Purpose: To determine the differences in dosimetric parameters of cervical cancer patients treated with interstitial and intracavitary high dose rate brachytherapy using Co-60 and Ir-192 sources.
Methods: CT-based treatment plans of 20 patients with cervical carcinoma treated with brachytherapy were retrospectively studied. Patients with interstitial implants were planned for 24 Gy in 4 fractions with inverse planning simulated annealing using Co-60 and Ir-192 source keeping same dose objectives. Patients of intracavitary brachytherapy (ICBT) were planned for 21 Gy in 3 fractions with both sources keeping the same dwell positions. The dosimetric parameters Co-60 and Ir-192-based plans were compared in terms of HR-CTV coverage, OAR doses, homogeneity index (HI), and conformity index (CI).
Results: In interstitial brachytherapy, mean V100 values for Co-60 and Ir-192-based plans were 97.03±1.99 % and 96.42±2.25 % respectively. Average values of D2cc in the bladder for Co-60 and Ir-192-based plans were 4.30±0.57 Gy and 4.27±0.54 Gy respectively while in the rectum were 3.96±0.43 Gy and 4.08±0.49 Gy respectively. There were no significant differences between V100 and D2cc values from both sources. Ir-192 based plans were more homogeneous (HI=0.68±0.09) than the Co-60 plans (HI=0.59±0.10), however, the conformity was similar with both the sources.In ICBT plans, mean D90 values for Co-60 and Ir-192 were 4.86±1.29 Gy and 4.94±1.43 Gy respectively. Mean D2cc values in the bladder for Co-60 and Ir-192-based plans were 6.19±2.72 Gy and 5.93±2.44 Gy respectively while in the rectum were 4.17±1.73 Gy and 4.29±1.94 Gy respectively. We did not find any significant difference in the dosimetric parameters of Co-60 and Ir-192-based ICBT plans.
Conclusion: There are no significant differences in dosimetric parameters and no clinical advantage of using Co-60 over Ir-192-based brachytherapy. However, when it comes to cost-management, Co-60 has a longer half-life, which reduces the cost of frequent source replacement and disposal.