A comparison of conventional and conformal radiotherapy of the oesophagus: work in progress

A retrospective treatment planning study was carried out in five patients to assess the effectiveness of conformal radiotherapy of the oesophagus. A two-phase conventional treatment plan was created for each patient, with a prescribed dose of 55 Gy. This plan was compared with a single-phase conformal plan consisting of the same field arrangement as the second phase of the conventional treatment, but with conformal blocks shaped to the beam's eye view of the planning target volume. A further comparison was made between the conventional plan and a two-phase plan using the same beam angles and weights as the conventional plan, but with conformal field shapes. The effectiveness of each treatment plan was assessed using dose--volume histograms and normal tissue complication probabilities for the lungs. On average, the single-phase conformal technique increased the mean lung dose from 22.5% (+/- 6.2 SD) of the prescribed dose to 29.5% (+/- 5.2 SD) compared with the conventional technique (p = 0.0001). This indicates that this technique did not offer any benefit in terms of reducing the risk of pneumonitis. However, the two-phase conformal technique reduced the mean lung dose from 22.5% (+/- 6.2 SD) of the prescribed dose to 19.8% (+/- 4.6 SD)(p = 0.03), showing that this technique should reduce the risk of pneumonitis. Further work is underway to study more patients and to investigate tumour control probability and dose escalation.