In this study we investigate the deliverability of dosimetric plans generated by the irregular surface compensator (ISCOMP) algorithm for 6 MV photon beams in Eclipse (Varian Medical System, CA). In ...contrast to physical tissue compensation, the electronic ISCOMP uses MLCs to dynamically modulate the fluence of a photon beam in order to deliver a uniform dose at a user defined plane in tissue. This method can be used to shield critical organs that are located within the treatment portal or improve dose uniformity by tissue compensation in inhomogeneous regions. Three site specific plans and a set of test fields were evaluated using the γ‐metric of 3%/ 3 mm on Varian EPID, MapCHECK, and Gafchromic EBT3 film with a clinical tolerance of >95% passing rates. Point dose measurements with an NRCC calibrated ionization chamber were also performed to verify the absolute dose delivered. In all cases the MapCHECK measured plans met the gamma criteria. The mean passing rate for the six EBT3 film field measurements was 96.2%, with only two fields at 93.4 and 94.0% passing rates. The EPID plans passed for fields encompassing the central ∼10 × 10 cm2 region of the detector; however for larger fields and greater off‐axis distances discrepancies were observed and attributed to the profile corrections and modeling of backscatter in the portal dose calculation. The magnitude of the average percentage difference for 21 ion chamber point dose measurements and 17 different fields was 1.4 ± 0.9%, and the maximum percentage difference was −3.3%. These measurements qualify the algorithm for routine clinical use subject to the same pre‐treatment patient specific QA as IMRT.
Postimplant analysis in permanent breast seed implant (PBSI) is performed at inconsistent times subsequent to seed implantation across cancer centers, creating challenges in the interpretation of ...dosimetric data and ultimately the correlation with clinical outcomes. The purpose of this study is to determine the most appropriate time postimplant to perform this analysis.
Nine patients treated at our institution with PBSI were included in this analysis. Each underwent 4 postimplant CT scans: 0, 15, 30, and 60 days postimplant. A model of the accumulated dose was created by deformably registering the Day 15, 30, and 60 postimplant CT scans and dose matrices to the Day 0 scan, scaling for seed decay. The results from this model were compared to each individual postplan by integral comparison of dose-volume histogram curves for a dose evaluation volume.
The Day 30 postplan showed the best agreement with the accumulated dose model and the smallest interpatient variability across the patient cohort. The mean (±SD) for the dose evaluation volume V
, V
, V
, and V
for the accumulated dose model was 90 ± 7%, 86 ± 8%, 66 ± 14%, and 41 ± 16%, respectively.
Based on the results of this patient cohort, we recommend that postimplant dosimetric analysis for PBSI be performed approximately 30 days following the implant.
In surgical operations, tissue manipulation can be automated to reduce the surgeon's workload. This work addresses the application of tissue manipulation in breast brachytherapy, which involves ...manipulating an internal target inside the breast. Unassisted breast brachytherapy causes excessive target movement that reduces seed implantation accuracy. To address this target movement in breast brachytherapy, first, the internal target point will be manipulated accurately and then the brachytherapy needle will be inserted into the immobilized tissue. In this paper, a model-based tissue manipulation method is introduced. To simulate nonlinear large tissue deformation for the first time, a minimum-energy-based deformable tissue solver is utilized. Based on the theory of positive bases, the optimal number of actuators is determined to guarantee controllability of the internal target. A model predictive controller (MPC) is designed to implement multi-point tissue manipulation. A breast phantom is used to test the accuracy of the deformation model and the effectiveness of the proposed control method. The results show that the tissue deformation simulation error is 1.6 mm and the internal target can be regulated with negligible steady-state errors using an MPC controller.
Purpose:
This retrospective study aims to quantify the positional accuracy of seed delivery in permanent breast seed implant (PBSI) brachytherapy at the Tom Baker Cancer Centre (TBCC).
Methods:
...Treatment planning and post-implant CT scans for 5 patients were rigidly registered using the MIM Symphony™ software (MIM Software, Cleveland, OH) and used to evaluate differences between planned and implanted seed positions. Total and directional seed displacements were calculated for each patient in a clinically relevant ‘needle coordinate system’, defined relative to the angle of fiducial needle insertion.
Results:
The overall average total seed displacement was 10±8 mm. Systematic seed displacements were observed in individual patients and the magnitude and direction of these offsets varied among patients. One patient showed a significant directional seed displacement in the shallow-deep direction compared with the other four patients. With the exception of this one patient outlier, no significant systematic directional displacements in the needle coordinate system were observed for this cohort; the average directional displacements were −1±5 mm, 2±3 mm, and −2±4 mm in the shallow-deep, up-down, and right-left directions respectively.
Conclusion:
With the exception of one patient outlier, the magnitude of seed displacements were relatively consistent among patients. The results indicate that the shallow-deep direction possesses the largest uncertainty for the seed delivery method used at the TBCC. The relatively large uncertainty in seed placement in this direction is expected, as this is the direction of needle insertion. Further work will involve evaluating deflections of delivered needle tracks from their planned positions.
In this paper, we propose a robotic ultrasound imaging method that scans the breast in two separate phases to acquire high-quality ultrasound images. Our proposed system controls five Degrees of ...Freedom (DoFs) of the robot that hold an ultrasound probe to perform precise scanning. This system finds the desired trajectory based on geometrical analysis of the target inside the breast in a pre-scan phase and uses this information to control the probe in a post-scan phase. The proposed method updates the desired values of rotational and translational movement of the probe in the post-scan by calculating the center of mass of segmented target in each acquired frame and the average of image confidence map. The proposed method has been tested experimentally on a plastisol phantom. Given a specific trajectory, the position and orientation of the probe have been controlled at each point of the trajectory. The experiments' result shows us that our proposed visual servoing algorithm successfully controls the probe to look at target tissue and is fast enough for use in a robotic control loop.
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