Sci‐AM2 Sat ‐ 03: Anatomy‐based MLC field optimization for the treatment of gynecologic malignancies

• Published in: Medical physics (Lancaster) Vol. 32; no. 7; p. 2425
• Main Authors: Nadeau, S, Bouchard, M, Germain, I, Raymond, P‐E, Beaulieu, F, Beaulieu, L, Roy, R, Harel, F, Gingras, L
• Format: Journal Article
• Language: English
• Published: American Association of Physicists in Medicine 01-07-2005
• Subjects: Anatomy; Cancer; Intensity modulated radiation therapy; Multileaf collimators
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.2031053

To evaluate the use of a new inverse planning system with anatomy‐based field segmentation, as an alternative between “4‐field box” and beamlet‐based IMRT, to treat whole pelvis of women with resected gynecologic malignancies. A class solution has been elaborated with the assistance of an in‐house optimization tool named Ballista. This inverse planning system can generate anatomy‐based MLC fields and simultaneously optimize their orientation and weight. The selected geometry consists of 7 coplanar and 2 noncoplanar incidences. For 10 patients planned to receive 45Gy for resected endometrial or cervix neoplasia, target volume and organ at risk (bowel, region “at risk to find bowel” (B‐RAR), bladder, rectum, bone marrow) were delineated. Using the Pinnacle3
planning system, four plans were generated for each patient: conventional 4‐field, enlarged 4‐field (aperture shaped to PTV),“step‐and‐shoot” IMRT and Ballista plans. Dose‐volume histograms, number of segments and monitor units (MU) were analyzed. Statistical significance is based on Student's paired t‐test. The mean volume of B‐RAR receiving 45Gy was: 4‐field, 49.7±7.1%; enlarged 4‐field, 63.4±5.8%; IMRT, 26.4±3.1%; Ballista, 29.0±3.0%. No statistical difference was noted between the ability of IMRT and Ballista to spare bowel (p=0.14), while both plans were better than 4‐field (p<0.001). The mean number of segments for Ballista was 33.3±2.3 vs 128.6±2.6 for IMRT and the mean number of MU was 325.0±11.8 vs 731.5±25.0. Weight optimization, with anatomy‐based MLC fields, is a good alternative between manual planning and IMRT for the treatment of gynecologic malignancies. Clinical results of treatment tolerance will follow.