**3. Radiotherapy for solitary plasmacytomas**

The solitary plasmacytoma is a localised accumulation of monoclonal plasma cells without systemic plasma cell disease manifestation. Regarding location, it can be classified into solitary plasmacytoma of bone (SBP) and extramedullary plasmacytoma (EMP) [25]. SBP generally occurs in the vertebra and skull; however, EMP is most frequently observed in head and neck [25]. Plasmacytomas are radiosensitive neoplasms, and radiotherapy has a potentially curative effect for both SBP and EMP [4].

## **3.1. Radiotherapy for solitary plasmacytoma of bone**

Radiotherapy with a curative intent is the treatment of choice, resulting in local control in more than 80% of patients with SBP [25, 26]. In some cases, as bone instability, rapid progression of neurological symptoms and surgical intervention are required, the results of surgery alone are not optimal and carry high rates of local relapse [27]. Currently, the standard of treatment for SBP is radiotherapy. Optimal-dosing guidelines have not been established due to the absence of prospective randomised studies. The United Kingdom Myeloma Forum recommend radiotherapy at least 40 Gy in 20 fractions [28]. For bulky disease (>5 cm), a higher-dose 50 Gy in 25 fractions was recommended [28]. Approximately 30% of patients who received higher doses than 50 Gy remained without evidence of any local disease failures [25]. In clinical practice, a radiation dose of 45–50 Gy in 20–25 fractions is recommended for the treatment of SBP.

The optimal target volume for radiotherapy planning in SBP is to encompass the tumour volume plus a margin of at least 1.5–2 cm on the tumour detectable by MRI [25, 26]. In case of vertebral involvement, fields typically include one to two uninvolved vertebrae above and below the affected level [25]. Prophylactic regional lymph node irradiation is not necessary in SBP.

#### **3.2. Radiotherapy for extramedullary plasmacytoma**

Like SBP, EMPs are highly radiosensitive; almost all patients (80–100%) achieve local control, and approximately 50–65% of patients remain free of disease longer than 10 years [26]. Due to a lesser number of patients and the absence of randomised prospective studies, the optimal dose of radiotherapy is not established. Current evidence-based recommendations by the United Kingdom Myeloma forum are similar to those for SBP [28]. The recommendations include radiotherapy dose of 40 Gy in 20 fractions for tumours of <5 cm and up to 50 Gy in 25 fractions for tumours of ≥5 cm with at least a 2-cm margin encompassing the primary tumour [28]. If cervical nodes are involved (or in Waldeyer's ring tumours), these should be included in the radiotherapy field [28].

Surgery may be an acceptable treatment method combined with radiotherapy. A combination of a higher dose of radiation and surgery predicted for better PFS [25]. Surgical procedures of the head and neck are not recommended, but surgery may be considered for other sites of the disease [26].
