Introduction: Treatment refractory and recurrent pituitary adenomas often require radiation therapy or stereotactic radiosurgery. Long-term control with radiation treatment is well known, but the pattern of volume response after radiation has not been characterized in detail. We sought to characterize tumor response to radiation therapy in order to improve clinical decision-making.
Methods: Patients with biopsy-proven pituitary adenomas were identified from pathology diagnoses at one institution between 2004 and 2014. Inclusion criteria were patients who had received radiation therapy for a pituitary adenoma, who had been followed for a minimum of 3 or more MRI scans, and were over 18 years in age. T1-weighted 3-plane post-contrast MR images were used; tumor dimensions were measured with orthogonal diameters and volumes using the ABC/2 method (simplified ellipsoid volume). In this series, all patients were treated with fractionated radiation therapy.
Results: Sixty-one MRI scans for 7 males (44%) and 9 females (66%) were evaluated. Tumor diameters ranged from 0.7cm to 4.22cm. Tumor volumes ranged from 0.12cc to 26.8cc. The median and mean volumes were 3.08cc and 5.25cc, respectively. Follow-up ranged from 8 to 70 months, with a median follow-up of 23 months. Among the 15 tumors that were included, trend of tumor volume growth over time is shown in figure 1.1. Three (20%) patients had progressive tumor growth after radiation, and the remainder (80%) had stable or decreasing volumes over time. A Bayesian linear mixed effect model was applied to predict future tumor volume. The comparisons between model prediction and the actual tumor volumes are shown in figure 2.1. The mean predicted volume change was -0.244 (SD=0.290) cc per month.
Conclusions: Analysis of scans showed that the majority of tumors respond to fractionated radiation treatment, and this treatment is effective for pituitary adenomas. Using our modeling, tumor response after radiation treatment can be effectively predicted.
Patient Care: If accurate response to radiotherapy can be predicted, future outcomes can be predicted and clinical decision-making can be better tailored to each individual patient, in order to improve symptom-development and overall survival.
Learning Objectives: By conclusion of this session, participants should be able to:
- Describe the ideal treatment for refractory and recurrent pituitary adenomas
- Describe the current state of radiation treatment response in pituitary adenomas
- Explain how growth models can be utilized to predict tumor response after radiation treatment in patients with pituitary adenomas
References: 1) Harrison G, Kano H, Lunsford LD, Flickinger JC, Kondziolka D. Quantitative tumor volumetric responses after Gamma Knife radiosurgery for meningiomas. J Neurosurg. 2016 Jan; 124(1):146-54.
2) Kong DS, Lee JI, Lim DH, Kim KW, Shin HJ, Nam DH, Park K, Kim JH. The efficacy of fractionated radiotherapy and stereotactic radiosurgery for pituitary adenomas: long-term results of 125 consecutive patients treated in a single institution. Cancer. 2007 Aug 15; 110(4):854-60.
3) Kopp C, Theodorou M, Poullos N, Jacob V, Astner ST, Molls M, Grosu AL. Tumor shrinkage assessed by volumetric MRI in long-term follow-up after fractionated stereotactic radiotherapy of nonfunctioning pituitary adenoma. Int J Radiat Oncol Biol Phys. 2012 Mar 1; 82(3):1262-7.
4) Milker-Zabel S, Debus J, Thilmann C, et al. Fractionated stereotactically guided radiotherapy and radiosurgery in the treatment of functional and nonfunctional adenomas of the pituitary gland. Int J Radiat Oncol Biol Phys 2001;50:1279–86.
5) Peterson AM, Meltzer CC, Evanson EJ, et al. MR imaging response of brain metastases after gamma knife stereotactic radiosurgery 1. Radiology 1999;211:807–14.