Hypofractionated radiation therapy using IMRT has a clear advantage

I was reticent to write about hypofractionation yet again after writing about it so often in the last year. See this link for my latest summary. In a sea of randomized trials demonstrating that hypofractionated radiation therapy (i.e., it is delivered in fewer treatments or fractions) was no worse in cancer control or in toxicity to conventionally fractionated (40-44 treatments), there was one study, the Dutch HYPRO study, where the toxicity was a bit worse. At the time (see this link), I speculated that that was because they included an older radiation technique called 3D-CRT rather than the IMRT technology that is now prevalent in the US. A new study from MD Anderson suggests that may indeed be the case.

Hoffman et al. presented the patient-reported outcomes of 173 men with localized prostate cancer who were treated at M.D. Anderson in Houston. They were randomized to receive either:

1. 75.6 Gy in 42 fractions (conventional fractionation) via IMRT
2. 72 Gy in 30 fractions (hypofractionation) via IMRT

The men filled out questionnaires at baseline, and at 2, 3, 4, & 5 years after treatment. Patients were probed on their urinary, rectal and sexual status. Patient-reported outcomes on validated questionnaires is a more reliable source of toxicity data because it does not rely on the patient volunteering information to the doctor or the doctor assessing or recording that information. Analysis of the two groups showed that:

• there was no difference with regard to rectal issues (urgency, control, frequency, or bleeding).
• there was no difference with regard to urinary issues (pain, blood in urine, waking to urinate at night, or leakage)
• there was no difference with regard to sexual issues (erections firm enough for intercourse)
• there were no differences at 2, 3, 4, or 5 years.

This should dispel any concerns that completing IMRT in less time may be more toxic. Just as with all forms of radiation, the technology has improved greatly over the years. In the hands of an experienced and careful radiation oncologist, there is no reason that external beam therapy cannot be completed in less time and at lower cost.

Why toxicity was higher with hypofractionation in Dutch trial

Aluwini et al. have published the toxicity outcomes of a randomized clinical trial (HYPRO) designed to test whether a hypofractionated external beam (EBRT) regimen compared to conventional fractionation. They will report on the oncological outcomes at a later date.

Between 2007 and 2010, 782 intermediate and high-risk patients were treated at 4 Dutch centers. About half were treated with the hypofractionated regimen, half with conventional dosing as follows:

• ·      Hypofractionation: 19 fractions of 3.4 Gy each
• ·      Conventional fractionation: 39 fractions of 2.0 Gy each
• ·      The relative biologically effective dose is 16% higher for the hypofractionated regimen.
• ·      Both groups were treated with conformal EBRT (3D-CRT and IMRT).

After a median followup of 60 months, the 3-year late-term toxicity outcomes were as follows:

• ·      Genitourinary toxicity, grade 2 or higher: 41% among the hypofractionated group vs. 39% for conventional fractionated.

o   Hazard ratio: 1.16 (Non-inferiority threshold: 1.11)

• ·      Genitourinary toxicity, grade 3 or higher: 19% among the hypofractionated group vs. 13% for conventional fractionated.

• ·      Gastrointestinal toxicity, grade 2 or higher: 22% among the hypofractionated group vs. 18% for conventional fractionated.

o   Hazard ratio: 1.19 (Non-inferiority threshold: 1.13)

• ·      Gastrointestinal toxicity, grade 3 or higher: 3% among the hypofractionated group vs. 3% for conventional fractionated.

Because the toxicity difference slightly exceeded the pre-established thresholds, the authors conclude that the hypofractionated regimen was not non-inferior to the conventionally fractionated regimen in terms of late term toxicity.

Because the hypofractionated regimen was a higher biologically effective dose, we might expect toxicity to be somewhat higher. Several recent major trials showed that hypofractionated IMRT was non-inferior to conventional fractionation in terms of both oncological control and late-term toxicity (see this link and this one, and this one). The lesson we learn from this study is that hypofractionation carries increased risk of toxicity. To avoid that, it is important to use well-planned IMRT or SBRT regimens. 3D-CRT is probably not the optimal platform for such treatment.