Dosimetric Comparison of Different Planning Techniques in Left-sided Whole-Breast Irradiation: A Planning Study

A generalized model of cardiac surface motion for evaluating left anterior descending coronary artery dose in left breast cancer radiotherapy

BACKGROUND

Retrospective studies indicate that radiation damage to left anterior descending coronary artery (LAD) may be critical for late-stage radiation-induced cardiac morbidity. Developing a method that accurately depicts LAD motion and perform dose assessment is crucial.

PURPOSE

To construct a generalized cardiac surface motion model for LAD dose assessment in left breast cancer radiotherapy.

METHODS

Cine MRI of 25 cases were divided into training and testing sets for model construction, and five external cases were gathered for generalization validation. Motion prediction from average intensity projection images (AIP) surface point cloud to that of each phase was realized by mapping the relationship between datum points and corresponding points with statistical shape modeling (SSM). Root mean square error (RMSE) for predicted corresponding points and Euclidean distance (ED) for predicted surface point cloud were used to assess model's accuracy. LAD dose assessment for 10 left breast cancer radiotherapy cases was perform by model application.

RESULTS

The RMSE in testing cases and external cases were 0.209 ± 0.020 mm to 0.841 ± 0.074 mm and 0.895 ± 0.093 mm to 1.912 ± 0.138 mm, respectively; while the ED were 1.399 ± 0.029 mm to 1.658 ± 0.100 mm, 1.571 ± 0.080 mm to 1.779 ± 0.104 mm, respectively, proving the generalized model's high accuracy. The volume of LAD characterizing motion range (WPLAD) (2.392 ± 0.639 cm3) was approximately twice that of LAD from superimposed images (SPLAD) (0.927 ± 0.326 cm3) with p < 0.05, and the former's Dmax (3582.06 ± 575.92 cGy) was significantly larger than latter's (3222.71 ± 665.37 cGy) (p < 0.05). While WPLAD's Dmean (1408.06 ± 413.06 cGy) was slightly smaller than that of SPLAD (1504.15 ± 448.03 cGy), the difference did not reach statistical significance (p > 0.05). WPLAD's V20 (23.42% ± 16.62%) was less than SPLAD's (29.18% ± 21.07%) with p < 0.05, but their comparison in V30 and V40 did not yield statistically significant results. It implies the conventional LAD dose assessment ignores motion impact and may not be justified.

CONCLUSIONS

The generalized cardiac surface motion model informs LAD dose accurate assessment in left breast cancer radiotherapy.

Off-isocentric VMAT technique for breast cancer: Effective dose reduction to organs at risk and its applicability based on patient anatomy

PURPOSE

This study aims to explore the off-isocentric volumetric modulated arc therapy (offVMAT) technique for breast cancer and determine its applicability based on patient anatomical parameters.

METHODS

We retrospectively analyzed 44 breast cancer patients with varied lymph node involvement using different arc designs. Off-isocentric techniques were benchmarked against previously published arc techniques: classic arcs (clVMAT), tangential arcs (tVMAT), and split arcs (spVMAT). During optimization, target coverage was made for all plans as close as possible to the criteria D99% > 95% and Dmax < 110% of the prescribed dose. A novel patient categorization, based on anatomical parameters (auxiliary structures) rather than lymph node involvement, is introduced. This categorization considers the volume of ipsilateral organs at risk (OARs) adjacent to the target. A binary regression model was developed on these anatomical parameters. It predicts the likelihood of offVMAT (P[offVMAT]) achieving better criteria.

RESULTS

Using the regression model, patients were divided into two groups: P(offVMAT) > 0.5 and P(offVMAT) < 0.5. For the P(offVMAT) > 0.5 group, most tVMAT plans are unable to achieve the clinical objectives. Comparing offVMAT with spVMAT, offVMAT exhibited better dose parameters for the heart (V20, V10, and D2 are 7.1, 2.4, and 1.5 times lower respectively), ipsilateral lung (V20, V10, V5 and the mean dose are 1.4, 1.3, 1.2, and 1.2 times lower respectively). The average doses to the contralateral side are consistent. In the P(offVMAT) < 0.5 group, the tVMAT technique showed increased doses at medium and high levels, yet reduced doses in contralateral OARs compared to spVMAT and offVMAT. spVMAT showed lower doses in the contralateral lung relative to the offVMAT technique, while clVMAT trailed in both groups. Validation of the model yielded a 90% accuracy rate.

CONCLUSIONS

The new off-isocentric breast planning technique effectively reduces doses to ipsilateral OARs, maintaining acceptable contralateral mean doses. This technique has an advantage over other techniques for patients with intricate anatomies. It is evaluated using anatomical parameters, which are also used to build binary regression model, which shows the dependence of anatomical parameters on whether offVMAT is preferred for individual patients. Also, such anatomical parameters provide a more objective and precise comparison between different planning techniques.

Retrospective Analysis for Dose Reduction to Organs at Risk with New Personalized Breast Holder (PERSBRA) in Left Breast IMRT

This study evaluated dose differences in normal organs at risk, such as the lungs, heart, left anterior descending artery (LAD), right coronary artery, left ventricle, and right breast under personalized breast holder (PERSBRA), when using intensity-modulated radiation therapy (IMRT). This study evaluated the radiation protection offered by PERSBRA in left breast cancer radiation therapy. Here, we retrospectively collected data from 24 patients with left breast cancer who underwent breast-conserving surgery as well as IMRT radiotherapy. We compared the dose differences in target coverage and organs at risk with and without PERSBRA. For target coverage, tumor prescribed dose 95% coverage, conformity index, and homogeneity index were evaluated. For organs at risk, we compared the mean heart dose, mean left ventricle dose, LAD maximum and mean dose, mean left lung receiving 20 Gy, 10 Gy, and 5 Gy of left lung volume, maximum and mean coronary artery of the right, maximum of right breast, and mean dose. Good target coverage was achieved with and without PERSBRA. When PERSBRA was used with IMRT, the mean dose of the heart decreased by 42%, the maximum dose of LAD decreased by 26.4%, and the mean dose of LAD decreased by 47.0%. The mean dose of the left ventricle decreased by 54.1%, the volume (V₂₀) of the left lung that received 20 Gy decreased by 22.8%, the volume (V₁₀) of the left lung that received 10 Gy decreased by 19.8%, the volume (V₅) of the left lung that received 5 Gy decreased by 15.7%, and the mean dose of the left lung decreased by 23.3%. Using PERSBRA with IMRT greatly decreases the dose to organs at risk (left lung, heart, left ventricle, and LAD). This study found that PERSBRA with IMRT can achieve results similar to deep inspiration breath-hold radiotherapy (DIBH) in terms of reducing the heart radiation dose and the risk of developing heart disease in patients with left breast cancer who cannot undergo DIBH.