Showing papers by "Keith A. Cengel published in 2020"
TL;DR: Using a novel RT apparatus that delivers FLASH proton RT (PRT) using double scattered protons with computed tomography guidance, it is found that FLASH-PRT decreases acute cell loss and late fibrosis after whole-abdomen and focal intestinal RT, whereas tumor growth inhibition is preserved between the 2 modalities.
Abstract: Purpose Recent studies suggest that ultrahigh-dose-rate, “FLASH,” electron radiation therapy (RT) decreases normal tissue damage while maintaining tumor response compared with conventional dose rate RT. Here, we describe a novel RT apparatus that delivers FLASH proton RT (PRT) using double scattered protons with computed tomography guidance and provide the first report of proton FLASH RT-mediated normal tissue radioprotection. Methods and Materials Absolute dose was measured at multiple depths in solid water and validated against an absolute integral charge measurement using a Faraday cup. Real-time dose rate was obtained using a NaI detector to measure prompt gamma rays. The effect of FLASH versus standard dose rate PRT on tumors and normal tissues was measured using pancreatic flank tumors (MH641905) derived from the KPC autochthonous PanCa model in syngeneic C57BL/6J mice with analysis of fibrosis and stem cell repopulation in small intestine after abdominal irradiation. Results The double scattering and collimation apparatus was dosimetrically validated with dose rates of 78 ± 9 Gy per second and 0.9 ± 0.08 Gy per second for the FLASH and standard PRT. Whole abdominal FLASH PRT at 15 Gy significantly reduced the loss of proliferating cells in intestinal crypts compared with standard PRT. Studies with local intestinal irradiation at 18 Gy revealed a reduction to near baseline levels of intestinal fibrosis for FLASH-PRT compared with standard PRT. Despite this difference, FLASH-PRT did not demonstrate tumor radioprotection in MH641905 pancreatic cancer flank tumors after 12 or 18 Gy irradiation. Conclusions We have designed and dosimetrically validated a FLASH-PRT system with accurate control of beam flux on a millisecond time scale and online monitoring of the integral and dose delivery time structure. Using this system, we found that FLASH-PRT decreases acute cell loss and late fibrosis after whole-abdomen and focal intestinal RT, whereas tumor growth inhibition is preserved between the 2 modalities.
226 citations
TL;DR: Multimodal treatment plans combining immune checkpoint inhibitors with other therapies, including photodynamic therapy (PDT), may help to expand treatment efficacy and minimize side effects.
Abstract: Immune checkpoints including PD-1 and CTLA-4 help to regulate the intensity and timeframe of the immune response Since they become upregulated in cancer and prevent sufficient antitumor immunity, monoclonal antibodies against these checkpoints have shown clinical promise for a range of cancers Multimodal treatment plans combining immune checkpoint inhibitors with other therapies, including photodynamic therapy (PDT), may help to expand treatment efficacy and minimize side effects PDT's cytotoxic effects are spatially limited by the light activation process, constraining PDT direct effects to the treatment field The production of damage-associated molecular patterns and tumor-associated antigens from PDT can encourage accumulation and maturation of antigen-presenting cells and reprogram the tumor microenvironment to be more susceptible to therapies targeting immune checkpoints
38 citations
TL;DR: Higher pretreatment C TCs and persistence of CTCs posttreatment is significantly associated with increased risk of recurrence outside the targeted treatment site, which suggests that CTC analysis may potentially identify patients at higher risk for regional or distant recurrences and who may benefit from either systemic therapy and/or timely locoregional salvage treatment.
Abstract: Purpose: Although stereotactic body radiation therapy (SBRT) is effective in early stage non-small cell lung cancer (NSCLC), ~10-15% of patients will fail regionally and 20-25% distantly. We evaluate a novel circulating tumor cell (CTC) assay as a prognostic marker for increased risk of recurrence following SBRT. Experimental Design: 92 subjects (median age 71y) with T1a (64%), T1b (23%), or T2a (13%) stage I NSCLC treated with SBRT were prospectively enrolled. CTCs were enumerated by utilizing a GFP-expressing adenoviral probe that detects elevated telomerase activity in cancer cells. Samples were obtained before, during, and serially up to 24m after treatment. SBRT was delivered to a median dose of 50Gy (range, 40-60Gy), mostly commonly in 4-5 fractions (92%). Results: 38 of 92 subjects (41%) had a positive CTC test prior to SBRT. A cutoff of ≥5 CTCs/mL before treatment defined favorable (n=78) and unfavorable (n=14) prognostic groups. Increased risk of nodal (p=0.04) and distant (p=0.03) failure was observed in the unfavorable group. Within 3m following SBRT, CTCs continued to be detected in 10 of 35 (29%) subjects. Persistent detection of CTCs was associated with increased risk of distant failure (p=0.04) and trended towards increased regional (p=0.08) and local failure (p=0.16). Conclusions: Higher pre-treatment CTCs and persistence of CTCs post-treatment is significantly associated with increased risk of recurrence outside the targeted treatment site. This suggests that CTC analysis may potentially identify patients at higher risk for regional or distant recurrences and who may benefit from either systemic therapy and/or timely locoregional salvage treatment.
31 citations
TL;DR: The standard deviation of light fluence uniformity for the Photofrin-mediated PDT is 10%, which can prove to improve treatment delivery with implementation in real-time in the surgical setting.
Abstract: Pleural photodynamic therapy (PDT) is performed intraoperatively for the treatment of microscopic disease in patients with malignant pleural mesothelioma. Accurate delivery of light dose is critical to PDT efficiency. As a standard of care, light fluence is delivered to the prescribed fluence using eight isotropic detectors in pre-determined discrete locations inside the pleural cavity that is filled with a dilute Intralipid solution. An optical infrared (IR) navigation system was used to monitor reflective passive markers on a modified and improved treatment delivery wand to track the position of the light source within the treatment cavity during light delivery. This information was used to calculate the light dose, incorporating a constant scattered light dose and using a dual correction method. Calculation methods were extensively compared for eight detector locations and seven patient case studies. The light fluence uniformity was also quantified by representing the unraveled three-dimensional geometry on a two-dimensional plane. Calculated light fluence at the end of treatment delivery was compared to measured values from isotropic detectors. Using a constant scattered dose for all detector locations along with a dual correction method, the difference between calculated and measured values for each detector was within 15%. Primary light dose alone does not fully account for the light delivered inside the cavity. This is useful in determining the light dose delivered to areas of the pleural cavity between detector locations, and can serve to improve treatment delivery with implementation in real-time in the surgical setting. We concluded that the standard deviation of light fluence uniformity for this method of pleural PDT is 10%.
14 citations
TL;DR: It is concluded that it is feasible to use an IR camera‐based system to track the motion of the light source during PDT and demonstrate its use to quantify the uniformity of light distribution, which deviated by a standard deviation of 18% from the prescribed light dose.
Abstract: Uniform light fluence distribution for patients undergoing photodynamic therapy (PDT) is critical to ensure predictable PDT outcomes. However, current practice when delivering intrapleural PDT uses a point source to deliver light that is monitored by seven isotropic detectors placed within the pleural cavity to assess its uniformity. We have developed a real-time infrared (IR) tracking camera to follow the movement of the light point source and the surface contour of the treatment area. The calculated light fluence rates were matched with isotropic detectors using a two-correction factor method and an empirical model that includes both direct and scattered light components. Our clinical trial demonstrated that we can successfully implement the IR navigation system in 75% (15/20) of the patients. Data were successfully analyzed in 80% (12/15) patients because detector locations were not available for three patients. We conclude that it is feasible to use an IR camera-based system to track the motion of the light source during PDT and demonstrate its use to quantify the uniformity of light distribution, which deviated by a standard deviation of 18% from the prescribed light dose. The navigation system will fail when insufficient percentage of light source positions is obtained (<30%) during PDT.
13 citations
TL;DR: Surgery and chemotherapy are disproportionately underutilized in female patients with MPM and female gender is independently associated with improved survival relative to males, suggesting gender disparities in MPM are warranted.
10 citations
TL;DR: Blood-flow-informed PDT (BFI-PDT) is introduced as a platform for personalized light delivery in PDT, the design of a clinically-relevant instrument is documents, and the benefits of BFI- PDT are established with respect to treatment outcome and duration.
Abstract: Fluence rate is an effector of photodynamic therapy (PDT) outcome. Lower light fluence rates can conserve tumor perfusion during some illumination protocols for PDT, but then treatment times are proportionally longer to deliver equivalent fluence. Likewise, higher fluence rates can shorten treatment time but may compromise treatment efficacy by inducing blood flow stasis during illumination. We developed blood-flow-informed PDT (BFI-PDT) to balance these effects. BFI-PDT uses real-time noninvasive monitoring of tumor blood flow to inform selection of irradiance, i.e., incident fluence rate, on the treated surface. BFI-PDT thus aims to conserve tumor perfusion during PDT while minimizing treatment time. Pre-clinical studies in murine tumors of radiation-induced fibrosarcoma (RIF) and a mesothelioma cell line (AB12) show that BFI-PDT preserves tumor blood flow during illumination better than standard PDT with continuous light delivery at high irradiance. Compared to standard high irradiance PDT, BFI-PDT maintains better tumor oxygenation during illumination and increases direct tumor cell kill in a manner consistent with known oxygen dependencies in PDT-mediated cytotoxicity. BFI-PDT promotes vascular shutdown after PDT, thereby depriving remaining tumor cells of oxygen and nutrients. Collectively, these benefits of BFI-PDT produce a significantly better therapeutic outcome than standard high irradiance PDT. Moreover, BFI-PDT requires ~40% less time on average to achieve outcomes that are modestly better than those with standard low irradiance treatment. This contribution introduces BFI-PDT as a platform for personalized light delivery in PDT, documents the design of a clinically-relevant instrument, and establishes the benefits of BFI-PDT with respect to treatment outcome and duration.
9 citations
TL;DR: A large cohort to predict radiation esophagitis in lung cancer patients was used and modern machine learning models were implemented to avoid repeats of previously published predictors of grade ≥ 3 radiation esphagitis.
8 citations
TL;DR: Investigating escalating doses of benzoporphyrin derivative‐mediated intraperitoneal PDT combined with the EGFR‐inhibitor cetuximab in a canine model observed a tolerable safety and toxicity profile related to the light dose received and found that BPD levels are higher in the small bowel compared with other anatomical regions.
Abstract: Peritoneal carcinomatosis (PC) can occur as an advanced consequence of multiple primary malignancies. Surgical resection, radiation or systemic interventions alone have proven inadequate for this aggressive cancer presentation, since PC still has a poor survival profile. Photodynamic therapy (PDT), in which photosensitive drugs are exposed to light to generate cytotoxic reactive oxygen species, may be an ideal treatment for PC because of its ability to deliver treatment to a depth appropriate for peritoneal surface tumors. Additionally, epidermal growth factor receptor (EGFR) signaling plays a variety of roles in cancer progression and survival as well as PDT-mediated cytotoxicity, so EGFR inhibitors may be valuable in enhancing the therapeutic index of intraperitoneal PDT. This study examines escalating doses of benzoporphyrin derivative (BPD)-mediated intraperitoneal PDT combined with the EGFR-inhibitor cetuximab in a canine model. In the presence or absence of small bowel resection (SBR) and cetuximab, we observed a tolerable safety and toxicity profile related to the light dose received. Additionally, our findings that BPD levels are higher in the small bowel compared with other anatomical regions, and that the risk of anastomotic failure decreases at lower light doses will help to inform the design of similar PC treatments in humans.
7 citations
6 citations
TL;DR: It is demonstrated that the pre-existing widely used photon based models fit the PBT data well with minor modifications and can aid in individualizing selection of the most optimal treatment technique for a particular patient.
Abstract: Purpose No validated models for predicting the risk of radiation pneumonitis (RP) with proton beam therapy (PBT) currently exist. Our goal was to externally validate and recalibrate multiple established photon-based normal tissue complication probability models for RP in a cohort with locally advanced nonsmall cell lung cancer treated with contemporary doses of chemoradiation using PBT. Methods and Materials The external validation cohort consisted of 99 consecutive patients with locally advanced nonsmall cell lung cancer treated with chemoradiation using PBT. RP was retrospectively scored at 3 and 6 months posttreatment. We evaluated the performance of the photon Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) pneumonitis model, the QUANTEC model adjusted for clinical risk factors, and the newer Netherlands updated QUANTEC model. A closed testing procedure was performed to test the need for model updating, either by recalibration-in-the-large (re-estimation of intercept), recalibration (re-estimation of intercept/slope), or model revision (re-estimation of all coefficients). Results There were 21 events (21%) of ≥grade 2 RP. The closed testing procedure on the PBT data set did not detect major deviations between the models and the data and recommended adjustment of the intercept only for the photon-based Netherlands updated QUANTEC model (intercept update: –1.2). However, an update of the slope and revision of the model coefficients were not recommended by the closed testing procedure, as the deviations were not significant within the power of the data. Conclusions The similarity between the dose-response relationship for PBT and photons for normal tissue complications has been an assumption until now. We demonstrate that the preexisting, widely used photon based models fit our PBT data well with minor modifications. These now-validated and updated normal tissue complication probability models can aid in individualizing selection of the most optimal treatment technique for a particular patient.
TL;DR: The lung volume receiving higher doses, such as V40Gy, may be used as an additional indicator for RP in LA-NSCLC patients treated with proton therapy.
Abstract: Purpose The dosimetric parameters used clinically to reduce the likelihood of radiation pneumonitis (RP) for lung cancer radiation therapy have traditionally been V20Gy ≤ 30% to 35% and mean lung dose ≤ 20 to 23 Gy; however, these parameters are derived based on studies from photon therapy. The purpose of this study is to evaluate whether such dosimetric predictors for RP are applicable for locally advanced non-small cell lung cancer (LA-NSCLC) patients treated with proton therapy. Methods and Materials In the study, 160 (78 photon, 82 proton) patients with LA-NSCLC treated with chemoradiotherapy between 2011 and 2016 were retrospectively identified. Forty (20 photon, 20 proton) patients exhibited grade ≥2 RP after therapy. Dose volume histograms for the uninvolved lung were extracted for each patient. The percent lung volumes receiving above various dose levels were obtained in addition to V20Gy and Dmean. These dosimetric parameters and patient characteristics were evaluated with univariate and multivariate logistic regression tests. Receiver operating characteristic curves were generated to obtain the optimal dosimetric constraints through analyzing RP and non-RP sensitivity and specificity values. Results The multivariate analysis showed V40Gy and Dmean to be statistically significant for proton and photon patients, respectively. V35Gy to V50Gy were strongly correlated to V40Gy for proton patients. Based on the receiver operating characteristic curves, V35Gy to V50Gy had the highest area under the curve compared with other dose levels for proton patients. A potential dosimetric constraint for RP predictor in proton patients is V40Gy ≤ 23%. Conclusions In addition to V20Gy and Dmean, the lung volume receiving higher doses, such as V40Gy, may be used as an additional indicator for RP in LA-NSCLC patients treated with proton therapy.
TL;DR: Proton-Beam Therapy: At the Heart of Cardiac Dose-Sparing in Mediastinal Radiotherapy for Thymic Carcinoma is presented.
TL;DR: Hemoglobin concentration, oxygenation and optical properties were determined to be highly heterogeneous between canines and at different anatomical locations within the same subject, so further development of PDT dosimetry systems will need to address this patient and location‐specific dose optimization.
Abstract: As part of a preclinical trial for the treatment of peritoneal carcinomatosis (PC) with photodynamic therapy (PDT), we have assessed changes in optical properties, tissue oxygenation and drug concentration as a result of benzoporphyrin derivative (BPD)-mediated PDT using diffuse reflectance and fluorescence measurements. PDT can effectively treat superficial disease spread, but treatment efficacy is influenced by physical properties of the treated tissue which can change over the treatment time. In this study, healthy canines were given BPD and irradiated with 690 nm light during a partial bowel resection, and spectroscopic and fluorescence measurements were made using an in-house built spectroscopic probe. Hemoglobin concentration, oxygenation and optical properties were determined to be highly heterogeneous between canines and at different anatomical locations within the same subject, so further development of PDT dosimetry systems will need to address this patient and location-specific dose optimization. Compared to other photosensitizers, we found no apparent BPD photobleaching after PDT.
TL;DR: Significantly improved outcomes in patients with early responses to therapy, as measured by TVR and NVR, were seen.
Abstract: Purpose There are no established imaging biomarkers that predict response during chemoradiation for patients with locally advanced non-small cell lung carcinoma. At our institution, proton therapy (PT) patients undergo repeat computed tomography (CT) simulations twice during radiation. We hypothesized that tumor regression measured on these scans would separate early and late responders and that early response would translate into better outcomes. Methods and Materials Patients underwent CT simulations before starting PT (CT0) and between weeks 1 to 3 (CT1) and weeks 4 to 7 (CT2) of PT. Primary tumor volume (TVR) and nodal volume (NVR) reduction were calculated at CT1 and CT2. Based on recursive partitioning analysis, early response at CT1 and CT2 was defined as ≥20% and ≥40%, respectively. Locoregional and overall progression-free survival (PFS), distant metastasis–free survival, and overall survival by response status were measured using Kaplan–Meier analysis. Results Ninety-seven patients with locally advanced non-small cell lung carcinoma underwent definitive PT to a median dose of 66.6 Gy with concurrent chemotherapy. Median TVR and NVR at CT1 were 19% (0-79%) and 19% (0-75%), respectively. At CT2, they were 33% (2-98%) and 35% (0-89%), respectively. With a median follow-up of 25 months, the median overall survival and PFS for the entire cohort was 24.9 and 13.2 months, respectively. Compared with patients with TVR and NVR Conclusions Significantly improved outcomes in patients with early responses to therapy, as measured by TVR and NVR, were seen. Further study is warranted to determine whether treatment intensification will improve outcomes in slow-responding patients.
TL;DR: Overall, PDT of the thoracic cavity resulted in moderate treatment‐averaged fluence rate that was consistent among treated tissue sites, despite instantaneous exposure to high fluence rates.
Abstract: The distributions of light and tissue oxygenation (St O2 ) within the chest cavity were determined for 15 subjects undergoing macroscopic complete resection followed by intraoperative photodynamic therapy (PDT) as part of a clinical trial for the treatment of malignant pleural mesothelioma (MPM). Over the course of light delivery, detectors at each of eight different sites recorded exposure to variable fluence rate. Nevertheless, the treatment-averaged fluence rate was similar among sites, ranging from a median of 40-61 mW cm-2 during periods of light exposure to a detector. St O2 at each tissue site varied by subject, but posterior mediastinum and posterior sulcus were the most consistently well oxygenated (median St O2 >90%; interquartile ranges ~85-95%). PDT effect on St O2 was characterized as the St O2 ratio (post-PDT St O2 /pre-PDT St O2 ). High St O2 pre-PDT was significantly associated with oxygen depletion (St O2 ratio < 1), although the extent of oxygen depletion was mild (median St O2 ratio of 0.8). Overall, PDT of the thoracic cavity resulted in moderate treatment-averaged fluence rate that was consistent among treated tissue sites, despite instantaneous exposure to high fluence rate. Mild oxygen depletion after PDT was experienced at tissue sites with high pre-PDT St O2 , which may suggest the presence of a treatment effect.
TL;DR: This small number of patients treated with pembrolizumab in malignant mesothelioma clinical trials have included small numbers of peritoneal MM patients, but the efficacy of P in the MPM sub...
Abstract: e21094Background: Clinical trials evaluating pembrolizumab (P) in malignant mesothelioma (MM) have included small numbers of peritoneal MM (MPM) patients (pts), but the efficacy of P in the MPM sub...
TL;DR: This first reported series of posterior intercostal lymph nodes revealed they independently more than doubled the risk of progression and death and in 11% of the patients were the only metastatic nodes.
TL;DR: In this first clinical report of TRT for LC on a 6X-FFF ORL, daily CBCT-guided treatment was fast and safe with respect to dosimetry and clinical outcomes, and use of this linac for TRT may increase LC patient throughput without a detriment in radiotherapy quality.
Abstract: Introduction Modern technologies, like intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), have improved the therapeutic ratio of thoracic radiotherapy (TRT) for lung cancer (LC). Halcyon™ (Varian Medical Systems, Palo Alto, CA, USA), a novel 6MV-flattening-filter-free O-ring linear accelerator (6X-FFF ORL), was designed to deliver IMRT and VMAT with greater speed than a C-arm linac. Herein, we report our initial clinical experience treating patients with LC on this linac. Methods All patients who received TRT for LC on the 6X-FFF ORL at our institution were retrospectively identified. Patients' clinicopathologic data, radiotherapy details, early disease-control and toxicity outcomes, dosimetric data, couch corrections, and treatment times are reported. Results Between 10/2018-12/2019, 30 consecutive patients (median age 66 years, range 54-94 years) received definitive or post-operative TRT for LC (median 66 Gy/33 fractions; range 5-70 Gy/2-37 fractions) following four-dimensional computed tomography (CT) simulation (97%) using daily kilovoltage KV cone-beam CT (CBCT) (100%) on a 6X-FFF ORL for non-small cell LC (84%) or small cell LC (16%), with 53% receiving VMAT, 43% receiving static-field IMRT, and 77% receiving concurrent systemic therapy. All plans were approved through institutional peer review. The average three-dimensional vector couch correction based on CBCT guidance was 0.90 ± 0.50 cm. The average beam-on and beam on plus CBCT times were 1.7 ± 1.1 min, and 5.0 ± 3.2 min, respectively. Grade 3 dyspnea and fatigue occurred in 3% and 3% of patients, respectively. There were no grade ≥4 toxicities. Conclusion In this first clinical report of TRT for LC on a 6X-FFF ORL, daily CBCT-guided treatment was fast and safe with respect to dosimetry and clinical outcomes. Thus, use of this linac for TRT may increase LC patient throughput without a detriment in radiotherapy quality.
TL;DR: Treatment provided symptom palliation and local control across multiple palliative scenarios, with minimal toxicity, acceptable dosimetry, and setup corrections and treatment times that compared favorably with other published experiences of MPM RT.
Abstract: Background Radiation therapy (RT) can provide effective symptomatic palliation in patients with malignant pleural mesothelioma (MPM). Advances in RT technology, including intensity-modulated RT (IMRT) and volumetric-modulated arc therapy (VMAT), have improved treatment conformality, potentially improving the therapeutic ratio of RT. A novel 6-MV flattening-filter-free O-ring linear accelerator, HalcyonTM (Varian Medical Systems, Palo Alto, CA, USA), was built to provide such advanced therapies, while possibly reducing treatment time. Here, we report the initial clinical experience using HalcyonTM to deliver palliative RT for patients with MPM. Methods We retrospectively assessed consecutive patients with MPM who received thoracic RT on HalcyonTM. Their electronic medical records were reviewed for clinical, RT planning, treatment timing, and image-guidance RT (IGRT) data. Results Four patients with metastatic MPM received palliative RT on HalcyonTM between 1/2017-1/2020 for severe pain (50%), dysphagia (25%), or dyspnea (25%). Targets included a combination of pleura, chest wall, lung, hilum, and mediastinum, with patient-specific dose and fractionation regimens ranging from 20-45 Gy in 5-15 fractions, and 75% of patients receiving concurrent systemic therapy. Pre-specified target and organ-at-risk constraints were met for nearly all plans. At a median follow-up of 2.2 months (range, 1.6-7.1 months), all patients experienced either improved (75%) or stable (25%) tumor-related symptoms following palliative RT. The mean 3D vector couch correction was 0.67±0.15 cm. The mean beam-on, treatment (beam-on plus cone-beam computed tomography times), and approximated total room usage times were 1.6±0.2, 1.8±0.2, and 9.8±0.2 min, respectively. Grade 2 fatigue and cough occurred in 25% and 25% of patients, and no patients experienced Grade ≥3 toxicity. Conclusions In this initial clinical experience treating patients with palliative RT for MPM on HalcyonTM, treatment provided symptom palliation and local control across multiple palliative scenarios, with minimal toxicity, acceptable dosimetry, and setup corrections and treatment times that compared favorably with other published experiences of MPM RT. Palliative RT on HalcyonTM can provide patients with MPM quick and safe tumor-related symptom relief, even in a frail, elderly population.