A quantitative treatment planning study evaluating the potential of dose escalation in conformal radiotherapy of the oesophagus

Background and purpose: This study aims to evaluate the reduction in radiat ion dose to normal thoracic structures through the use of conformal radioth erapy techniques in the treatment of oesophageal cancer, and to quantify th e resultant potential for dose escalation. Materials and methods: Three different CT-derived treatment plans were crea ted and compared for each of ten patients. A two-phase treatment with conve ntional straight-edged fields and standard blocks (CV2), a two-phase confor mal plan (CF2), and a three-phase conformal plan where the third phase was delivered to the gross tumour only (CF3), were considered for each patient. Escalated dose levels were determined for techniques CF2 and CF3, which by virtue of the conformal field shaping, did not increase the mean lung dose . The resulting increase in tumour control probability (TCP) was estimated. Results: A two-phase conformal technique (CF2) reduced the volume of lung i rradiated to 18 Gy from 19.7 +/- 11.8 (1 SD) to 17.1 +/- 12.3% (P = 0.004), and reduced the normal tissue complication probability (NTCP) from 2.4 +/- 4.0 to 0.7 +/- 1.6% (P = 0.02) for a standard prescribed dose of 55 Gy. Co nsequently, technique CF2 permitted a target dose of 59.1 +/- 3.2 Gy withou t increasing the mean lung dose. Technique CF3 facilitated a prescribed dos e of 60.7 +/- 4.3 Gy to the target, the additional 5 Gy increasing the TCP from 53.1 +/- 5.5 to 68.9 +/- 4.1%. When the spinal cord tolerance was rais ed from 45 to 48 Gy, technique CF3 allowed 63.6 +/- 4.1 Gy to be delivered to the target, thereby increasing the TCP to 78.1 +/- 3.2%. Conclusions: Conformal radiotherapy techniques offer the potential for a 5- 10 Gy escalation in dose delivered to the oesophagus, without increasing th e mean lung dose. This is expected to increase local tumour control by 15-2 5%. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.