| In radiation oncology, technological advances are constantly being made and applied. However, as each potential advance is made, the physics behind the delivered dose of ionizing radiation must first be tested clinically in a phantom. Recent advances in therapeutic dose delivery now enable us to deliver highly conformal doses to diseased tissues while sparing healthy, critical organs and other structures. Intensity modulated radiation therapy (IMRT), which is presently being implemented or considered by many institutions, and Monte Carlo simulation of dose distributions in regions surrounding air cavities, must both now be tested experimentally to understand the nature of electronic dis-equilibrium in regions containing air cavities such as the nasopharynx, lungs and bowel. Here at Tufts New England Medical Center, the use of tomotherapy (multiple arcing beam therapy) implementing a small pencil beam of radiation approximately 2 cm x 2 cm at isocenter (point of rotation of the gantry) is used. Dose distribution was studied and, it is believed, verified experimentally utilizing GAFchromic and x-ray films along with Monte Carlo code, in order to test the hypothesis that current doses determined using radiation treatment planning systems under the assumption of charged particle equilibrium in the vicinity surrounding air cavities vary significantly from Monte Carlo calculated results. Similarly, experimental film results were scanned and isodose (equal dose) lines were drawn. |
