Radiation Dose to Hippocampus With Increasing Planning Target Volume in Patients With Pituitary Adenoma Treated With Hypofractionated Radiation Therapy

Abstract

Radiation Dose to Hippocampus With Increasing Planning Target Volume in Patients With Pituitary Adenoma Treated With Hypofractionated Radiation Therapy R. Meral,1 N. Gurdal,1 G. Kemikler,2 M. Okutan,2 D. Sahin,3 A. Ahmedova,2 M. Altun,1 A. Sencer,2 A.K. Uzum,2 and E. Hatipoglu2 ; 1 Istanbul University, Istanbul 34390, Turkey, 2 Istanbul University, Istanbul, Turkey, 3 Istanbul University, Institute of Oncology, Department of Radiology, Istanbul, Turkey Purpose/Objective(s): To decide how radiation dose to hippocampus changed with increasing planning target volume (PTV) in patients with pituitary adenoma (PA) treated with hypofractionated radiation therapy (HFRT). Materials/Methods: Fifty three patients with residual or recurrent PAs after surgical or medical treatments have been treated with HFRT for symptoms related to persistent high hormonal levels or mass effect of the PA. Forty nine of 53 (92.4%) patients treated with HFRT were diagnosed as secretuar PAs. Twenty seven (50.9%) patients received a total dose of 21 Gy in 3 daily fractions, thirteen (24.5%) 25 Gy in 5 daily fractions, and nine (17.0%) 30 Gy in 10 daily fractions to >95% of the PTV. Planning target volume is defined as the adenoma; gross tumor volume (GTV) with a 0-1 mm margin. If the adenoma cannot be localized PTV is defined as pituitary gland and the cavernous sinuses. Four (7.6%) patients who have been treated with radiation therapy or radiosurgery before received a total dose of 20 Gy in 5 daily fractions. We contoured the hippocampus according to the RTOG 0933 hippocampal contouring atlas. Doseevolume histograms were generated with the treatment planning system. The biologically equivalent doses (BED) in 2-Gy fractions assuming an a/b ratio of 2 Gy were computed for maximal point dose and mean dose of the hippocampus with the linear quadratic model. The correlation of PTV and mean BED to hippocampus was analyzed with t-test. Results: The median age of the study group was 48 (range 22 to 75) years and female to male ratio was 1.41. Twenty seven of 53 (50.9%) patients had recurrent and 23 (43.4%) had residual disease following surgery and medical treatment before HFRT of which 4 patients have been treated initially with conventional radiation therapy (2) and radiosurgery (2). Only three (5.7%) patients received definitive HFRT. For the right hippocampus, maximal point and mean BEDs were calculated as 3.5 Gy and 0.7 Gy, Volume 93 Number 3S Supplement 2015 Poster Viewing Session E83 respectively. For the left hippocampus, maximal point and mean BEDs were calculated as 4 Gy and 1.1 Gy, respectively. The median PTV was 3.4 ml (range 0.1 ml to 64.8 ml). The patients with smaller PTV (<3.4 mL) received less mean BED to the right and left hippocampus, 0.85 0.59 Gy and 1.37 0.87 Gy, respectively. The patients who had a larger PTV (3.4 mL) received higher BED to the right and left hippocampus, 2.80 3.07 Gy and 3.88 2.70 Gy, respectively. T-test revealed a correlation between increasing PTV and radiation dose to the hippocampi (for the right and left hippocampus Levene’s test for equality variances p Z 0.015 and pZ 0.011, respectively). Conclusion: Radiation dose to the hippocampus increases with PTV in patients with pituitary adenomas treated with HFRT and sparing of hippocampus is particularly suggested when the cavernous sinuses are included in the PTV and for patients treated with initial radiation therapy before HFRT. Author Disclosure: R. Meral: None. N. Gurdal: None. G. Kemikler: None. M. Okutan: None. D. Sahin: None. A. Ahmedova: None. M. Altun: None. A. Sencer: None. A.K. Uzum: None. E. Hatipoglu: None.