Dosimetric investigation of breath-hold intensity-modulated radiotherapy for pancreatic cancer
Example of an abdominal motion pattern observed by the external respiratory monitoring system during EE–BH. Variations in abdominal motion derived from pulsation of the abdominal aorta and baseline drift were observed.
Phantom setup. The phantom was made of polystyrene with dimensions of 40 × 40 × 10 cm, and set on a motor-driven base. EDR2 x-ray film was placed at a depth of 4 cm in the phantom, perpendicular to the beam axis. The source–surface distance was 95 cm.
Boxplots of the ionization chamber measurements. The 95th percentiles of dose deviations between stationary and moving conditions were within ±3%.
(a) Isodose comparison between stationary (solid) and moving (dashed) conditions, and the γ pass/fail map with the criterion of (b) 2%/1 mm, (c) 3%/3 mm, and (d) 5%/3 mm for the area receiving more than 50% dose for the case with the lowest γ3%/3mm.
Dose profiles in (left column) lateral direction and (right column) longitudinal direction for the cases with the (a, b) the highest (patient 1, field V) and (c, d) the lowest (patient 7, field V) γ3%/3mm.
Correlation between BH time and the γ2%/1mm for baseline drift. Negative strong and weak correlations were observed between BH time and the γ2%/1mm for BD0.2mm/s (R = −0.72; p < 0.01) and BD0.4mm/s (R = −0.62; p < 0.01), respectively.
Histograms of the minimal γ passing rate. Black bar shows the minimal γ3%/3mm and gray the minimal γ5%/3mm. When γ3%/3mm and γ5%/3mm > 90% was considered acceptable, a drift of 5 mm would be the cutoff point.
Treatment information for each field.
The γ passing rate for baseline drift.
Correlations between BH time and the γD%/dm m for BD0.2mm/ s and BD0.4mm/ s.
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