Title: Analysing the dose to lacrimal glands in Carcinoma Nasopharynx: Is there a need for Ophthalmic prophylaxis?
Authors: Poornachandra Tejaswi, Jagannath Kunigal Puttaswamy, Lokesh Vishwanath, Poojar Sridhar, Vijay Calmuge Raghu, Saritha Sunny Pullan
Objective: To evaluate the relationship between lacrimal gland dose and ocular toxicity among the patients treated by Intensity Modulated Radiotherapy (IMRT) for Carcinoma Nasopharynx.
Material and Methods: 20 patients of Carcinoma Nasopharynxwere treated by IMRT techniqueto a curative dose of 70Gy. The lacrimal glands were contoured as Organ at risk (OARs) and the minimum dose, maximum dose, mean dose and V30 were evaluated. Radiation Therapy Oncology Group (RTOG) toxicity criteria was used to report on conjunctivitis, corneal ulceration and keratitis.
Results: The minimum dose, maximum dose and mean dose received by right lacrimal gland was 3.86Gy, 19.20Gy and 9.34Gy respectively and by left lacrimal gland was 3.84Gy, 23.02Gy and 9.94Gy respectively.
PTV volume (in cc) was evaluated. The minimum, maximum and mean PTV volumes were 193.9cc, 1444.6 cc and 550.6 cc respectively. In the patients who developed ocular toxicity, the mean PTV volume was 835.3cc.
The mean distance between lacrimal gland and PTV was found to be 0.6cm. 8 patients reported with Grade-I ocular toxicity. In all these patients, the lacrimal gland was found to be in close proximity to the PTV.V30 of left lacrimal gland was 11.87% and V30 of right lacrimal gland was 6.2% respectively in the patients who developed ocular toxicities.
Conclusion: This study documents that the mean dose and maximum dose to lacrimal gland is important for analysing the acute and late ocular toxicities. Hence, lacrimal gland should be contoured as Organ at risk in Carcinoma Nasopharynx and dose constraints should be given to minimise the toxicity and prevent Dry Eye Syndrome.
Keywords: Lacrimalgland, Nasopharynx, Keratitis sicca, Intensity Modulated Radiotherapy, Radiation Therapy Oncology Group.