To the limit.
Top Line: What are the tolerances of the brachial plexus and esophagus when performing lung SBRT
The Study: Here are two relatively large retrospective studies of brachial plexus (BP) and esophageal toxicity after SBRT. The first was an analysis of 78 patients treated with definitive SBRT for early stage, apical NSCLC. All patients received 40-60 Gy in 3-5 fractions with most receiving 50 Gy in 5 fractions. Importantly, BP dose was not constrained during treatment planning. A total of 5 patients (6.4%) reported BP injury (BPI = pain, weakness, or sensory changes) with a median time to symptom onset of 11.9 months. Median BP Dmax EQD2(3) (32.1 Gy v 5.13 Gy) were higher in those who developed BPI than the overall cohort. While three BPI patients had BP Dmax > 60 Gy EQD2(3), at least 3 times as many patients who didn’t experience BPI received that dose. In addition, one BPI patient had a BP Dmax < 20 Gy. Their NTCP model estimated a ~5% risk of BPI at a Dmax ~50 Gy EQD2(3) and a ~10% risk around 85-90 Gy EQD2(3). The second study analyzed esophageal toxicity following SBRT. In total, 55 out of >2000 patients had plans where the esophagus received at least 65% of the prescription dose. Out of those, the GTV abutted the esophagus in a third and the PTV abutted the esophagus in half. Max dose to the esophagus was typically constrained (for example 32.5 Gy max in 5 fractions), however when the PTV overlapped the esophagus, max dose was limited to 105% of the prescription. Within 60 days of treatment, 25% experienced grade 2 esophageal toxicity with no grade 3 or higher events. That rate was 39% when the PTV overlapped the esophagus compared to 8% when it did not. Achieving a Dmax (BED10) <62 Gy, a D1cc (BED10) <48 Gy, a D2cc (BED10) <43 Gy, and a Dmax ≤85% of the prescription were all associated with a <20% risk of grade 2+ esophagitis.
TBL: While increasing dose increases the risk of brachial plexus injury after SBRT for apical lung tumors, the relationship is highly variable. Esophageal toxicity is relatively mild and self-limited after SBRT to targets that abut or even overlap the esophagus. | Morse, Pract Radiat Oncol 2021 & Sodji, Int J Radiat Oncol Biol Phys 2021