Total Body Irradiation on the Moving Table with Dynamic Shielding
Total body irradiation (TBI) is often used in combination with chemotherapy prior to bone marrow transplantation (BMT) for a number of malignant conditions and a few non-cancerous diseases. TBI at low doses of 300-600 cGy (equivalent single dose TBI) has been shown to be the single most effective immunosuppressive agent for bone marrow transplantation.
There exists a variety of total body irradiation procedures and the particular method utilized is limited by the facilities available at the institution. Most TBI treatments are done in the standing, lying or crouched position in which the entire body is encompassed by a stationary radiation beam. The most accurate and reproducible treatment requires the anterior/posterior (AP/PA) beam exposure and patient lying supine and prone, especially when shielding and bolusing is compulsory. This method requires, however distances between the source and the patient large enough to allow the vertically directed radiation beam to cover the full length of the body. For virtually all adults and for many children this requirement cannot be satisfied unless dedicated facilities are constructed specifically for this purpose. The unavailability of such facilities results in setups for TBI treatment that are often deficient in terms of Dosimetry, shielding of critical structures, lung block placing reproducibility and patient comfort. Furthermore, those setups are not easily applicable in treatment of children since patient cooperation is essential and even with anesthesia problems mentioned about would exist.
It is desirable to therefore to convert to a system that would allow patient to lie supine or prone on a table moving longitudinally under the radiation beam. In this case the beam does not have to encompass instantaneously the whole length of the body. This arrangement eliminates the need for large machine to patient distances in AP/PA vertical exposures. In result, it enables AP/PA TBI treatment in the most comfortable supine and prone position.
In the Department of Radiation Oncology, Indiana University School of Medicine we are able to treat our patients with this technique in the Cobalt-60 unit radiation beam since the construction of a dedicated moving table was completed in May 1996. Patient comfort and ease of immobilization reduce significantly setup times for the treatment, facilitate patient cooperation and reduce considerably the time radiation oncologist has to devote to treatment. Moreover, careful examinations of the patient dosimetry during TBI treatments on the moving table have shown significant dose uniformity enhancements (and shielding accuracy enhancements) relative to stationary treatments.
Thus our technique provides few distinct advantages over other methods of TBI treatment:
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