A Morphing Technique to Estimate Lung Cancer Deformation Due to Breathing in Radiotherapic Treatment

A morphing technique aimed to correlate lung cancer patient’s chest cross circumference variations with tumor morphology during quiet respiration is here described. Two CT slices corresponding to the same tumor section are acquired at forced inspiration and forced expiration and correlated with chest circumference values. An image sequence has been obtained by applying a linear morphing transformation. Each image of the sequence has been associated with a chest circumferential value and a sequence subset images corresponding to subject’s tidal volume has then been selected and compared with a CT slice acquired at tidal volume. Images showing the minimum pixel differences with slice at tidal volume were identified and associated with chest circumference values, allowing to estimate in which phase of the breathing period the CT scan was carried out. CT exams in free-breathing and breath-hold conditions have been conducted on a lung cancer patient in order to correlate the acquired slices with the variations of patient’s chest circumference measured with a pneumatic strain gauge. The here described methodology could allow to define the area to be irradiated during a particular phase of the breathing period, considering the cancer area in the morphing simulation frame corresponding to this phase as target.