What is your approach to brain reirradiation in the setting of recurrent/progressive gliomas?
A lot of factors need to be considered prior to offering brain reRT in such a setting, most importantly- interval since the 1st course of RT, patient's ECOG and neurologic function, age, perceived life expectancy, size of the lesion, location of the lesion, WHO grade of glioma, patient's expectations regarding treatment outcomes (e.g. a lot of patients prioritize quality of the remaining weeks/months/years over quantity). It's very important to ask a patient what they expect from the treatment with regards to its effect on quality of life, prolonging life, improving symptoms, alleviating neurologic disturbances, etc.
For patients with poor performance status (ECOG >2), significant neurologic disturbances, high grade glioma, short interval since the 1s course of RT (<1 yr), reRT has limited value and palliative approach should be strongly considered (if surgery, or systemic therapy, or clinical trial is not an option). Glioma reRT in such situations often results in added treatment burden, further impairs patient's quality of life, and offers marginal therapeutic benefit. Patients who are plegic, with significant vision deficits, aphasia, brainstem/cerebellar deficits as a result of recurrent tumor, are unlikely to get better w/ reRT, hence it's important to counsel them that re-treatment may potentially halt disease progression and prolong their life by a few weeks to a couple of months, but will likely NOT improve their existing neurologic and neurocognitive deficits.
For patients with ECOG 1-2, modest neurologic function, and modest prognosis (6-12 months), one may consider a shorter course of reRT (35 Gy/10 fx, or 30 Gy/5 fx, or even SRS 12-16 Gy for smaller lesions) although, once again, I would discuss palliative care route (if surgery, or systemic therapy, or clinical trial is not an option).
For otherwise healthy patients with excellent performance status, good neurologic function, extended time since completing 1st course of RT (2+ years) [and assuming a 50% tissue recovery since prior RT], lower grade gliomas (WHO gr. II-III) I would consider re-treating to a full dose (50 Gy and higher, using 1.8-2.0 Gy/fx), granted your cumulative brain Dmax (EQD2 a/b 3) is under 120 Gy, brainstem - under 100 Gy, optic apparatus - under 90 Gy. The third course of RT is not an option, therefore, I would try to deliver tumoricidal 'curative-intent' doses (50 Gy+) as opposed to palliative doses. Ideally, I would use proton pencil-beam scanning technique, specifically, IMPT, but we re-treated a couple of patients with recurrent gliomas in our institution with VMAT and they tolerated treatment well, without any grade 3+ toxicities during treatment and within the 1st year of follow-up post-treatment. Regarding the target and margins, I agree with Dr. @Dr. First Last and would include contrast-enhancing and areas of new FLAIR abnormality, but I would often add a tight margin (3-5 mm) to CTV, if feasible.
Regardless of treatment technique (VMAT, or proton beam therapy), I would counsel all my patients that the risk of grade 3+ toxicities with brain re-irradiation is probably >20%. QUANTEC data, after all, quotes a 7-20% risk of grade 3+ toxicity for optic apparatus with doses higher than 60 Gy; if you assume a 50% tissue recovery, even if your ON/OC previously received 54 Gy, you still have room for ~33 Gy extra for a 7-20% risk of grade 3 toxicity; regarding brain tissue, QUANTEC quotes that Dmax up to 90 Gy gives you a toxicity risk (symptomatic necrosis) of about 10% (therefore in reRT setting and assuming a 50% tissue recovery, I am okay with 120 Gy Dmax to brain). However often, your recurrent tumor is immediately adjacent to the brainstem and/or ON/OC, so you may need to exceed that dose in order to achieve adequate target coverage (otherwise you'll be delivering palliative doses in those regions), hence, it's critical to be honest with the patient and inform them that the risk of significant, potentially debilitating and life-threatening RT morbidity is fairly high.
Most data on reRT are retrospective. Below are some references:
I assume that grade II glioma was treated with 54 Gy, and there was sufficient time interval for re-irradiation, and other treatment options were also discussed. I use fractionated radiourgery: 8 Gy x 4 fractions to the contrast enhancing lesion (total 32 Gy) and 6 Gy x4 to the area of new flair abnormality (total 24 Gy) simultaneously. There is no margin. This experience is from a series of recurrent GBM after standard treatment. It gives about 35% tumor control, and reduces local-regional progression, and there was survival benefit in the responders...Reference: JNO 116:291-297. 2014 doi: 10.1007/s11060-013-1290-4. Epub 2013 Oct 31. PMID: 24173682.