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SU‐FF‐T‐275: Improving IMRT Plans Delivery for Head and Neck Cases Using Aperture‐Based MLC Segments
Author(s) -
Lavoie C,
Beaulieu F,
Gingras L,
Nadeau S,
Sévigny C,
Tremblay D,
Beaulieu L
Publication year - 2006
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 - 10.1118/1.2241195
Subject(s) - pinnacle , nuclear medicine , medicine , radiation treatment planning , head and neck , radiation therapy , subtraction , dosimetry , radiology , surgery , mathematics , arithmetic
Purpose: To investigate the possibility of performing IMRT in head and neck treatment sites with less segments and monitor units (MU). Materials and Methods: Six pharyngeal cases (n = 6) were analysed and four cases (n = 4), in the sinonasal region. For each one, an IMRT plan was first realized using a commercial software (P 3 IMRT, Pinnacle 3 — IMFAST segmentation algorithm). These patients had to receive 32 fractions of simultaneous integrated boost external beam radiotherapy at 1.8 and 2.15 Gy/fraction, respectively to the low and high risk planning target volumes (PTV1 and PTV2). Then, an‐in‐house inverse planning system, called Ballista , based on predetermined segments, was used to realize comparable plans. Its segments are generated with the subtraction of the projection of the OARs with the PTV (planning target volume). Results: For the pharyngeal Ballista plans, the average volume of the PTV that received at least 100% of the prescribed dose (V 100 ) was 85.0±4.5% for the first prescription (PTV1) and the V 100 for the second prescription (PTV2 — simultaneous integrated boost —) was 78.5±10.9%. With Pinnacle 3 ,the V 100 value was 86.6±4.8% and 81.5±12.4% respectively for PTV1 and PTV2 (see figure 2a and 2b). On average, Ballista plans have required 932±124 MU and 52±10 segments compared to 1238±230 MU and 117±7 segments for Pinnacle 3 . For the sinonasal Ballista plans, the average V 100 obtained was 80.0±3.1%. With Pinnacle 3 , the V 100 gave 75.7±2.7%. Ballista plans have required an average of 406±54 MU and 22±1 segments compared to 697±133 MU and 99±14 segments for beamlet‐based IMRT. Conclusion: In step‐and‐shoot head and neck IMRT, an anatomy‐based MLC optimization system can achieve similar dosimetric plans comparable to traditional beamlet‐based IMRT with less number of segments and MU.