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Validation of target volume and position in respiratory gated CT planning and treatment
Author(s) -
Shen Sui,
Duan Jun,
Fiveash John B.,
Brezovich Ivan A.,
Plant Brian A.,
Spencer Sharon A.,
Popple Richard A.,
Pareek Prem N.,
Bonner James A.
Publication year - 2003
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 - 10.1118/1.1626121
Subject(s) - gating , scanner , nuclear medicine , imaging phantom , fiducial marker , volume (thermodynamics) , medical imaging , expiration , materials science , biomedical engineering , medicine , physics , optics , radiology , respiratory system , physiology , quantum mechanics
The capability of a commercial respiratory gating system based on video tracking of reflective markers to reduce motion‐induced CT planning and treatment errors was evaluated. Spherical plastic shells (2.8–82 cm 3 ), simulating the gross target volume (GTV), were placed in a water‐filled body phantom that was moved sinusoidally along the longitudinal axis of the CT scanner and the accelerator for ±1 cm at 15–30 cycle/min. During gated CT imaging, the x‐ray exposure was initiated by the gating system shortly before the end of expiration (so that the imaging time would be centered at the end of expiration); it was terminated by the scanner after completion of each slice. In nongated CT images, the target appeared distorted and often broken up. GTVs volume errors ranged 16%–110% in axial scans, and 7%–36% in spiral scans. In gated CT images, the spheres appeared 3 and 5 mm longer than their actual diameters (volume errors 2%–16%), at the respective respiration rates of 15 and 20 cycles/min. At 30 cycles/min the target appeared 1 cm longer, and volume error ranged 25%–53%. During treatment, gating kept the beam on for a duration equal to the CT acquisition time of 1 s/slice. The difference in positional errors between gated CT and portal films was 1 mm, regardless the size of residual motion errors. Because of the potential of suboptimal placement of the gating window between CT imaging and treatment, an extra 1.5–2.5 mm safety margin can be added regardless of the size of residual motion error. For respiratory rates ⩾30 cycles/min, the effectiveness of gating is limited by large residual motion in the 1 s CT acquisition time.