Integral radiation dose to normal structures with conformal external beam radiation

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Background: This study was designed to evaluate the integral dose (ID) received by normal tissue from intensity modulated radiotherapy (IMRT) for prostate cancer.Materials and Methods: Twenty-five radiation treatment plans, including MRT using a conventional linac with both 6 (6MV-IMRT) and 20 MV (20MV-IMRT) as well as 3DCRT using 6 (6MV-3DCRT) and 20 MV (20MV-3DCRT), and IMRT using tomotherapy (6MV) (Tomo-IMRT), were created for five patients with localized prostate cancer. The ID (mean dose X tissue volume) received by normal tissue (NTID) was calculated from dose-volume histograms.Results: 6MV-IMRT resulted in 5.0% lower NTID than 6MV-3DCRT; 20MV beam plans resulted in 7.7-11.2% lower NTID than 6 MV-3DCRT. Tomo-IMRT NTID was comparable to 6 MV-IMRT. Compared to 6MV-3DCRT, 6MV-IMRT reduced IDs to the rectal wall and penile bulb by 6.1% and 2.7%, respectively. Tomo-IMRT further reduced these IDs by 11.9% and 16.5%, respectively. 20MV did not reduce IDs to those structures.Conclusions: The difference of NTID between 3DCRT and IMRT is small. 20MV plans somewhat reduced NTID compared to 6MV plans. The advantage of tomotherapy over conventional IMRT and 3DCRT for localized prostate cancer was demonstrated in regard to dose sparing of rectal wall and penile bulb without increasing NTID.