Automatic base-dose planning for a robust field junction in total marrow irradiation

Purpose: Total marrow (lymph-node) irradiation (TMI/TMLI) is a radiotherapy technique irradiating the whole body of a patient. The limited couch travel range in modern linacs (130–150 cm) forces to split the TMI/TMLI delivery into two plans with opposite orientation. A dedicated field junction is necessary to achieve satisfactory target coverage in the overlapping region of the two plans. In a recent study, we implemented an automatic tool (AT) using the Eclipse Scripting API for the creation of a field junction and optimization of TMI/TMLI. In this work, we improved the AT by developing an automatic base-dose planning approach. Methods: Ten patients were selected to compare the manual procedure, original automatic planning approach, and new base-dose approach. Treatment plans were evaluated with the D98%, Dmean, and D2% for the planning target volume at the junction (PTV_J), while Dmean and D2% were considered for the PTV without the junction (PTVNoJ) and healthy tissues. Results: Base-dose planning significantly improved the PTV_J coverage compared with the manual approach, with unaltered Dmean, consistently lower D2% (2.24 Gy vs. 2.30 Gy) and higher D98% (1.98 Gy vs. 1.89 Gy). Moreover, it significantly reduced the hotspots in healthy tissues (2.02 Gy vs. 2.15 Gy). No significant differences for PTVNoJ dose statistics were observed among the procedures, demonstrating that the automatic approaches produced a target coverage similar to the one obtained manually. Conclusions: Base-dose planning improved the field junction optimization of TMI/TMLI. Automatic planning tools can incrementally improve procedures that would be challenging or error-prone to achieve manually.