The importance of radiation conformity for locally-advanced non-small cell lung cancer – IMRT, proton therapy and fallacy of the low dose bath

Abstract

Improvements in technology and lung cancer management over the past three decades have yielded dramatic improvements in the survival of locally-advanced non-small cell lung cancer. While modern technologies such as intensity modulated radiotherapy (IMRT) and particle therapy are now widely available, there remains controversy regarding the appropriate use of these advanced technologies and radiation plan optimization for lung cancers. In particular, there remains considerable controversy regarding the spread of the low dose bath (lung V5-10 Gy) generated by modern radiation plans that is needed in order to achieve conformity. This presentation will review the pertinent evidence to support utilization of advanced technologies to improve radiation conformity for locally-advanced lung cancers and fallacies of historic concerns over the spread of the low dose bath. Although there have been anecdotal and theoretical concerns about the low dose bath, emerging prospective evidence has cast doubt on these historic arguments. With increasing data linking survival outcomes with cardiac doses, this presentation will also cover the rationale for use of techniques such as particle therapy to reduce exposure of the heart to radiation. Additionally, flash radiotherapy has also emerged as a promising strategy to deliver tumoricidal radiation doses while altering the radiobiologic effects on normal tissues. As unprecedented survival is now being achieved with chemoradiation and PD-L1 directed checkpoint immune therapy, conformity and late radiation side effects can no longer be an afterthought. Substantial numbers of patients with locally-advanced lung cancer now survive long-term and strategies to mitigate unnecessary radiation exposure to the heart, lungs and esophagus will likely play increasingly important roles to improve both oncologic outcomes and patient-reported quality of life.