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 cm(3)) and larger (>= 30 cm(3)) high-risk clinical target volume (CTVHR). 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) ICBTTarget-focused plan: The priority was adequate coverage of CTVHR. Then, the OARs were spared as much as possible. (2) ICBTOARs-focused plan: The priority was given to the OAR sparing. Then, highest CTVHR 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 CTVHR. In IS-ICBT plans, EQD2(10) CTVHR D90 doses were significantly higher compared with ICBTOARs-focused plans (Delta dose: 10.5 +/- 6.2 Gy, p<0.001), whereas EQD23 OAR D2cc doses were significantly lower compared with ICBTTarget-focused plans (Average Delta dose, 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 CTVHR in terms of increment doses of both target and OARs. CONCLUSION IS-BT provides significant therapeutic advantage over IC-BT for patients both with small and large CTVHR.