This issue is very thorny one in the neuro-oncology community. How do you measure the quality of life objectively?
A RANO working group has defined that outline and is aware of it. We, as radiation oncologists, aren’t oblivious to the fact that radiation therapy offers one single shot to give the maximum chance of cure. I am not discussing the issue of re-irradiation here, but the idea is to minimise the impact of existing delivery mechanisms.
Beyond the tumour volumes (2-3 cm for high-grade gliomas), this is both empirical and observational. They observed that bulk of failures happened in the high dose region. It brings us to two important questions here.
1) If we know that it is going to happen in the 95% isodose, why don’t we focus on intentional dose heterogeneity, at the expense of conformity? We could explore mathematical formulations for it- how best to predict which dose fractionation would be best suitable for the likely outcomes, where the failure is expected to take place and escalate the dose to that region.
2) Some tumours usually fail elsewhere, outside the treatment area. If this is the case, why not “lower” the dose to the treatment area (so-called “de-escalation”)?
Do you see the immediate impact?
Lower the total dose to the normal brain!
Now, that leads us to two more questions.
1) Why don’t we lower the dose to 55+Gy for Grade III tumours, because they have a better outcome?
2) Does Temozolomide also act as a radiation sensitiser?
The problems with these very broad-based assumptions are that we do not have a robust criterion for pre-operative or even intra-operative validation of tumour subsets by use of MR spectroscopy or perfusion (or use of any other metabolites, for that matter). Likewise, after intense scrutiny and numerous workshops, we have just been able to define the glioblastomas/grade III astrocytomas along with the molecular data (or even other variants) objectively. Previously, palisading necrosis was all that we had from my pathology colleagues. Now, we are wading in molecular soup, and no one has the complete picture of how things can be nailed!
However, use of these molecular methods isn’t widespread.
One way out is to sequence the tumours completely, follow up patients standard course fractionation and prospectively identify patterns of failure.
It would be akin to a very preliminary “precision medicine” and not the hype cycle that seeks to identify the “molecular targets”.
No, we don’t need more “research” on something that is being duplicated across the labs. But we need to be able to channelise something that we have learned.
Who is going to bell the cat?
I think, currently, we are just trying to identify who the cat is.