A comparison of conformal and intensity-modulated techniques for oesophageal radiotherapy

Background and purpose: To investigate the potential of intensity-modulated radiotherapy (IMRT) to reduce lung irradiation in the treatment of oesopha geal carcinoma with radical radiotherapy. Materials and methods: A treatment planning study was performed to compare two-phase conformal radiotherapy (CFRT) with IMRT in five patients. The CFR T plans consisted of anterior, posterior and bilateral posterior oblique fi elds, while the IMRT plans consisted of either nine equispaced fields (9F), or four fields (4F) with orientations equal to the CFRT plans. IMRT plans with seven, five or three equispaced fields were also investigated in one p atient. Treatment plans were compared using dose-volume histograms and norm al tissue complication probabilities. Results: The 9F IMRT plan was unable to improve on the homogeneity of dose to the planning target volume (PTV), compared with the CFRT plan (dose rang e, 16.9 +/- 4.5 (1 SD) vs. 12.4 +/- 3.9%; P = 0.06). Similarly, the 9F IMRT plan was unable to reduce the mean lung dose (11.7 +/- 3.2 vs. 11.0 +/- 2. 9 Gy; P = 0.2). Similar results were obtained for seven, five and three equ ispaced fields in the single patient studied. The 4F IMRT plan provided com parable PTV dose homogeneity with the CFRT plan (11.8 +/- 3.3 vs. 12.4 +/- 3.9%; P = 0.6), with reduced mean lung dose (9.5 +/- 2.3 vs 11.0 +/- 2.9 Gy ; P = 0.001). Conclusions: IMRT using nine equispaced fields provided no improvement over CFRT. This was because the larger number of fields in the IMRT plan distri buted a low dose over the entire lung. In contrast, IMRT using four fields equal to the CFRT fields offered an improvement in lung sparing. Thus, IMRT with a few carefully chosen field directions may lead to a modest reductio n in pneumonitis, or allow tumour dose escalation within the currently acce pted lung toxicity. (C) 2001 Elsevier Science Ireland Ltd. All rights reser ved.