Quality Assurance of Immobilization and Target Localization Systems for Frameless Stereotactic Cranial and Extracranial Hypofractionated Radiotherapy
The success of stereotactic radiosurgery has stimulated significant interest in the application of such an approach for the treatment of extracranial tumors. The potential benefits of reduced healthcare costs and improved patient outcomes that could be realized in a high-precision, hypofractionated treatment paradigm are numerous. Image-guidance technologies are eliminating the historic requirement for rigid head fixation and will also accelerate the clinical implementation of the approach in extracranial sites. An essential prerequisite of "frameless" stereotactic systems is that they provide localization accuracy consistent with the safe delivery of a therapeutic radiation dose given in one or few fractions. In this report, we reviewed the technologies for frameless localization of cranial and extracranial targets with emphasis on the quality assurance aspects.
Available from: Mattia Falchetto Osti
- "More recently, as an alternative to the invasive patient fixation technique, different frameless stereotactic systems have been implemented. A variable positioning accuracy of 1-4 mm has been reported for frameless stereotactic systems [6-14], reflecting, at least in part, different methods in patient fixation, positioning, and assessment of accuracy. The use of small margin of safety that must be added to the target volume for errors in localization and set-up is essential in order to minimize the potential treatment-related complications of SRS. "
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ABSTRACT: To assess the accuracy of patient repositioning and clinical outcomes of frameless stereotactic radiosurgery (SRS) for brain metastases using a stereotactic mask fixation system.
One hundred two patients treated consecutively with frameless SRS as primary treatment at University of Rome Sapienza Sant'Andrea Hospital between October 2008 and April 2010 and followed prospectively were involved in the study. A commercial stereotactic mask fixation system (BrainLab) was used for patient immobilization. A computerized tomography (CT) scan obtained immediately before SRS was used to evaluate the accuracy of patient repositioning in the mask by comparing the isocenter position to the isocenter position established in the planning CT. Deviations of isocenter coordinates in each direction and 3D displacement were calculated. Overall survival, brain control, and local control were estimated using the Kaplan-Meier method calculated from the time of SRS.
The mean measured isocenter displacements were 0.12 mm (SD 0.35 mm) in the lateral direction, 0.2 mm (SD 0.4 mm) in the anteroposterior, and 0.4 mm (SD 0.6 mm) in craniocaudal direction. The maximum displacement of 2.1 mm was seen in craniocaudal direction. The mean 3D displacement was 0.5 mm (SD 0.7 mm), being maximum 2.9 mm. The median survival was 15.5 months, and 1-year and 2-year survival rates were 58% and 24%, respectively. Nine patients recurred locally after SRS, with 1-year and 2-year local control rates of 91% and 82%, respectively. Stable extracranial disease (P = 0.001) and KPS > 70 (P = 0.01) were independent predictors of survival.
Frameless SRS is an effective treatment in the management of patients with brain metastases. The presented non-invasive mask-based fixation stereotactic system is associated with a high degree of patient repositioning accuracy; however, a careful evaluation is essential since occasional errors up to 3 mm may occur.
Available from: Maurizio Valeriani
- "Accuracy and reproducibility of patient repositioning is mandatory for FSRT. Several non-invasive stereotactic fixation systems have been developed based on masks [14-20], bite blocks [5-11] or infrared camera guidance . We used a commercial stereotactic system based on a thermoplastic mask, assessing the accuracy of isocenter relocation by serial CT scans and portal imaging. "
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ABSTRACT: To assess the accuracy of fractionated stereotactic radiotherapy (FSRT) using a stereotactic mask fixation system.
Sixteen patients treated with FSRT were involved in the study. A commercial stereotactic mask fixation system (BrainLAB AG) was used for patient immobilization. Serial CT scans obtained before and during FSRT were used to assess the accuracy of patient immobilization by comparing the isocenter position. Daily portal imaging were acquired to establish day to day patient position variation. Displacement errors along the different directions were calculated as combination of systematic and random errors.
The mean isocenter displacements based on localization and verification CT imaging were 0.1 mm (SD 0.3 mm) in the lateral direction, 0.1 mm (SD 0.4 mm) in the anteroposterior, and 0.3 mm (SD 0.4 mm) in craniocaudal direction. The mean 3D displacement was 0.5 mm (SD 0.4 mm), being maximum 1.4 mm. No significant differences were found during the treatment (P=0.4). The overall isocenter displacement as calculated by 456 anterior and lateral portal images were 0.3 mm (SD 0.9 mm) in the mediolateral direction, -0.2 mm (SD 1 mm) in the anteroposterior direction, and 0.2 mm (SD 1.1 mm) in the craniocaudal direction. The largest displacement of 2.7 mm was seen in the cranio-caudal direction, with 95% of displacements<2 mm in any direction.
The results indicate that the setup error of the presented mask system evaluated by CT verification scans and portal imaging are minimal. Reproducibility of the isocenter position is in the best range of positioning reproducibility reported for other stereotactic systems.
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ABSTRACT: In this paper, the system performance of MC-CDMA over frequency-selective Nakagami-m fading channel is analyzed. Bit error rates are obtained for an uplink MC-CDMA system with MRC reception, in which both correlated and independent subcarrier scenarios are considered and compared. In the literature independency among subcarriers was often assumed in MC-CDMA performance study in the presence of Nakagami-m fading. Our results show, however, that a frequency-selective Nakagami-m fading channel model may have been overemphasized for MC-CDMA compared to a frequency-selective Rayleigh fading model when, this independency is addressed.
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