Relationship between radiation doses to heart substructures and radiation pneumonitis in patients with thymic epithelial tumors

Natsuo Tomita,Masato Iida,Katsuhiro Okuda,Yasutaka Ogawa,Yuta Shibamoto,Kaoru Uchiyama,Yuta Eguchi,Ryoichi Nakanishi,Taiki Takaoka,Yuto Kitagawa

doi:10.1038/s41598-020-68168-y

Natsuo Tomita, Masato Iida + Show 8 more

Open Access

https://doi.org/10.1038/s41598-020-68168-y

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Abstract

Radiation doses to the heart are potentially high in patients undergoing radiotherapy for thymoma or thymic carcinoma because of their origin site and propensity for pericardial invasion. We investigated potential relationships between radiation pneumonitis (RP) and the dosimetric parameters of lung and heart substructures in patients with thymic epithelial tumors. This retrospective study included 70 consecutive patients who received definitive or postoperative radiotherapy at a median dose of 58.3 Gy. Heart substructures were delineated according to a published atlas. The primary end point of ≥ grade 2 RP was observed in 13 patients (19%) despite a low lung dose; median lung V20 (i.e. percentage of the volume receiving at least 20 Gy) was only 16.6%. In a univariate analysis, four lung parameters, heart V35, three pulmonary artery (PA) parameters, two left ventricle parameters, and left atrium V35 were associated with the development of RP. In a multivariate analysis, only PA V35 remained significant (hazard ratio 1.04; 95% CI 1.01–1.07, p = 0.007). PA V35 of the RP versus non-RP groups were 84.2% versus 60.0% (p = 0.003). The moderate dose sparing of PA could be a candidate as a planning constraint for reducing the risk of RP in thoracic radiotherapy.

Highlights

Radiation doses to the heart are potentially high in patients undergoing radiotherapy for thymoma or thymic carcinoma because of their origin site and propensity for pericardial invasion
In the present study on 70 Thymic epithelial tumors (TET) patients treated with RT, the univariate analysis revealed that some dosimetric parameters of the lung and heart substructures correlated with the development of radiation pneumonitis (RP), and the percentage of pulmonary artery (PA) volume receiving at least 35 Gy (i.e. PA V35) showed the strongest correlation in the multivariate analysis
This result suggests that the moderate dose sparing of PA minimizes the risk of RP in mediastinal RT, and may be applied to thoracic RT in LANSCLC patients

Summary

Introduction

Radiation doses to the heart are potentially high in patients undergoing radiotherapy for thymoma or thymic carcinoma because of their origin site and propensity for pericardial invasion. We investigated potential relationships between radiation pneumonitis (RP) and the dosimetric parameters of lung and heart substructures in patients with thymic epithelial tumors This retrospective study included 70 consecutive patients who received definitive or postoperative radiotherapy at a median dose of 58.3 Gy. Heart substructures were delineated according to a published atlas. Potential relationships between doses to heart substructures and non-cancer death have been investigated in early-stage NSCLC patients treated with stereotactic body radiation therapy (SBRT)[3] These studies left one shared question unanswered: the uncertainty of the cause of death. Huang et al.[11] investigated the impact of the heart dose on the incidence of radiation pneumonitis (RP) in LANSCLC patients treated with definitive RT They reported that heart V65 was more strongly associated with the development of RP than lung parameters[11]. We examined the incidence of RP and dosimetric parameters of the heart, heart substructures, and lungs in TET patients, and investigated potential relationships between these dosimetric parameters and RP

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