Pediatric Sarcomas Are Targetable by MR-Guided High Intensity Focused Ultrasound (MR-HIFU): Anatomical Distribution and Radiological Characteristics

Abstract

Background: Despite intensive therapy, children with metastatic and recurrent sarcoma or neuroblastoma have a poor prognosis. Magnetic resonance guided high intensity focused ultrasound (MR-HIFU) is a noninvasive technique allowing the delivery of targeted ultrasound energy under MR imaging guidance. MR-HIFU may be used to ablate tumors without ionizing radiation or target chemotherapy using hyperthermia. Here, we evaluated the anatomic locations of tumors to assess the technical feasibility of MR-HIFU therapy for children with solid tumors.

Procedure: Patients with sarcoma or neuroblastoma with available cross-sectional imaging were studied. Tumors were classified based on the location and surrounding structures within the ultrasound beam path as (i) not targetable, (ii) completely or partially targetable with the currently available MR-HIFU system, and (iii) potentially targetable if a respiratory motion compensation technique was used.

Results: Of the 121 patients with sarcoma and 61 patients with neuroblastoma, 64% and 25% of primary tumors were targetable at diagnosis, respectively. Less than 20% of metastases at diagnosis or relapse were targetable for both sarcoma and neuroblastoma. Most targetable lesions were located in extremities or in the pelvis. Respiratory motion compensation may increase the percentage of targetable tumors by 4% for sarcomas and 10% for neuroblastoma.

Conclusions: Many pediatric sarcomas are localized at diagnosis and are targetable by current MR-HIFU technology. Some children with neuroblastoma have bony tumors targetable by MR-HIFU at relapse, but few newly diagnosed children with neuroblastoma have tumors amenable to MR-HIFU therapy. Clinical trials of MR-HIFU should focus on patients with anatomically targetable tumors.

Keywords: MR-HIFU; ablation; hyperthermia; neuroblastoma; sarcoma.

Conflict of interest statement

Conflict of Interest

Robert Staruch is a paid employee of Philips. No other authors report any conflicts of interest.

© 2016 Wiley Periodicals, Inc.

Figures

Figure 1

Dimensions of ultrasound beam and tumor measurements. “a” represents the distance from skin to center of lesion. “b” represents the safety margin of 4 cm past the focus. “c” represents the length of the lesion. Nominal angle of the ultrasound beam is 60 degrees “d.”

Figure 2

Radiographic examples of targetable and non-targetable lesions. A, B) axial and coronal captures of right tibia osteosarcoma targetable with the current MR-HIFU system. C, D) axial and coronal captures of right proximal humerus osteosarcoma targetable if breath holding was used to reduce MR temperature mapping artifacts caused by motion of the nearby lungs. E, F) coronal and sagittal captures of thoracic spine Ewing sarcoma not targetable due to presence of ribs in the way and presence of highly reflecting lung within the far field safety margin.

Figure 3

Number of sarcoma lesions and neuroblastoma lesions and their targetability by anatomical location for primary vs. metastatic lesions (left vs. right sides of the body), at initial diagnosis and relapse. One patient with sarcoma at relapse was excluded due to inadequate imaging.

Figure 4

Targetability of primary sarcoma and neuroblastoma lesions at diagnosis based on histology and location.

Figure 5

Distance from skin to center of targetable sarcoma and neuroblastoma tumors (including primary and metastatic tumors at diagnosis and relapse) by location. For each lesion, color of circle indicates targetability, size indicates tumor volume. Green band indicates range of ideal target distance for existing MR-HIFU system.