Analiza wyników weryfikacji geometrycznej obrazów megawoltowych u pacjentek napromienianych w obszarze lewego gruczołu piersiowego

Aim

The aim of this study was to analyze the influence of the size of the clinical target volume (CTV) on the displacement obtained from the patients irradiated because of the left breast cancer using the geometric verification with the megavoltage images.

Material and method

Examined group of 100 patients was treated with the three-dimensional conformal radiotherapy. The analysis was performed on the 396 megavoltage images. The examined group of patients was divided into two subgroups according to the breast's CTV volume. The first subgroup (I) was the patient with the CTV ≤ 700 cm³ and the second (II) one CTV > 700 cm³. The displacements were obtained in the three directions: anterior-posterior (AP), crania-caudal (CC) and left-right (LR). The systematic (Σ), random (σ) errors and safety margins (SM) were calculated.

Results

The range of the Σ error was 0,20–0,34 cm for the (I) and 0,26–0,42 cm for the (II). The maximum value of the σ error was 0,46–0,26 cm, respectively. The lowest value of the SM was in the AP and the largest one in the CC direction. The SM ranges were 0,65–1,00 cm for CTV ≤ 700 cm³ and 0,88–1,37 cm for CTV > 700 cm³. SM for the whole group of the breast patient was in the range 0,80–1,24 cm.

Conclusions

The set-up of the breast patient with the smaller volume of the CTV ≤ 700 cm³ is much accurate and connected with smaller values of the geometric displacements. Safety margin used during the treatment planning should be selected individually depending on the size of the breast volume – CTV.