Study of the dosimetric differences between 192Ir and 60Co sources of high dose rate brachytherapy for breast interstitial implant

AimThe study intends to compare 192Ir source against the 60Co source for interstitial breast metal implant in high dose rate brachytherapy.BackgroundFew studies have been reported to compare 60Co and 192Ir on HDR brachytherapy in gynaecology and prostate cancer and very few with reference to breast cancer.Materials and methodsTwenty patients who had undergone interstitial template guided breast implant were treated in HDR 192Ir brachytherapy unit. Plans were generated substituting 60Co source without changing the dwell positions and optimization. Cumulative dose volume histograms were compared.ResultsThe reference isodose line enclosing CTV (CTVref) and the 2.34% difference seen in the volume enclosed by the reference isodose line (Vref) between the two isotopes show small but statistically significant difference (p < 0.05). In DHI, no difference was observed in the relative dose between the two sources (p = 0.823). The over dose volume index showed 11% difference. The conformity index showed 2.32% difference compared to 192Ir (p < 0.05).Dmean (%) and Dmax (%) for the heart, ipsilateral lung, ipsilateral ribs, skin presented very small difference. V5% and V10% of the heart shows 25% and 32% difference in dose. D2cc (%) and D0.1cc (%) for the contralateral breast, contralateral lung and D2cc (%) of the skin displayed significant difference (p < 0.05). However, D0.1cc (%) of the skin indicated no noteworthy difference with p = 0.343.ConclusionBased on the 3D dosimetric analysis of patient plans considered in this study, most of the DVH parameters showed statistically significant differences which can be reduced by treatment planning optimization techniques. 60Co isotope can be used as a viable alternative because of its long half-life, logistic advantages in procurement, infrequent need of source replacement and disposal of used source.