Diaphragm and lung dose in liver high-dose-rate interstitial brachytherapy: A dosimetry and toxicity report

The aim of this study was to retrospectively analyze and report on dose-volume and clinical toxicity of liver high-dose-rate interstitial brachytherapy (HDR-IBT) used in diaphragm and lung tissue.

Computed tomography (CT)-based liver HDR-IBT using Oncentra Brachy treatment planning system (TPS) plans of patients with malignant liver tumor (MLT) from September 2018 to June 2023 were reviewed to identify patients, whose diaphragm and lung tissue were within 100% prescription isodose. These organs at risk (OARs) were contoured in axial CT slices. Maximum point dose (D_max), dose to 0.2 cc, 0.5 cc, 1 cc (D_0.2cc, D_0.5cc, D_1cc), and volume receiving 30 Gy and 50 Gy (V_30Gy and V_50Gy) were analyzed. Toxicity data of these patients were retrieved from hospital electronic records.

The analysis included 27 patients with 43 and 36 MLTs, whose 100% prescription isodose of liver HDR-IBT plan was within diaphragm and lung tissue. Median prescription dose was 25 Gy (range, 15-25 Gy) in single-fraction. Median D_max, D_0.2cc, D_0.5cc, and D_1cc of the diaphragm were 302 Gy (range, 54-396 Gy), 68 Gy (range, 38-234 Gy), 48 Gy (range, 32-128 Gy), and 35 Gy (range, 27-88 Gy), while for the lung, 90 Gy (range, 39-295 Gy), 55 Gy (range, 32-207 Gy), 44 Gy (range, 29-117 Gy), and 34 Gy (range, 25-79 Gy), respectively. Median V_30Gy and V_50Gy for the diaphragm were 1.1 cc (range, 0-5.8 cc) and 0.2 cc (range, 0-2.5 cc), while for the lung, 0.8 cc (range, 0-10.1 cc) and 0.1 cc (range, 0-2.3 cc), receptively. Two patients with repeated HDR-IBT sessions received cumulative D_max diaphragm of 698 Gy and 792 Gy. At median follow-up of 23 months, no patient reported any suspicious symptom of radiation-induced diaphragm or lung injury.

This is the first publication reporting diaphragm and lung tissue dose-volume and clinical toxicity in liver HDR-IBT. Small volume of diaphragm and lung tissue tolerated extreme high radiation doses [5 times of stereotactic body radiotherapy (SBRT) range in single fraction] without clinically significant toxicity. A standardized reporting for diaphragm and lung dose volume is needed for future liver HDR-IBT studies. The results of the current study can be employed in future for expanded indication of brachytherapy, such as CT-guided trans-thoracic lung brachytherapy.