Three-dimensional treatment planning and treatment protocol in embryonal rhabdomyosarcoma and orthognathic surgery: A case report

Abstract

Rhabdomyosarcoma (RMS) is one of the most common soft tissue sarcomas encountered in paediatric patients. Embryonal rhabdomyosarcoma (ERMS), a variant of RMS, is observed in more than 70% of the cases and predominantly arises from head and neck region and genitourinary tract of children and young adults. Treatment is dependent on the size, location and extent of the tumor. This case report describes a 10 years old patient who received chemo- and radiotherapy. Three-dimensional (3D) conformal radiation therapy planning was carried out. The patient later suffered from asymmetric facial growth which was corrected with orthognathic surgery following 3D virtual surgical planning.

Highlights

  • Embryonal rhabdomyosarcoma predominantly arises from head and neck region and genitourinary tract.

  • The combined radio- and chemotherapy effect influences growth retardation and causes jaw deviation.

  • Three-dimensional virtual radiotherapy and orthgnathic surgery planning can reduce the amount of complications.

Introduction

Rhabdomyosarcoma (RMS) is a malignant tumor of neoplastic mesenchymal cells encompassing variable degrees of striated muscle cell differentiation [ ]. RMS (Greek origin: rhabdo = rod, myo = muscle, sarkoma = fleshy growth) was first described by Weber (1854). Later on in 1946, Stout documented the distinct histopathological morphology of rhabdomyoblasts in this tumor [ ]. RMS histological classification consists of four distinct subtypes, namely embryonal, alveolar, pleomorphic and undifferentiated form [ ].

Embryonal rhabdomyosarcoma (ERMS) is considered to be the most common variant, accounting for more than 70% of RMS cases [ ]. Based on its embryonal origin, it can occur at any anatomical location of the body irrespective of the skeletal muscle involvement. ERMS predominantly arises from head and neck region and genitourinary tract of children and young adults. Head and neck ERMS is most commonly observed in orbital and parameningeal areas, which include nasopharynx, nasal cavity, paranasal sinuses, pterygopalatine/infratemporal fossa and parapharyngeal space. In addition, non-parameningeal sites (oral cavity, oropharynx, larynx and parotid gland) can also be involved [ ].

In RMS, three-dimensional conformal radiation therapy (3D CRT) planning is considered a valuable technique which specifically targets the tumor, thereby, avoiding the involvement of healthy tissue [ ]. At the same instance, 3D planning in orthognathic surgery plays a vital role in improving the functional and aesthetic outcomes of a patient by overcoming the limitations associated with conventional two-dimensional planning [ ]. We here describe a case with 3D treatment planning and treatment protocol in ERMS and orthognathic surgery.

Case report

This case report was in compliance with the World Medical Association Declaration of Helsinki on medical research. Ethical approval was obtained from the Ethical Review Board of the University Hospitals Leuven (Reference number: S58253) and informed consent was attained from the patient.

At the age of 10 years 10 months a female patient presented with ear pain and inability to eat for 2 weeks. Following evaluation from paediatric oncology clinic, ERMS was identified in the right parapharyngeal space with invasion of the right side of the oropharynx and nasopharynx with lung metastasis [ Figure-1 ].

Fig. 1
Embryonal rhabdomyosarcoma spread to right parapharyngeal space, right side of the oropharynx and nasopharynx.

Chemotherapy was initiated according to Malginant Mesenchymal Tissue (MMT) 98 protocol (Ifosfamide, Vincristine and Adriamycin) [ ]. Subsequently, radiation therapy treatment planning was performed in Eclipse software (version 8.6, Varian Medical Systems, Palo Alto, CA). Hereafter, a computed tomography (CT) scan (120 kVp, 3 mm slice thickness) of the patient, immobilized in treatment position using a 5-points thermoplastic mask, was acquired on a SOMATOM Sensation CT scanner (Siemens Healthineers, Erlangen, Germany) and rigidly co-registered with pre-chemo T2-weighted magnetic resonance images. Two clinical target volumes (CTV) were delineated, based on the gross tumor volumes (GTV) and accounting for potential microscopic spread and anatomical boundaries. CTV 1 included the pre-chemo GTV while CTV 2 included the post-chemo GTV. Organs at risk to be spared during treatment planning were delineated as well. To take into account positioning uncertainties during radiation therapy delivery, planning target volumes (PTV) were created by expanding the CTVs with a margin of 10 mm. The dose prescription was 50.4Gy to PTV 1 and 55.8 to PTV 2 , both in fractions of 1.8 Gy using a sequential boost. Intensity-modulated radiation therapy planning was performed using a 5-field (gantry/couch angles: 325°/0°, 35°/0°, 150°/0°, 270°/350°; 20°/270°) sliding window technique on a Clinac 2100 C/D (Varian Medical Systems). Delivery of the plan was verified before the start of the treatment using portal dosimetry [ ]. Thereafter, maintenance chemotherapy involving high risk arm RMS2005 was initiated, with daily oral administration of cyclophosphamide and D1, D8, D15 Vinorelbine IV (6 cycles for total period of 6 months) which led to the complete regression of the tumor [ ].

Patient’s skull and radiotherapy (RT) volume were segmented and registered in Amira software 6.5 for observing the 3D spread of radiation in maxillofacial area [ Figure-2 ]. The patient developed postradiotherapy growth hormone (GH) deficiency and partial adrenocorticotropic hormone (ACTH) deficiency for which she received somatotropin (Nutropin Aq 1mg/day) and hydrocortisone (13mg/day). At the age of 14, patient developed central hypothyroidism for which she received elthyrone 50μg/day.

Fig. 2
3D registration and visualization of planning target volume (PTV). A, B, Dose prescription of 50.4Gy to PTV 1 . C, D, Dose prescription of 55.8Gy to PTV 2 .

At the age of 17, patient was referred to oral and maxillofacial surgery clinic by her orthodontist for consultation regarding asymmetric face with mandible deviated towards the right side. Patient had a family history of breast cancer and burkitt’s lymphoma. Dental history revealed agenesis of left mandibular permanent 2nd premolar, correction of posterior crossbite with hyrax palatal expansion device and orthodontic treatment for alignment of teeth. Systemic examination revealed normal cardiovascular, nervous, respiratory and abdominal functions.

Extra-oral findings revealed skeletal class II, convex profile, obtuse nasolabial angle and deviation of the chin towards the right side. Patient had posterior facial asymmetry with elongated mandible on the left side and a pronounced right cheek when compared to the left side [ Figure-3a ]. Maximum mouth opening of 36mm with no deviation on opening and closing of jaw. Facial height showed a ratio of 1:1:0.9. Intra-orally patient showed mandibular dental midline deviation of 1mm towards right. Skeletal midline deviation was observed 1mm and 4mm towards right side for maxilla and mandible respectively [ Figure-3b ]. The patient had an overjet of 3mm and overbite of 2mm.

Aug 8, 2020 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Three-dimensional treatment planning and treatment protocol in embryonal rhabdomyosarcoma and orthognathic surgery: A case report
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