A phantom study for the reconstruction defects of moving target volume decision by spiral CT

Objective: To investigate reasonable method of deciding internal target volume (ITV) by comparing physical phantom volumes (including moving volume) with reconstruction volumes of spiral CT scanning. Methods: The various-volume wax blocks which were labeled No.1-9 were made and put on the respiratory motion simulator. The range of motion was set 2.5 cm and frequency 18 beats/min. All blocks were scanned 10 times continuously and imported into the Eclipse TPS. All blocks volumes were calculated and then compared with the true physical volumes and paired t-test. Results: The reconstruction volumes of 1-9 blocks were bigger than their stationary volumes (121.77 cm³ vs. 103.14 cm³, P = 0.038), but significantly smaller than their moving volumes (121.77 cm³ vs. 161.75 cm³, P = 0.045). The results can be gotten in different volume block scanning. The relative deviation of reconstruction volumes and the moving volumes tends to increase as the stationary physical volume decreases. Conclusions: As to moving targets, conventional spiral CT scanning speed is too fast to collect all volume information of targets. So the one-time-scanning volume does not represent the ITV. (authors)