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Purpose: In radiation therapy, surface guidance can be used for patient setup and intra‐fraction motion monitoring. The surface guided radiation therapy (SGRT) system from Varian Medical systems, IDENTIFYTM, consists of three pods, including cameras and a random pattern projector, mounted on the ceiling. The information captured by the cameras is used to make a reconstruction of the surface. The aim of the study was to assess the technical performance of this SGRT system on a closed‐bore linac. Methods: Phantom measurements were performed to assess the accuracy, precision, reproducibility and temporal stability of the system, both in align and in load position. Translations of the phantoms in lateral, longitudinal, and vertical direction, and rotations around three axes (pitch, roll and yaw) were performed with an accurate, in‐house built, positioning stage. Different phantom geometries and different surface colors were used, and various ambient light intensities were tested. Results: The accuracy of the IDENTIFYTM system at the closed‐bore linac was 0.07 mm and 0.07 degrees at load position, and 0.06 mm and 0.01 degrees at align position for the white head phantom. The precision was 0.02 mm and 0.02 degrees in load position, and 0.01 mm and 0.02 degrees in align position. The accuracy for the Penta‐Guide phantom was comparable to the white head phantom, with 0.06 mm and 0.01 degrees in align position. The system was slightly less accurate for translations of the CIRS lung phantom in align position (0.20 mm, 0.05 degrees). Reproducibility measurements showed a variation of 0.02 mm in load position. Regarding the temporal stability, the maximum drift over 30 min was 0.33 mm and 0.02 degrees in load position. No effect of ambient light level on the accuracy of the IDENTIFYTM system was observed. Regarding different surface colors, the accuracy of the system for a black phantom was slightly worse compared to a white surface, but not clinical relevant. Conclusion: The IDENTIFYTM system can adequately be used for motion monitoring on a closed‐bore linac with submillimeter accuracy. The results of the performed measurements meet the clinical requirements described in the guidelines of the AAPM and the ESTRO. [ABSTRACT FROM AUTHOR]

Temperature-sensitive liposomes (TSLs) loaded with doxorubicin (Dox), and Magnetic Resonance Imaging contrast agents (CAs), either manganese (Mn 2 + ) or [Gd(HPDO3A)(H 2 O)], provide the advantage of drug delivery under MR image guidance. Encapsulated MRI CAs have low longitudinal relaxivity ( r 1 ) due to limited transmembrane water exchange. Upon triggered release at hyperthermic temperature, the r 1 will increase and hence, provides a means to monitor drug distribution in situ. Here, the effects of encapsulated CAs on the phospholipid bilayer and the resulting change in r 1 were investigated using MR titration studies and 1 H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles. Our results show that Mn 2 + interacted with the phospholipid bilayer of TSLs and consequently, reduced doxorubicin retention capability at 37 °C within the interior of the liposomes over time. Despite that, Mn 2 + -phospholipid interaction resulted in higher r 1 increase, from 5.1 ± 1.3 mM − 1 s − 1 before heating to 32.2 ± 3 mM − 1 s − 1 after heating at 60 MHz and 37 °C as compared to TSL(Gd,Dox) where the longitudinal relaxivities before and after heating were 1.2 ± 0.3 mM − 1 s − 1 and 4.4 ± 0.3 mM − 1 s − 1 , respectively. Upon heating, Dox was released from TSL(Mn,Dox) and complexation of Mn 2 + to Dox resulted in a similar Mn 2 + release profile. From 25 to 38 °C, r 1 of [Gd(HPDO3A)(H 2 O)] gradually increased due to increase transmembrane water exchange, while no Dox release was observed. From 38 °C, the release of [Gd(HPDO3A)(H 2 O)] and Dox was irreversible and the release profiles coincided. By understanding the non-covalent interactions between the MRI CAs and phospholipid bilayer, the properties of the paramagnetic TSLs can be tailored for MR guided drug delivery. [ABSTRACT FROM AUTHOR]

Purpose: In radiation therapy, surface guidance can be used for patient setup and intra-fraction motion monitoring. The surface guided radiation therapy (SGRT) system from Varian Medical systems, IDENTIFY TM , consists of three pods, including cameras and a random pattern projector, mounted on the ceiling. The information captured by the cameras is used to make a reconstruction of the surface. The aim of the study was to assess the technical performance of this SGRT system on a closed-bore linac., Methods: Phantom measurements were performed to assess the accuracy, precision, reproducibility and temporal stability of the system, both in align and in load position. Translations of the phantoms in lateral, longitudinal, and vertical direction, and rotations around three axes (pitch, roll and yaw) were performed with an accurate, in-house built, positioning stage. Different phantom geometries and different surface colors were used, and various ambient light intensities were tested., Results: The accuracy of the IDENTIFY TM system at the closed-bore linac was 0.07 mm and 0.07 degrees at load position, and 0.06 mm and 0.01 degrees at align position for the white head phantom. The precision was 0.02 mm and 0.02 degrees in load position, and 0.01 mm and 0.02 degrees in align position. The accuracy for the Penta-Guide phantom was comparable to the white head phantom, with 0.06 mm and 0.01 degrees in align position. The system was slightly less accurate for translations of the CIRS lung phantom in align position (0.20 mm, 0.05 degrees). Reproducibility measurements showed a variation of 0.02 mm in load position. Regarding the temporal stability, the maximum drift over 30 min was 0.33 mm and 0.02 degrees in load position. No effect of ambient light level on the accuracy of the IDENTIFY TM system was observed. Regarding different surface colors, the accuracy of the system for a black phantom was slightly worse compared to a white surface, but not clinical relevant., Conclusion: The IDENTIFY TM system can adequately be used for motion monitoring on a closed-bore linac with submillimeter accuracy. The results of the performed measurements meet the clinical requirements described in the guidelines of the AAPM and the ESTRO., (© 2024 The Authors. Journal of Applied Clinical Medical Physics is published by Wiley Periodicals, Inc. on behalf of The American Association of Physicists in Medicine.)

Purpose: To develop a clinically feasible method for dose calculations on cone beam CT (CBCT) images of two different vendors, and to determine the accuracy of these dose calculations for lung cancer patients., Methods: Lung cancer patients with CBCT imaging (n = 10 for Elekta, n = 6 for Varian) and a repeated planning CT scan on the same day were selected. For CBCT dose calculations, an adapted Hounsfield units-to-mass density table (HU table) was used which was obtained by comparing CT values of corresponding points on the CBCT and the repeated planning CT scan. Dose calculations with three different HU tables were compared: a patient-specific, a general thorax-CBCT, and the standard CT HU table. Planning CT data were used to compensate for the limited field of view (FOV) (Elekta) or scan length (Varian) of the CBCT. For evaluation, clinically relevant dose metrics were compared between the repeated CT and CBCT to assess the accuracy of dose calculations on CBCT for both vendors., Results: For both vendors, isodose lines and dose volume histograms were very similar between dose calculation on CBCT and CT. For Varian, average differences between CT and CBCT dose calculations were 2%-3% for most dose metrics when the standard CT HU table was used. A better agreement was observed when a thorax-CBCT HU table was used, with differences of 1%-2%. No added value was found by using a patient-specific HU table, showing similar results as the general thorax-CBCT HU table. For Elekta, the dose metrics showed large deviations when the CT HU table was used, but using a patient-specific HU table resulted in similar accuracy as for Varian CBCT dose calculations, with average differences between repeated CT and CBCT dose metrics below 3%, and for most dose metrics even below 2%., Conclusions: Differences between Elekta and Varian CBCT, including hardware, reconstruction software, HU calibration, FOV, and scan length, resulted in different challenges for CBCT dose calculations for the different vendors. For Elekta CBCT scans, the procedure with a patient-specific HU table resulted in similar accuracy as for Varian CBCT dose calculations with a general HU correction for all thorax patients. The vendor-specific corrective methods used in this study resulted in dose calculations feasible for treatment re-evaluation for both Elekta and Varian CBCT scans.