SU‐E‐T‐787: Noncoplanar Intensity‐Modulated Radiation Therapy for Young Female Patients with Mediastinal Lymphoma

Purpose: To propose a new technique, noncoplanar intensity‐modulated radiation therapy (Nonco_IMRT), for young female patients with mediastinal lymphoma, and to evaluate its dosimetric features. Methods: We used to adopt a coplanar IMRT technique (Co_IMRT) to treat patients with mediastinal lymphoma. Typically it has 7 equal‐spaced beams starting from gantry angle of 206°. Large volume of lungs were irradiated, and also bilitaral breasts if the patient were female. Recently, we switched to apply Nonco_IMRT technique which use 2 noncoplanr beams in sagital plane (couch angle 90°, collimator angle 90°,gantry angle 330° and 30°) replace the 2 beams of Co_IMRT that irradiate breasts and lungs directly. Nonco_IMRT was compared against Co_IMRT through a planning comparison study of 15 young female patients. PTV coverage and OAR dose parameters were analyzed. Results: For all patients, the PTV coverage, heart V30 and spinal cord dose were approximately equal between two techniques (P>0.05). But the mean dose and low dose region of bilateral breasts and lungs significantly decreased in noncoplanar IMRT (P<0.05). The reduction of the breast V2.5 and lung V5 was 33.1% and 9.28%, respectively. Conclusions: Compared to conventional Co_IMRT, Nonco_IMRT significantly reduces dose to breasts and lungs, and consequently reduces the possibility of breast second cancer and pulmonary toxity. Besides young female patients,Nonco_IMRT can benefit other mediastinal lymphoma patients as well.