A Dosimetric Comparison of Intensity-Modulated Proton Therapy, Volumetric-Modulated Arc Therapy, and 4π Non-Coplanar Intensity-Modulated Radiation Therapy for a Patient with Parameningeal Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and manifests as two major histological subtypes: embryonal and alveolar. The five-year local failure rate for RMS at parameningeal sites (middle ear, mastoid region, nasal cavity, etc.) is around 17% despite multiple Intergroup Rhabdomyosarcoma Study Group (IRS) trials conducted to determine the optimal radiation treatment regimen. This case report explores the use of intensity-modulated proton therapy (IMPT) for a 10-year-old child who presented with left eye irritation, facial pain, and headaches and was found to have an alveolar parameningeal rhabdomyosarcoma. He received systemic therapy as well as radiation therapy to 5,640 cGy and 4,320 cGy over 24 fractions, prescribed for gross tumor extension and adjacent high-risk involved sites, respectively, via simultaneous integrated boost. Approximately two years following treatment, the patient has had no recurrence of his RMS with no distant metastases. In addition, his presenting symptom of left eye irritation has improved. His only side effect from radiation at this point is short stature, possibly due to growth hormone deficiency. The patient’s IMPT plan was compared with volumetric-modulated arc therapy (VMAT) and 4π non-coplanar intensity-modulated radiation therapy (IMRT) plans, and comparisons of isodose lines show decreased dose to the distal brain tissue with preserved target conformality by IMPT. IMPT also allowed for increased sparing of the patient's retina, lens, and lacrimal gland. All radiation plans achieved conformal dose coverage to the planning/scanning target volumes, while the IMPT plan is potentially better at sparing the patient from developing long-term optic apparatus side effects and neurocognitive defects. In this case, IMPT is comparable, if not favorable, when long-term side effects can be reduced while maintaining dose conformality and local control.