Challenges in treating lung tumours are related to the respiratory-induced tumour motion and the accuracy of dose calculation in charged particle disequilibrium condition. The dosimetric characteristics near the interface of lung and Perspex media in a moving phantom during respiratory-gated and non-gated radiotherapy were investigated using Gafchromic EBT2 and the MOSkin detector. The MOSkin detectors showed good agreement with the EBT2 films during static and gated radiotherapy. In static radiotherapy, the penumbral widths were found to be 3.66 mm and 7.22 mm in Perspex and lung media, respectively. In non-gated (moving) radiotherapy with 40 mm respiratory amplitude, dose smearing effect was observed and the penumbral widths were increased to 28.81 mm and 26.40 mm, respectively. This has been reduced to 6.85 mm and 9.81 mm, respectively, in gate d radiotherapy with 25% gating window. There were still some dose discrepancies as compared to static radiotherapy due to the residual motion. This should be taken into account in the margin generation for the target tumour.