Image-guided adaptive brachytherapy dose escalation for cervix cancer via fractionation compensation

In image-guided adaptive brachytherapy (IGABT), dose distributions are optimized for each fraction. Optimum fractional dose can be constant or adapted to previous fractions and a conjecture about the future ones. We evaluate the efficacy of different fraction size schemes, derived from total IGABT dose constraints, against constant per-fraction constraints.

This retrospective planning study included 20 IGABT patients where four different fractionation schedules were compared based on modern planning recommendations. A total high-risk-clinical target volume D₉₀ (minimum dose in 90% of the volume) dose aim of 90.0 Gy with constant per-fraction organs at risk (OARs) dose constraint planning (CONST) was compared with conservative and aggressive fractionation compensation (COMP) techniques. COMP allows variations in the per-fraction dose constraints. Dose accumulation was performed through dose summation at a given volume and equivalent uniform dose (EUD) worst-case dose estimates.

No significant differences were identifiable between dose metrics of CONST and COMP in the total patient population. However, a subgroup of patients with alternating dose-limiting OARs had significant benefit from COMP. Median high-risk-clinical target volume dose escalation ranged from 5% to 12%, whereas OAR dose increases were lower and ranged from 3% to 8%. EUD-based planning delivered similar tumor doses, although slightly lower OAR doses. By distributing the treatment aim over an increased number of treatment fractions, median tumor dose could be increased by a further 8% per additional treatment fraction at the same OAR dose levels for both CONST and COMP.

COMP is effective in patients with alternating dose-limiting OARs and is enhanced using more treatment fractions and EUD constraints.