Lung Cancer Radiotherapy: Can Breathing Movement Evaluation be Improved By More Than One 4D-CT?

Abstract

A recent national survey showed that a significant number of radiation oncologists resorted to more than one 4D-CT scans before lung cancer treatment planning. To our best knowledge, only two studies investigated whether only one 4D-CT was sufficient to evaluate breathing-induced motion of pulmonary tumors. However, the results were limited by the number of patients (10 to 26), and the old-generation scan machines. The present study was carried out to update the available data. The aim of the study was to assess the benefit of processing more than one 4D-CT in lung cancer patients as well as the immediate impact on patient’s quality of life. Data about all consecutive patients undergoing a curative radiotherapy for lung tumor (primary or metastases) were prospectively collected between April and July 2017. Patients had several 4D-CTs within a maximum of seven days but not on the same day. The ITV was contoured on each 4D-CT. The center of mass (used as a surrogate of the tumor position) was defined as the position of the barycenter of the tumor and was collected on each phase along with its standard deviation. The peak to peak tumor motion (distance between extreme tumor positions within one breathing cycle) and the three-dimensional tumor motion (left-right, supero-inferior and antero-posterior direction) were assessed. Patient’s self-reported quality of life was collected. 24 patients had two 4D-CT and were included. Mean age was 63 (range: 18-83). Contrast agent infusion was performed in 5 patients (20.8%). Abdominal compression was applied to 10 patients (41.7%) The mean volume of ITV was 125 cm3 (SD± 71,9 cm3). Between the repeated 4D-CTs, the ITV volume did not significantly vary (mean ITV variation: 8% i.e. 9 cm3, p=0.06). A variation of the ITV≥10% was observed in 9 patients (37.5%). The maximum variation of ITV volume between repeated 4D-CTs was 24.6%. The maximal mean peak to peak tumor motion in the prominent direction (i.e. possibly combining motions in the three different directions) was 1,79 ± 1,09 cm. Between 4D-CT, a relevant variation (≥2mm) was observed only in three patients. No variation reached 3mm, whatever the considered direction. The position of the center of mass did not significantly vary between repeated 4D-CTs (p=0.06). The mean three-dimensional tumor motion was 2,36 ± 1,33 cm (range : -3,04 cm to +1,92 cm). The mean tumor motion was higher at the first 4D-CT than at the second (p=0.035). Between repeated 4D-CTs, 4 patients (16%) had a mean tumor motion>5mm, with a 9mm motion in 2 patients (8%). Repeated 4D-CTs had no impact on patient’s quality of life. The repetition of 4D-CT did not highlight variations in tumor movement for most patients. However in 16% of patients, the second 4D-CT revealed an extra tumor motion that exceeded the standard additional margins used in SBRT. Although a second 4D-CT does not seem useful in normo-fractionnated radiotherapy given the usual margins, it seems essential for an accurate definition of ITV in SBRT.