimeters (diameter 3 mm, height 2 mm) were produced and employed for 2D dosimetry of stereotactic radiosurgery (SRS). An anthropomorphic head phantom with an in-house made insert holding 45 lithium formate dosimeters was used. A spherical target was outlined centrally in planning CT images of the head and an SRS dose plan with three arcs was made using the iPlan planning system. Beam collimation was achieved with the BrainLAB m3 micro-MLC. The minimum target dose was 15 Gy. The planned dose distribution was compared to measurements. For dosimetry, a dosimeter calibration series was generated with doses from 1 to 20 Gy. At the treatment unit, three replicate measurement series were performed. The measurements gave on average 2.2% lower dose at the plateau of the dose distribution compared to the dose plan. Larger differences were seen in the penumbra, where the dose plan underestimated the dose gradients. By repeated measurements, the systematic and random error in the SRS delivery was estimated to less than 1 mm. In conclusion, the planning system produced an intracranial dose distribution with tolerable accuracy. Furthermore, small lithium formate EPR dosimeters were useful for measuring SRS dose distributions.
Applied Radiation and Isotopes, 2006
A high-resolution radiochromic film dosimetry (Hr-RCFD) method has been applied to verify a small-field stereotactic radiosurgery (SRS) plan. This was done by exposing a RCF in a Perspex head phantom undergoing the same treatment plan as the patient. The dose distribution obtained by the Hr-RCFD was verified against that calculated by the stereotactic treatment planning system and the result was satisfactory. The Hr-RCFD method has been found to be an accurate and practical tool in verifying small-field SRS plans. r
Characteristics of a novel treatment system for linear accelerator-based stereotactic radiosurgery
Journal of Applied Clinical Medical Physics, 2015
I. INTRODUCTION Since the term "stereotactic radiosurgery" was coined by Lars Leksell in 1951, there have been many technological, biological, and clinical advances in the field of stereotactic radiosurgery. (1-4) The accuracy of linear accelerators (linacs) has been improved significantly since the 1980s (5-7) and linac-based radiosurgery has been widely adopted over the subsequent decades. Since the 1990s, various technological advances have taken place to allow very precise treatments. The dedicated linacs have been designed exclusively for radiosurgery to further improve the targeting accuracy and high-dose-rate delivery. The mechanical isocenter accuracy of the C-arm linac has reached submillimeter levels. (8,9) The flattening filter was first redesigned to be more efficient and later completely removed in order to deliver higher dose rates. (10,11) The multileaf collimators' (MLC) leaf resolution is also improving, with 2.5 mm leaf widths at the isocenter, in order to improve the dose conformality to the target. (12) Treatment delivery methods have advanced to further improve conformality to complex geometric targets, while limiting dose to critical organs, such as dynamic conformal arc (DCA), Intensity Modulated Radiation Therapy (IMRT), and Volumetric Modulated Arc Therapy (VMAT). (13-16) In the era of image guidance, numerous methods have been developed for stereotactic treatment delivery, including optical surface monitoring, in-room CT, stereoscopic X-ray imaging, ultrasound, and cone-beam computed tomography (CBCT). (17-20) Image-guided frameless treatment has been systematically studied and the positioning accuracy has been validated for use in stereotactic treatments. (20,21) The latest platform for linac-based SRS treatments (the Edge, Varian Medical Systems, Palo Alto, CA) offers multiple imaging modalities for treatment localization, including an optical surface monitoring system (OSMS) for surface tracking, 2.5 MV portal images for verification, automatically triggered monoscopic kV imaging to track intrafractional motion, 4D CBCT to evaluate tumor motion offline, extended CBCT images by stitching multiple CBCT scans together, and a Calypso/Varian electromagnetic beacon-based tracking system. The new couch (PerfectPitch) supports six degrees of freedom (6DoF) corrections from multiple imaging modalities for precise patient setup. The flat panel imager is designed with a greater dynamic range, faster image readout rate, and a larger active area. This technology also has a stereotactic accessory package which includes conical cones ranging in diameter from 4 to 17.5 mm. Here we describe a comprehensive commissioning process suitable for modern, linac-based SRS/ SBRT with focus on the characterization of beam parameters, conical cones, 6DoF couch, dosimetric verification, and integrated end-to-end tests of this new technology. II. MATERIALS AND METHODS A. Flattening filter-free (FFF) beam commissioning Beam data were measured for the purpose of generating a beam model for the convolution/ superposition dose algorithm (anisotropic analytical algorithm, AAA v 11.0.31 within the Eclipse Treatment Planning System (TPS), Varian Medical Systems). Measurements were performed for the two beam energies configured for our linac (flattening filter-free photons, 6X FFF and 10X FFF). AAPM task group report No. 45 "AAPM Code of Practice for Radiotherapy Accelerators" recommendations were followed for commissioning tasks. (22) Selection of different detectors for water phantom measurements were based on AAPM task group report No. 106 and small field dosimetry specification (23) (Table 1). Field sizes ranged from 1 × 1 cm 2 to 40 × 40 cm 2 which were determined by the jaw (i.e., data were acquired with the MLCs parked).
Dosimetric verification of clinical radiotherapy treatment planning system
Vojnosanitetski Pregled, 2022
Background/Aim. In the past two decades, we have witnessed the emergence of new radiation therapy techniques, radiotherapy treatment planning system (TPS) with calculating algorithms for the dosage calculation in a patient, units for multislice computed tomography (CT) and image-guided treatment delivery. The aim of the study was investigating the significant difference in dosimetric calculation of radiotherapy TPS in relation to the values obtained by measuring on the linear accelerator (LINAC), and the accuracy of dosimetric calculation between calculating algorithms Analytical Anisotropic Algorithm (AAA) and Acuros XB in various tissues and photon beam energies. Methods. For End-to-End test we used the heterogeneous phantom CIRS Thorax002LFC, which anatomically represents human torso with a set of inserts known as relative electron densities (RED) for obtaining a CT calibration curve, comparable to the "reference" CIRS 062M phantom. For the AAA and Acuros XB algorithms and for 6 MV and 16 MV photon beams in the TPS Varian Eclipse 13.6, four 3D conformal (3DCRT), and one intensity modulated (IMRT) and volumetric modulated arc (VMAT) radiotherapy plans were made. Measurements of the absolute dose in Thorax phantom, by PTW-Semiflex ionization chamber, were carried out on three Varian-DHX LINACs. Results. The difference between "reference" and measured CT conversion curves in the bone area was 3%. For 476 phantom measurements, the difference between measured and TPS calculated dose of 3-6%, was found in 30 (6.3%) cases. According to regression analysis, the standardized Beta coefficient for relative errors, 6 MV vs. 16 MV, was 0.337 (33.7%, p < 0.001). Mean relative errors for AAA and Acuros XB, using Mann-Whitney test, for bones were 1.56% and 2.64%, respectively (p = 0.004). Conclusion. End-to-End test on Thor-ax002LFC phantom proved the accuracy of TPS dose calculation in relation to the one delivered to a patient by LINAC. There was a significant difference for photon energies relative errors (higher values are obtained for 16 MV vs. 6 MV). A statistically significant minor relative error in AAA vs. Acuros XB was found for the bone.