ESTRO 2024 - Abstract Book

S641

Clinical - Breast

ESTRO 2024

heart substructures and PTVs between free breathing (FB) and DIBH using two different plans, one in 3DCRT and other in H-VMAT for both breathing techniques.

Material/Methods:

37 left breast cancer patients were included. Six heart substructures were delineated following the guidelines (1): whole heart, left ventricle, left main coronary artery (LMCA), left anterior descending coronary artery (LADCA), circumflex coronary artery (Cx) and right coronary artery (RCA). For each patient, four dosimetric plans were generated: two using 3DCRT field-in-field plans, and the other two combining 3DCRT with two half-arcs (H-VMAT) for each breathing technique. The heart substructures were evaluated using the following dosimetric parameters: Dmean, V25Gy(%), and V30Gy(cm 3 ) of the whole heart; Dmean and V5Gy(%) of the left ventricle, LMCA, LADCA, Cx and RCA. For PTVs were obtained D98%, D2%, D50% and V95% or V90% depending on the PTV. Data were summarized as median (percentile 25, percentile 75). A Friedman Test with Benjamini Hochberg adjustment was used to determine the significance difference of four techniques with Bonferroni correction to adjust for multiple comparisons. A p-value less than 0.05 was considered statistically significant and multiple comparisons tests were considered one sided.

Results:

Friedman Test showed significance differences between all four techniques for the dosimetric parameters studied except RCA V5Gy(%) and D50%(%) PTV2.

For all but one heart substructures, 3DCRT in DIBH showed statistically significant lower doses than from H-VMAT DIBH and FB, according to a previous study (2). In terms of PTVs, when H-VMAT was used, D98% is increased and D2% is decreased than the use of 3DCRT in both breathing techniques.

Conclusion:

As compared to other techniques, 3DCRT in DIBH provides the lower heart substructure dosimetric parameters for all six heart substructures except for Cx and V25Gy whole heart.

Keywords: DIBH, Heart substructures, Hybrid VMAT

References:

(1) Duane et al,. A cardiac contouring atlas for radiotherapy. Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology vol. 122,3: 416-422. doi:10.1016/j.radonc.2017.01.008

(2) Vikström et al,. A comparison of conventional and dynamic radiotherapy planning techniques for early-stage breast cancer utilizing deep inspiration breath-hold. Acta oncologica. vol. 57,10 : 1325-1330. doi:10.1080/0284186X.2018.1497294