Tailored stereotactic radiotherapy technique using deep inspiration breath-hold to reduce stomach dose for cardiac radioablation

Article information

Radiat Oncol J. 2021;39(3):167-173

Publication date (electronic) : 2021 June 16

doi : https://doi.org/10.3857/roj.2021.00276

Myung-Jin Cha¹, Phillip S. Cuculich², Clifford G. Robinson³, Ji Hyun Chang^,4

¹Cardiovascular Division, Department of Internal Medicine, Seoul National University Hospital, Seoul, Korea

²Cardiovascular Division, Department of Internal Medicine, Washington University, St Louis, MO, USA

³Department of Radiation Oncology, Washington University, St Louis, MO, USA

⁴Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea

Correspondence: Ji Hyun Chang Department of Radiation Oncology, Seoul National University College of Medicine, 101 Daehak-ro, Jongno-gu, Seoul 03080, Korea. Tel: +82-2-2072-4940 E-mail: jh.chang@snu.ac.kr

Received 2021 February 22; Revised 2021 April 12; Accepted 2021 April 14.

Abstract

Introduction

Noninvasive cardiac radioablation, delivered with stereotactic body radiotherapy (SBRT), was recently introduced as a treatment option for life threatening refractory ventricular tachycardia (VT) [1,2]. Depending on location of the target within the ventricle, a variety of organs-at-risk such as the esophagus, stomach, and bowel could be exposed to high doses of radiation. Although few high-grade late complications have been described [3], one patient on the ENCORE-VT trial (electrophysiology-guided noninvasive cardiac radioablation for ventricular tachycardia) developed a grade 3 gastropericardial fistula 2-year after treatment [4], and another patient treated by Ostrava group developed a grade 5 esophageal fistula [5]. Therefore, the radiation risk of luminal internal organs in particular should be considered during treatment planning.

Cardiac radioablation targets along the inferior wall of the ventricle represent a particular emerging challenge due to their inherent proximity to structures such as the esophagus, stomach, and bowel. At present, no specific techniques have been described to improve dosimetry for these complex targets. Furthermore, the heart does not stick to adjacent internal organs, but moves and rotates with thoraco-diaphragmatic movement. Herein, we report a successful cardiac radioablation using the deep inspiration breath-hold (DIBH) technique to minimize toxicity to the stomach during cardiac radioablation.

Materials and Methods

1. Patient information and target definition

With Institutional Review Board approval of Seoul National University Hospital (No. 2011-151-1175), cardiac radioablation was considered for the medically intractable VT because catheter ablation was contraindicated due to the previous cardiac valve surgeries. Informed consent of the patient for radiotherapy under clinical trial (blinded) [6] was obtained. The detailed patient information was described in Supplement A.

Based on the 12-leads electrocardiography (Fig. 1), the VT seemed to originate from the mid-inferior left ventricle (LV). Cardiac magnetic resonance imaging (MRI) confirmed a transmural and subendocardial delayed enhancement in the mid-inferior and inferolateral segments, indicating myocardial scarring (Fig. 2).

Fig. 1.

Electrocardiography of ventricular tachycardia.

Fig. 2.

Myocardial scar on cardiac magnetic resonance imaging. Ao, aorta; pAV, prosthetic aortic valve; LV, left ventricle; RV, right ventricle; Sto, stomach.

2. CT simulation and target delineation

The patient underwent the four different computed tomography (CT) scans with slice thickness of 2 mm using the Brilliance CT Big Bore system (Phillips, Cleveland, OH, USA): (1) DIBH, (2) full expiration breath-hold, (3) four-dimensional (4D) CT without abdominal compression, and (4) 4D-CT with abdominal compression. The respiration-gated 10 phase 4D-CT images were acquired using the Real-time Position Management system (RPM; Varian Medical Systems, Palo Alto, CA, USA). The VT focus shown in electrocardiography and cardiac MRI was delineated as gross target volume (GTV). The margin for clinical target volume (CTV) was 1 cm, and 0.5 cm was additionally expanded for planning target volume (PTV). Generally, electrophysiological mapping could provide more accurate information on the location of the VT focus, however in this case, invasive 3D mapping could not be performed due to patient’s previous surgical history. Therefore, the CTV was extended to account for possible spread of myocardial scar at border lesions, which might have not been visualized on MRI. To further limit the radiation dose to the stomach, the stomach planning organ-at-risk volume (PRV) was determined as stomach plus 0.5 cm. Of the four scans, the largest distance between the stomach and LV scar was achieved on the DIBH scan (Fig. 3). The closest distance between the stomach and the PTV was 0.67 cm in DIBH, 0.49 cm in average image of 4D CT without abdominal compression and 0 cm (overlapped) in full expiration breath-hold and average image of 4D CT with abdominal compression. Meanwhile, GTV, CTV, PTV, stomach, and stomach PRV delineation on the CT scans with full expiration, average intensity 4D CT image (4DCT-AVG) with abdominal compression, and 4DCT-AVG without abdominal compression showed abutment or overlap of PTV and stomach PRV. Therefore, treatment planning was performed using the DIBH scan.

Fig. 3.

(A) Representative coronal images showing largest distance between the clinical target volume (orange), planning target volume (purple) and the stomach (yellow) and stomach planning organs-at-risk volume (light green) in deep inspiration breath-hold (DIBH, left) and full expiration breath-hold (right). (B) Axial images showing shortest distance in DIBH, full expiration breath-hold, average image of four-dimensional computed tomography with and without abdominal compression.

3. VMAT planning

The prescribed dose to the PTV was 25 Gy in a single fraction. The Eclipse system (Varian Medical Systems) was used for treatment planning, and volumetric modulated arc therapy (VMAT) planning was performed using three half arcs with a 10-MV flattening filter-free beam (Fig. 4). The plan was optimized to achieve a PTV coverage of V_98% = 100% while applying maximum dose constraint to stomach PRV of 10 Gy. The maximum dose within the PTV was 113% of the prescribed dose. The actual maximum dose to the stomach PRV and stomach was 14.6 and 9.8 Gy, respectively.

Fig. 4.

Volumetric modulated arc therapy planning using deep inspiration breath-hold computed tomography.

Results

1. Cardiac radioablation using DIBH

The Varian TrueBeam linear accelerator (Varian Medical Systems) was used for cardiac radioablation. Prior to on-board cone-beam CT (CBCT) acquisition, fluoroscopy guidance tracking using implantable cardioverter defibrillator (ICD) lead tip and prosthetic valve contour projection was performed. As the patient could tolerate a breath-hold state for approximately 20 seconds, CBCT was performed with three DIBHs, and the treatment was performed with multiple DIBHs. CBCT matching was performed using contours of the cardiac outline and adjacent organs, including the bronchus and bones. The patient could successfully reproduce DIBH by coaching. Under breath-hold mode, the beam was manually turned on only when the inspiration level was achieved (Fig. 5). Total monitor unit (MU) was 2175 + 3171 + 3431 MU and delivered at 600 MU/min. The total beam-on time was 15.2 minutes.

Fig. 5.

Deep inspiration breath-hold using Real-time Position Management system. The yellow box represents beam-on state.

The patient kept fasting before radioablation and no preventive prescription was given to the patient.

Discussion and Conclusion

To the best of our knowledge, this is the first report to show that gastrointestinal irradiation could be minimized during cardiac radioablation in the inferior LV using a tailored radiotherapy with DIBH. We tried DIBH to overcome the possibility of a gastropericardial fistula during irradiation reported from ENCORE-VT trial [1,4]. In this case, the target was the inferior LV (the portion of the heart closest to the stomach) [7]. The Ostrava group reported one grade 5 esophagi-pericardial fistula in abstract form, therefore the detailed information would be available later [5].

Several studies have attempted to reduce the heart dose by DIBH in cases of gastric lymphoma and breast cancer [8-10]. The DIBH technique is gated irradiation during deep inspiration, investigated by several studies, mostly focused on reducing the dose to the heart. In this case, we conversely used DIBH to reduce the radiation dose to the stomach for cardiac radioablation. During deep inspiration, the heart descends with the diaphragm and becomes more elongated. Additionally, an inspiratory intrathoracic pressure decrease causes a LV volume decrease [11]. Furthermore, the heart rotates medially because part of the pericardium attaches to the diaphragm [12]. Consequently, the LV is physically separated from the stomach, which moves downward with the diaphragm during deep inspiration.

RT-related gastrointestinal toxicities include bleeding, ulceration, perforation, or fistula [13]. The tolerance dose for grade ≥2 gastroduodenal toxicity in SBRT is variable among studies [14-17]; however, most of the studies have applied fractionated SBRT. The Quantitative Analyses of Normal Tissue Effects in the Clinic report recommended V_22.5 to be minimized and ideally constrained to <4% [18]. This constraint was used for a study in Stanford University, and the authors reported a dosimetric model of duodenal toxicity after a single-fraction SBRT for pancreatic cancer and reported that V₁₅ ≥ 9.1 cm³, V₂₀ ≥ 3.3 cm³, and D_max ≥ 23 Gy were related to increased duodenal toxicity [15]. According to these data, our dosimetric parameters satisfied dose constraints far below the cut-off values.

The possible short-term and long-term toxicity data should be monitored after cardiac radioablation. Furthermore, it is important to predict and prevent possible complications depending on the target location. In preclinical data, bronchomediastinal fistula, conduction block, or sudden death have been reported [19-21]. In clinical studies, some patients experienced radiation pneumonitis, pericarditis, or pericardial effusion that were mostly managed with observation or medications, except gastrointestinal fistula. Overall, most patients showed a good safety profile associated with irradiation [22]. Therefore, cardiac radioablation is potentially safe for intractable VT patients. To improve the safety of cardiac radioablation, using DIBH in VT patients would be applicable in patients with the target near the stomach, which could be mostly inferior LV, but it would depend on each patient’s anatomical differences. It is essential to consider tailored radiotherapy techniques in each case and the DIBH technique would be one option for securing the distance between the heart and stomach.

In conclusion, to gain the best benefit from cardiac radioablation for fatal VTs, understanding the possible toxicity in adjacent organs is crucial. Successful treatment could be achieved by applying the DIBH technique while saving the stomach from excessive radiation, which could have caused serious complications.

Supplementary Materials

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