Volumetrical changes of liver associated with breathing and its impact to normal tissue complication probability

The aim of this study is to investigate geometrical and volumetrical changes of liver due to breathing and its impact to NTCP. In order to attain better treatment results it should be considered deliberately during planning session. Seven patients were examined in this study who have done TACE for accurate tumor margin drawing. After contrast media injection, C-T scan data were obtained in supine position during breathing free, inhalation and exhalation, respectively. For all patients C-T scan were done with same scanning parameters- 5 mm index, 5 mm thickness and pitch 1. Based on C-T data we have measured differences of each variables between breathing status such as changes of total and remained liver volumes, GTV, beam path length and superior to inferior shift. NTCP were calculated using Lyman's effective volume DVH reduction scheme and for this NTCP calculation, the V50 was computed from DVH and each m, n value were referred from Burmans data. The measured total tilter volume and the remained liver volume changed between inspiration and expiration about 1.2-7.7%(mean+2.7%) and 2.5-13.23%(mean=5.8%) respectively, and these results were statistically significant(p>0.1). The GTV difference in each patient varied widely from 1.17% to 30.69%, but this result was not statistically significant. Depending on the breathing status, the beam path length was changed from 0.5 cm to 1.1 cm with the average of 0.7 cm, and it was statistically significant(p=0.006). The measured superior to inferior shifts were ranged from 0.5 cm to 3.74 cm. The NTCPs were changed relatively small in each patient, but the variation was large between the patients. The mean NTCP difference was 10.5%, with the variation ranged from 7% to 23.5%. Variations of liver volume and of beam path length were changed significantly depending on the breathing statues and the range of variation itself was very different between the patients. Since this variance could seriously affect the clinical outcomes of radiation treatments, the breathing of patients need to be accounted when a final treatment planning is derided.