ESTRO 2024 - Abstract Book

S252

Brachytherapy - Gynaecology

ESTRO 2024

replanned to take into account interfractional changes in target volumes and OARs. If the predicted total HR CTVD90 EQD2 dose was not according to recommendations [2], new virtual needles were added and needle depths were changed if necessary as with real plans. Biological 2 Gy equivalent total doses were calculated for target volumes and organs at risk for both free hand needle treatment plans and for treatment plans without any free hand needles. The dosimetric differences between the two planning approaches were compared. Statistical analysis was calculated with Microsoft Excel using one-tailed paired t-test, 0,05 being threshold for statistical significance.

Results:

For the HR-CTV, mean EQD2 dose (α/β=10) to 90 % of the volume (D90) was 88,8 Gy without using any free hand needles as with free hand needle plans it was 91,5 Gy (p=0,043), respectively. For the GTV dose to 98 % of the volume (D98) values were respectively 101,3 Gy and 103,9 Gy (p=0,161). The results are shown graphically in Figure 1. For OARs, EQD2 mean doses (α/β=3) to the 2 cm3 volume of the organ (D2cc) were: bladder 87,5 Gy / 86,2 Gy without and with free hand needles p=0,017). The respective doses for the other OAR were: rectum 70,2 Gy / 69,2 Gy (p=0,022), sigmoid 70,1 Gy / 69,3 Gy (p=0,065), bowel 53,1 Gy / 52,6 Gy (p=0,127) and vaginal wall point (recto vaginal-point) 79,0 Gy / 81,9 Gy (p=0,137). The average OAR doses are also illustrated in Figure 2.

The mean volume of HR-CTV and GTV within the studied patient group were 69,7 cm3 and GTV 17,6 cm3, respectively. It shall be noted that the mean volume of HR-CTV in EMBRACE-I group was 28 cm3 [3].

Figure 1. Cumulative EQD2 doses to the GTVD98 and HR-CTVD90 with and without free hand needles. (FHN=free hand needle)