DISSCUSION:
Higher median perfusion index in malignant lesions than for those with benign lesions and the normal parenchyma can be explained on the basis of intrinsic high neoangiogenic activity of tumor or a secondary response to tissue hypoxia
The arteriovenous shunts have very low resistance to flow, which results in markedly increased blood flow and shorter MTT.
Benign lesions constitutes dense normal parenchyma and does not show much distortion in the vascular architecture and thus shows similar perfusion indices as that of the normal parenchyma
As shown in the present study, median perfusion index was found to be lowest in stage T3,4 tumours, which was in keeping with the results of Miles et al. There study also indicated a trend for blood flow to be lower in the larger lung carcinomas.
As the tumour grows, perfusion might be decreased because of a number of other biophysical parameters, such as infection, hypoxia, and necrosis. As a result, decrease of blood volume could lead to low perfusion status in a large tumour.
Present study shows that necrosis might be one of the important intrinsic factors influencing tumor perfusion, especially in fast-growing tumors
Perfusion CT predicted the neoadjuvant chemotherapy response at the earlier phase (within 2wks) prior to actual gross tumor volume reduction on conventional CT, hence predicting the antiangiogenic response at a much early stage and guarding the further use of the therapy.
Patient who received palliative CTRT , there follow CTp parameters suggested that vascular tumor showed high response to treatment than necrotic tumors, thus making it a noninvasive method of predicting vascularity.
LIMITATIONS:
We did not study tumor permeability, which might have served as an independent predictor of tumor grade or response.
The observational period was relative short, and the clinical outcomes based on the perfusion parameters obtained using dynamic CT could could have been affected by it.
CONCLUSION:
In conclusion, the protocol used in the present study showed that 64-detector row CT P was feasible and confers a worthwhile enhancement to the conventional CT for evaluating of lung cancer.
One of the important applications of this technique is the indication of a highly perfused area, which could be used to guide biopsy to the site of the most active tumour, reducing the chance of sampling error.
The results of this study demonstrated that perfusion parameters of lung carcinoma were associated with tumour size, necrosis and stage, these findings contribute valuable information for antiangiogenic therapeutic approaches.
Consensual change of tumor volume and tumor perfusion following neo-adjuvant therapy has been statistically demonstrated, showing the potential of CTp for monitoring such therapy at a very early phase of the treatment.
Criterions such as high BF and BV and low MTT can predict high tumor volume reduction following therapy and these parameters can be used as pretreatment prognostication factors.
Finally, perfusion CT tool is helpful in lung oncology, providing a higher degree of diagnosis security, differentiation of malignancy and for the therapeutical follow-up