Re-irradiation of spinal column metastases by IMRT: impact of setup errors on the dose distribution.
BACKGROUND
This study investigates the impact of an automated image guided patient setup correction on the dose distribution for ten patients with in-field IMRT re-irradiation of vertebral metastases.


METHODS
10 patients with spinal column metastases who had previously been treated with 3D-conformal radiotherapy (3D-CRT) were simulated to have an in-field recurrence. IMRT plans were generated for treatment of the vertebrae sparing the spinal cord. The dose distributions were compared for a patient setup based on skin marks only and a Cone Beam CT (CBCT) based setup with translational and rotational couch corrections using an automatic robotic image guided couch top (Elekta - HexaPOD™ IGuide® - system). The biological equivalent dose (BED) was calculated to evaluate and rank the effects of the automatic setup correction for the dose distribution of CTV and spinal cord.


RESULTS
The mean absolute value (± standard deviation) over all patients and fractions of the translational error is 6.1 mm (±4 mm) and 2.7° (±1.1 mm) for the rotational error. The dose coverage of the 95% isodose for the CTV is considerable decreased for the uncorrected table setup. This is associated with an increasing of the spinal cord dose above the tolerance dose.


CONCLUSIONS
An automatic image guided table correction ensures the delivery of accurate dose distribution and reduces the risk of radiation induced myelopathy.
Department of Radiotherapy, University Medical Center, Regensburg, Germany. christian.groeger@klinik.uni-regensburg.de.
Christian
C
Gröger
Matthias G
MG
Hautmann
Rainer
R
Loeschel
Natalia
N
Repp
Oliver
O
Kölbl
Barbara
B
Dobler
D001331:Automation; D054893:Cone-Beam Computed Tomography; D006801:Humans; D009362:Neoplasm Metastasis; D009364:Neoplasm Recurrence, Local; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted; D061106:Radiotherapy Setup Errors; D020266:Radiotherapy, Conformal / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012307:Risk Factors; D012371:Robotics; D013116:Spinal Cord / Q000528:radiation effects; D013118:Spinal Cord Diseases / Q000532:radiotherapy; D013125:Spinal Neoplasms / Q000532:radiotherapy* / Q000556:secondary