TITLE:
An Evaluation of Inter-Fractional Set-Up Errors in Patients Treated with Distinct Immobilization Equipment for Varying Anatomical Regions
AUTHORS:
Sibel Karaca, Hamit Başaran, Timur Koca, Ferhat Özbayrak
KEYWORDS:
Hi-Art Helical Tomotherapy, IGRT, Inter-Fractional Set-Up Errors, Rotational Variation, Translational Variation
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.5 No.2,
May
19,
2016
ABSTRACT: This study aims to evaluate inter-fractional set-up errors in patients treated with distinct immobilization
equipment (thermoplastic mask, knee-fix and feet-fix, wing board and vac-lok) for four
anatomical regions including brain, head and neck (HN), thorax and pelvis. Data of randomly selected
140 patients who were treated for four anatomical regions were obtained using Hi-Art Helical
Tomotherapy (HT) system. Pre-treatment planning was based on automatic registration
readings of computed tomography (CT) and mega-voltage computed tomography (MVCT) on a
daily basis. Distinct immobilization equipment was used for varying anatomical regions. Individual
mean set-up error (M), systematic error (Σ), and random error (σ) values were calculated
through daily translational and rotational deviation values. The size of translational, systematic
and random error was 1.31 - 4.93 mm for brain, 2.28 - 4.88 mm for HN, 4.04 - 9.90 mm for thorax,
and 6.34 - 14.68 mm for pelvis. Rotational values were as follows: 0.06° - 0.73° for brain, 0.42° - 0.6°
for HN, 0.48° - 1.14° for thorax and 0.65° - 1.05° for pelvis. The highest translational, systematic and
random error value was obtained from the pelvic regional. The highest standard and random error
value in pitch and roll was produced in the rotational direction of the pelvis (0.05° and 0.71°),
while the highest error value in yaw was (1.14°) produced from thorax. Inter-fractional set-up errors
were most commonly produced in the pelvis, followed by thorax. Our study results suggest
that the highest systematic and random errors are found for thorax and pelvis. Distinct immobilization
equipment was important in these results. Safety margins around the clinical target volume
(CTV) are changeable for different anatomical regions. A future work could be developed to new
equipment for immobilization because of the reduced margins CTV.