Purpose: To investigate the effects of tissue inhomogeneity corrections on the dose delivered to prostate cancer patients treated with Intensity-Modulated Radiation Therapy (IMRT). Methods and Materials: For five prostate cancer patients, IMRT treatment plans were generated using 6 MV or 10 MV X-rays. In each plan, seven equally spaced ports of photon beams were directed to the isocenter, neglecting the tissue heterogeneity in the body. The dose at the isocenter, mean dose, maximum dose, minimum dose and volume that received more than 95% of the isocenter dose in the planning target volume (V_p＞95%) were measured. The maximum doses to the rectum and the bladder, and the volumes that received more than 50, 75 and 90% of the prescribed dose were measured. Treatment plans were then recomputed using tissue inhomogeneity correction maintaining the intensity profiles and monitor units of each port. The prescription point dose and other dosimetric parameters were remeasured. Results: The inhomogeneity correction reduced the prescription point dose by an average 4.9 and 4.0% with 6 and 10 MV X-rays, respectively. The average reductions of the V_p＞95% were 0.8 and 0.9% with the 6 and 10 MV X-rays, respectively. The mean doses in the PTV were reduced by an average of 4.2 and 3.4% with the 6 and 10 MV X-rays, respectively. The irradiated volume parameters in the rectum and bladder were less decreased; less than 2.1% (1.2%) of the reduction in the rectum (bladder). The average reductions in the mean dose were 1.0 and 0.5% in the rectum and bladder, respectively. Conclusions: Neglect of tissue inhomogeneity in the IMRT treatment of prostate cancer gives rise to a notable overestimation of the dose delivered to the target, whereas the impact of tissue inhomogeneity correction to the surrounding critical organs is less significant.

KeywordsInhomogeneity corrections, IMRT, Density correction, Prostate