Optimization of arc angles in rotational therapy.
Data is presented that will aid in optimizing the arc angles used for rotational therapy for a 6 Mv x-ray beam. Computer calculations of isodose distributions were carried out and the Ap and Lateral dimensions of the 95 and 100% isodose line were tabularized as a function of the field width (6-14 cm), distance between isocenter and patient midline (0-3 cm), and bilateral 120 or 100 degrees arc angle. The 300 degrees rotation cases we studied were generally found to be inferior to 120 degrees or 100 degrees bilateral arc rotations. 120 degrees arcs are best when the target center is within 2 cm of the patient's Ap center. As that separation increases, the bilateral arc angle should be decreased or wedges should be rotated through 300 degrees to avoid maximum doses greater than 105%. The data tables can be used as a starting point for computer calculations to select the field width and the arc angle for a particular target location and size. Of note is the degree to which the dimensions of the 100% isodose line decreases for small field widths and large isocenter to patient midline distances.
Olch
A J
AJ
Kaiser Permanente Radiation Oncology Department, Los Angeles, California 90027.
Kagan
A R
AR
Wollin
M
M
Bellotti
J
J
D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011882:Radiotherapy, High-Energy / Q000379:methods*; D012399:Rotation