Know it, to control it

Radiation for cancers

Radiation therapy was applied for treatment of cancers empirically after the discovery of radium. The acute and long term side effects were recorded clinically as patients started outliving tumors. The combination of radiation before or after surgery and subsequent addition of chemotherapy has revolutionized the way cancer is treated.

Today radiation therapy is one of the most important treatment modalities for cancer therapy alongside surgery and chemotherapy. Every tumor is approached through a multimodality discussion such that the toxicity of treatment can be reduced with maximum curative potential. Cancer care has become more holistic in approach, as therapists understand the complex basics of radiation interaction within the human body.

So much so that insight into molecular interactions occurring within a cancer cell, have been translated into novel medical treatments, and a variety of technological advances have allowed new surgical and radio-therapeutic techniques. When radiation therapy faced the limitation of locally controlling the tumor, researchers began exploring radio-sensitizers, compounds that enhance the intrinsic sensitivity of cancer cells to ionizing radiation (IR)

Within the discipline of radiation oncology, fusion of state-of the-art tumor imaging with precision radiation treatment delivery systems has created an opportunity to shift from the classic radiation therapy paradigm of administering thirty or more individual allow-dose treatments towards much briefer, more intense and potent regimens, in which a much higher dose per treatment is used for greater clinical effect.

Stereotactic body radiation therapy (SBRT) emerged as a radiotherapy procedure that is highly effective in controlling early stage primary and oligometastatic cancers at locations throughout the abdominopelvic and thoracic cavities, and at spinal and paraspinal sites.

The major feature that separates SBRT from conventional radiation treatment is the delivery of large doses in a few fractions, which results in high biological effective dose (BED). In order to minimize the normal tissue toxicity, conformation of high doses to the target and rapid fall-off doses away from the target is critical.

In SBRT, radiation is targeted almost exclusively to the tumor, while tissues not grossly involved with the tumor are skillfully spared. However, unique radiobiology of SBRT that ensures maximal tumor control but minimal normal tissue complication is what really sets SBRT apart from other radiotherapy techniques.

Additional defining characteristics of SBRT include the abilities to securely immobilize the patient for the typically long treatment sessions; to accurately duplicate patient position between simulation and treatment; to minimize normal tissue exposure through the use of multiple- or large angle, arcing, small aperture fields; to rigorously account for organ motion; to stereo-tactically register tumor target and normal tissue structures; and to deliver ablative dose fractions with sub-centimeter accuracy to the patient

The practice of SBRT, therefore, requires a high level of confidence in the accuracy of the entire treatment delivery process.

(Blog content extracted from a few chapters of the book titled “Frontiers in Radiation Oncology”)