Top Line: How does simultaneous integrated boost during whole breast radiation compare to standard sequential boost.
The Study: The main downside is a doubling of fibrosis risk, most closely correlated with absolute boost volume. The UK IMPORT HIGH trial aimed to test the efficacy and tolerability of a simultaneous integrated boost using intensity modulated therapy (IMRT) using the broad definition of either forward or inverse planning. In true UK fashion, this trial was both huge and somewhat convoluted. It enrolled 2617 women receiving whole breast irradiation following breast-conserving surgery. The first third (n=871) served as the control group that received 40 Gy in 15 fractions to the whole breast followed by a sequential boost of 16 Gy in 8 fractions to the tumor bed or lumpectomy cavity. There were two further test groups treated with simultaneous integrated boost (SIB). In both groups, there were three treatment volumes: the tumor bed plus a 5mm PTV margin, the partial breast boost volume (a 1.5 cm expansion of the tumor bed plus a 1cm PTV margin), and the whole breast (plus a 1cm PTV margin). In both arms, the whole breast received 36 Gy in 15 fractions, and the partial breast boost volume received a 40 Gy SIB. Finally, patients in the experimental arms were randomized to receive either a 48 Gy SIB (n=874) or a 53 Gy SIB (n=872) to the tumor bed. As best we can tell from the protocol, IMPORT HIGH used a relatively small boost volume even in the standard arm consisting of just a 5mm margin around tumor bed clips and any architectural distortion on CT. The goal was to keep the volume of this high dose target to <5% of the breast volume. Dosimetrist satisfaction for each arm was not measured in the trial. A supraclavicular field was added when indicated for regional nodal irradiation. The primary endpoint of in-breast tumor recurrence was deemed non-inferior in both test groups (2.0% and 3.2%, respectively) when compared to the control (1.9%). As we can see, recurrence was numerically a little higher in the highest dose group suggesting no benefit to dose escalation. Granted, the volumes treated with these higher doses were not the same boost volumes we typically think of with sequential boost. So,Clinician-reported moderate or marked breast induration was similar between the control (12%) and test group 1 (11%) but significantly worse in test group 2 (16%).
TBL:IMPORT HIGH found that 15 fraction breast IMRT with a lower whole breast dose, standard partial breast dose, and simultaneous integrated boost to the tumor bed resulted in non-inferior local control. A dose-escalated SIB did not improve control and resulted in worse toxicity. Across all arms, a relatively small boost volume resulted in low rates of local recurrence. | Coles, Lancet 2023
The Study: The main downside is a doubling of fibrosis risk, most closely correlated with absolute boost volume. The UK IMPORT HIGH trial aimed to test the efficacy and tolerability of a simultaneous integrated boost using intensity modulated therapy (IMRT) using the broad definition of either forward or inverse planning. In true UK fashion, this trial was both huge and somewhat convoluted. It enrolled 2617 women receiving whole breast irradiation following breast-conserving surgery. The first third (n=871) served as the control group that received 40 Gy in 15 fractions to the whole breast followed by a sequential boost of 16 Gy in 8 fractions to the tumor bed or lumpectomy cavity. There were two further test groups treated with simultaneous integrated boost (SIB). In both groups, there were three treatment volumes: the tumor bed plus a 5mm PTV margin, the partial breast boost volume (a 1.5 cm expansion of the tumor bed plus a 1cm PTV margin), and the whole breast (plus a 1cm PTV margin). In both arms, the whole breast received 36 Gy in 15 fractions, and the partial breast boost volume received a 40 Gy SIB. Finally, patients in the experimental arms were randomized to receive either a 48 Gy SIB (n=874) or a 53 Gy SIB (n=872) to the tumor bed. As best we can tell from the protocol, IMPORT HIGH used a relatively small boost volume even in the standard arm consisting of just a 5mm margin around tumor bed clips and any architectural distortion on CT. The goal was to keep the volume of this high dose target to <5% of the breast volume. Dosimetrist satisfaction for each arm was not measured in the trial. A supraclavicular field was added when indicated for regional nodal irradiation. The primary endpoint of in-breast tumor recurrence was deemed non-inferior in both test groups (2.0% and 3.2%, respectively) when compared to the control (1.9%). As we can see, recurrence was numerically a little higher in the highest dose group suggesting no benefit to dose escalation. Granted, the volumes treated with these higher doses were not the same boost volumes we typically think of with sequential boost. So,Clinician-reported moderate or marked breast induration was similar between the control (12%) and test group 1 (11%) but significantly worse in test group 2 (16%).
TBL:IMPORT HIGH found that 15 fraction breast IMRT with a lower whole breast dose, standard partial breast dose, and simultaneous integrated boost to the tumor bed resulted in non-inferior local control. A dose-escalated SIB did not improve control and resulted in worse toxicity. Across all arms, a relatively small boost volume resulted in low rates of local recurrence. | Coles, Lancet 2023