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

Abstract

Aim

The study intends to compare ¹⁹²Ir source against the ⁶⁰Co source for interstitial breast metal implant in high dose rate brachytherapy.

Background

Few 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 methods

Twenty 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.

Results

The reference isodose line enclosing CTV (CTV_ref) 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[[ce:hsp sp="0.25"/]]<[[ce:hsp sp="0.25"/]]0.05). In DHI, no difference was observed in the relative dose between the two sources (p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.823). The over dose volume index showed 11% difference. The conformity index showed 2.32% difference compared to ¹⁹²Ir (p[[ce:hsp sp="0.25"/]]<[[ce:hsp sp="0.25"/]]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 D_0.1cc (%) for the contralateral breast, contralateral lung and D_2cc (%) of the skin displayed significant difference (p[[ce:hsp sp="0.25"/]]<[[ce:hsp sp="0.25"/]]0.05). However, D_0.1cc (%) of the skin indicated no noteworthy difference with p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]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. 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.