Room: AAPM ePoster Library
Purpose: induced toxicities during lung SBRT, such as cardiovascular disease, radiation pneumonitis, and immune suppression could have a negative impact on overall survival. We compared dosimetric parameters relevant to these toxicities between protons, and photons within RTOG 0813 and 0915 criteria.
Methods: analyzed 87 patients who received lung SBRT in our institution. For each patient the Dmax, V25 for great vessels; V5, V25, mean dose for heart; V5, V10, V15, V20 for total lung – ITV were recorded. We utilized an in-house model to obtain the above mentioned static organ doses as well as the overall immune suppression per given plan using a blood flow simulation model combined with an immune cell kill model and pre-treatment immune values.
Results: vessel maximum doses from photon plans range between 0 – 60 Gy with a mean values varying between 16.7-21.7 Gy, while proton plans great vessel maximum doses range between 0-55Gy with mean values varying between 5.2-8.9 Gy. Mean heart dose from photon plans vary between 0 -8 (mean =2.2) Gy while the mean heart dose from proton plans vary between 0-1.5 (mean = 0.1) Gy. V5 of total lung-ITV from photon plans has the largest variation with a mean of 266.8 cc for protons, and a mean of 683.4 cc for photons. Mean V20 of total lung-ITV is 180.4cc for photons, and 106.3cc for protons. Our re-planning study has demonstrated significant improvements to photon based lung SBRT plans to reduce radiation therapy related toxicity.
Conclusion: a handful of patients had great vessel dose-tolerance limit of Dmax > 52.5 Gy with photons that is shown to give a 1.2% risk of grade 3-5 toxicity. V20 for total lung –ITV that lead to radiation pneumonitis, and Dmax for great vessels are comparable between proton and photon plans with stringent planning constraints.