Dosimetric considerations in the choice of photon energy for external beam radiation therapy: clinical examples

Laughlin, Mohan, and Kutcher have evaluated photon beams for Co-60 through 24 MV for eight clinical disease sites plus pediatrics and concluded that two energy ranges are required for the best patient care: a 4 to 6 MV beam and a 10 to 18 MV beam. The present study investigates the question which two energies in a dual energy machine are optimum for the average patient mix. The method used is to calculate two dimensional sample cases including breast, head and neck, and pelvic tumors on the same treatment planning system using machine data including Co-60, 4 MV, 6 MV, 10 MV, and 18 MV x-ray beams. The resulting plans were evaluated considering tumor doses, spinal cord doses, doses to subcutaneous tissues and doses to other radiosensitive structures. The conclusion is that the optimum two beams are 6 and 10 MV.