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SU‐E‐T‐482: Measuring Planned and Delivered Dose Discrepancies of Gated IMRT
Author(s) -
Geneser S,
Fahimian B,
Xing L
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 - 10.1118/1.3612435
Subject(s) - imaging phantom , gating , torso , nuclear medicine , dosimetry , breathing , radiation treatment planning , biomedical engineering , medicine , radiation therapy , materials science , radiology , physiology , anatomy
Purpose: Respiration‐gated radiation therapy restricts delivery to a window around a specific phase or amplitude of the external breathing trace. In planning, the computed doses assume no motion within the gating window and ignores the residual motion within the gating window. We deliver IMRT to a torso phantom while (1) stationary and (2) undergoing 2 cm superior‐inferior motion, measure the resulting dose distributions using gafchromic film, and compare the delivered and the planned doses. Methods: A respiration‐gated treatment planned in Eclipse was delivered to a Quasar torso phantom on a 1D motion stage under two situations; non‐gated delivery to the stationary phantom and gated delivery while the phantom underwent sinusoidal translation. The resulting dose depositions were measured using gafchromic film, scanned, and quantified. The delivered dose distributions were compared to one another and the planned distribution and the dosimetric dependence caused by residual motion within the gating window was analyzed.Results: The static delivered dose matched the planned gated dose within 5%. The largest dose discrepancies occur primarily in the regions where high dose derivative (quick dose falloff) are perpendicular to the direction of movement. With up to 0.6 cm translation during the gating window, the static delivered and gated delivered doses showed differences as high as 0.4 Gy or 20% of the PTV prescribed dose. Much of the significant under‐dosing occurs within the PTV, while the overdosed areas of 0.2 Gy and higher occur outside of the PTV in the ipsilateral lung. Conclusions: Residual motion may lead to large dosimetric discrepancies from the gated treatment plan generated on the static patient model corresponding to the gating phase, and an effective way to mitigate this should be developed in the future for accurate gated planning and dose delivery.