Brachial plexopathy after stereotactic body radiation therapy for apical lung cancer: Dosimetric analysis and preliminary clinical outcomes

Abstract

Purpose: The treatment of apical lung tumors with stereotactic body radiation therapy (SBRT) is challenging due to the proximity of the brachial plexus and the concern for nerve damage.

Methods and materials: Between June 2009 and February 2017, a total of 75 consecutive patients underwent SBRT for T1-T3N0 non-small cell lung cancer involving the upper lobe of the lung. All patients were treated with 4-dimensional computed tomography (CT)-based image guided SBRT to a dose of 40 to 60 Gy in 3 to 5 fractions. For dosimetric analysis, only apical tumors as defined by the location of the tumor epicenter superior to the aortic arch were included. The anatomical brachial plexus was delineated using the Radiation Therapy Oncology Group atlas.

Results: Thirty-one patients with 31 apical lung tumors satisfied the anatomical criteria for inclusion. The median age was 73 years (range, 58-89). The median planning target volume was 26.5 cc (range, 8.2-81.4 cc). The median brachial plexus, brachial plexus maximum dose (Dmax), Dmax per fraction, V22 (cc, 3-4 fractions), V30 (cc, 5 fractions), and biologically effective dose 3 Gy were 15.8 Gy (range, 1.7-66.5 Gy), 3.4 Gy (range, 0.6-14.7 Gy), 0.0 cc (range, 0-0.9 cc), 0.06 cc (range, 0-2.5 cc), and 31.5 Gy (range, 3.3-133.1 Gy), respectively. At a median follow-up of 17 months, the observed incidence of brachial plexopathy was 0%.

Conclusions: There is significant variation in dose to the brachial plexus for patients treated with SBRT for apical lung tumors. Although the incidence of neuropathic symptoms in this series was zero, further attention should be focused on the clinical implications of these findings.

Figure 1

Coronal slice of brachial plexus depicted using the Radiation Therapy Oncology Group contouring atlas (A) compared with a coronal slice that was obtained from a digital reconstructed radiograph of a patient who was treated with stereotactic body radiation therapy in this review. The orange structure outlines the contoured ipsilateral brachial plexus (B).

Figure 2

Graphical representation demonstrating the large dosimetric variation in brachial plexus maximum dose per fraction in (A) all apical tumors (n = 31, left pie chart) and (B) the high-risk subpopulation with tumors in close proximity to the brachial plexus (n = 18). The higher-risk cohort pie chart further demonstrates that actual doses delivered to the brachial plexus often far exceed current protocol guidelines.

Figure 3

Depiction of dose distribution color wash in relationship to ipsilateral brachial plexus in a patient with a left apical T2aN0 non-small cell lung cancer treated with 50 Gy in 5 fractions exhibiting a brachial plexus maximum dose of 54.1 Gy. Sequential images from left to right characterize (A) a representative axial slice, (B) coronal digital reconstructed radiograph, and (C) corresponding coronal slice with the isodose color wash and brachial plexus contoured in orange.