2 Materials and methods
2.1 Patients
Under the guidance of the Ethics Committee of Peking University School
and Hospital of Stomatology, 7
pediatric patients with DT in HN
treated with 125I seed brachytherapy from January 2008
to June 2018 in the Peking University School of Stomatology were
included in this study. All the pediatric patients’ guardians signed
their informed consents, which were well documented. Among the included
patients, 4 were male and 3 were female. The median age was 3 years old,
ranging from 3 to 8 years old. The median of maximum diameter of the
primary tumor was 6.0 cm, ranging from 2.5 to 10.0 cm. The median
follow-up time was 57 months,
ranging from
43 to 135 months. The site tumor
involved including 4 at the parapharyngeal region and 3 at the skull
base region. The detailed
patients’ characteristics were
listed in Table 1. The R stage was classified as R0 with microscopically
negative margin according to pathological examination, R1 with
macroscopically negative margin according to the surgeon but
microscopically positive margin, and R2 with macroscopically positive
margin.
2.2 Treatment
After evaluation by an experienced medical group, 4 to 6 weeks before
brachytherapy, 2 patients underwent surgery with R2 margin for vital
organ preservation, and 1 to 2 weeks before brachytherapy, biopsies were
performed on the other five patients with tumors invading the critical
structures in HN, such as skull base, facial nerves and any other vital
nerves or vessels. The pathological specimens were examined and
diagnosed by two centers with expert pathologists in consensus. Then the
computed tomography (CT) scanning of the HN with a slice thickness of
0.75 mm, tube voltage of 120 kV, and tube current of 225–300 mA was
performed on all patients using a GE Optima CT680 scanner. Then all the
Digital Imaging and Communications in Medicine (DICOM) data were
transferred into a brachytherapy treatment planning system (BTPS,
Beijing Atom and High Technique Industries). Referring to the tumor
boundary based on the magnetic resonance imaging (MRI), the planning
target volume (PTV) were contoured by extending the gross tumor volume
(GTV) with a distance of 0.5 to 1.0 cm in the BTPS based on CT imaging.
The prescription doses were set
from 10 000 cGy to 12 000 cGy according to the size, subsite and the
tolerance doses of the adjacent vital structures, with a median of 12
000 cGy, in the BTPS, using the 125I seeds with a
surface radioactivity of 18.5 MBq per seed (type 6711, t1/2, 59.4 days,
Beijing Atom and High Technique Industries, Beijing, China).
Three-dimensional printed individual templates12 along with
intraoperative CT or a
far-infrared
navigation guidance system (iPlan 3.0, Brainlab, Feldkirchen, Germany)
were used to assist the 125I seeds distribution. Then
the 125I brachytherapy were performed under general
anesthesia according to the previous design. Finally, the post-implant
dosimetry parameters were calculated based on the post-implant CT by
BTPS (Figure 1).
2.3 Follow-up
Patients received physical examination, CT and (or) MR every two months
in the first half year, and every three or six months thereafter, and
core-needle biopsy when confirmation for tumor response was needed. The
safety were evaluated with radiation-relevant toxicities according to
the Radiation Therapy Oncology Group (RTOG) grading system13. The effectiveness
was evaluated with local control (LC) rate. And LC were defined as the
absence of tumor after surgery combined with brachytherapy, or
complete response (CR) and
partial response (PR) according to the Response Evaluation Criteria in
Solid Tumors (RECIST), version 1.114 after sole
brachytherapy.