(Singapore--January 29, 2021 9:35 a.m. SPT/January 28, 2021 8:35 p.m. EST)--Two radiation oncology trials presented at the IALSC World Conference on Lung Cancer Singapore highlight how some researchers are exploring use of higher radiation boost doses to only PET-positive regions in locally-advanced non-small cell lung cancer (NSCLC). A previous large RTOG phase III trial revealed that the unform delivery of a high dose to the entire tumor led to poorer survival.

In one study, Prof. Feng-Ming (Spring) Kong, Case Western Reserve University School of Medicine, in Cleveland, Ohio presented the results of a multicenter trial which aimed to determine whether adaptive isotoxic radiation dose escalation to mid-treatment FDG-PET provides superior local tumor control compared to a standard uniform dose of 60 Gy in patients with stage III NSCLC.

Prof. Kong and the research centers involved in the trials enrolled 138 patients with stage III NSCLC who were medically fit for concurrent chemoradiation. The patients were randomly assigned by a 1:2 ratio to standard (60 Gy) arm or to an adaptive-therapy arm, with dose individualized to 20 Gy mean lung dose (MLD), and adapted to residual tumor on the mid-treatment FDG-PET/CT. All patients had FDG-PET performed around 40 Gy mid-treatment, and radiation therapy was delivered in 30 daily fractions (Fx).
Of 138 patients enrolled between February 2012 and March 2017, 127 were eligible and analyzable, with 43 and 84 patients in the standard and adaptive arms, respectively, with a minimum follow-up of 3.7 and 3.4 years for surviving patients, also respectively.

The adaptive arm consisted of an initial plan of 2.2 Gy/Fx for 21 Fx followed by an adaptive radiation therapy boost to mid-treatment FDG-PET target using a variable prescription of 2.2-3.8 Gy/Fx for the final 9 Fx. The primary endpoint of this report was 2-year local-regional tumor progression free (LRPF), with inclusion of overall and in-field LRPF, assessed independently and blindly by radiologists.

There were no significant differences in lung, esophagus, and heart toxicities, though the adaptive arm had numerically higher mean doses of these organs at risk. The 2-year overall LRPF rates were 59.5% (95% CI: 37.9, 75.7) on the standard arm, and 54.6% (95% CI: 39.9, 67.0) on the adaptive arm. The median LRPF time was 27.5 months (95% CI: 14.3, not reached) on the standard arm and 28.4 months (95% CI: 19.1, not reached) on the adaptive arm. There were no significant differences in overall survival, progression-free survival, or lung cancer-specific survival between the two arms, according to the presentation by Dr. Kong.

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