Deep inspiration breath-hold radiation therapy in left-sided breast cancer patients: a single-institution retrospective dosimetric analysis of organs at risk doses.

BACKGROUND: Radiotherapy can induce cardiac injury in left-sided breast cancer cases. Cardiac-sparing irradiation using the deep inspiration breath-hold (DIBH) technique can achieve substantial dose reduction to vulnerable cardiac substructures compared with free breathing (FB). This study evaluated the dosimetric differences between both techniques at a single institution. METHODS: From 2017 to 2019, 130 patients with left-sided breast cancer underwent breast-conserving surgery (BCS; n = 121, 93.1%) or mastectomy (ME; n = 9, 6.9%) along with axillary lymph node staging (n = 105, 80.8%), followed by adjuvant irradiation in DIBH technique; adjuvant systemic therapy was included if applicable. 106 (81.5%) patients received conventional and 24 (18.5%) hypofractionated irradiation. Additionally, 12 patients received regional nodal irradiation. Computed tomography (CT) scans in FB and DIBH position were performed for all patients. Intrafractional 3D position monitoring of the patient surface in deep inspiration and breath gating was performed using Sentinel and Catalyst HD 3D surface scanning systems (C-RAD, Catalyst, C­RAD AB, Uppsala, Sweden). Individual coaching and determination of breathing amplitude during the radiation planning CT was performed. Three-dimensional treatment planning was performed using standard tangential treatment portals (6 or 18 MV). The delineation of cardiac structures and both lungs was done in both the FB and the DIBH scan. RESULTS: All dosimetric parameters for cardiac structures were significantly reduced (p < 0.01 for all). The mean heart dose (Dmean) in the DIBH group was 1.3 Gy (range 0.5-3.6) vs. 2.2 Gy (range 0.9-8.8) in the FB group (p < 0.001). The Dmean for the left ventricle (LV) in DIBH was 1.5 Gy (range 0.6-4.5), as compared to 2.8 Gy (1.1-9.5) with FB (p < 0.001). The parameters for LV (V10 Gy, V15 Gy, V20 Gy, V23 Gy, V25 Gy, V30 Gy) were reduced by about 100% (p < 0.001). The LAD Dmean in the DIBH group was 4.1 Gy (range 1.2-33.3) and 14.3 Gy (range 2.4-37.5) in the FB group (p < 0.001). The median values for LAD such as V15 Gy, V20 Gy, V25 Gy, V30 Gy, and V40 Gy decreased by roughly 100% (p < 0.001). An increasing volume of left lung in the DIBH position resulted in dose sparing of cardiac structures. CONCLUSION: For all ascertained dosimetric parameters, a significant dose reduction could be achieved in DIBH technique.

Incidental irradiation of the regional lymph nodes during deep inspiration breath-hold radiation therapy in left-sided breast cancer patients: a dosimetric analysis.

BACKGROUND: Radiotherapy using the deep inspiration breath-hold (DIBH) technique compared with free breathing (FB) can achieve substantial reduction of heart and lung doses in left-sided breast cancer cases. The anatomical organ movement in deep inspiration also cause unintended exposure of locoregional lymph nodes to the irradiation field. METHODS: From 2017-2020, 148 patients with left-sided breast cancer underwent breast conserving surgery (BCS) or mastectomy (ME) with axillary lymph node staging, followed by adjuvant irradiation in DIBH technique. Neoadjuvant or adjuvant systemic therapy was administered depending on hormone receptor and HER2-status. CT scans in FB and DIBH position with individual coaching and determination of the breathing amplitude during the radiation planning CT were performed for all patients. Intrafractional 3D position monitoring of the patient surface in deep inspiration and gating was performed using Sentinel and Catalyst HD 3D surface scanning systems (C-RAD, Catalyst, C-RAD AB, Uppsala, Sweden). Three-dimensional treatment planning was performed using standard tangential treatment portals (6 or 18 MV). The delineation of ipsilateral locoregional lymph nodes was done on the FB and the DIBH CT-scan according to the RTOG recommendations. RESULTS: The mean doses (Dmean) in axillary lymph node (AL) level I, II and III in DIBH were 32.28 Gy (range 2.87-51.7), 20.1 Gy (range 0.44-53.84) and 3.84 Gy (range 0.25-39.23) vs. 34.93 Gy (range 10.52-50.40), 16.40 Gy (range 0.38-52.40) and 3.06 Gy (range 0.21-40.48) in FB (p < 0.0001). Accordingly, in DIBH the Dmean for AL level I were reduced by 7.59%, whereas for AL level II and III increased by 22.56% and 25.49%, respectively. The Dmean for the supraclavicular lymph nodes (SC) in DIBH was 0.82 Gy (range 0.23-4.11), as compared to 0.84 Gy (range 0.22-10.80) with FB (p = 0.002). This results in a mean dose reduction of 2.38% in DIBH. The Dmean for internal mammary lymph nodes (IM) was 12.77 Gy (range 1.45-39.09) in DIBH vs. 11.17 Gy (range 1.34-44.24) in FB (p = 0.005). This yields a mean dose increase of 14.32% in DIBH. CONCLUSIONS: The DIBH technique may result in changes in the incidental dose exposure of regional lymph node areas.

Dense feature-based motion estimation in MV fluoroscopy during dynamic tumor tracking treatment: preliminary study on reduced aperture and partial occlusion handling.

Quality assurance solutions to complement available motion compensation technologies are central for their safe routine implementation and success of treatment. This work presents a dense feature-based method for soft-tissue tumor motion estimation in megavoltage (MV) beam's-eye-view (BEV) projections for potential intra-treatment monitoring during dynamic tumor tracking (DTT). Dense sampling and matching principles were employed to track a gridded set of features landmarks (FLs) in MV-BEV projections and estimate tumor motion, capable to overcome reduced field aperture and partial occlusion challenges. The algorithm's performance was evaluated by retrospectively applying it to fluoroscopic sequences acquired at ∼2 frames s-1 (fps) for a dynamic phantom and two lung stereotactic body radiation therapy (SBRT) patients treated with DTT on the Vero SBRT system. First, a field-specific train image is initialized by sampling the tumor region at, S, pixel intervals on a grid using a representative frame from a stream of query frames. Sampled FLs are locally characterized in the form of descriptor vectors and geometric attributes representing the target. For motion tracking, subsequent query frames are likewise sampled, corresponding feature descriptors determined, and then patch-wise matched to the training set based on their descriptors and geometric relationships. FLs with high correspondence are pruned and used to estimate tumor displacement. In scenarios of partial occlusions, position is estimated from the set of correctly (visible) FLs on past observations. Reconstructed trajectories were benchmarked against ground-truth manual tracking using the root-mean-square (RMS) as a metric of positional accuracy. A total of 19 fluoroscopy sequences were analyzed. This included scenarios of field aperture obstruction during three-dimensional conformal, as well as step-and-shoot intensity modulated radiotherapy (IMRT) delivery assisted with DTT. The algorithm resolved target motion satisfactorily. The RMS was <1.2 mm and <1.8 mm for the phantom and the clinical dataset, respectively. Dense tracking showed promising results to overcome localization challenges at the field penumbra and partial obstruction by multi-leaf collimator (MLC). Motion retrieval was possible in ∼66% of the control points studied. In addition to MLC obstruction, changes in the external/internal breathing dynamics and baseline drifts were a major source of estimation bias. Dense feature-based tracking is a viable alternative. The algorithm is rotation-/scale-invariant and robust to photometric changes. Tracking multiple features may help overcome partial occlusion challenges by the MLC. This in turn opens up new possibilities for motion detection and intra-treatment monitoring during IMRT and potentially VMAT.

Suitability of markerless EPID tracking for tumor position verification in gated radiotherapy.

PURPOSE: To maximize the benefits of respiratory gated radiotherapy (RGRT) of lung tumors real-time verification of the tumor position is required. This work investigates the feasibility of markerless tracking of lung tumors during beam-on time in electronic portal imaging device (EPID) images of the MV therapeutic beam. METHODS: EPID movies were acquired at ∼2 fps for seven lung cancer patients with tumor peak-to-peak motion ranges between 7.8 and 17.9 mm (mean: 13.7 mm) undergoing stereotactic body radiotherapy. The external breathing motion of the abdomen was synchronously measured. Both datasets were retrospectively analyzed in PortalTrack, an in-house developed tracking software. The authors define a three-step procedure to run the simulations: (1) gating window definition, (2) gated-beam delivery simulation, and (3) tumor tracking. First, an amplitude threshold level was set on the external signal, defining the onset of beam-on/-off signals. This information was then mapped onto a sequence of EPID images to generate stamps of beam-on/-hold periods throughout the EPID movies in PortalTrack, by obscuring the frames corresponding to beam-off times. Last, tumor motion in the superior-inferior direction was determined on portal images by the tracking algorithm during beam-on time. The residual motion inside the gating window as well as target coverage (TC) and the marginal target displacement (MTD) were used as measures to quantify tumor position variability. RESULTS: Tumor position monitoring and estimation from beam's-eye-view images during RGRT was possible in 67% of the analyzed beams. For a reference gating window of 5 mm, deviations ranging from 2% to 86% (35% on average) were recorded between the reference and measured residual motion. TC (range: 62%-93%; mean: 77%) losses were correlated with false positives incidence rates resulting mostly from intra-/inter-beam baseline drifts, as well as sudden cycle-to-cycle fluctuations in exhale positions. Both phenomena can lead to considerable deviations (with MTD values up to a maximum of 7.8 mm) from the intended tumor position, and in turn may result in a marginal miss. The difference between tumor traces determined within the gating window against ground truth trajectory maps was 1.1 ± 0.7 mm on average (range: 0.4-2.3 mm). CONCLUSIONS: In this retrospective analysis of motion data, it is demonstrated that the system is capable of determining tumor positions in the plane perpendicular to the beam direction without the aid of fiducial markers, and may hence be suitable as an online verification tool in RGRT. It may be possible to use the tracking information to enable on-the-fly corrections to intra-/inter-beam variations by adapting the gating window by means of a robotic couch.