Therapeutic benefit of intracavitary-interstitial brachytherapy in cervical cancer patients with small and large high-risk clinical target volume

OBJECTIVE: We aimed to investigate the added value of interstitial brachytherapy (IS-BT) over classical intracavitary BT (IC-BT) in terms of target coverage and organ at risk (OAR) sparing among patients for whom an optimal dose distribution could not be provided without IS-ICBT and also to determine if the magnitude advantage provided by IS-BT is similar in patients smaller (<30 cm³) and larger (≥30 cm³) high-risk clinical target volume (CTV_HR ).

METHODS: 24 patients treated with IS-ICBT were included in this study. IS-BT was performed 76 of 93 BT fractions. For each patient, two additional IC-BT planning were created: (1) ICBT_{Target-focused} plan: The priority was adequate coverage of CTV_HR . Then, the OARs were spared as much as possible. (2) ICBT_OARs-focused plan: The priority was given to the OAR sparing. Then, highest CTV_HR coverage was tried to achieve within the allowed OAR dose limits. The IS-ICBT plans were compared with these two plans in terms of target coverage and OAR doses.

RESULTS: 13 patients had large and 11 patients had small CTV_HR . In IS-ICBT plans, EQD2₁₀ CTV_HR D90 doses were significantly higher compared with ICBT_OARs-focused plans (Δdose: 10.5±6.2 Gy, p<0.001), whereas EQD2₃ OAR D2cc doses were significantly lower compared with ICBT_{Target-focused} plans (Average Δdose, bladder: 24.5±25.9 Gy [p<0.001], rectum: 7.6±9.7 Gy [p=0.001], sigmoid: 18.3±15.3 Gy [p<0.001]). There was no significant difference between patients with small and large CTV_HR in terms of ∆doses of both target and OARs.

CONCLUSION: IS-BT provides significant therapeutic advantage over IC-BT for patients both with small and large CTV_HR .