[Optimal postoperative radiotherapy treatment of orbital rhabdomyosarcoma].

INTRODUCTION: Rhabdomyosarcoma (RMS) is the most common sarcoma of the soft tissue, mostly affecting the region of head and neck (orbit, paranasal sinus). Histological types include embryonal (66-70%) with better prognosis, and alveolar type (20%) with poorer prognosis. There are also diffuse anaplastic and undifferentiated sarcomas (10%). Due to multimodal therapy approach (surgery, chemotherapy and radiotherapy), RMS survival rate is considerably improving. Nevertheless, early diagnosis of RMS is of crucial importance for the outcome of treatment. Standard conformal radiation therapy is very complex due to closeness of many critical structures of head and neck, thus limiting optimal tumor dose coverage. CASE OUTLINE: Patient aged 59 years, surgically treated for RMS of nasal cavity several times before radiation therapy treatment. Due to relapse, patient was re-operated, when subtotal re-resection of the maxilla with exenteration of the right orbit was done. The patient received IV cycles of polychemotherapy postoperatively. Standard procedure and planning for conformal radiation therapy did not lead to acceptable irradiation plan, and hence modification in the patient's preparation was done, resulting in optimal therapeutic plan according to internationally recognized recommendations. CONCLUSION: The reported case shows a rare pediatric tumor, which often occurs in children but extremely rare in adults. The problem of inadequate isodose distribution obtained by standard conformal plan was solved by placing bolus material into the orbital cavity.The outcome of the treatment plan showed much better isodose distribution and tumor bed coverage.

Dosimetric verification of radiotherapy treatment planning systems in Serbia: national audit.

BACKGROUND: Independent external audits play an important role in quality assurance programme in radiation oncology. The audit supported by the IAEA in Serbia was designed to review the whole chain of activities in 3D conformal radiotherapy (3D-CRT) workflow, from patient data acquisition to treatment planning and dose delivery. The audit was based on the IAEA recommendations and focused on dosimetry part of the treatment planning and delivery processes. METHODS: The audit was conducted in three radiotherapy departments of Serbia. An anthropomorphic phantom was scanned with a computed tomography unit (CT) and treatment plans for eight different test cases involving various beam configurations suggested by the IAEA were prepared on local treatment planning systems (TPSs). The phantom was irradiated following the treatment plans for these test cases and doses in specific points were measured with an ionization chamber. The differences between the measured and calculated doses were reported. RESULTS: The measurements were conducted for different photon beam energies and TPS calculation algorithms. The deviation between the measured and calculated values for all test cases made with advanced algorithms were within the agreement criteria, while the larger deviations were observed for simpler algorithms. The number of measurements with results outside the agreement criteria increased with the increase of the beam energy and decreased with TPS calculation algorithm sophistication. Also, a few errors in the basic dosimetry data in TPS were detected and corrected. CONCLUSIONS: The audit helped the users to better understand the operational features and limitations of their TPSs and resulted in increased confidence in dose calculation accuracy using TPSs. The audit results indicated the shortcomings of simpler algorithms for the test cases performed and, therefore the transition to more advanced algorithms is highly desirable.