A hot mess.

A hotly debated topic in thoracic radiation oncology is the best balance of tumor control and treatment toxicity when treating inoperable ultra-central lung tumors. A recent review landed on 7.5 Gy x 8 as a good option, recognizing a single prescription can result in vastly different plans depending on the allowable hot spot. This week the phase 2 HILUS trial reported on outcomes among 65 patients receiving 7 Gy x 8 to tumors within 1 cm of the proximal bronchial tree (i.e. the highest of high-risk ultracentral tumors). In fact, the median distance was actually touching the proximal bronchial tree. Unfortunately, grade 3+ toxicities occurred in over one-third of patients (n=22) including 10(!) grade 5 toxicities due to bronchopulmonary hemorrhage (n=8), pneumonitis (n=1), and fistula (n=1). Critics would argue it was the allowed hot spot (150%), not the prescription, that was to blame. And, indeed, dosimetric modeling revealed max dose to 0.2cc of the main bronchi/trachea was a primary predictor of lethal bronchopulmonary hemorrhage. | Lindberg, J Thorac Oncol 2021

Comments

  1. One of the key limitations of this trial which no one appears to be focusing on in the Twitter realm is that endobronchial involvement was not assessed at baseline (despite median distance touching the PBT). Endobronchial involvement is associated with a ~20% risk of grade 5 toxicity when treated with SBRT (Range 17-33%). https://www.jto.org/article/S1556-0864(19)30315-6/abstract

    However, some of the key points in the Twittersphere (e.g,. Palma) highlight the Rx IDL to 67%, which allows for 150% hot spot in the target. There is no mention of a PBT contour as an ITV (many contour on average), and with such sharp dose dropoffs, the PBT may actually be receiving higher point doses than the plan indicates without 4D contouring of the PBT. Compare this to the ongoing ultracentral SUNSET trial, which mandates the hotspot be between 111-120% without such sharp dose dropoff.

    Would love to hear what others think! Endobronchial component is likely an important contributor to toxicity, especially with SBRT.

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