The effect of a carbon-fiber couch on the depth-dose curves and transmission properties for megavoltage photon beams.
OBJECTIVE
To investigate the attenuation of a carbon-fiber tabletop and a combiboard, alongside with the depth-dose profile in a solid-water phantom.


METHODS
Depth-dose measurements were performed with a Roos chamber for 6- and 10-MV beams for a typical field size (15 cm x 15 cm, SSD [source-surface distance] 100 cm). A rigid-stem ionization chamber was used to measure transmission factors.


RESULTS
Transmission factors varied between 93.6% and 97.3% for the 6-MV beam, and 95.1% and 97.7% for the 10-MV photon beam. The lowest transmission factors were observed for the oblique gantry angle of 150 degrees with the table-combiboard combination. The surface dose normalized to a depth of 5 cm increased from 59.4% (without table, 0 degrees gantry), to 108.6% (tabletop present, 180 degrees gantry), and further to 120% (table-combiboard combination) for 6-MV photon beam. For 10 MV, the increase was from 39.6% (without table), to 88.9% (with table), and to 105.6% (table-combiboard combination). For the 150 degrees angle (tablecombiboard combination), the dose increased from 59.4% to 120% (6 MV) and from 39% to 108.1% (10 MV).


CONCLUSIONS
Transmission factors for tabletops and accessories directly interfering with the treatment beam should be measured and implemented into the treatment-planning process. The increased surface dose to the skin should be considered.
Poppe
Björn
B
Clinic of Radiotherapy and Oncology, Pius Hospital Oldenburg, Oldenburg, Germany.
Chofor
Ndimofor
N
Rühmann
Antje
A
Kunth
Wolfgang
W
Djouguela
Armand
A
Kollhoff
Ralf
R
Willborn
Kay C
KC
D001513:Beds; D002244:Carbon; D000077482:Carbon Fiber; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017785:Photons / Q000627:therapeutic use*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation* / Q000379:methods; D012542:Scattering, Radiation
D000077482:Carbon Fiber; D002244:Carbon