The impact of PET/CT scanning on the size of target volumes, radiation exposure of organs at risk, TCP and NTCP, in the radiotherapy planning of non-small cell lung cancer
Abstract
Aim: To compare radiotherapy plans made according to CT and PET/CT examinations in the same patient and to investigate the impact of changes in target volume sizes on tumor control probability (TCP) and normal tissue complication probability (NTCP) and the impact of combined PET/CT examination on the staging of the disease and treatment strategy. Background: In the current practice of radiotherapy planning and target volume determination in patients suffering from the non-small cell lung cancer (NSCLC), a contrast-enhanced CT is standard procedure.
Contemporary studies have proven that PET/CT examination attains higher sensitivity and specificity in the diagnosis of lung cancer and also leads to higher accuracy in the process of target-volume delineation in NSCLC. Results: PET/CT scan information led to a significant decrease in the sizes of target volumes: median GTVCT = 61 cm3 + 92.6 (range 19.4 – 431.7 cm3), median GTVPET/CT = 52.5 cm3 + 70.3 (range 15.7 – 399 cm3); p=0.001.
Our study also observed a size change of target volumes that had a statistically insignificant impact on the radiation exposure of lung tissue, but there was a significant impact on radiation exposure of the oesophagus, heart and spinal cord. Although a significant reduction of the target volumes sizes was found, it wasn´t reflected in the significant increase of the TCP value: median TCPCT was 68.1 % + 34.8 (range 4.4 – 88 %) and median TCPPET/CT 69.1 % + 32.5 (range 4.2 - 88 %); p=0.857.
We also found that there is a very strong direct linear relationship between all evaluated dosimetric parameters and NTCP values of all evaluated organs at risk. Conclusion: Our study found that the use of planning PET/CT in the radiotherapy planning of NSCLC has a crucial impact on the precise determination of target volumes, more precise staging of the disease and thus also an impact on possible changes of treatment strategy.