Dual partial arc volumetric-modulated arc therapy: The game changer for accelerated hypofractionated whole-breast radiotherapy with simultaneous integrated tumor cavity boost in early breast cancer - A comparative dosimetric study with single partial arc volumetric-modulated arc therapy.

Introduction: In a previous study, we demonstrated clinical and dosimetric feasibility of single partial arc volumetric modulated arc therapy (VMAT) for accelerated hypofractionated whole breast radiotherapy with simultaneous integrated boost (SIB) to lumpectomy cavity for early breast cancer. In this dosimetric study, we compared dual partial arcs versus single arc.

Patients And Methods: Fifteen consecutive patients for treatment with hypofractionated accelerated radiotherapy with SIB using VMAT were planned with single partial arc in an earlier study, initial result of which is published elsewhere. The comparative dosimetric plan was created using two partial arcs. Skewness and kurtosis test, Paired Student's t-test, and Wilcoxon signed-rank test were applied for statistical analysis. P < 0.05 was considered statistically significant.

Results: Most planning targets are better achieved with dual arc technique. Coverage of planning target volume (PTV) whole breast (PTV and PTV lumpectomy cavity (PTV) was significantly improved with dual partial arc without significant difference in conformity index and homogeneity index. Dual arc improved dosimetric parameter significantly. Mean dose (D) and maximum dose (D) of whole breast PTV as well as D of PTV; ipsilateral and contralateral lung D, D, 5 Gy volume (V); contralateral lung D, D, V; Heart V and V; D of 5 mm thickness skin; D and D of ribs; and D and D of contralateral breast were improved with dual arc.

Conclusion: This is first of its kind study establishing the advantage of dual partial arcs in the current context. Dual partial arcs improved dosimetry over single partial arc. Significant dose reduction can be achieved for multiple crucial organs at risk.