RADIATION MEDICINE INNOVATIONS FOR THE NEW MILLENIUM

27 Jan
2010

technological advances

Recent technological advances are having a profound impact on radiation. New equipment and enhanced computer technologies foster the radiation oncologist’s ability to deliver radiation more precisely, increasing the dose to tumor targets and reducing the dose to normal tissues and critical structures. New treatment protocols have the potential to improve tumor control and cure rates with reduced complications. Some of the most significant technological developments of the past decade are highlighted in this article. It is the intent of the authors to elucidate some of these exciting areas of clinical radiotherapy such that practicing clinicians develop a greater comfort level when referring patients to a radiation oncologist.

COMPUTERIZED THREE-DIMENSIONAL CONFORMAL TREATMENT PLANNING

The ability to define tumor volume accurately and to tailor radiation dose to this volume has been a constant challenge for the radiation oncologist.
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The introduction of axial computerized tomography (CT) technology in treatment planning has allowed for increasingly more precise anatomic definition of tumor volumes and surrounding normal tissues. The CT data set provides the basis for a three-dimensional rendering of tumor volumes and more accurate radiation dose calculations. The individual CT slices that define targets and normal tissues can be stacked like dishes, and the reconstructed figures provide images that can be viewed from any angle. Although research in three-dimensional (3-D) dose calculations and display began as early as 1973, it is only within the past four years that functional 3-D radiation treatment planning systems have become available to community cancer centers; the full potential of these systems in now being realized. The importance of three-dimensional CT-based treatment planning on tumor control and reduced treatment complications has been recognized.

In lung cancer, researchers at Memorial Sloan-Kettering Cancer Center compared conventional and 3-D treatment planning for predominately stage III, non-small cell lung cancer (NSCLC). They were able to deliver higher doses of radiation to the tumor volume with the 3-D technique, while treating less volume of normal lung, and postulated an improvement in the therapeutic ratio with the use of 3-D technology. Colleagues at the University of Michigan at Ann Arbor demonstrated that doses in excess of 84 Gy to limited tumor volumes using 3-D planning are possible with acceptable toxicity. Dose escalation is, therefore, thought to be an important factor in improving local control and is believed by some to be essential in improving long-term survival. In addition, quantitative ventilation/perfusion and single photon emission computed tomography (SPECT) imaging can also complement the information provided by the CT scan in order to design treatment ports that spare larger volumes of functional lung.

For prostate cancer, 3-D treatment planning has allowed dose-escalation in excess of 90 Gy. It is unknown whether this will translate into greater long-term local control and survival. A recent article reported an actuarial survival and biochemical PSA (prostate-specific antigen) failure -free rate at eight years of 95% and 85%, respectively. Toxicity appeared to be reduced. Of more than 700 patients treated, the actuarial risk of Radiation Therapy Oncology Group (RTOG) grade 3-4 rectal complications was 3% at five years. In addition, up to two-thirds of patients maintained sexual potency following external beam radiation using this technology, contributing to a superior quality of life. An ongoing phase I/II RTOG trial is underway and may clarify the potential benefits of 3-D treatment planning for localized prostate cancer.

In head and neck cancer, xerostomia (dry mouth) is often a long-term complication from treatment to the salivary glands. This can be minimized with 3-D treatment planning. Eisbruch et al. demonstrated that it is feasible to treat sites of disease and spare the contralateral parotid gland, without compromising local control. Tumors in this region of the body are often located close or adjacent to critical structures such as the spinal cord and major salivary glands. The use of 3-D planning has proven helpful in minimizing toxicity and complications in these challenging patients. order levitra

For hepato-biliary tract malignancies, 3-D treatment planning has been able to limit the amount of normal liver treated and minimize development of radiation-induced liver disease (RILD). Doses in excess of 80 Gy have been safely delivered to localized hepatic tumors with only 5% (1 of 21 patients) developing RILD, an improvement over predicted normal tissue complication probability models. Although this sophisticated computational technology is now readily available, the degree of accuracy in the planning and daily delivery of radiation treatment is extremely critical, and demands highly trained and meticulous personnel.

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