Personalized Medicine and Radiation Therapy

Winter Spence, MRT(T), MHSc, BSc

Radiation therapy (RT) has long been considered a personalized form of cancer therapy, owing in part to the advancements in pre-treatment imaging capabilities. With the advent of image-guided RT (IGRT), RT plans are able to be made highly conformal to the tumour or tumour bed area while limiting the radiation dose reaching normal tissues. This has allowed for higher radiation doses to be delivered, achieving greater disease control and limiting dose to surrounding areas and therefore minimizing treatment related side effects. However, modern medicine suggests that “one size does not fit all”, and treatment plans can be further personalized to the unique characteristics of each individual’s disease. The need to further personalize RT has emerged at a time when human genome sequencing is accessible, large-scale bioinformatics systems are a reality, and functional medical imaging is available. These factors give rise to the concept of personalized medicine, allowing practitioners to fully exploit recent advancements made in diagnostic and treatment capabilities. Radiation therapy has a lot to gain from the implementation of personalized medicine in clinical practice.

Identifying certain tumour characteristics, including tumour hypoxic status, will have an impact on an individual patient’s RT plan. When tissue oxygen levels fall below normal values, normal cellular processes are impacted and the cells become more radioresistant and promote aggressive malignancy. There are several strategies that are designed to minimize the effect of hypoxia on RT outcome, including proton therapy and dose escalation in RT. There is also some evidence to support the use of hypoxic-targeting agents. Using these techniques for patients with identified hypoxic tumours will ultimately improve patient outcomes and drive an individualized approach to cancer management.

Drivers of certain diseases, including cancer, have been identified from the study of personal genetic information. There is a vast heterogeneity in outcomes following RT for cancer management, and certain genetic markers may be identified to account for this. There is a need to identify an accurate and reliable marker of prognosis and treatment response, which may be possible with current developments in next-generation sequencing. Single nucleotide polymorphisms (SNPs) are variations in a single base pair in a DNA sequence, and contribute to the likelihood of a patient developing a certain disease and also responding to treatment. By identifying which SNP correlate with certain outcomes following RT, we can personalize a more accurate RT treatment plan at diagnosis based on tissue biopsies, and further improve outcomes following RT.

There are many factors that contribute to a patient’s outcome following RT, and many more yet to be identified. Individual tumour characteristics, such as hypoxia, as well as individual patient factors, including genomic profile, will be important factors in determining the appropriate course of RT for patients. In the future, using the concepts of precision medicine to further personalize RT treatments will lead to more accurate treatments, superior outcomes and minimal complications for patients.

Winter is a radiation therapist in the Palliative Radiation Oncology Clinic at the Cross Cancer Institute in Edmonton; however, she will soon be talking a temporary role within CancerControl Alberta as a Senior Consultant. Winter recently graduated from the University of Toronto Masters of Health Science in Medical Radiation Sciences program.

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