An audit of Organ at Risk (OAR) constraints achieved for carcinoma of the nasopharynx treated with intensity modulated radiotherapy

Abstract

Author(s): Greeshma KE, Geetha Muttath*, Joneetha Jones, Nabeel Yahia, Vinin N V, Arun P Narendran and Akhil P Suresh

Background: In Nasopharyngeal Carcinomas (NPC), due to its anatomical location and radio sensitivity, the primary treatment modality is radical radiotherapy. Intensity Modulated Radiotherapy (IMRT) provides excellent loco regional control and sparing of Organs at Risk (OARs) and it has become the technique of choice for radiotherapy of NPCs. Still late toxicities can occur in up to 40% of patients. The present study analyses the organ at risk doses achieved in patients with NPC treated with IMRT. Materials and Methods: A retrospective audit of NPC treated with IMRT from January 2013 to August 2018 was done. The prescription dose for PTV HR, PTV IR and PTV LR were 69.3 Gy, 59.4Gy and 54 Gy respectively in 33 fractions. Concurrent chemotherapy was added for patients with stage II and above with Cisplatin 100 mg /m2 every 21 days. OAR constraints were restricted to the tolerance doses as per the recommendations. The data was analysed for the degree of adherence to the recommended dose volume constraints for OARs and the correlation of achieved OAR doses against Gross Tumour Volume (GTV) of primary, nodes and total GTV was analysed using Pearson’s correlation coefficient. Results: Plans of 40 patients were analysed. Adequate target dose coverage (D95 for PTV HR, IR and LR) was achieved in the majority (93% of patients for PTV HD, 100% of patients for PTV ID and 98% of patients for PTV LD) of our patients. More than 80% of patients had met the dose constraints for brainstem, spinal cord, v69 of temporal lobe, v75 of mandible, eyes, optic chiasm and optic nerves. The achieved doses for parotids and temporal lobes in particular were higher. Significant positive correlation was noted for OARs close to the primary site against GTV primary and GTV total. Conclusions: Adherence to the recommended dose volume constraints were achieved for optic and neuronal structures close to the primary site as well as for mandible in majority of patients. But a higher priority needs to be given for parotids and temporal lobes during radiation treatment planning.

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