An isotoxic planning comparison study for stage II-III non-small cell lung cancer: is intensity-modulated radiotherapy the answer?

Aims: Recent clinical series suggest that treating patients with isotoxic twice-daily radiotherapy may be beneficial. This dosimetric planning study compared the use of intensity-modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3DRT) to deliver isotoxic treatment for non-small cell lung cancer (NSCLC) patients.

Materials and methods: Twenty patients with stage II/III NSCLC were selected. A dose-escalated plan was produced retrospectively for each using three different methods: (i) three to five beams 3DRT; (ii) seven beams inverse-planned conformal radiotherapy; (iii) seven beams IMRT. The starting point for dose escalation was 55.8 Gy in 1.8 Gy per fraction twice-daily. The number of fractions was then increased until one or more organ at risk tolerance dose was exceeded or a maximum dose of 79.2 Gy was reached.

Results: The median escalated doses were 70.2, 66.6 and 64.8 Gy for IMRT, 3DRT and inverse-planned conformal radiotherapy, respectively. IMRT allowed a significant dose increase in comparison with the other two methods (P < 0.05), whereas no significant difference was found between 3DRT and inverse-planned conformal radiotherapy. IMRT was more successful at escalating dose in patients where the brachial plexus and spinal canal were close to the planning target volume. IMRT did not allow the escalation of dose beyond 70.2 Gy (82.8 Gy BED10, 69 Gy EQD2) due to the proximity of disease to the great vessels and the proximal bronchial tree.

Conclusions: IMRT allows increased dose escalation compared with conformal radiotherapy. However, there is limited opportunity to escalate the prescription dose beyond 70.2 Gy twice-daily in disease close to the central mediastinal structures.