ESTRO 2024 - Abstract Book

S5943

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

Analysis of variance was performed to compare different groups and unpaired t-tests were used to test differences in the mean values of DVH; a significance level of p<0.01 was set - the analysis was conducted using the scipy library in Python [1].

Results:

Despite the target isodose coverage was similar (CTV V98% > 96%), the VMAT technique appears to be more conformal with a 54% higher COIN index (p<0.001) compared to the 3D-CRT technique. Additionally, considering the ipsilateral lung, a link between V20Gy and the MTIL is observed for the 3D-CRT technique (Figure 1); this correlation can be considered linear (Pearson correlation coefficient R=0.80). In the case of VMAT there is no relation between this two value, in fact the V20Gy data are flatten around its mean value of 10.8% as the MTIL varies (Pearson correlation coefficient R=0.21). Regarding the other OARs (Heart, Contralateral Lung, and Contralateral Breast), there is an increase in low doses, represented by a rise in the mean dose for the VMAT technique, amounting to 2 Gy each (p<0.001), and an increase in the V5Gy isodose ranging between 10% and 20% (p<0.001) as reported in Table 1.

Structure

Parameter

3D-CRT

VMAT

Homolateral Lung

Mean[Gy]

6.91 ± 0.50

8.91 ± 0.90

V20Gy

9.50 ± 1.63

10.50 ± 1.01

Controlateral Lung

Mean[Gy]

0.41 ± 0.07

2.12 ± 0.56

V5Gy

0

7.95 ± 4.29

Heart

Mean[Gy]

1.45 ± 0.16

3.24 ± 0.75

V5Gy

0.49 ± 0.51

21.57 ± 10.19

Controlateral breast

Mean[Gy]

0.87 ± 0.13

3.27 ± 0.71

V5Gy

0.08 ± 0.17

16.27 ± 6.61

Table 1: Dosimetric results.