Comparison of Internal Target Volume (ITV) Generated with Lung Optimization Treatment (LOT) and Maximum Intensity Projection (MIP) by 4-Dimensional CT scan in Radiosurgery Treatment of Early Lung Cancer

Background: Comparison ofinternal target volume (ITV) generated with lung optimization treatment (LOT) and 4-dimenstional computed tomography (4D-CT) measured maximum intensity projection (MIP) methods in lung tumour treatment. Materials and Methods: 18 patients with lung cancer (n=8, stage T1A: 2, Stage T2: 6 pt, mean GTV 12.6 cc) and lung metastasis (n=10) accrued. 13/18 (72%) had right sided tumour, 12/18 (66%) had upper lobe tumour and 11 (61%) had 2-views on LOT. CT simulation (inhale and exhale phase) done for LOT based ITV generation (ITV-L). Same patient cohort underwent ITV generation with 4D-CT measured MIP methods (ITV-M). Comparison was done between the ITV in these two different methods. Results: Mean GTV was 12.6cc, ITV-L and ITV-M was 29.1 and 57.6 cc. Mean GTV, ITV-L and ITV-M in 1-view, 2-view, right lung, left lung, upper lobe, middle, lower lobe and primary lung cancer and lung metastasis were 3.2, 18.5,13.4, 10.7, 16.5, 6.3, 3.6, 25.5, 2.4 cc; 15.1, 38.1, 30.6, 25.1, 35.9, 19.7, 11.3, 49.9, 12.4 and 24.1, 79.1, 49.2, 79.8, 73.7, 34.1, 17.2, 106.4, 18.7 cc respectively. In 1-view and 2-view, ITV-L and ITV-M were 29.1, 57.6 (p-value: 0.001) and 38.1, 79.1 (p-value-0.009) respectively. Right lung tumour ITV-L and ITV-M were 30.6, 49.2 (p-value-0.001) and in left lung tumours 25.1 and 79.8 cc (p-value- 0.0.14) respectively. In upper, middle and lower lobe tumour, ITVs were 35.9, 73.7 (p-value-0.004); 19.7, 34.1 (p-value-0.474) and 11.3, 17.2 (p-value-0.001) respectively. In primary lung tumour and metastasis disease, ITVs were 49.9, 106.4 (p-value-0.071) and 12.4, 18.7 (p-value-0.001). Increase in mean ITV volume with MIP in all patient cohort was 49% [(ITV-M - ITV-L)x100 / ITV-M], in 1-view cohort 37%, 2-view 52%, right lung 38%, left lung 68.5%, upper lobe lung 51%, middle lobe 42%, lower lobe 34%, primary lung cancer 53% and metastatic lung cancer 34% respectively. Conclusions: MIP generated ITV volumes are significantly larger compared to LOT generated volume. ITV-M is larger in relation to lobes, side of tumour and type of tumour. There may be higher lung tissue necrosis when treated with ITV-M, as the 'high dose' volumes are more in this patient cohort.