Pelvic Ewing sarcomas. Three-dimensional conformal vs. intensity-modulated radiotherapy.

PURPOSE: The goal of the present work was to assess the potential advantage of intensity-modulated radiotherapy (IMRT) over three-dimensional conformal radiotherapy (3D-CRT) planning in pelvic Ewing's sarcoma.

PATIENTS AND METHODS: A total of 8 patients with Ewing sarcoma of the pelvis undergoing radiotherapy were analyzed. Plans for 3D-CRT and IMRT were calculated for each patient. Dose coverage of the planning target volume (PTV), conformity and homogeneity indices, as well as further parameters were evaluated.

RESULTS: The average dose coverage values for PTV were comparable in 3D-CRT and IMRT plans. Both techniques had a PTV coverage of V95 > 98 % in all patients. Whereas the IMRT plans achieved a higher conformity index compared to the 3D-CRT plans (conformity index 0.79 ± 0.12 vs. 0.54 ± 0.19, p = 0.012), the dose distribution across the target volumes was less homogeneous with IMRT planning than with 3D-CRT planning. This difference was statistically significant (homogeneity index 0.11 ± 0.03 vs. 0.07 ± 0.0, p = 0.035). For the bowel, Dmean and D1%, as well as V2 to V60 were reduced in IMRT plans. For the bladder and the rectum, there was no significant difference in Dmean. However, the percentages of volumes receiving at least doses of 30, 40, 45, and 50 Gy (V30 to V50) were lower for the rectum in IMRT plans. The volume of normal tissue receiving at least 2 Gy (V2) was significantly higher in IMRT plans compared with 3D-CRT, whereas at high dose levels (V30) it was significantly lower.

CONCLUSION: Compared to 3D-CRT, IMRT showed significantly better results regarding dose conformity (p = 0.012) and bowel sparing at dose levels above 30 Gy (p = 0.012). Thus, dose escalation in the radiotherapy of pelvic Ewing's sarcoma can be more easily achieved using IMRT.