Correspondence Address:
Dr. Nagraj G Huilgol
Division of Radiation Oncology, Nanavati Hospital, Mumbai, Maharashtra
India

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IGRT, a popular acronym, stands for image-guided radiotherapy. This much touted acronym which has been around, since, over two decades has limited the scope of possibilities. Instead, information-guided radiation therapy would have expanded the scope of integrating multiple variables such as sensitivity, hypoxia, cellularity, aggressiveness, heterogeneity, angiogenesis, and genomics for treatment planning and delivery. Precision medicine in radiation oncology now aims to improve patient outcomes and care by integrating above-mentioned multiple variables to personalize treatment approach. Technology of delivering radiotherapy currently can ensure high conformation and heterogeneous distribution, while sparing organ at risk. Moderate and extreme hypofractionation in selected cases is now being practiced routinely. Integration of chemotherapy, immunotherapy, and hyperthermia with radiation has improved outcomes. Hypoxic cell sensitizers and normal tissue radio protectors sadly did not become a part of routine practice. Brachytherapy after a renaissance in the eighties has plateaued while proton particles in radiotherapy have gained in popularity. Precision medicine and personalized medicine sometimes are used interchangeably. Instead information-guided personalized medicine seems a better alternative.

Radiation therapy, in the recent years with physical optimization, and adaptive technique has an ability to sculpt doses differentially is a significant step towards personalization of treatment. Fractionation schedules, however, remain to be a class decision. For instance, radiation following breast conservative surgery will be either 60 Gy in 6 weeks or 40 Gy in 15 fractions with boost to tumor up to 50 Gy. “Fast forward” trial[1] has demonstrated equivalence 26 Gy over a week with 40 Gy in 15 fractions. These fractionation schedules were largely motivated by the ideal of convenience and reduction of cost to exchequer. Radiobiology of hypofractionation is slowly catching up, the patient remains a statistical average and the choice of treatment is not predicated by the optimal schedule for the patient. Currently, standardization of treatment has shown to give best yield as compared to idiosyncratic prescription and treatment.[1]

Genomically guided therapeutics has started emerging as an important component of precision medicine. This has been enthusiastically embraced by medical oncologists. Radiation Oncologists have been slow on integrating genomics for individualizing treatment planning. Intrinsic radiation sensitivity is one of the variables to influence the outcome following radiation therapy. “Radiation sensitivity index” (RSI), is a multigene expression model based on expression of 10 genes.[2] RSI has shown promise in number of sites and types of cancer for predicting response to radiation.[3] Intratumoral localization of hypoxia for individualized dose escalation is an exciting possibility. These are 15 gene and 26 gene hypoxia signature being-tested in clinical trials. Hypoxia plays an important role in response to radiation therapy, besides, intrinsic sensitivity. DAHANCA 30 is a noninferiority randomized trial of hypoxia-profile guided treatment with nimorazole during chemoradiation designed to explore such a possibility. It is an ongoing trial which is accruing patients. Similarly, there are studies exploring intrinsic sensitivities of normal tissues. They include genetic changes such as single-nucleotide polymorphisms (SNPs), copy number variations, insertions, and deletions. Attempts to loom for genetic factors influencing response to radiation are centered around candidate gene studies and genome wide association studies of SNPs. This is a nascent science in its early days. Integration of genomics will take time. A concerted attempt of specialist spanning from radiation oncologist, medical Physicists to experts in data analytics is required to promote the specialty. Radiogenomic which is a derivative of genomics has also gained fraction. Radiogenomics for planning and individualizing treatment is doable in the immediate future.[4] After all, images are at the heart of radiation therapy planning and execution. It involves texture analysis and images such as computed tomography scans, magnetic resonance imaging, and positron emission tomography scans using statistics. Texture can be correlated with biological realities like angiogenesis, hypoxia expression of receptors, and genomic changes. All this is a herculean task, nevertheless an achievable goal and not a vanishing chimera. Hence, information-guided personalized treatment, it is, in the years to come. A paradigm shift waiting to be explored.

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