What happened to Rachel?
The Study: Here we have publications of two phase 1 dose-escalation trials: One is from Timmerman et al. at UTSW while the other is from South Korea. Both trials included up to T2 tumors of the glottic larynx with one also including Tis disease. In the UTSW trial, doses went from 50 Gy / 15 daily→ 45 Gy / 10 three times per week→ 42.5Gy / 5 twice per week. In the Korean trial, doses went from 59.5Gy / 17 daily → 55 Gy / 11 two-three times per week → 45 Gy / 5. The target in the UTSW trial was the GTV on 4D-CT plus a 2 mm CTV margin to include anterior commissure or arytenoid if involved plus a 3 mm PTV margin. Radiation was delivered exclusively with CyberKnife, requiring implanted fiducials in the thyroid cartilage. You’ll wanna read through all the dosimetric details. The Korean trial had two targets: CTV1 was the GTV while CTV2 was your traditional larynx CTV, and PTV margins were again 3 mm. Radiation was delivered with VMAT plans using an SIB approach. How bad did it hurt? Ahem, well, both trials ran into dose-limiting toxicities that typically happened well after treatment. These mainly included laryngeal edema, mucosal ulceration, or cartilage necrosis, and all were in active smokers. More notably, the UTSW trial had 5 local failures among just 29 patients.
Bottom Line: SBRT for early stage glottic larynx cancer is interesting, but there’s a long way to go before it's proven both safe and effective. | Sher & Kang, Int J Radiat Oncol Biol Phys 2019