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

Aim: The study intends to compare Ir-192 source against the Co-60 source for interstitial breast metal implant in high dose rate brachytherapy. Background: Few studies have been reported to compare Co-60 and Ir-192 on HDR brachytherapy in gynaecology and prostate cancer and very few with reference to breast cancer. Materials and methods: Twenty patients who had undergone interstitial template guided breast implant were treated in HDR Ir-192 brachytherapy unit. Plans were generated substituting Co-60 source without changing the dwell positions and optimization. Cumulative dose volume histograms were compared. Results: The reference isodose line enclosing CTV (CTVref) and the 2.34% difference seen in the volume enclosed by the reference isodose line (V-ref) 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 Ir-192 (p <0.05). D-mean (%) and D-max (%) for the heart, ipsilateral lung, ipsilateral ribs, skin presented very small difference. V-5% and V-10% of the heart shows 25% and 32% difference in dose. D-2cc (%) and Do fcc (%) for the contralateral breast, contralateral lung and D2cc (%) of the skin displayed significant difference (p < 0.05). However, Do fcc (%) of the skin indicated no noteworthy difference with p = 0.343. Conclusion: Based 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. Co-60 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. (C) 2016 Greater Poland Cancer Centre. Published by Elsevier Sp. z o.o. All rights reserved.