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Radiation Dose to Hippocampus With Increasing Planning Target Volume in Patients With Pituitary Adenoma Treated With Hypofractionated Radiation Therapy By: Meral, R.; Gurdal, N.; Kemikler, G.; et al. Conference: 57th Annual Meeting of the American-Society-for-Radiation-Oncology (ASTRO) Location: San Antonio, TX Date: OCT 18-21, 2015 Sponsor(s): Amer Soc Radiat Oncol INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Volume: 93 Issue: 3 Supplement: S Pages: E83-E84 Meeting Abstract: 2211 Published: NOV 1 2015, Texas, Amerika Birleşik Devletleri, 18 - 21 Ekim 2015, cilt.93, sa.2211, ss.83-84
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.