Clinical implementation of a hybrid solitary dynamic portal radiotherapy for left-sided post-mastectomy chest-wall and regional nodal irradiation using Monaco TPS.

Background: A hybrid solitary dynamic portal radiotherapy (h-SDPRT) technique for complex chest-wall and regional nodal irradiation was clinically implemented on the Monaco treatment planning system (TPS) by effectively adapting the Eclipse-based h-SDPRT method with minimal amendments to align with Monaco-specific technical constraints while maintaining consistent and reproducible dosimetric outcomes. Materials and methods: This technique was evaluated on ten left-sided post-mastectomy radiotherapy (PMRT) patients, delivering 80-85% of the prescribed dose through asymmetric static open field apertures with the Elekta Agility multileaf collimator (MLC), and the remaining 15-20% via a unidirectional solitary dynamic field with differential blocks, composed of 10-15 MLC control points (4-5% of the dose per segment). Results: The h-SDPRT plans demonstrated excellent dose coverage to the chest-wall target (D99 ≥ 96.3 ± 0.2%) and regional nodes (D99 ≥ 96.4 ± 0.8%), optimal conformity (1.5 ± 0.1), and superior homogeneity (0.104 ± 0.01), while effectively sparing critical organs-at-risk (OAR) viz., ipsilateral lung (V20 ≤ 26.7 ± 2.0% and Dmean: 14.3 ± 5.7 Gy) and heart (V25 ≤ 6.4 ± 3.8% and Dmean: 6.1 ± 1.6 Gy), with complete sparing of contralateral lung (V5 ≤ 0.1 ± 0.2% and Dmean: 1.3 ± 0.3 Gy) and breast (V5 ≤ 1.5 ± 1.0% and Dmean: 1.6 ± 0.2 Gy). Gamma evaluation (γ) showed > 95% pixels passing the standard 3% dose difference and 3 mm distance-to-agreement γ criteria, with results closely aligning with Eclipse TPS data. Conclusions: The h-SDPRT technique minimizes the risk of "geometrical miss" and reduces delivery uncertainties associated with irregular or thin chest-wall with comprehensive nodal irradiation. By combining dominant static portals with simplified unidirectional dynamic field sequencing strategy, this approach provides a feasible and effective solution for PMRT.