Objective: To evaluate the effect of tumour volume regression on adaptive treatment planning, reduction in doses to organs at risk (OARs) and dose escalation.
Methods: 20 patients undergoing radical chemoradiotherapy were imaged in the fifth week of radiotherapy (CT_45) to evaluate differences in tumour volume regression between concurrent and sequential chemoradiotherapy. Replanning was carried out in the CT_45 in those with >20% regression (n = 10) and evaluated for change in target coverage indices (the coverage index and external volume index) and doses to the OAR [mean lung dose, V20 and V5 of whole and ipsilateral lung (MLDWL, V20WL, V5WL, MLDIL, V20IL, V5IL); mean oesophagus dose, V50oesophagus; and maximum spinal cord doses]. The feasibility of maximum dose escalation was explored keeping the limit of the OAR below their tolerance limits.
Results: Tumour regression was higher with concurrent chemoradiotherapy as compared with sequential chemoradiotherapy (p = 0.02). With the adaptive plan, the mean coverage index improved from 0.96 (±0.14) to 1.29 (±0.36), the mean external volume index changed from 1.39(±0.60) to 1.41(±0.56) and the reduction in doses to the OARs were MLDWL 10.6%, V20WL 1.3%, V5WL 1.2%, MLDIL 6.6%, V20IL 1.5%, V5IL 2.3%, mean oesophagus dose 7%, V50oesophagus 31% and maximum cord dose 0.35%. Dose escalation was possible in four patients in CT_45.
Conclusion: There is 35% reduction in tumour volume with chemoradiotherapy at 45 Gy which allows improvement in conformality, reduction in doses to the OARs and dose escalation in 40% of patients. Advances in knowledge: This article emphasizes that adaptive planning with a single diagnostic scan at 45 Gy has the potential for improvement of radiotherapy planning indices, dose escalation while respecting the dose to the OAR. This simple strategy can be helpful in radiotherapy planning upto 60 Gy in 40% of the patients of locally advanced non-small-cell lung cancer in countries with limited resources.