High-dose-rate brachytherapy of rhabdomyosarcoma limited to the external auditory canal

Abstract

PURPOSE To report on the single-catheter high-dose-rate brachytherapy treatment of a 21-month-old girl child with an embryonal, botryoid-type, rhabdomyosarcoma limited to the external auditory canal (EAC). METHODS AND MATERIALS A 2.4-mm diameter catheter was inserted into the right EAC and placed against the tympanic membrane. A computed tomography simulation scan was acquired. A brachytherapy treatment plan, in which 21 Gy in seven fractions was prescribed to a 1-mm depth along the distal 2 cm of the catheter, was generated. Treatments were delivered under anesthesia without complication. A dosimetric comparison between this plan and an intensity-modulated radiation therapy (IMRT) plan was then conducted. A clinical target volume (CTV), which encompassed a 1-mm margin along the distal 2 cm of the catheter, was delineated for both plans. Given positioning uncertainty under image guidance, a planning target volume (PTV = CTV + 3-mm margin) was defined for the IMRT plan. The IMRT plan was optimized for maximal CTV coverage but subsequently normalized to the same CTV volume receiving 100% of the prescription dose (V100) of the brachytherapy plan. RESULTS The IMRT plan was normalized to the brachytherapy CTV V100 of 82.0%. The PTV V100 of this plan was 34.1%. The PTV exhibited dosimetric undercoverage within the middle ear and toward the external ear. Mean cochlea doses for the IMRT and brachytherapy plans were 26.7% and 10.5% of prescription, respectively. CONCLUSIONS For rhabdomyosarcomas limited to the EAC, a standard brachytherapy catheter can deliver a highly conformal radiation plan that can spare the nearby cochlea from excess radiation.

Rhabdomyosarcoma of the Head and Neck: A Multimodal Approach

“…2 for an example of a brachytherapy radiation treatment plan versus an external beam treatment plan for RMS of the external auditory canal. 21 Brachytherapy has been used as part of a multidisciplinary treatment approach for the treatment of nonorbital HNRMS in the Netherlands since 1990. This approach, named the AMORE technique, involves consecutive Ablative Surgery, MOld technique with afterloading brachytherapy and immediate surgical REconstruction after induction chemotherapy.…”