Abstract IA16: Midtreatment metabolic imaging as a biomarker of treatment response
Authors: Le Quynh-Thu 
Published: December 2017

Abstract
Our present approach to prescribing radiation dose to solid cancer utilizes primarily knowledge of the tumor location, histology and surrounding normal tissue sensitivity to radiation. For example, we typically treat a squamous cell carcinoma of the head and neck to 70 Gy, anal canal to 54 Gy, and cervix to 90 Gy because of surrounding normal tissue sensitivity even though all three tumor types are HPV driven squamous cells carcinomas. We do not take into account intrinsic sensitivity of individual tumor or normal tissue in individual patients. It is therefore desirable to identify biomarkers that would inform treatment outcomes for individual patients to tailor radiation field, dose and fractionation; mid-treatment imaging studies can serve as such a marker. Early assessment using mid-treatment imaging provides a window of opportunity to deliver more intensified radiation doses to poorly or non-responding patients for improved tumor control and a lower dose for those with excellent response to minimize toxicity. Such a tailored approach has been applied to tumor responses to induction chemotherapy but not to that of radiation, since simple measurements such as tumor size may not change rapidly within the first 1-2 weeks of radiotherapy. However, early changes can be identified by metabolic imaging such as 18FDG PET CT or 18F-MISO PET CT for hypoxia imaging. Although novel PET tracers have been developed to image different tumors, trials to test modification of RT dose, volume or schedule based on metabolic treatment response with these tracers are few and far between. NRG-oncology is testing whether individualized adaptive radiotherapy replanning after mid treatment 18FDG PET-CT will improve local control and survival in patients with stage III NSCLC (NCT01507428). Similarly, investigators from MSKCC is testing whether dose de-escalation in patients with resolution of hypoxia based on 18F -MISO imaging study 2 weeks into treatment will result in similar local control as those with standard treatment (NCT00606294). A promising and clinically amenable approach is radiomics, which is a sophisticated computerized method to extract a rich set of quantitative information from images. Radiomic analysis has been shown to significantly improve upon human interpretation as well as to detect early subtle radiation-induced changes in the normal tissue for late toxicity prediction. Therefore, radiomic analysis of pre- and mid-treatment PET-CT and MRI scans during radiation therapy may allow physicians to personalize radiation dose prescription to achieve an optimal balance between tumor control and toxicity. If successful, these biomarkers hold the promise to transform the clinical management of patients treated with radiotherapy.
Citation Format: Quynh-Thu Le. Midtreatment metabolic imaging as a biomarker of treatment response [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr IA16.