FMISO-PET as Biomarker of Early Response to Targeted Therapy in EGFR-Mutant Non-Small Cell Lung Cancer (NSCLC)

Volume 87  Number 2S  Supplement 2013 Purpose/Objective(s): Hypoxic tumor has a significantly poorer outcome following radiation therapy because hypoxic cells are resistant to radiation. With improvements in radiation treatment planning such as IMRT and Partial RT, it will be possible to precisely deliver appropriate doses to chronically hypoxic and acutely hypoxic area in the tumor when such zones are identified a priori using pO2 imaging techniques. Pulsed electron paramagnetic resonance imaging (EPRI) is a novel imaging method to directly monitor the pO2 in the tumor on a quantitative basis with useful spatial and temporal resolutions. The purpose of this work was to assess the intra-tumor pO2 profiles by EPRI and compare with images representing tumor perfusion by gadolinium-enhanced T1-weighted magnetic resonance imaging (Gd-MRI) findings in murine model of human cancer. Materials/Methods: HT29 solid tumors were (n Z 6) implanted by injecting 5  105 cells s.c. into the right hind legs of mice. Experiments were initiated when tumors grew to approximately 1 cm3 in size. Imaging tumor pO2 was accomplished with EPRI using an oxygen-sensitive OX63 as a paramagnetic tracer and dissolved tissue oxygen its contrasting molecule. The dose of OX63 used for imaging (1.125 mmol/kg) was well below the maximally tolerated dose of 2.5-7.0 mmol/kg and the LD50 of 8.0 mmol/kg. Dynamic 3D EPRI were obtained every 3 minutes for 30 minutes. EPRI was done with a 300 MHz pulsed EPRI system, then GdMRI was done every 20 seconds for 30 minutes with a controlled 7 T scanner. We defined hypoxia (average pO2 < 8 mm Hg), acute hypoxia (8 mm Hg < average pO2 < 20 mm Hg), and normal regions (20 mm Hg < average pO2) by EPRI, respectively. And one radiologist defined the every pO2 status in Gd-MRI in reference to the value of Gd concentrations. We evaluated the sensitivity and specificity of Gd-MRI by making comparisons with EPRI findings, which served as the gold standard in this analysis. Results: We reliably found chronic hypoxia (15%), acute hypoxia (55%), and normal regions (32%) in the tumor by EPRI. Especially, acute hypoxia was a significant spatiotemporal heterogeneous phenomenon in the dynamics of tumor pO2. We could also define Gd- hypoxia (28%), Gdacute hypoxia (37%), and Gd- normal regions (36%) in the tumor by GdMRI. The sensitivity and specificity of Gd- hypoxia is 31% and 64%, these of Gd- acute hypoxia is 34% and 74%, these of Gd- normal region is 46% and 63%, respectively. Conclusions: We can identify chronically hypoxic, acutely hypoxic and normal region intra-tumor mapping by EPRI. There is a limitation using Gd-MRI to characterize pO2 status. Thus, in the near future, pO2 imaging techniques such as EPRI have a promise to obtain intra-tumor pO2 images rather than Gd-MRI. Author Disclosure: M. Matsuo: None. S. Matsumoto: None. K. Saito: None. Y. Takakusagi: None. D. Morris: None. J. Munasinghe: None. N. Devasahayam: None. S. Subramanian: None. J. Mitchell: None. M. Krishna: None.

3157 Cardiac Isodose Distributions and Increases in Focal 18FFluorodeoxyglucose Uptake on Positron Emission Tomography After Thoracic Stereotactic Ablative Radiation Therapy J.D. Evans,1,2 D.R. Gomez,2 J.Y. Chang,2 G.W. Gladish,3 J.J. Erasmus,3 N. Rebueno,2 J. Banchs,4 R. Komaki,2 and J.W. Welsh2; 1Texas Tech University Health Sciences Center School of Medicine, Lubbock, TX, 2 Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 3Department of Radiology, The University of Texas MD Anderson Cancer Center, Houston, TX, 4 Department of Cardiology, The University of Texas MD Anderson Cancer Center, Houston, TX Purpose/Objective(s): The use of stereotactic ablative radiation therapy (SABR) for thoracic tumors has been increasing rapidly, underscoring the need to define dose limits for normal thoracic structures exposed during the course of SABR. We retrospectively reviewed the outcomes of patients treated with SABR close to the heart and attempted to establish correlations between isodose lines and observed changes in cardiac uptake of 18Ffluorodeoxyglucose (FDG) on positron emission tomography (PET).

Poster Viewing Abstracts S645 Poster Viewing Abstract 3157; Table Heart dose and proposed constraints grouped according to FDG-PET uptake in the heart Pts with Pts with no change increased in FDG FDG uptake All pts uptake after after SABR (n Z 39) SABR (n Z 30) (n Z 9) P Value Mean heart dose, cm3 (SEM) V10 Gy 63.1 (14.1) V20 Gy 10.7 (2.4) V30 Gy 2.2 (0.8) Heart dose constraints, no.(%)  60 cm3 of heart 11 (28) V10 Gy 3 28 (72) < 60 cm of heart V10 Gy 3 19 (49)  5 cm of heart V20 Gy 3 20 (51) < 5 cm of heart V20 Gy

32.5 (1.5) 5.6 (0.3) 1.4 (0.2)

164.9 (13.5) <.0001 27.8 (2.0) <.0001 4.7 (0.6) .0836

4 (13)

7 (78)

.0006

26 (87)

2 (22)

.0006

10 (33)

9 (100)

.0004

20 (67)

0 (0)

.0004

Recent studies have shown that these cardiac changes in FDG uptake may be an indicator of myocardial injury. Materials/Methods: Initial screening of 325 patients treated with SABR for lung tumors revealed 39 patients with tumors within 6 cm of the heart that had been treated with 50 Gy delivered in 4 fractions. Patients were grouped according to whether they had or did not have changes in cardiac FDG-PET uptake within the radiation field; and cardiac dose limits, predisposing factors, and cardiac toxicity were examined in both groups. Results: At a median follow-up interval of 39 months (range, 6-81 months), nine patients (23%) showed increased cardiac uptake within the radiation field. Increased uptake was associated with heart V10 and V20 (p < 0.0001). Of the 19 patients who received 20 Gy to 5 cm3 of the heart, nine (47%) developed increased FDG uptake (vs 0% for the 20 patients who received 20 Gy to <5 cm3) (p Z 0.0004), all within the 20Gy isodose line. These changes in uptake remained apparent at a median 15 months after SABR. Patients with hypercholesterolemia were also more likely to show increased uptake as well (p Z 0.0190). Conclusions: Increased FDG uptake in the heart after SABR was seen when the 20-Gy isodose line exceeded 5 cm3 of the heart. Pending further prospective investigation of this phenomenon, which may reflect inflammation or cardiac injury, we suggest limiting the cardiac V20 for patients undergoing thoracic SABR. Author Disclosure: J.D. Evans: None. D.R. Gomez: None. J.Y. Chang: None. G.W. Gladish: None. J.J. Erasmus: None. N. Rebueno: None. J. Banchs: None. R. Komaki: None. J.W. Welsh: None.

3158 FMISO-PET as Biomarker of Early Response to Targeted Therapy in EGFR-Mutant Non-Small Cell Lung Cancer (NSCLC) N.D. Arvold,1 P. Heidari,2 A. Kunawudhi,2 L.V. Sequist,2 and U. Mahmood2; 1Dana-Farber/Brigham & Women’s Cancer Center, Boston, MA, 2Massachusetts General Hospital, Boston, MA Purpose/Objective(s): Hypoxia is associated with resistance to radiation therapy and chemotherapy. Functional imaging of hypoxia in NSCLC before and after initiation of therapy could allow early assessment of tumor response and guide subsequent therapies. EGFR inhibition with the tyrosine kinase inhibitor erlotinib has been shown to reduce hypoxia in vivo. [18F]-fluoromisonidazole (FMISO) is a radiolabeled tracer that selectively accumulates in hypoxic cells. Materials/Methods: We performed a prospective IRB-approved pilot study in patients with EGFR-mutant metastatic NSCLC, and a correlative preclinical study in nude mice with human EGFR-mutant lung adenocarcinoma xenografts. Patients underwent a baseline FMISO-PET scan of the thorax and began erlotinib within 7 days. Follow-up FMISO-PET scans

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International Journal of Radiation Oncology  Biology  Physics

were performed 10-12 days after erlotinib initiation. Changes in SUV were compared to standard chest CT (CCT) scans performed 6 weeks after erlotinib initiation. Preclinical experiments were performed in triplicate; mice bearing flank xenografts underwent baseline FMISO-PET scan, then received oral erlotinib or empty vehicle. Follow-up FMISO-PET scans were performed 5 days after erlotinib initiation. Descriptive statistics and ANOVA tests were used to analyze changes in SUV, with pooled analyses for the 3 mice in each group (baseline, post-vehicle, and post-erlotinib). Results: The mean (SEM) SUVmean of the xenograft tumors was 0.17  0.014, 0.14  0.008, and 0.06  0.004 for baseline, post-vehicle, and post-erlotinib groups, respectively, with significantly lower SUVmean when comparing the post-erlotinib group to baseline and to post-vehicle groups (p < .05) but not between baseline and post-vehicle groups. Changes on preclinical PET imaging were striking, with near-complete disappearance of FMISO uptake after erlotinib initiation. Two female patients with minimal smoking history were enrolled on the pilot study. In the first patient’s primary tumor, SUVmean increased by 21% after erlotinib initiation, and the tumor exhibited marked progression on 6-week CCT accompanied by clinical deterioration and death after 4.8 months. In the second patient’s tumor, SUVmean decreased by 7% after erlotinib initiation, and the tumor exhibited marked regression on 6-week CCT accompanied by clinical improvement; the patient was alive with stable disease at last follow-up at 14.5 months. Conclusions: This pilot study suggests FMISO-PET is a promising imaging biomarker of early response to hypoxia-directed therapy in EGFR-mutant NSCLC, with the potential to predict eventual clinical response well before anatomic changes on CCT scan. If validated in a larger cohort, these data suggest that non-responding patients could be identified early, allowing for a change or intensification of therapy. Author Disclosure: N.D. Arvold: None. P. Heidari: None. A. Kunawudhi: None. L.V. Sequist: G. Consultant; Boehringer Ingelheim, Clovis Oncology, Merrimack Pharmaceuticals, GSK. U. Mahmood: None.

the optical signal compared to the controls; Au25-Transferrin and Au25-Human Serum Albumin had w3- and w6-times fold increase, respectively. Conclusions: Development of new optical imaging probes may lead to a new paradigm of cancer imaging. This will allow us to take an advantage of the desirable features of optical molecular imaging and achieve substantially improved spatiotemporal resolution, sensitivity and specificity for tumor detection at the cellular and sub cellular levels. Author Disclosure: O. Volotskova: None. Y. Osakada: None. G. Pratx: None. B. Cui: None. L. Xing: None.

3159 Development of a Novel Optical Imaging Probe for Cancer Detection: X-ray Activated Gold Nanoclusters O. Volotskova, Y. Osakada, G. Pratx, B. Cui, and L. Xing; Stanford University, Stanford, CA Purpose/Objective(s): At the moment, clinically available imaging methods have significant shortcomings in the characterization and identification of benign and malignant lesions for radiation treatment planning and monitoring. Tumor-specific nanoparticles that can probe biochemical processes in vivo and deliver a therapeutic payload are actively being investigated. In particular, radioluminescent nanoparticles (RLNPs) are the ideal platform for X-ray-mediated imaging and synergistic therapy during radiation treatment. These unique particles can emit visible light under Xray irradiation. However, existing RLNPs based on lanthanides may cause toxicity in vivo. Here we report new intriguing radioluminescent properties of gold nanoclusters, a type of nanoparticles made by arranging a small number of gold atoms. The objective of this work is to characterize and compare the optical signal produced by several types of gold nanoclusters under X-ray irradiation. Materials/Methods: Gold nanoparticles (4 and 1.8 nm) and gold nanoclusters (Au25-BSA, Au25-(11-Mercaptoundecyl)-N,N,N-trimethy lammonium bromide, Au25-Lysozyme, Au25-Transferrin, Au25-HumanAlbumine, Au44-(11-Mercaptoundecyl)-N,N,N-trimethylammonium bromide, AgX-ssDNA) of various concentrations were used. Imaging was performed by irradiating the samples with X-ray (30-80 kVp, 10-30 mA) while acquiring 10 s frames with an EM-CCD (Princeton Instruments, 300-900 nm). The samples were further characterized by using a custom PMT-based system. The spectral properties of the emission were measured under both optical and X-ray excitation using a sensitive spectrometer. Results: It was found that tested gold nanoprobes had different responses to x-ray excitation. It was observed that Au25-BSA is the most promising candidate for x-ray luminescence imaging, with up to 8-fold increase in

3160 X-ray Fluorescence Computed Tomography (XFCT) for High-Sensitivity Imaging of Cisplatin M. Bazalova, G. Pratx, and L. Xing; Stanford University, Stanford, CA Purpose/Objective(s): X-ray fluorescence computed tomography (XFCT) imaging has been explored for molecular imaging of probes containing high atomic number materials. Up to date, XFCT imaging techniques have been based on excitation and detection of K-shell x-rays characteristic to the probe material. However, reported XFCT imaging sensitivities have not been high enough to pick out clinically relevant concentrations. In this work, we have focused on significantly increasing XFCT sensitivity to image Cisplatin. We have achieved this by XFCT imaging with L-shell x-rays and by developing an iterative reconstruction algorithm incorporating attenuation correction. Materials/Methods: XFCT images of a 2-cm diameter acrylic phantom containing 0.6-2.2 mm diameter vials with 0.1-0.4% Cisplatin solutions with were simulated in a modified version of the EGSnrc/DOSXYZnrc Monte Carlo code. X-ray spectra detected by a 2-cm wide 270 -detector arc for 110 detector positions and 360 x-ray tube angles over 360 were acquired. In the next step, all platinum fluorescence peaks were extracted and XFCT sinograms generated and reconstructed with three algorithms: 1) simple filtered back-projection (FBP), 2) maximum likelihood expectation maximization (ML-EM) iterative reconstruction with no correction, and 3) ML-EM with attenuation correction. Three excitation x-ray beam energies were studied to investigate the improvements of L-shell imaging over K-shell imaging and to evaluate the attenuation effects of the excitation and fluorescence x-rays. Specifically, L-shell XFCT images were generated with 15 keV and 30 keV x-rays and K-shell imaging were generated with 80 keV x-rays. Results: XFCT imaging sensitivity using L-shell x-rays generated with 15 keV increased by a factor of 3.6 compared to K-shell imaging with 80 keV when FBP without attenuation corrections was applied. Due to the lack of attenuation correction, the contrast of the vials in the L-shell XFCT images decreased significantly towards the center of the phantom, up to by a factor of 7.0 and 2.2 for the 15 keV and 30 keV images, respectively. After attenuation correction, the contrast of all vials regardless of their location within the phantom was within 20% for all energies. The attenuation correction applied on the ML-EM images further increased the 15 keV image contrast by 50%. In summary, Cisplatin concentration as low as 16 mg/mL was detectable for imaging dose of 2.5 mGy. Conclusions: Monte Carlo simulations demonstrated that compared to K-shell imaging, L-shell imaging sensitivity is increased by a factor of 5.4 when attenuation correction is included in image reconstruction. Clinically relevant Cisplatin concentrations of 6 mg/mL can be imaged with a low imaging dose of 18 mGy. Author Disclosure: M. Bazalova: None. G. Pratx: None. L. Xing: None.

3161 Significance of Daily Fractionated Administration of Wortmannin Combined With Gamma-Ray Irradiation in Terms of Local Tumor Response and Lung Metastatic Potential S. Masunaga, Y. Sakurai, H. Tanaka, M. Suzuki, N. Kondo, M. Narabayashi, A. Maruhashi, and K. Ono; Research Reactor Institute, Kyoto University, Kumatori, Osaka, Japan