Can intensity-modulated radiation therapy of the Paraaortic region overcome the problems of critical organ tolerance?

BACKGROUND AND PURPOSE: The recent RTOG guidelines for future clinical developments in gynecologic malignancies included the investigation of dose escalation in the paraaortic (PO) region which is, however, very difficult to target due to the presence of critical organs such as kidneys, liver, spinal cord, and digestive structures. The aim of this study was to investigate intensity-modulated radiotherapy's (IMRT) possibilites of either increasing, in a safe way, the dose to 50-60 Gy in case of macroscopic disease or decreasing the dose to organs at risk (OR) when treatment is given in an adjuvant setting. MATERIAL AND METHODS: The dosimetric charts of 14 patients irradiated to the PO region at the Department of Radiation Oncology, University Hospital of Liege, Belgium, in 2000 were analyzed in order to compare six-field conformal external-beam radiotherapy (CEBR) and five-beam IMRT approaches. Both CEBR and IMRT investigations were planned to theoretically deliver 60 Gy to the PO region in the safest way possible. Dose-volume histograms (DVHs) were calculated for clinical target volume (CTV), planning target volume (PTV), and OR. Student's t-test was used to compare the paired DVH data issued from CEBR and IMRT planning. RESULTS: The IMRT approach allowed to cover the PTV at a higher level as compared to CEBR. Using IMRT, the maximal dose to the spinal cord was reduced from 42.5 Gy to 26.2 Gy in comparison with CEBR (p < 0.00001). Doses to the kidneys were significantly reduced, with < 20% receiving >or= 20 Gy in the IMRT approach (p < 0.00001). Irradiation of digestive structures was not different, with < 25% receiving 35 Gy. Doses to the liver remained low regardless of the method used. CONCLUSION: At 60 Gy, IMRT is largely sparing the spinal cord and kidneys as compared to CEBR and represents an interesting approach not only for dose escalation up to 50-60 Gy (probably facilitating the radiochemotherapy approaches) but also in an adjuvant setting at lower doses. The dosimetric data of this study are in the same range as those published recently with a dynamic arc conformal approach.