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SU‐E‐T‐801: VMAT for the Treatment for Cervical Carcinoma and Para‐Aortic Nodes
Author(s) -
Lee C
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612765
Subject(s) - medicine , nuclear medicine , rectum , dosimetry , cervical carcinoma , radiation treatment planning , cervical cancer , radiation therapy , radiology , cancer , surgery
Purpose: The PTV of cervical carcinoma and para‐aortic nodes is unique for its large width and length which pose a challenge to VMAT because of the MLC leaf length, speed and gantry rotation speed restrictions. This study establishes a field arrangement for VMAT and assesses the differences between VMAT and IMRT plans. Methods: Six patients were randomly selected for the study. The CTV included the areas of subclinical risk around the GTV and associated lymph node drainage sites. The PTV margin includes a 0.7cm expansion around the lymph nodes and 0.5cm margin elsewhere. Organs at risk included rectum, bladder, small bowel and kidneys. Six plans, each consisting of three arcs (collimator angle 90 degrees on one and 0 on others) and 9 field IMRT plans were generated with Eclipse treatment planning system and delivered with a 6MV beam and 120 leaf MLC. Planning goals for both VMAT and IMRT plans were: V100 of the PTV covered by 98% prescription dose with a maximum dose <112%, V15 < 33% for both kidneys, V40<60% for bladder and rectum and mean small bowel dose < 30Gy. Treatment time was measured from when the beam data was loaded into the treatment console to the end of beam delivery. Results: The average PTV was 1850cm3. The PTV coverage met the constraints on all plans. The average rectal V40 (VMAT: 56%; IMRT: 62%), bladder V40 (VMAT: 55%; IMRT: 59%) and mean small bowel dose (VMAT: 23Gy; IMRT: 24Gy) were comparable. The mean left and right kidneys V15 were substantially reduced with VMAT (VMAT: 15%; IMRT: 28.1%) and (VMAT: 14.1%; IMRT: 29.5%). VMAT reduced the average MU from 2581 to 662 resulting mean delivery time of 791s to 292s. Conclusions: VMAT results substantial kidney sparing for the same coverage while reducing treatment time and monitor units.