[An in-vivo dosimetric study of the scattered radiation during the treatment of breast carcinoma]. / Studio dosimetrico in vivo della radiazione diffusa durante il trattamento del carcinoma mammario.

ABSTRACT

In the last decade, radiation therapy has been increasingly used to treat breast cancer conservatively and some authors showed their concern about the radiogenic effects of irradiation outside the treated area. Our aim was to measure the scattered dose to the contralateral breast, thyroid and gonads during radiation therapy after conservative breast surgery. Thermoluminescent dosimeters, LiF Mn Ti (3 x 3 x 0.9 mm3), were used to measure scattered radiations outside the treated area. They were positioned on the skin of the patients in small (2 cm in diameter and 1 cm thick) perspex holders. Each measurement was performed once per treatment and six dosimeters were used--two on the contralateral breast, one on the midpoint of the medial side and one on the midpoint of the lateral side; two on thyroid lobes and two on the pelvis. The minimum dose to the contralateral breast (p < 0.002) and the maximum dose to the gonads (p < 0.003) were significantly higher in the 60Co group than in the LINAC6 group. The mean values of the minimum doses to the contralateral breast were significantly different (p < 0.007) in the whole series when beam area values were lower or higher than the median value (176 cm2). In the whole series the beam area and the minimum dose to the contralateral breast were correlated (Pearson, p < 0.001); the beam area and the minimum dose to the contralateral breast (p < 0.005), the gantry angle for the lateral beam and the minimum dose to the contralateral breast (Spearman, p < 0.001) exhibited statistically significant correlations. Of 30 patients, 16 were irradiated with 60Co (group A) and 14 with LINAC6 (group B). In group A the average scattered dose to the contralateral breast ranged 0.53-2.15 Gy, 0.66-1.91 Gy in the thyroid, 0.14-0.19 Gy in the gonads. In group B the average scattered dose to the contralateral breast ranged 0.36-2.07 Gy, 0.53-0.98 Gy in the thyroid and 0.08-0.12 Gy in the gonads. In the LINAC6 group the beam area and the minimum dose to the thyroid exhibited a statistically significant correlation (p < 0.009), as well as the beam area and the maximum dose to the gonads (p < 0.006), the beam area and the minimum dose to the gonads (p < 0.02), the gantry angle of the lateral beam and the minimum dose to the contralateral breast (p < 0.02). In the 60Co group no correlation was statistically significant, except for the correlation between the beam area and the minimum dose to the gonads (p < 0.001). Our experience confirms the scattered dose to depend on head treatment, beam area, gantry angle and wedge angle. Finally, the literature on this subject is reviewed.