Linear accelerator‐based stereotactic radiosurgery (SRS) or radiotherapy (SRT) is a well accepted technique for the treatment of cranial primary and metastatic lesions and acoustic neuromas. The ...requirements in terms of accuracy and reliability of the linac are more stringent for these modalities than they are for more highly fractionated treatments. However these requirements have been identified and standardized in the TG142 report on external beam quality assurance (QA). It is usually not difficult for a newly purchased modern linac to meet these requirements, giving users a wider variety of choice when considering starting an SRS/SRT program. The compatibility of these linacs with SRS/SRT‐specific equipment and software, such as cones, frames or treatment planning systems, must be established. I will report on the use at our institution of a Siemens Artiste™ linac for cranial SRS/SRT, in conjunction with the Brainlab iPlan® treatment planning system. I will discuss the various combinations of using the Brainlab SRS cones or the Siemens 160‐leaf multileaf collimator (160‐MLC) for beam shaping; the Brainlab frame or frameless system for immobilization; the Brainlab target positioning system or the Siemens MVision™ MV‐CBCT system for localization. I will describe the commissioning steps of the system, including data acquisition for beam modeling in iPlan® and end‐to‐end testing. Various issues that arose throughout the use of this Siemens/Brainlab hybrid system over the last 3 years will be discussed.
Learning Objectives:
1. To assess the safety and usefulness of a multivendor solution for cranial SRS/SRT.
2. To understand the commissioning and quality assurance steps of a Siemens Artiste™ / Brainlab iPlan® hybrid system for cranial SRS/SRT
3. To understand the limitations of the hybrid system.
Purpose: To describe a method using pretreatment and intrafraction fluoroscopic verification of the gated treatment of a liver lesion located near the diaphragm. Methods: A 74‐year‐old female ...patient, who had previously received radiation to the lung, presented with a 13.8 cc tumor located 0.5 cm inferior to the superior border of the liver, moving 2 cm in the cranio‐caudal direction with breathing. A planning CT with contrast in full exhale breath hold (FEBH) was acquired to reduce motion artifact, followed by a 4‐dimensional (4D) CT. The gross target volume (GTV) was contoured on the FEBH CT and propagated only to the 25% inspiration (25In) and 25% expiration (25Ex) phases of the 4D‐CT, in order to reduce lung dose. An internal target volume (ITV) was created encompassing all 3 phases. A plan was created to deliver 50 Gy to the PTV (ITV+0.3cm laterally and inferiorly) in 5 fractions using 3D conformal planning gated on the FE, 25In and 25Ex phases. Digitally reconstructed radiographs (DRR) were created for each beam angle and for each of the 3 respiratory phases included in the gating window. Prior to treatment, a mega‐voltage (MV)‐CBCT was acquired and its projections were analyzed in cine‐mode. Intrafraction motion verification was monitored using MV‐fluoroscopy. On both cine and fluoroscopy movies, the respiratory phase was identified using the position of the diaphragm, and the frames were compared to the corresponding DRRs. Results: Qualitative analysis on both the pretreatment cine and intrafraction fluoroscopy movies showed a clinically acceptable agreement between plan and treatment position. Conclusion: We described a treatment verification method for gated SBRT of lesions near the dome of the liver, using pre‐treatment and intrafraction fluoroscopic movies. This method is a good gated treatment quality assurance tool allowing to confidently spare lung tissue.
The (2)H(e,e'p)n cross section at a momentum transfer of 3.5 (GeV/c)(2) was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a ...function of the neutron recoil angle θ(nq) and to extract missing momentum distributions for fixed values of θ(nq) up to 0.55 GeV/c. In the region of 35°≤θ(nq)≤45° recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration.
Purpose: The primary benefit of removing the flattening filter of a linear accelerator is to increase the dose rate by a factor of 3 to 6. Additionally, change in scatter conditions in the head of ...the accelerator may also decrease the penumbra, which could lead to better target conformality. The purpose of this work is to evaluate this effect on a Siemens Artiste linear accelerator. Methods: Profiles of 10 ×10 cm2 flat and flattening‐filter‐free (FFF) fields were measured in water using a scanning diode with 0.3 mm steps. The penumbra created by both the 160‐leaf multileaf collimator (MLC) and the backup jaw (Y‐jaw) was measured. The profile of the FFF beam was renormalized so that for both flat and FFF beams, the penumbra was defined as the distance between the points with 20% and 80% of the central flat beam dose. The penumbra was measured every 5 cm along the major axes and around the central axis at four depths from 1.5 to 20 cm. Results: The average penumbra defined by the MLC and Y‐jaw was 4.9 mm and 5.9 mm, respectively for the flat beam, and 4.9 mm and 5.2 mm for the FFF beam. The flat beam penumbra increased with depth from 4.6 to 9.2 mm and 5.5 to 10.1 mm for the MLC and Y‐jaw respectively. The corresponding increase for the FFF beam penumbra was 4.6 to 9.2 mm and 4.6 to 8.8 mm. The average paired difference was <0.1 mm for the MLC and 0.8 mm for the Y‐jaw. Conclusion: The MLC penumbra was not affected by removing the flattening filter, while the decreased scattering in the FFF beam reduced the Y‐jaw penumbra by 0.8 mm. Removing the flattening filter does not clinically significantly improve the way the MLC can conform to the target.
This research was partially supported by Siemens Medical Solutions.
Purpose: To compare the performance of the biological‐based treatment planning system (TPS) CMS Monaco with the dose‐based TPS CMS XiO, for treatment of head and neck patients on the Siemens Artiste ...Linear Accelerator. Method and Materials: Three head and neck patients treated on the Artiste and planned with XiO were replanned using Monaco. The Monaco plans were developed using the same clinical objectives concerning the prescription dose to the target and the maximum allowed dose to the organs at risk. The XiO plans were optimized using the Superposition algorithm employing dose‐volume and minimum/maximum dose constraints. The Monaco plans were optimized with the Monte Carlo algorithm using biological cost functions. Minimum, maximum and mean doses were compared as well as the equivalent uniform dose (EUD), total number of segments and monitor units (MU) required. The plans were delivered onto the Sun Nuclear MapCheck diode array with a 3%/3mm distance to agreement criterion. Results: Target coverage was similar in both plans. The average reduction in the Monaco mean dose was 4.7, 1.7, 9.3 and 11.2 Gy for the spinal cord, brainstem and, right and left parotid, respectively, compared to the XiO plans. The number of segments was comparable for two patients and was reduced by 63 for the third patient. The number of MU's for the Monaco plans were greater in all three cases. Conclusion: The three plans developed with Monaco were deemed to be clinically acceptable and were dosimetrically equivalent or superior to plans developed using XiO. The Monaco plans had superior organ at risk sparing whilst maintaining the same target coverage achieved with the XiO system.
Purpose: To evaluate mega‐voltage cone‐beam computed tomography (MV‐CBCT) imaging of moving tumors. Method and Materials: Five patients treated for early stage non‐small cell lung cancer using ...stereotactic body radiation therapy (SBRT) were analyzed. Simulation images were obtained with a Siemens Sensation Open 4D‐CT scanner. The Internal Target Volume (ITV) comprised of the tumor in each phase and on the free‐breathing CT was created. Daily localization was performed with MV‐CBCT on a Siemens Artiste linear accelerator with the in‐line kView system, using a 4.2 MeV electron beam incident on a carbon target without flattening filter to increase the yield of low energy photons. The tumor was contoured on each daily CB image. The size of the ITV contours on the planning CT and MV‐CBCT was compared in the anterior‐posterior (AP), left‐right (LR) and superior‐inferior (SI) directions. Results: In the majority of cases the standard deviation of the MV‐CBCT contour size from day to day was less than 2 mm. The average difference between the planning CT and MV‐CBCT contours varies widely from patient to patient. The largest difference (10.1 mm) was seen in the SI direction for a patient for whom breathing motion was large (18 mm), and the contrast between the tumor and its surroundings in the expected tumor position during the full‐inhale phase was reduced. The second largest difference (7.2 mm) was seen in the SI direction in a patient for whom the proximity of the tumor to a large blood vessel also reduced the contrast. Conclusion: There is a possibility of inaccurate registration between the planning CT and MV‐CBCT and less effective localization when the contrast is adversely affected because of large tumor motion or proximity to other structures. This should be taken into account in the Planning Target Volume margin. Research partially supported by Siemens Medical Solutions.
Purpose: To investigate the accuracy and precision of Mega‐Voltage Cone Beam Computed Tomography (MV‐CBCT) localization for intracranial stereotactic treatment deliveries. Method and Materials: A ...Rando head phantom containing a metal ball bearing (BB) was mounted with a head frame. A treatment plan targeting the BB was generated and three localization methods were compared. The first, was the standard technique using laser micro‐alignment to the isocenter projected onto target positioning sheets. Second, a standard MV‐CBCT was acquired, using skull based registration with the treatment planning CT and millimeter precision correction using the motorized treatment couch. For the third, a micro‐adjustment of the head frame position using a Vernier scale was used to apply the MV‐CBCT correction with a 0.1 mm accuracy. After localization with each method was achieved, a series of 1.0 × 1.0 cm fields from gantry angles 0, 90, 180 and 270 degrees was used to asses target alignment by measuring the BB position relative to the beam central axis. Results: The standard localization technique resulted in an average displacement of the BB with respect to the beam central axis of 1.2 ± 0.1 mm. Skull‐based localization with MV‐CBCT using millimeter precision couch offsets resulted in a displacement of the BB with respect to the beam central axis of 2.3 mm. Localization with MV‐CBCT and micro‐adjustment resulted in a displacement of the BB with respect to the beam central axis of 1.2 ± 0.2 mm. Conclusion: After modifications were applied to the MV‐CBCT localization technique, accuracy was as good as the standard approach for head frame cases. When MV‐CBCT localization is applied to a frameless case, the anatomy‐based alignment eliminates the variability of interfraction patient positioning within the immobilizing mask.
Conflict of Interest: Research partially funded by Siemens Medical Solutions.
Purpose: To present a quantitative evaluation of the impact of scan length, monitor unit (MU)/projection, and total MU on the image quality in mega‐voltage cone‐beam computed tomography (MV‐CBCT). We ...present results of a systematic comparison of contrast‐to‐noise ratio and modulation transfer function obtained for 9 varying acquisition protocols with the MVision system (Siemens Medical Solutions, Concord, CA). Method and Materials: Image quality is characterized by contrast, noise and spatial resolution. Utilizing the manufacturer.s image quality phantom, we obtained sets of images from 9 different acquisition protocols of varying scan length, MU/projection, and total MU. The images are analyzed in terms of contrast‐to‐noise ratio (CNR) and modulation transfer function (MTF), which quantifies spatial resolution. Results: The CNR data suggest that the image contrast is not enhanced by increasing the MU/projection beyond 0.0675, but rather may be diminished. However, for comparable MU/projection the CNR is reduced from 7.25 to 4.8 by lowering the total MU from 15 to 8. For the same MU/projection the CNR is slightly better for the 360° scan compared to the 200° scan. On the other hand, the MTF analysis shows that neither the scan length, nor the sampling rate, nor the total MU have an effect on spatial resolution. Furthermore, the MTF analysis indicates that objects of spatial frequency larger than 0.3 line pair/mm cannot be resolved adequately with current MV‐CBCT imaging irrespective of the scanning protocol utilized. Conclusion: The study shows that spatial resolution is not affected by acquisition or reconstruction parameters in MV‐CBCT. However, the system is optimally used in terms of contrast‐to‐noise ratio with the default setting of 1 projection every degree. Conflict of Interest: This research was partially supported by Siemens Medical Solutions.
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