Improvement in tumour control probability with active breathing control and dose escalation: a modelling study.

Introduction: The prognosis from non-small cell lung cancer remains poor, even in those patients suitable for radical radiotherapy. The ability of radiotherapy to achieve local control is hampered by the sensitivity of normal structures to irradiation at the high tumour doses needed. This study aimed to look at the potential gain in tumour control probability from dose escalation facilitated by moderate deep inspiration breath-hold. Method: The data from 28 patients, recruited into two separate studies were used. These patients underwent planning with and without the use of moderate deep inspiration breath-hold with an active breathing control (ABC) device. Whilst maintaining the mean lung dose (MLD) at the level of the conventional plan, the ABC plan dose was theoretically escalated to a maximum of 84 Gy, constrained by usual normal tissue tolerances. Calculations were performed using data for both lungs and for the ipsilateral lung only. Resulting local progression-free survival at 30 months was calculated using a standard logistic model. Results: The prescription dose could be escalated from 64 Gy to a mean of 73.7 ± 6.5 Gy without margin reduction, which represents a statistically significant increase in tumour control probability from 0.15 ± 0.01 to 0.29 ± 0.11 (p < 0.0001). The results were not statistically different whether both lungs or just the ipsilateral lung was used for calculations. Conclusion: A near-doubling of tumour control probability is possible with modest dose escalation, which can be achieved with no extra increase in lung dose if deep inspiration breath-hold techniques are used.