Quantification of the skin sparing effect achievable with high-energy photon beams when carbon fiber tables are used

PurposeTo quantify the skin doses resulting from the use of carbon fiber couches (CFCs) for patient support.Materials and methodsBrainLab’s CFC was evaluated for five prostate patients and five lung patients. For each patient PTV, organs at risk (OARs), and a 0.3 cm thick skin contour on the patient’s posterior surface were outlined. Two sets of IMRT plans, each consisting of 4, 5, 7, and 9 beams, were generated per patient. The sets were identical with the exception that in the first set only 6 MV energy was used, while in the second set (mixed energy) the photon energy of the beams traversing the CFC was 18 MV. The plans for each patient were normalized to deliver the same dose to 95% of the PTV. The CFC skin dose was evaluated by the maximum dose received by 1% (D1%) of the skin volume. Paired one-tailed t-tests were used to establish the statistical significance.ResultsThe mixed energy plans resulted in D1% increase from 18% to more than 23% as the number of beams in the plan was decreased from 9 to 4.ConclusionsSkin doses as high as ∼70% of the prescription dose were found even in 9-beam mixed energy plans. Therefore mixed energy plans may be more beneficial for patients treated with higher fractional doses.