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SU‐E‐T‐179: Clinical Impact of IMRT Failure Modes at Or Near TG‐142 Tolerance Criteria Levels
Author(s) -
Faught J Tonigan,
Balter P,
Johnson J,
Kry S,
Court L,
Stingo F,
Followill D
Publication year - 2015
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 - 10.1118/1.4924540
Subject(s) - imaging phantom , radiation treatment planning , nuclear medicine , pinnacle , collimator , multileaf collimator , biomedical engineering , medicine , radiation therapy , physics , radiology , optics
Purpose: Quantitatively assess the clinical impact of 11 critical IMRT dose delivery failure modes. Methods: Eleven step‐and‐shoot IMRT failure modes (FMs) were introduced into twelve Pinnacle v9.8 treatment plans. One standard and one highly modulated plan on the IROC IMRT phantom and ten previous H&N patient treatment plans were used. FMs included physics components covered by basic QA near tolerance criteria levels (TG‐142) such as beam energy, MLC positioning, and MLC modeling. Resultant DVHs were compared to those of failure‐free plans and the severity of plan degradation was assessed considering PTV coverage and OAR and normal tissue tolerances and used for FMEA severity scoring. Six of these FMs were physically simulated and phantom irradiations performed. TLD and radiochromic film results are used for comparison to treatment planning studies. Results: Based on treatment planning studies, the largest clinical impact from the phantom cases was induced by 2 mm systematic MLC shift in one bank with the combination of a D95% target under dose near 16% and OAR overdose near 8%. Cord overdoses of 5%–11% occurred with gantry angle, collimator angle, couch angle, MLC leaf end modeling, and MLC transmission and leakage modeling FMs. PTV coverage and/or OAR sparing was compromised in all FMs introduced in phantom plans with the exception of CT number to electron density tables, MU linearity, and MLC tongue‐and‐groove modeling. Physical measurements did not entirely agree with treatment planning results. For example, symmetry errors resulted in the largest physically measured discrepancies of up to 3% in the PTVs while a maximum of 0.5% deviation was seen in the treatment planning studies. Patient treatment plan study results are under analysis. Conclusion: Even in the simplistic anatomy of the IROC phantom, some basic physics FMs, just outside of TG‐142 tolerance criteria, appear to have the potential for large clinical implications.