## 3 Results
### Plan Complexity and Total MUs  
The total MUs necessary to deliver the plans had a median [range] of 927.4 MU [704.4-993.2].  
All the calculated and delivered plans were highly complex, with a median (range) MCS of 0.158 [0.127-0.204]. HNCa plans were more complex than PCa plans. In addition, the MUs increased if the MCS value decreased (and thus the plan complexity increased): this behavior is shown in Figure 2, while the AAV and the LSV component have the same descending trend for both clinical cases when MUs are increasing.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Site**} & \multirow{2}{*}{**OAR**} & \multirow{2}{*}{**Constraint**} & \multicolumn{2}{c}{**Median [Min; Max]**} \\ \cline{3-5}  & & & **Deliverable** & **Not Deliverable** \\ \hline PCa & Bladder & V65 Gy \(\leq\) 15\% & 16.8\% [15.9; 17.2] & 16.9\% [12.8; 20.7] \\  & & V40 Gy \(\times\) 40\% & 32.3\% [30.2; 33.5] & 32.5\% [26.7; 37.9] \\  & & Rectum & V65 Gy \(\leq\) 5\% & 4.6\% [3.9; 5] & 4.7\% [2.8; 11.9] \\  & & D\({}_{\text{max}}\)\(\leq\) 68 Gy & 0 Gy [0; 0.2] & 0 Gy [0; 9.1] \\  & & V40 Gy \(\leq\) 20\% & 26.3\% [19.1; 30.5] & 28.2\% [17.3; 50.5] \\ \hline HNCa & Brainsteam & D0.03 cc \(<\) 52 Gy & 49.1 Gy [48.6; 49.9] & 49.4 Gy [47.6; 52.6] \\  & Right Inner Ear & D0.03 cc \(<\) 35 Gy & 27.4 Gy [26.8; 28] & 27.8 Gy [26.7; 30.4] \\  & Left Inner Ear & D0.03 cc \(<\) 37 Gy & 29 Gy [16.7; 29.8] & 29.5 Gy [16.2; 30.6] \\  & Lips & V30 Gy \(<\) 20\% & 7.3\% [45.8] & 7.6\% [49.3; 38.5] \\  & Right Parotid & Mean \(<\) 24 Gy & 23.8 Gy [23.2; 33.9] & 24.1 Gy [23.1; 37.8] \\  & Larynx & Mean \(<\) 45 Gy & 21.6 Gy [21.4; 21.8] & 21.8 Gy [21.5; 30.4] \\  & Spinal Cord & D0.03 cc \(<\) 48 Gy & 45.5 Gy [44.8; 46.1] & 45.6 Gy [44.1; 56.7] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Summary of dose–volume constraints for HNCa and PCa plans.  
As a result, the CLM was found to be particularly effective for delivery accuracy. As reported in Figure 3, the \(\gamma\)-passing rate decreases, while the CLM increases with the minimum value achieved when no limit is applied. The best plan is obtained when the CLM is set to 0.8 cm/deg with \(\gamma\) equal to 95.6%, corresponding to the less complex (with MCS equal to 0.17), clinically acceptable (i.e., all the required constraints are achieved) plan. For what concerns the MSA, increasing values resulted in a slight increase of the \(\gamma\)-passing rate (with a maximum percentage difference of 2%) at the cost of deterioration of the plan modulation: for MSA equal to 30 cm\({}^{2}\), the constraints on the maximum dosage on the rectum and the rectum volume receiving 40 Gy were not met.  
To identify the most relevant variables affecting the dose distribution, the DVHs were extracted and analyzed and grouped by the modified parameter; the most influencing are reported and discussed below.  
Regarding CLM, a value from 0.48 to 0.8 cm/deg is optimal for generating acceptable plans regarding OAR sparing, target coverage, and higher \(\gamma\)-passing rates in PCa and HNCa plans.  
In Evolution 16.4.x/18.0.1, CLM is stricter during optimization, tightly linking gantry rotation speed and MLC motion. A typical CLM value (\(\sim\)0.5) often slows MLC speeds for  
Figure 3: CLM influence of \(\gamma\)-passing rates for HNCa (red dot) and PCa plans (blue dot).  
Figure 2: **(a)** MCS, **(b)** AAV, and **(c)** LSV parameters of calculated HNCa (red dot) and PCa plans (blue dot) versus the calculated monitor units (MUs).  
complex plans, reducing modulation and plan quality. For less complex plans, variable dose rates compensate for slower MLC speeds [29].  
In addition, the estimated MSA resulted in a good compromise between plan modulation (sufficient to reach the constraints) and total calculated MUs.