Trying to better understand limits on radiation treatments. I am looking into doing a 5-day 200 rad plus a 400 rad boost treatment as apposed to a 200 rad 6 week fraction treatment.
The current standard of care is a 6 week 200 rad (plus a boost) using IMRT, known as hyper-fractionation, and the trial is using 5 fractions (daily) of 200 rad plus a simultaneous 'boost' of 400 rad, for a total daily of 600 rad, over 5 fractions. This will be using SRT and is called hypo-fractionation.
So there will be irradiation at 200 rad around the tumor cavity plus 400 rad focused on the tumor area. The tumor is a GBM grade IV, that was fully rebulked during surgery. Both hypo and hyper-fractionations would be done with concurrent TMZ dosing, and both would have follow-on TMZ at the full 6 weeks of sessions.
Note that the total radiation exposure for the hypo session would be 600 rad X 5 sessions, or 3000 rad. The hyper session would calculate out to 200 rad X 30 sessions, or 6000 rad total. So the hypo vs. the hyper would be half the total rad exposure, for the hypo protocol.
[The SRT and hypo-fractionation is a clinical trail (phase 3) and the hyper-fractionation is the 'normal' currently excepted protocol, but using IMRT vs. SRT.]
I have just read the blog post from 2011: "Published February 3, 2011 | By Dr Loiselle" concerning "“FRACTIONATED” Radiation Therapy: Why Weeks of Treatment?"
From that discussion I have summarized that the hypo-fractionation protocol suggested by the P3-Trail, this would be the better treatment option, that the longer and higher overall exposure that is double the trail exposure by one-half.
My concern / reservations are: 1. treatments done a 200+400 rad SRT --is this higher amount more of an issue, could cause more "latent" (DNA) damage to healthy cells? 2. The amount of energy needed to get to 600 rad is more than getting to 200 rad (dosimetry) --will this be more detrimental a higher eV to tissue transient by the beams? Big Q: hypo = best?
Reply # - November 26, 2017, 08:35 AM
Hi robhenders,
Hi robhenders,
Welcome to GRACE. As with many cancer treatment decisions, there isn't necessarily a "best" option. The standard of care developed over time as a balance between efficacy and toxicity. The hypofractioned dosing schedules being tested, such as the one you describe, are an effort to minimize inconvenience and cost, and possibly increase tumor cell kill rates. You can read a discussion of such efforts in this report (the most relevant part of the discussion can be found in the sections on IMRT, hypofractionation and ultra-hypofractionation.
There may also be factors which favor one methodology over the other, such as size and location of the tumor, which you may want to discuss with your medical team.
Good luck with whichever dosing scheme you choose.
JimC
Forum moderator