Conformal radiation therapy for retinoblastoma: Comparison of various 3d proton plans
摘要
Conventional radiation treatment for retinoblastoma can result in potentially severe cosmetic and functional long-term side effects. In the present study, 3 different tumor locations (temporal, central, and nasal) in the retina were assumed and various field approaches were tested to optimize the dose distribution to target and non-target tissues, using the 160 MeV, fixed, horizontal proton beam of the Harvard Cyclotron Laboratory. CT-scans were obtained with 3 different eye positions: straight, temporal, and nasal rotations. Tumor volume, microscopic target and critical structures were drawn and 3-D treatment plans were performed. Different oblique beam arrangements with outward or inward rotation of the eye were compared with the lateral beam orientation with straight eye position. Full coverage of the tumor and microscopic target to total doses of 46 CGE (Cobalt Gray Equivalent) and 40 CGE was obtained. Neither plan delivered significant dose to pituitary gland, controlateral eye, or brain tissue. For all 3 tumor locations (temporal, central, and nasal), isodoses on the treatment plans and dose-volume histograms demonstrated improved dose distribution by using a 45° oblique latero-anterior field. With this arrangement, the lens was almost completely spared: 50%received less than 0.5 CGE. The advantage was most evident for orbital bone and soft tissues. In particular, this technique was able to spare the growth centers located in the medial and lateral aspects of the orbital rim, therefore permitting normal orbital growth.