Aortic dose constraints when reirradiating thoracic tumors

Abstract

Background and purpose: Improved radiation delivery and planning has allowed, in some instances, for the retreatment of thoracic tumors. We investigated the dose limits of the aorta wherein grade 5 aortic toxicity was observed after reirradiation of lung tumors.

Material and methods: In a retrospective analysis, 35 patients were identified, between 1993 and 2008, who received two rounds of external beam irradiation that included the aorta in the radiation fields of both the initial and retreatment plans. We determined the maximum cumulative dose to 1 cm(3) of the aorta (the composite dose) for each patient, normalized these doses to 1.8 Gy/fraction, and corrected them for long-term tissue recovery between treatments (NIDR).

Results: The median time interval between treatments was 30 months (range, 1-185 months). The median follow-up of patients alive at analysis was 42 months (range, 14-70 months). Two of the 35 patients (6%) were identified as having grade 5 aortic toxicities. There was a 25% rate of grade 5 aortic toxicity for patients receiving composite doses ≥120.0 Gy (vs. 0% for patients receiving <120.0 Gy) (P=0.047).

Conclusions: Grade 5 aortic toxicities were observed with composite doses ≥120.0 Gy (NIDR ≥90.0 Gy) to 1cm(3) of the aorta.

Fig. 1

Proportion of patients who did or did not develop aortic toxicity at defined composite doses. (A) Treatment of 1 cm³ of aorta to ≥120 Gy (without normalization of isoeffective dose or correction for aortic recovery), produced aortic toxicity in 25% of patients (P=0.047 vs. raw dose <120 Gy). (B) Treatment of 1 cm³ of aorta to ≥90 Gy (when the dose had been normalized to 1.8 Gy/fraction and corrected for long-term aortic recovery) resulted in aortic toxicity in 29% of patients (P=0.035 vs. NID_R <90 Gy).

Fig. 2

Axial views of thoracic treatment plans for a woman who died of radiation-induced aortic damage. The aorta is contoured in yellow. (A) The initial plan involved treatment to 50.4 Gy (green isodose line; blue isodose line is 39.6 Gy). (B) The second plan involved treatment to 66.0 Gy (blue isodose line; green isodose line is 69.0 Gy). (C) The composite plan illustrates a green hot spot in the aorta (arrow) that received 120.0 Gy. (D) Dose volume histogram for the composite plan. GTV, gross tumor volume.

Fig. 3

Axial views of thoracic treatment plans for a man who died of radiation-induced aortic damage. The aorta is contoured in yellow. (A) The initial plan involved treatment to 60.4 Gy (blue isodose line; green isodose line is 59.0 Gy). (B) The second plan involved treatment to 63.0 Gy (blue isodose line; green isodose line is 68.0 Gy). (C) The composite plan illustrates a green hot spot in the aorta (arrow) that received 127.0 Gy. (D) Dose volume histogram for the composite plan. GTV, gross tumor volume.