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 (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, EQD210 CTVHR D90 doses
were significantly higher compared with ICBTOARs-focused plans (?dose: 10.5±6.2 Gy, p<0.001), whereas
EQD23 OAR D2cc doses were significantly lower compared with ICBTTarget-focused plans (Average ?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 Δdoses of
both target and OARs.
CONCLUSION
IS-BT provides significant therapeutic advantage over IC-BT for patients both with small and large CTVHR.