Analysis of volumetric response of pituitary adenomas receiving adjuvant CyberKnife stereotactic radiosurgery with the application of an exponential fitting model

Abstract

Tumor control rates of pituitary adenomas (PAs) receiving adjuvant CyberKnife stereotactic radiosurgery (CK SRS) are high. However, there is currently no uniform way to estimate the time course of the disease. The aim of this study was to analyze the volumetric responses of PAs after CK SRS and investigate the application of an exponential decay model in calculating an accurate time course and estimation of the eventual outcome.A retrospective review of 34 patients with PAs who received adjuvant CK SRS between 2006 and 2013 was performed. Tumor volume was calculated using the planimetric method. The percent change in tumor volume and tumor volume rate of change were compared at median 4-, 10-, 20-, and 36-month intervals. Tumor responses were classified as: progression for >15% volume increase, regression for ≤15% decrease, and stabilization for ±15% of the baseline volume at the time of last follow-up. For each patient, the volumetric change versus time was fitted with an exponential model.The overall tumor control rate was 94.1% in the 36-month (range 18–87 months) follow-up period (mean volume change of −43.3%). Volume regression (mean decrease of −50.5%) was demonstrated in 27 (79%) patients, tumor stabilization (mean change of −3.7%) in 5 (15%) patients, and tumor progression (mean increase of 28.1%) in 2 (6%) patients (P = 0.001). Tumors that eventually regressed or stabilized had a temporary volume increase of 1.07% and 41.5% at 4 months after CK SRS, respectively (P = 0.017). The tumor volume estimated using the exponential fitting equation demonstrated high positive correlation with the actual volume calculated by magnetic resonance imaging (MRI) as tested by Pearson correlation coefficient (0.9).Transient progression of PAs post-CK SRS was seen in 62.5% of the patients receiving CK SRS, and it was not predictive of eventual volume regression or progression. A three-point exponential model is of potential predictive value according to relative distribution. An exponential decay model can be used to calculate the time course of tumors that are ultimately controlled.

Volumetric tumor response assessment is inefficient without overt clinical benefit compared to conventional, manual veterinary response assessment in canine nasal tumors

“…Accurately and efficiently measuring tumor burden and tumor response to therapy remains challenging in oncology, with limitations in response evaluation criteria in solid tumors being well described. [22][23][24] This study utilized automated software that removes variability in choosing the axial slice at which to assess the longest diameter and 19,21,40 Interobserver variability is well documented with response evaluation criteria in solid tumors categorization. 22,23,30 This was also found in this study, where agreement categorization varied from poor to mod- head and neck tumors for radiation therapy planning, but also acknowledge the need to review any automatically generated contours prior to planning.…”

“…15,16 Evaluation of solid tumor response to therapy is currently commonly conducted using the simplified response evaluation criteria in solid tumors guidelines, although other criteria may be defined as investigators search for improved methods. [17][18][19][20][21] The is high interobserver and intraobserver variability due to challenges associated with determining lesion borders and in the perception of the longest diameter. [22][23][24] These recognized limitations have led to approaches that fully or semi-automate lesion segmentation (ie, contouring tumor margins) for response evaluation criteria in solid tumors or volume assessment in order to reduce subjectivity and improve reliability and reproducibility, given that response assessment impacts clinical decision-making.…”

The efficacy of microperimetry and contrast sensitivity test in the diagnosis of optic chiasm compression due to pituitary adenomas

“…Kinetic visual field (VF) is very useful at advanced stages of the disease and in patients who have difficulties in performing a static VF. Although Octopus static perimetry test is helpful in the diagnosis of pituitary tumours, it may not reveal early optic nerve damage [10] and it should be noted that prolonged compression to the optic chiasm may produce deep and irreversible visual field defects [11].…”

Stereotactic Radiation Therapy in Pituitary Adenomas, is it Better than Conventional Radiation Therapy

“…Interestingly, an early transient increase of the tumour volume post RT (> 15%) has been shown in 62.5% of 34 patients treated with CK (93% having NFPA), mainly in the first 4 months. Fortunately, this was not predictive of the eventual tumour regression or progression (54). The median time for a tumour that initially progressed to tumour volume stability was 9.2 months (54).…”

“…Fortunately, this was not predictive of the eventual tumour regression or progression (54). The median time for a tumour that initially progressed to tumour volume stability was 9.2 months (54). Transient swelling has also been reported in 9% of 45 patients with NFPA treated with GK (55).…”