In gated radiation therapy procedures, the lung tumor position is used directly (by implanted radiopaque markers) or indirectly (by external surrogate methods) to decrease the volume of irradiated healthy tissue. Due to a risk of pneumothorax, many clinics do not implant fiducials, and the gated treatment is primarily based on a respiratory induced external signal. The external surrogate method relies upon the assumption that the internal tumor motion is well correlated with the external respiratory induced motion, and that this correlation is constant in time. Using a set of data that contains synchronous internal and external motion traces, we have developed a dynamic data analysis technique to study the internal-external correlation, and to quantitatively estimate its underlying time behavior. The work presented here quantifies the time dependent behavior of the correlation between external respiratory signals and lung implanted fiducial motion. The corresponding amplitude mismatch is also reported for the lung patients studied. The information obtained can be used to improve the accuracy of tumor tracking. For the ten patients in this study, the SI internal-external motion is well correlated, with small time shifts and corresponding amplitude mismatches. Although the AP internal-external motion reveals larger time shifts than along the SI direction, the corresponding amplitude mismatches are below 5 mm.
Purpose: In respiratory‐gated treatments, the successful delivery of the planned dose distribution and sparing of the health tissue is highly dependent upon the assumption of a strong correlation between the external motion and the internal tumor motion. We will present a new internal/external correlation study based on a unique data set. Method and Materials: Radiopaque fiducial markers inside or near the target were implanted and visualized in real time by means of stereoscopic diagnostic x‐ray fluoroscopy. The fluoroscopic images were recorded continuously in synchronization with an external respiratory motion monitoring system. A data analysis methodology was developed in order to assess the correlation of the external breathing motion with the internal 3D position of the implanted fiducials. The methodology is based on a dynamic correlation technique and used to extract global correlation parameters as well as to reveal their instantaneous behavior. Results: We have found that in some cases, the poor internal/external correlation is caused by a time mismatch between the motion of the internal fiducial markers and the external breathing motion. For some cases, there is a sizeable time delay between the internal tumor motion and the external motion of up to 0.8 seconds, revealing that internal‐external motion coupling is dependent on the tumor position. We have also found that the time delay itself is time‐dependent. Conclusion: The proposed technique reveals one of the causes for poor internal‐external correlation and it could be used to improve the current gated treatment methodology by combining the amplitude gating technique with the measured time‐delay. In the course of these investigations, we also found that our technique can reveal difficulties in extracting the underlying time delay (due to its own time dependence) and that one has to be careful of how the time delay is implemented for gating.
The technique of femtosecond coherence spectroscopy is applied to a variety of photostable and photochemically active heme protein samples. With the exception of cobalt-substituted myoglobin, strong oscillations are detected near 40 cm-1 in all of the samples studied. Additional modes near 80, 120, and 160 cm-1 are observed in the photochemically active samples. The amplitude and phase behavior of the low-frequency modes are studied by tuning the pump/probe carrier wavelength across the Soret absorption spectrum. A simple harmonic model is not able to account for the observed relative intensities of these modes or the carrier wavelength dependence of their frequency and phase. As a result, we develop an anharmonic model where the oscillatory signal is damped as the result of heterogeneity in the potential surface. The underlying source of the heterogeneity in the anharmonic potential surface is found to be correlated with the inhomogeneous broadening of the Soret band. The presence of the higher harmonics in the photochemically active samples demonstrates that the anharmonic mode is strongly coupled to the ligand photodissociation reaction (i.e., upon photolysis it is displaced far from equilibrium). Moreover, the observation of the ∼40 cm-1 oscillations in all of the iron-based heme protein samples, including porphine and protoporphyrin IX model compounds, suggests that this mode is associated with nuclear motion of the core of the porphyrin macrocycle. Since normal mode calculations and prior kinetic models predict the frequency of the heme "doming mode" to be near 50 cm-1, we suggest that the reaction coupled oscillations at ∼40 and ∼80 cm-1 are a direct reflection of anharmonic heme doming dynamics. Evidence for coupling between the heme doming dynamics and the Fe−His stretching mode is also presented.
Abstract In non-small cell lung cancer (NSCLC) treatment, targeted therapies help a subset of patients, and radiotherapy responses are not durable and toxicity limits therapy. Most advanced-stage NSCLC patients have brain metastases that render an abysmal prognosis. Standard-of-care radiation therapy for NSCLC brain metastasis includes stereotactic radiosurgery (SRS) if the number of lesions is less than ten, otherwise whole brain radiation therapy (WBRT) is administered. Challenges in applying radiotherapy include overcoming radiation resistance and reducing significant associated co-morbidities. Cancer neuroscience is an evolving area, and the purpose of this study is to determine if activation of GABA(A) receptors intrinsic to NSCLC cells can improve radiation efficacy in primary NSCLC and its brain metastasis. We find that a GABA(A) receptor activator, AM-101, impairs the viability and clonogenicity of NSCLC primary and brain metastatic cells. Employing a human-relevant ex vivo ‘chip’, AM-101 is as efficacious as docetaxel, a chemotherapeutic used with radiotherapy for advanced-stage NSCLC. In vivo, AM-101 potentiates radiation, including conferring a significant survival benefit to mice bearing NSCLC intracranial tumors generated using a patient-derived metastatic line. GABA(A) receptor activation stimulates a selective-autophagic response via multimerization of GABA(A) Receptor-Associated Protein (GABARAP), stabilization of mitochondrial receptor Nix, utilization of ubiquitin-binding protein p62, and upregulation of Beclin-1. A high-affinity peptide disrupting Nix binding to GABARAP inhibits the cytotoxicity of AM-101. This supports a model of GABA(A) receptor activation driving a GABARAP-Nix multimerization axis that triggers autophagy. In NSCLC brain metastases patients, GABA(A) receptor activation may improve radiation efficacy and tumor control while allowing radiation dose de-intensification to reduce toxicity. Citation Format: Debanjan Bhattacharya, Riccardo Barrile, Donatien Kamdem Toukam, Vaibhavkumar S. Gawali, Laura Kallay, Taukir Ahmed, Hawley Brown, Sepideh Rezvanian, Aniruddha Karve, Pankaj B. Desai, Mario Medvedovic, Kyle Wang, Dan Ionascu, Nusrat Harun, Chenran Wang, Andrew M. Baschnagel, Joshua A. Kritzer, James Cook, Daniel A. Pomeranz Krummel, Soma Sengupta. GABA(A) receptor activation drives GABARAP-Nix mediated autophagy to radiosensitize primary and metastatic lung adenocarcinoma tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 703.
Purpose : To track the target trajectory during the treatment based on the pre‐treatment CBCT projection images when the gantry is selectively slowed down at the treatment angles, the synchronized 3D surface imaging and the EPID in movie mode. Methods and Materials : A gantry‐speed device slows down the CBCT gantry speed (2min/360degrees) by half for a 6 degrees arc centered on the MV treatment beam, allowing us acquire twice as many frames within the treatment arc (22frames/5.5fps). The treatment arc is chosen to accommodate a typical full breathing period (4s). A CBCT kV beam‐on trigger is used to acquire 3D surface images using the AlignRT cameras. Phantom experiments were performed using a programmable respiratory motion platform. During the treatment delivery, MV imaging was performed in movie mode (3fps) while the surface cameras tracked the chest‐wall component. A mutual information algorithm was employed to compare the kV an MV images. Results : CBCT reconstruction was performed using every other frame when in the slow treatment arc for correct reconstruction. The longer scanning times were translated in ∼10–15% additional CBCT dose when 4 beams were used. For simple trajectory, the kV and MV images were phase correlated ∼98% of the time for the high contrast tumor and ∼92% for the low contrast tumor. Phase knowledge provided by the surface cameras increased the later kV‐MV correlation to ∼97%. Patient‐like trajectories were tested where the most irregular trace (3mm baseline‐shift) showed a moderate kV‐MV correlation, enabling one to interrupt the treatment for a second on‐line baseline correction. Conclusion : The selective beams‐eye‐view slow‐arc CBCT technique in conjunction with surface cameras and MV imaging has been demonstrated to be an effective tool for tumor tracking due to its treatment time immediacy and minimal impact on treatment flow.
We present temperature-dependent kinetic measurements of ultrafast diatomic ligand binding to the “bare” protoheme (L 1 -FePPIX-L 2 , where L 1 = H 2 O or 2-methyl imidazole and L 2 = CO or NO). We found that the binding of CO is temperature-dependent and nonexponential over many decades in time, whereas the binding of NO is exponential and temperature-independent. The nonexponential nature of CO binding to protoheme, as well as its relaxation above the solvent glass transition, mimics the kinetics of CO binding to myoglobin (Mb) but on faster time scales. This demonstrates that the nonexponential kinetic response observed for Mb is not necessarily due to the presence of protein conformational substates but rather is an inherent property of the solvated heme. The nonexponential kinetic data were analyzed by using a linear coupling model with a distribution of enthalpic barriers that fluctuate on slower time scales than the heme–CO recombination time. Below the solvent glass transition ( T g ≈ 180 K), the average enthalpic rebinding barrier for H 2 O-PPIX-CO was found to be ≈1 kJ/mol. Above T g , the barrier relaxes and is ≈6 kJ/mol at 290 K. Values for the first two moments of the heme doming coordinate distribution extracted from the kinetic data suggest significant anharmonicity above T g . In contrast to Mb, the protoheme shows no indication of the presence of “distal” enthalpic barriers. Moreover, the wide range of Arrhenius prefactors (10 9 to 10 11 s −1 ) observed for CO binding to heme under differing conditions suggests that entropic barriers may be an important source of control in this class of biochemical reactions.
