Keqin Q. Tang MD, PhD, Presenter: Nothing to Disclose

Shalini Pandya MS, Abstract Co-Author: Nothing to Disclose

Maria T. Vlachaki MD, PhD, Abstract Co-Author: Nothing to Disclose

Purpose/Objective(s): This study is undertaken to compare the dosimetry of 3DCRT, IMRT and HT techniques in the treatment of bilateral RB. Materials/Methods: A 20-month old male with progression of bilateral RB despite treatment with chemotherapy and focal laser therapy was referred for external beam radiation therapy. Computed tomography was used for treatment planning with 3DCRT, IMRT and HT. The clinical target volume (CTV) included both eyes and 5 mm of the adjacent distal optic nerve, excluding lenses and cornea. The planning target volume (PTV) was generated by applying 3 mm circumferential expansion to the CTV but also, it did not include lenses and cornea. The prescribed dose was 45 Gy delivered at 1.8 Gy per fraction. Dose constraints for the normal tissues were: cornea ó 30 Gy; pituitary gland ó 10 Gy. Dose Volume Histograms and generalized equivalent uniform doses (gEUD) were generated and compared. Results: The minimum, mean and maximum PTV doses with 3DCRT, IMRT and HT were 21.3/47.2/48.7 Gy, 27.2/45.4/48.9 Gy, 37.6/48.0/51.2 Gy to the left eye and 23.8/47.3/48.7 Gy, 28.1/45.2/47.7 Gy, 30.3/48.0/51.2 Gy to the right eye, respectively. The minimum, mean and maximum doses with 3DCRT, IMRT and HT were 6.7/13.5/29.2 Gy, 16.0/23.8/31.2 Gy, 16.4/22.3/30.7 Gy to the left cornea and 7.7/14.3/29.2 Gy, 14.5/21.8/31.5 Gy, 18.7/24.3/32.8 Gy to the right cornea, respectively. gEUDs for 3DCRT, IMRT and HT were 44.9, 45.5, 47.4 Gy for the left eye PTV, and 46.4, 45.3, 47.3 Gy for the right eye PTV, respectively. Pituitary gland doses ranged between 5 and 10 Gy with IMRT and HT while 3DCRT dose was below 5 Gy. Mean dose to soft tissues (body volume minus PTV) was 2.73, 4.87 and 3.45 Gy for 3DCRT, IMRT and HT, respectively. Conclusions: All three techniques achieved satisfactory target dosing. 3DCRT minimized normal tissue radiation exposure and this is important consideration in these patients with genetic predisposition for secondary cancers. Techniques involving image guided radiation therapy are recommended to optimize treatment delivery in patients with bilateral RB.

Tang, K, Pandya, S, Vlachaki, M, Three Dimensional Conformal Therapy (3DCRT), Intensity Modulated Radiation Therapy (IMRT), and Helical Tomotherapy (HT) in Bilateral Retinoblastoma (RB): A Dosimetric Comparison.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8501452.html