Effect of a carbon fiber tabletop on the surface dose and attenuation for high-energy photon beams.
OBJECTIVE
The dose changes in the buildup region and beam attenuation by a carbon fiber tabletop were investigated for 6-and 18-MV photon beams.


METHODS
Measurements were performed for 2 x 2 cm to 40 x 40 cm field sizes. The surface dose and percentage depth doses (PDD) were measured by a Markus parallel plate chamber. Attenuation measurements were made at the cylindrical phantom for 180 degrees rotation of the beam.


RESULTS
A carbon fiber tabletop increases the surface dose from 7.5% to 63.0% and from 4% to 43% for small fields at 6 and 18 MV, respectively. The increase was nearly fivefold for the 10 x 10 cm field and nearly twofold for the 40 x 40 cm field. Beam attenuation of the tabletop varies from 3.0% to 5.6% for 180 degrees and 120 degrees gantry angles for 6 MV.


CONCLUSIONS
The carbon fiber tabletop significantly decreases the skin-sparing effect. The dosimetric effect of the tabletop may be higher, especially for the intensity-modulated radiation therapy depending on the beam orientation. Attenuation should be considered and corrected such as any material under the patient at the treatment planning stage.
Meydanci
Tülay P
TP
Department of Radiation Oncology, Kocaeli Medical School, University of Kocaeli, Kocaeli, Turkey.
Kemikler
Gönül
G
D002244:Carbon; D000077482:Carbon Fiber; D003764:Dental Materials; D004867:Equipment Design; D006801:Humans; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D011882:Radiotherapy, High-Energy / Q000295:instrumentation* / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods
D000077482:Carbon Fiber; D003764:Dental Materials; D002244:Carbon