## 2 Materials and Methods
The first three plans were head and neck, mediastinum, and thorax cases. For each plan, eight replanning strategies were considered, acting on different TPS parameters:  
1. Manual re-optimization (MRO): performed by an expert planner who had the flexibility to modify the plan's parameters (e.g., jaw apertures, isocenter position) and to adjust weights and constraints during the optimization. 2. Optimization restart (NoChanges): restarting the optimization process from scratch without any changes during the optimization. 3. MU limitation (MUlimit): capping the maximum value of MUs to 70% of the original plan's value. 4. Aperture Shape Controller (ASC) levels--a specific tool of Eclipse to limit plan complexity: utilizing the five available ASC levels, i.e., very low (ASC_VL), low (ASC_L), medium (ASC_M), high (ASC_H), and very high (ASC_VH). Except for the MRO strategy, which served as a control sample, all plans were optimized with unaltered constraints and no changes during the optimization to enable automatic execution without human intervention. MU limits were imposed based on previous works showing an improved plan deliverability without compromising the overall clinical plan quality [16; 17]. On the other hand, preliminary studies have shown that similar results can be achieved using the ASC [18; 19]. ASC was recently introduced in the Eclipse TPS for the PO algorithm to favor apertures of minimal local curvature. The ASC strength is controlled by the user via a calculation option that can be set to five different values, ranging from very low to very high. An increasing strength applies a larger penalization weight to the total cost function of PO. As a result, the occurrence of disconnected apertures reduces, effectively limiting the complexity of MLC movement and modulation. \begin{table}
\begin{tabular}{c c c c c} \hline
**Treatment** & **Number of Cases** & **Prescription** & \multicolumn{2}{c}{**Clinical Constraints**} \\ \hline \multirow{8}{*}{Thorax} & \multirow{8}{*}{1} & \multirow{8}{*}{30 Gy/15 fr} & Esophagus & Spinal cord \\  & & & \(\bullet\) & Dmean \textless{} 27 Gy & \(\bullet\) & Dmax \textless{} 40 Gy \\  & & & \(\bullet\) & D0.1 cc \textless{} 54 Gy & \(\bullet\) & D0.1 cc \textless{} 40 Gy \\  & & & \(\bullet\) & V42 Gy \textless{} 32\% & \(\bullet\) & D5 cc \textless{} 39 Gy \\  & & & \(\bullet\) & D5 cc \textless{} 45 Gy & Heart \\  & & & \(\bullet\) & Dmax \textless{} 54 Gy & \(\bullet\) & D15 cc \textless{} 42 Gy \\  & & & & \(\bullet\) & D0.1 cc \textless{} 48.9 Gy \\  & & & & \(\bullet\) & Dmax \textless{} 48.9 Gy \\  & & & & \(\bullet\) & Dmean \textless{} 29 Gy \\ \hline \multirow{8}{*}{Prostate} & \multirow{8}{*}{3} & \multirow{8}{*}{67.5 Gy/25 fr} & Small bowel & \multirow{2}{*}{Rectum} \\  & & & \(\bullet\) & V36 Gy \textless{} 195 cc & \(\bullet\) & D1 cc \textless{} 68 Gy \\  & & & \(\bullet\) & Femoral heads & \(\bullet\) & Dmax \textless{} 68 Gy \\  & & & \(\bullet\) & V40 Gy \textless{} 10\% & \(\bullet\) & V50 Gy \textless{} 30\% \\  & & & & \(\bullet\) & V40 Gy \textless{} 50\% \\  & & & & Bladder & \\  & & & & \(\bullet\) & V50 Gy \textless{} 50\% \\  & & & & \(\bullet\) & Dmean \textless{} 40 Gy \\ \hline \end{tabular} Abbreviations: CTV = clinical target volume, PTV = planning target volume.  
\end{table} 
Table 1: _Cont._The modulation complexity score (MCS) was selected to characterize the complexity of the VMAT arcs [20]. MCS combines information on the variability in leaf positions, irregularity in field shape, segment weight, and area, into a single score ranging from 0 (high complexity) to 1 (open rectangular field, no complexity). For each plan, PSQA was measured using the EPID attached to the machines' gantry and the analyses were performed with Portal Dosimetry software v15.6 (Varian Medical Systems, Palo Alto, CA, USA). At the start of each QA session, the EPID was re-calibrated. Then, the gamma analysis of the images obtained from the PSQA was executed automatically for each arc.