Dose uncertainty induced by respiratory motion remains a major concern for treating thoracic and abdominal lesions using particle beams. This Task Group report reviews the impact of tumor motion and ...dosimetric considerations in particle radiotherapy, current motion‐management techniques, and limitations for different particle‐beam delivery modes (i.e., passive scattering, uniform scanning, and pencil‐beam scanning). Furthermore, the report provides guidance and risk analysis for quality assurance of the motion‐management procedures to ensure consistency and accuracy, and discusses future development and emerging motion‐management strategies. This report supplements previously published AAPM report TG76, and considers aspects of motion management that are crucial to the accurate and safe delivery of particle‐beam therapy. To that end, this report produces general recommendations for commissioning and facility‐specific dosimetric characterization, motion assessment, treatment planning, active and passive motion‐management techniques, image guidance and related decision‐making, monitoring throughout therapy, and recommendations for vendors. Key among these recommendations are that: (1) facilities should perform thorough planning studies (using retrospective data) and develop standard operating procedures that address all aspects of therapy for any treatment site involving respiratory motion; (2) a risk‐based methodology should be adopted for quality management and ongoing process improvement.
Over the last few years, magnetic resonance image‐guided radiotherapy systems have been introduced into the clinic, allowing for daily online plan adaption. While quality assurance (QA) is similar to ...conventional radiotherapy systems, there is a need to introduce or modify measurement techniques. As yet, there is no consensus guidance on the QA equipment and test requirements for such systems. Therefore, this report provides an overview of QA equipment and techniques for mechanical, dosimetric, and imaging performance of such systems and recommendation of the QA procedures, particularly for a 1.5T MR‐linac device. An overview of the system design and considerations for QA measurements, particularly the effect of the machine geometry and magnetic field on the radiation beam measurements is given. The effect of the magnetic field on measurement equipment and methods is reviewed to provide a foundation for interpreting measurement results and devising appropriate methods. And lastly, a consensus overview of recommended QA, appropriate methods, and tolerances is provided based on conventional QA protocols. The aim of this consensus work was to provide a foundation for QA protocols, comparative studies of system performance, and for future development of QA protocols and measurement methods.
Four-dimensional (4D) radiotherapy is the explicit inclusion of the temporal changes in anatomy during the imaging, planning, and delivery of radiotherapy. Temporal anatomic changes can occur for ...many reasons, though the focus of the current investigation is respiration motion for lung tumors. The aim of this study was to develop 4D radiotherapy treatment-planning methodology for DMLC-based respiratory motion tracking. A 4D computed tomography (CT) scan consisting of a series of eight 3D CT image sets acquired at different respiratory phases was used for treatment planning. Deformable image registration was performed to map each CT set from the peak-inhale respiration phase to the CT image sets corresponding to subsequent respiration phases. Deformable registration allows the contours defined on the peak-inhale CT to be automatically transferred to the other respiratory phase CT image sets. Treatment planning was simultaneously performed on each of the eight 3D image sets via automated scripts in which the MLC-defined beam aperture conforms to the PTV (which in this case equaled the GTV due to CT scan length limitations) plus a penumbral margin at each respiratory phase. The dose distribution from each respiratory phase CT image set was mapped back to the peak-inhale CT image set for analysis. The treatment intent of 4D planning is that the radiation beam defined by the DMLC tracks the respiration-induced target motion based on a feedback loop including the respiration signal to a real-time MLC controller. Deformation with respiration was observed for the lung tumor and normal tissues. This deformation was verified by examining the mapping of high contrast objects, such as the lungs and cord, between image sets. For the test case, dosimetric reductions for the cord, heart, and lungs were found for 4D planning compared with 3D planning. 4D radiotherapy planning for DMLC-based respiratory motion tracking is feasible and may offer tumor dose escalation and/or a reduction in treatment-related complications. However, 4D planning requires new planning tools, such as deformable registration and automated treatment planning on multiple CT image sets.
Respiratory gating is a commercially available technology for reducing the deleterious effects of motion during imaging and treatment. The efficacy of gating is dependent on the reproducibility ...within and between respiratory cycles during imaging and treatment. The aim of this study was to determine whether audio-visual biofeedback can improve respiratory reproducibility by decreasing residual motion and therefore increasing the accuracy of gated radiotherapy.
A total of 331 respiratory traces were collected from 24 lung cancer patients. The protocol consisted of five breathing training sessions spaced about a week apart. Within each session the patients initially breathed without any instruction (free breathing), with audio instructions and with audio-visual biofeedback. Residual motion was quantified by the standard deviation of the respiratory signal within the gating window.
Audio-visual biofeedback significantly reduced residual motion compared with free breathing and audio instruction. Displacement-based gating has lower residual motion than phase-based gating. Little reduction in residual motion was found for duty cycles less than 30%; for duty cycles above 50% there was a sharp increase in residual motion.
The efficiency and reproducibility of gating can be improved by: incorporating audio-visual biofeedback, using a 30-50% duty cycle, gating during exhalation, and using displacement-based gating.
To analyze tumor position reproducibility of feedback-guided voluntary deep inspiration breath-hold (FGBH) gating for cone beam computed tomography (CBCT)-based stereotactic body radiotherapy (SBRT).
...Thirteen early-stage lung cancer patients eligible for SBRT with tumor motion of >1cm were evaluated for FGBH-gated treatment. Multiple FGBH CTs were acquired at simulation, and single FGBH CBCTs were also acquired prior to each treatment. Simulation CTs and treatment CBCTs were analyzed to quantify reproducibility of tumor positions during FGBH. Benefits of FGBH gating compared to treatment during free breathing, as well treatment with gating at exhalation, were examined for lung sparing, motion margins, and reproducibility of gross tumor volume (GTV) position relative to nonmoving anatomy.
FGBH increased total lung volumes by 1.5 times compared to free breathing, resulting in a proportional drop in total lung volume receiving 10 Gy or more. Intra- and inter-FGBH reproducibility of GTV centroid positions at simulation were 1.0 ± 0.5 mm, 1.3 ± 1.0 mm, and 0.6 ± 0.4 mm in the anterior-posterior (AP), superior-inferior (SI), and left-right lateral (LR) directions, respectively, compared to more than 1 cm of tumor motion at free breathing. During treatment, inter-FGBH reproducibility of the GTV centroid with respect to bony anatomy was 1.2 ± 0.7 mm, 1.5 ± 0.8 mm, and 1.0 ± 0.4 mm in the AP, SI, and LR directions. In addition, the quality of CBCTs was improved due to elimination of motion artifacts, making this technique attractive for poorly visualized tumors, even with small motion.
The extent of tumor motion at normal respiration does not influence the reproducibility of the tumor position under breath hold conditions. FGBH-gated SBRT with CBCT can improve the reproducibility of GTV centroids, reduce required margins, and minimize dose to normal tissues in the treatment of mobile tumors.
We prospectively compared computed tomography (CT)- and magnetic resonance imaging (MRI)-based high-risk clinical target volume (HR-CTV) contours at the time of brachytherapy for cervical cancer in ...an effort to identify patients who might benefit most from MRI-based planning.
Thirty-seven patients who had undergone a pretreatment diagnostic MRI scan were included in the analysis. We delineated the HR-CTV on the brachytherapy CT and brachytherapy MRI scans independently for each patient. We then calculated the absolute volumes for each HR-CTV and the Dice coefficient of similarity (DC, a measure of spatial agreement) for the HR-CTV contours. We identified the clinical and tumor factors associated with (1) a discrepancy in volume between the CT HR-CTV and MRI HR-CTV contours; and (2) DC. The mean values were compared using 1-way analysis of variance or paired or unpaired t tests, as appropriate. Simple and multivariable linear regression analyses were used to model the effects of covariates on the outcomes.
Patients with International Federation of Gynecology and Obstetrics stage IB to IVA cervical cancer were treated with intracavitary brachytherapy using tandem and ovoid (n=33) or tandem and cylinder (n=4) applicators. The mean CT HR-CTV volume (44.1 cm
) was larger than the mean MRI HR-CTV volume (35.1 cm
; P<.0001, paired t test). On multivariable analysis, a higher body mass index (BMI) and tumor size ≥5 cm with parametrial invasion on the MRI scan at diagnosis were associated with an increased discrepancy in volume between the HR-CTV contours (P<.02 for both). In addition, the spatial agreement (as measured by DC) between the HR-CTV contours decreased with an increasing BMI (P=.013).
We recommend MRI-based brachytherapy planning for patients with tumors >5 cm and parametrial invasion on MRI at diagnosis and for those with a high BMI.
Recent advances in integrating 1.5 Tesla magnetic resonance (MR) imaging with a linear accelerator (MR-Linac) allow MR-guided stereotactic body radiotherapy (SBRT) for prostate cancer. Choosing an ...optimal strategy for daily online plan adaptation is particularly important for MR-guided radiotherapy. We analyzed deformable dose accumulation on scans from four patients and found that daily anatomy changes had little impact on the delivered dose, with the dose to the prostate within 0.5% and dose to the rectum/bladder mostly less than 0.5 Gy. These findings could help in the choice of an optimal strategy for online plan adaptation for MR-guided prostate SBRT.
While current MR-Linac (MRL) treatment workflows utilize a large table overlay during CT simulation to convert indexing between the two machines, we developed a look-up-table (LUT) as an alternative ...approach. After populating the LUT, index conversion factors were verified at three separate table locations. The resultant root-mean-square isocenter shifts on the MRL were 0.04/0.08 cm, 0.08/0.07 cm, and 0.09/0.08 cm with/without using the table overlay during simulation in the lateral, longitudinal, and vertical directions, respectively, which is within registration tolerance. Clinical implementation of the LUT has resulted in a more efficient MRL treatment workflow while maintaining accurate patient setup.
To determine the optimal approach to delineating patient-specific internal gross target volumes (IGTV) from four-dimensional (4-D) computed tomography (CT) image data sets used in the planning of ...radiation treatment for lung cancers.
We analyzed 4D-CT image data sets of 27 consecutive patients with non-small-cell lung cancer (stage I: 17, stage III: 10). The IGTV, defined to be the envelope of respiratory motion of the gross tumor volume in each 4D-CT data set was delineated manually using four techniques: (1) combining the gross tumor volume (GTV) contours from ten respiratory phases (IGTVAllPhases); (2) combining the GTV contours from two extreme respiratory phases (0% and 50%) (IGTV2Phases); (3) defining the GTV contour using the maximum intensity projection (MIP) (IGTVMIP); and (4) defining the GTV contour using the MIP with modification based on visual verification of contours in individual respiratory phase (IGTVMIP-Modified). Using the IGTVAllPhases as the optimum IGTV, we compared volumes, matching indices, and extent of target missing using the IGTVs based on the other three approaches.
The IGTVMIP and IGTV2Phases were significantly smaller than the IGTVAllPhases (p < 0.006 for stage I and p < 0.002 for stage III). However, the values of the IGTVMIP-Modified were close to those determined from IGTVAllPhases (p = 0.08). IGTVMIP-Modified also matched the best with IGTVAllPhases.
IGTVMIP and IGTV2Phases underestimate IGTVs. IGTVMIP-Modified is recommended to improve IGTV delineation in lung cancer.
We integrated a brachytherapy procedural workflow within an existing diagnostic 3.0-T (3T) MRI suite. This setup facilitates intraoperative MRI guidance for optimal applicator positioning, ...particularly for interstitial needle placements in gynecologic cases with extensive parametrial involvement.
Here we summarize the multidisciplinary collaboration, equipment, and supplies necessary to implement an intraoperative MRI-guided brachytherapy program; outline the operational workflow via process maps; and address safety precautions. We evaluate internal resource utilization associated with this progressive approach via time-driven activity-based costing methodology, comparing institutional costs to that of a traditional workflow (within a CT suite, followed by separate postprocedure MRI) over a single brachytherapy procedural episode.
Resource utilization was only 15% higher for the intraoperative MRI-based workflow, attributable to use of the MRI suite and increased radiologist effort. Personnel expenses were the greatest cost drivers for either workflow, accounting for 76-77% of total resource utilization. However, use of the MRI suite allows for potential cost-shifting opportunities from other resources, such as CT, during the procedural episode. Improvements in process speed can also decrease costs: for each 10% decrease in case duration from baseline procedure time, total costs could decrease by roughly 8%.
This analysis supports the feasibility of an intraoperative MRI-guided brachytherapy program within a diagnostic MRI suite and defines many of the resources required for this procedural workflow. Longer followup will define the full utility of this approach in optimizing the therapeutic ratio for gynecologic cancers, which may translate into lower costs and higher value with time, over a full cycle of care.
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