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Dr Loiselle

Not Black or White…

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It is Gray – after L.H. Gray (known as “Hal” Gray), a British radiation scientist and researcher (1905-1965), after whom contemporary radiation dose measurement was named in his honor in 1975.  The radiation dose in Gray refers to the amount of absorbed radiation energy per unit of mass in the body – one Gray is specifically one joule per kilogram. 

Cancers have known dose thresholds at which elimination of the tumor is likely.  Normal tissues have thresholds at which toxicity of radiation therapy may ensue.  These dose values vary across different organs in the body, and depend on factors such as the absolute and relative volume of the organ under irradiation as well as the orientation of the radiation dose regions to the organ structure.  In this discussion we will focus on dose limits of normal tissues as they relate to the treatment of lung cancer. 

In and around the lungs are a myriad of critical normal tissues.  First of all, there is the lung itself, and the major airways which feed its air supply: the trachea and bronchi.  In the middle of the chest between the lungs (this area is known as the “mediastinum”) are found the esophagus (swallowing tube that connects the mouth and stomach), the vertebral column (bones of the spine) and spinal cord (nerves of the spine), and the great blood vessels of the chest: the aorta and vena cava.  Adjacent to all of these is the heart (somewhat to the left side as we all know).  Wrapping around the outside are the ribs, muscles of the chest wall, skin and breast tissue. 

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Potential Improvements in Whole Brain Radiation Therapy

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We have often discussed on the GRACE forum the pros and cons of various approaches to address brain metastases from non-small cell lung cancer, such as whole brain radiation therapy and stereotactic radiosurgery. One concern with regard to whole brain radiation therapy is the potential long term impact on cognitive function, in particular potential reduction in skills related to short term memory, learning and multi-tasking.

Multiple lines of research evidence point towards one particular area of the brain as very important for learning and memory – the hippocampus. The hippocampus is located in the medial aspect of the temporal lobe of the brain. In the human brain, there is a right and a left hippocampus. Nearly all right handed people are left brain dominant, and the majority of left handed people are also left brain dominant – thus the left hippocampus frequently may play a stronger contributive role in cognitive function.

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V20: What is it, and why do we care?

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Radiation Oncologists are highly cognizant and careful with regard to the potential side effects of radiation therapy on the normal tissues and organs of the body. In the care of patients with lung cancer, the Radiation Oncologist must carefully examine potential radiation doses (depending on specific clinical situations) to the heart, chest wall (ribs and musculature), spinal cord, esophagus, and to the lung itself.

With regard to the healthy, normal lung tissue surrounding a lung cancer, it has been long known that radiation therapy can cause an inflammatory reaction in the lungs with a potentially significant negative impact on the patient’s health and respiratory function. When significant enough volume of the lung is exposed to significant enough radiation doses, the risk for causing a radiation induced lung problem is real. As a result of radiation exposure, a condition known as radiation pneumonitis can develop.

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What is SBRT, and which patients are good SBRT candidates?

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SBRT stands for Stereotactic Body Radiation Therapy, a radiation therapy approach which delivers high dose radiation to a target within the body, in either a single treatment session or up to  approximately five treatment sessions (each session is typically referred to as a “fraction”).

The first term in the acronym, “stereotactic” refers to precise three dimensional localization of a tumor target.  The incorporation of the second term in the acronym, “body,” is of historical derivation.  Stereotactic radiation therapy was first invented for the treatment of brain tumors with tools like the Gamma Knife – which has been in practice for a half century.  Extension of stereotactic high-dose radiotherapy techniques to tumor targets outside of the brain and cranium is relatively novel, an advent of the past decade.   Thus the use of the term “body” delineates that the technique is being applied to extracranial (non-brain) tumors. Continue reading


Postoperative Radiation Therapy after Surgery for Lung Cancer

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When technically and medically possible, surgery is often the best upfront therapy for non-small cell lung cancer (NSCLC).  In some circumstances, radiation therapy after surgery can increase the chance of controlling cancer at its primary site and in regional lymph nodes.  Let’s discuss some of those settings.

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