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Price RA , Paskalev K , McNeeley S , Ma CM
Elongated beamlets: a simple technique for segment and MU reduction for sMLC IMRT delivery on accelerators utilizing 5 mm leaf widths
Physics in Medicine and Biology. 2005 Oct 7;50(19) :N235-N242
AbstractThe focus of this work is to demonstrate the effects of using an elongated beamlet to achieve similar dose conformity as achieved with a square beamlet while reducing the number of segments and subsequent MU required. A series of 10 patients were planned for IMRT delivery to the prostate using minimum beamlet sizes of 5 x 5 mm(2) (default scheme), 10 x 5 mm(2) with the short axis parallel to the prostate-rectum interface (scheme 1), and 10 x 5 mm(2) with the short axis perpendicular to the prostate-rectum interface (scheme 2). All other parameters between plans were left unchanged. Plans were appropriately normalized and evaluated for R65, R40, conformity index, total number of segments and MU. All plans were generated using the Corvus inverse planning system. The average number of segments in this study decreased by approximately 49% for both schemes 1 and 2. The subsequent number of MU required decreased by approximately 34.6%. The resultant modified modulation scaling fac tor (MSFmod) decreased by approximately 34.3%. Additionally, we found that each isodose distribution using scheme 2 would still meet our clinical acceptance criteria with no visible degradation in the dose distribution as compared with the default scheme. In conclusion, we have demonstrated that it is possible to achieve similar results as those obtained using a 5 x 5 mm(2) beamlet with respect to target coverage and critical structure sparing by using strategically oriented elongated beamlets. This technique directly translates to a decreased MSFmod allowing for decreased leakage dose to the patient, a decreased risk of exceeding secondary shielding limits in pre-existing vaults, and shorter treatment times.