## 3 Results  
All patients underwent contact interventional radiotherapy treatment using the Freiburg applicator (Elekta) with a median number of 10 plastic catheters (range 4-27). The CTV volumes ranged from 1 to 142.2 cc, with a mean of 24.6 cc. Patients 1-8 belonged to group A, patients 9-16 to group B, and patients 17-25 to group C.  
The comparison of the three techniques showed that the coverage of the CTV for the IRT plan is higher compared to the other techniques. Of the 25 patients included in the study, 2 (specifically, 1 from group A and 1 from group C) could not have an electron beam therapy plan created because it was not feasible due to the extensive size of the clinical target volume (CTV). In particular, patient 18 had a CTV volume of 142.2 cc, and patient 5 had a CTV volume of 75.1 cc, making electron therapy impractical for these cases. Figure 1 shows the 95% dose coverage of the CTV for the IRT and VMAT treatment plans for these two patients. Analysis of the D\({}_{\text{mean}}\)CTV reveals that IRT plans deliver a statistically significant higher mean dose to the CTV compared to VMAT and electron plans. The corresponding \(p\)-values are as follows: group A (* \(p\) = 0.001), group B (* \(p\) = 0.0004, ** \(p\) = 0.0002), and group C (* \(p\) = 0.0002). Figure 2 presents the mean dose results to the CTV across the three prescription groups, highlighting that the mean dose achieved with IRT is significantly greater than with both the VMAT and electron techniques. Figure 1: A 95% dose coverage of the CTV for the IRT and VMAT plans for two patients where the electron plan was not feasible due to the extensive CTV volume. Figure 3 illustrates the V95%CTV values for all patients and treatment plans. The figure indicates that both IRT and VMAT provide high, comparable CTV coverage, while the electron plans result in significantly lower coverage. On average, the V95%CTV was 97.89% for IRT, 98.44% for VMAT, and 89.65% for electron plans, with 14 out of 23 electron plans achieving less than 95% coverage. The differences in coverage were statistically significant, with * \(p\) = 0.0002 for the comparison between IRT and electron plans and **\(p\) = 0.00001 for the comparison between VMAT and electron plans. The D2 cbrain (Gy) showed no significant difference between the three techniques, with \(p\) > 0.05 (Figure 4). Figure 3: Percentage of CTV receiving 95% of the prescribed dose (V95%CTV) for the three techniques, with a statistically significant difference between the electron plan and the other techniques (* \(p\)= 0.0002, **\(p\) = 0.00001). Figure 2: Mean dose (Dmean) to the CTV for IRT, VMAT, and electron beam techniques, showing a statistically significant difference (group a * \(p\) = 0.001; group b * \(p\) = 0.0004, **\(p\) = 0.0002; group c * \(p\) = 0.0002) between IRT and VMAT and IRT and electron plans across all three prescription groups. An interesting observation was made when comparing the dose profiles of IRT and VMAT in depth. For all patients with VMAT plans using two partial arcs (13 out of 25 patients), a dose profile inversion was found. As illustrated in Figure 5, IRT delivered a higher dose within the first 5 mm (CTV area), but beyond 2 cm, IRT delivered a lower dose compared to VMAT. This inversion is consistent across the entire CTV length, indicating that despite IRT delivering a higher mean dose, it results in a lower deep tissue dose, thereby limiting exposure to surrounding OARs. Figure 4: D2 cbrain (Gy) for the three techniques showing no significant difference (\(p>0.05\)). Figure 5: Dose profile comparison of IRT and VMAT. The top panel shows the 95% dose profile for a thorax lesion from the skin to a depth of 4.5 cm for patient 11. The bottom panel shows the 95% dose profile for a head lesion for patient 13, illustrating the dose profile inversion between IRT and VMAT, with IRT delivering a higher dose near the surface and a lower dose at greater depths. The arrows in different colors indicate the depth at which the dose profile was acquired.