Interfractional variation in whole-breast VMAT irradiation: a dosimetric study with complementary SGRT and CBCT patient setup.

BACKGROUND: The dosimetric effect of setup uncertainty and tissue deformations in left-sided whole-breast irradiation with complementary surface-guided radiotherapy (SGRT) and cone-beam computed tomography (CBCT) setup was evaluated. METHOD: Treatment courses of 40.05 Gy prescribed dose in 15 fractions were simulated for 29 patients by calculating the dose on deformed CT images, that were based on daily CBCT images, and deforming and accumulating the dose onto the planning CT image. Variability in clinical target volume (CTV) position and shape was assessed as the 95% Hausdorff distance (HD95) between the planning CTV and deformed CTV structures. DVH metrics were evaluated between the planned and simulated cumulative dose distributions using two treatment techniques: tangential volumetric modulated arc therapy (tVMAT) and conventional 3D-conformal radiotherapy (3D-CRT). RESULTS: Based on the HD95 values, the variations in CTV shape and position were enclosed by the 5 mm CTV-PTV margin in 85% of treatment fractions using complementary CBCT and SGRT setup. A residual error of 8.6 mm was observed between the initial SGRT setup and CBCT setup. The median CTV V95% coverage was 98.1% (range 93.1-99.8%) with tVMAT and 98.2% (range 84.5-99.7%) with 3D-CRT techniques with CBCT setup. With the initial SGRT-only setup, the corresponding coverages were 96.3% (range 92.6-99.4%) and 96.6% (range 84.2-99.4%), respectively. However, a considerable bias in vertical residual error between initial SGRT setup and CBCT setup was observed. Clinically relevant changes between the planned and cumulative doses to organs-at-risk (OARs) were not observed. CONCLUSIONS: The CTV-to-PTV margin should not be reduced below 5 mm even with daily CBCT setup. Both tVMAT and 3D-CRT techniques were robust in terms of dose coverage to the target and OARs. Based on the shifts between setup methods, CBCT setup is recommended as a complementary method with SGRT.

Breast deformation during the course of radiotherapy: The need for an additional outer margin.

PURPOSE: The aim of this retrospective study was to investigate and quantify the extent of breast deformation during the course of breast cancer (BC) radiotherapy (RT). The magnitude of breast deformation determines the additional outer margin needed for treatment planning to deliver a full dose to the target volume. This is especially important when using inverse planning techniques. METHODS: A total of 93 BC patients treated with RT and with daily CBCT image guidance were selected for this study. Patients underwent either only breast-conserving surgery (BCS) (n = 5), BCS with sentinel node biopsy (n = 57) or BCS with radical axillary node dissection (n = 31). The treatment area included the whole breast and chest wall (54%) or also the axillary lymph nodes (46%). 3D-registration was conducted between 1731 CBCT images and the respective planning CT images to assess the difference in breast surface. RESULTS: The largest maximum breast surface expansion (MBSE) was 15 mm; the average was 2.4 ±â€¯2.1 mm. In 294 fractions (17%), the MBSE was ≥5 mm. An outer margin of 8 mm would have been required to cover the whole breast in 95% of the treated fractions. There was a statistically significant correlation between the MBSE and body mass index (r = 0.38, p = 0.001). CONCLUSIONS: Significant changes in the breast surface occur during the course of BC RT which should be considered in treatment planning. An additional margin outside the breast surface of at least 8 mm is required to take into account the anatomical changes occurring during BC RT.

Bioimpedance-based measurement method for simultaneous acquisition of respiratory and cardiac gating signals.

Respiratory and cardiac motion artefacts impair the quality and reliability of medical imaging, particularly in nuclear medicine. At worst, the interpretation of distorted images may lead to inadequate or unnecessary treatment. Image artefacts can be minimized by gating the image acquisition according to respiratory phase and cardiac contractions. However, currently there are no clinically established dual-gating methods in nuclear medicine imaging. The aim of this study is to validate a previously determined optimized bioimpedance measurement configuration against traditional respiratory and cardiac measurement systems in 12 volunteers. High agreement and excellent correlations (r = 0.944-0.999) were found between respiratory peak-to-peak amplitudes as well as temporal respiratory and cardiac intervals. Above all, good quality respiratory and cardiac gating signals were obtained from all test subjects with a fairly regular sinus rhythm. Importantly, both signals were acquired simultaneously with a single device. Due to the simplicity of this inexpensive method, the technique has high potential to be adopted for dual-gating in clinical practice in the future.