Fewer fractions, more segments.

Top Line: Does the use of IMRT for whole breast radiation reduce clinically significant toxicity in the real world?

The Study: This comparative effectiveness analysis from the Michigan Radiation Oncology Quality Consortium (MROQC) sought to determine if the use of IMRT for whole breast radiation reduces acute toxicity. From 2011 to 2018, over 5000 patients received whole breast radiation at 24 different centers and were included in this prospective cohort study. Keep in mind, though, that patients were treated according to routine practice at all centers and treatment allocation and planning and delivery methods were not standardized. The line between modern 3DCRT and IMRT for fixed gantry angle breast tangents is a blurry (some might say arbitrary) one. For this analysis, treatment type was divided into 3 categories: inverse-planned IMRT (i.e. computer optimized), forward planned IMRT (≥ 5 segments per unique gantry angle), and 3D conformal (everything else). Just over half of patients (51%) had hypofractionation with 49% of those using 3DCRT, 27% forward planned IMRT, and 24% inverse planned IMRT. Among those conventionally fractionated, 47% used 3DCRT, 30% forward planned IMRT, and 23% inverse planned IMRT. Propensity scoring was used to account for the underlying patient and treatment characteristics that may have led to the decision to use one type of fractionation or planning technique over another. Acute, clinically significant toxicity (pain or moist desquamation) was significantly less with inverse planned IMRT compared to 3DCRT for both conventional (OR 0.64) and hypofractionation (OR 0.41). Just as important though, the rate of acute toxicity was significantly lower with hypofractionation (26% with IMRT, 33% with 3DCRT) than with conventional fractionation (42% with IMRT, 55% with 3DCRT). In fact, patients treated with hypofractionation were less likely to have grade 3+ acute toxicity and less likely to have a treatment break than conventionally fractionated patients. So, if you’re eager to adopt IMRT “to reduce toxicity,” you should be just as eager to adopt hypofractionation.

TBL: Hypofractionation and inverse planned IMRT for whole breast radiation significantly reduces the rate of acute, clinically significant toxicity in this large, prospective real-world cohort. | Jagsi, Int J Radiat Oncol Biol Phys 2021