Purpose: To identify the current state of dose trade-offs between ipsilateral lung and heart as a function of PTV size and target distance from heart. This study will investigate whether one organ should be systematically spared over the other, with the potential to investigate different levels of dose trade-offs between ipsilateral lung and heart.
Methods: The dosimetric data of 118 consecutive patients, who were treated for lung cancer with IMRT/VMAT or SBRT were retrospectively collected. The dose volume histograms of heart and left lung were obtained from each patient and used to calculate the corresponding normal tissue control probability (NTCP) values. The Relative Seriality model was used to calculate NTCP values. The mean lung dose (MLD), mean heart dose (MHD), lung V20, and heart V5 were also obtained from each patient treatment plan. The minimum distance from target to heart was measured directly on the planning CT.
Results: The median PTV volume was 93cc and the mean minimum distance between the target and heart was 3.5cm, respectively. The patients with PTV > 93cc had an average lung NTCP value of 11.6%, which is much larger than the average heart NTCP of 3.0% (p=0.001). For PTV < 93cc the corresponding NTCP values are almost equivalent (0.2% vs 0.1%, respectively). Regarding the target to heart distance for both cut-offs with the average lung and heart NTCP values being 9.6% vs 2.5%, respectively for the 3cm cut-off and 8.2% vs 2.1%, respectively for the 5cm cut-off.
Conclusion: Our results show that there is an unbalanced level of sparing between left lung and heart, which varies based on the minimum target to heart distance and PTV size. Using NTCP metrics for heart and lung would help in finding better levels of sparing.
Not Applicable / None Entered.