Assessment of MRI image distortion based on 6 consecutive years of annual QAs and measurements on 14 MRI scanners used for radiation therapy.

PURPOSE: To determine the magnitude of MRI image distortion based on 6 consecutive years of annual quality assurances/measurements on 14 MRI scanners used for radiation therapy and to provide evidence for the inclusion of additional margin for treatment planning. METHODS AND MATERIALS: We used commercial MRI image phantoms to quantitatively study the MRI image distortion over period of 6 years for up to 14 1.5 and 3 T MRI scanners that could potentially be used to provide MRI images for treatment planning. With the phantom images collected from 2016 to 2022, we investigated the MRI image distortion, the dependence of distortion on the distance from the imaging isocenter, and the possible causes of large distortion discovered. RESULTS: MRI image distortion increases with the distance from the imaging isocenter. For a region of interest (ROI) with a radius of 100 mm centered at the isocenter, the mean magnitude of distortion for all MRI scanners is 0.44 ± 0.18 mm $0.44 \pm 0.18\;{\rm{mm}}$ , and the maximum distortion varies from 0.52 to 1.31 mm $0.52\;{\rm{to}}\;1.31\;{\rm{mm}}$ depending on MRI scanners. For an ROI with a radius of 200 mm centered at the isocenter, the mean magnitude of distortion increases to 0.84 ± 0.45 mm $0.84 \pm 0.45\;{\rm{mm}}$ , and the range of the maximum distortion increases to 1.92 - 5.03 mm $1.92 - 5.03\;{\rm{mm}}$ depending on MRI scanners. The distortion could reach 2 mm at 150 mm from the isocenter. CONCLUSION: An additional margin to accommodate image distortion should be considered for treatment planning. Imaging with proper patient alignment to the isocenter is vital to reducing image distortion. We recommend performing image distortion checks annually and after major upgrade on MRI scanners.

Plasma-based biomaterials for the treatment of cutaneous radiation injury.

Cutaneous wounds caused by an exposure to high doses of ionizing radiation remain a therapeutic challenge. While new experimental strategies for treatment are being developed, there are currently no off-the-shelf therapies for the treatment of cutaneous radiation injury that have been proven to promote repair of the damaged tissues. Plasma-based biomaterials are biologically active biomaterials made from platelet enriched plasma, which can be made into both solid and semi-solid forms, are inexpensive, and are available as off-the-shelf, nonrefrigerated products. In this study, the use of plasma-based biomaterials for the mitigation of acute and late toxicity for cutaneous radiation injury was investigated using a mouse model. A 2-cm diameter circle of the dorsal skin was irradiated with a single dose of 35 Gy followed by topical treatment with plasma-based biomaterial or vehicle once daily for 5 weeks postirradiation. Weekly imaging demonstrated more complete wound resolution in the plasma-based biomaterial vs. vehicle group which became statistically significant (p < 0.05) at weeks 12, 13, and 14 postmaximum wound area. Despite more complete wound healing, at 9 and 17 weeks postirradiation, there was no statistically significant difference in collagen deposition or skin thickness between the plasma-based biomaterial and vehicle groups based on Masson trichrome staining nor was there a statistically significant difference in inflammatory or fibrosis-related gene expression between the groups. Although significant improvement was not observed for late toxicity, plasma-based biomaterials were effective at promoting wound closure, thus helping to mitigate acute toxicity.

Safety and Feasibility of Stereotactic Radiosurgery for Patients with 15 or more Brain Metastases.

Background: Current standard of care treatment for patients with ≥15 brain metastases (BM) is whole brain radiation therapy (WBRT), despite poor neurocognitive outcomes. We analyzed our institutional experience of treating these patients with stereotactic radiosurgery (SRS), with the aim of evaluating safety, cognitive outcomes, and survival metrics. Methods: Patients who received SRS for ≥15 BMs in 1 to 5 fractions from 2014 to 2022 were included. Cognitive outcomes were objectively evaluated using serial Patient-Reported Outcome Measurement Information System (PROMIS) scores. The Kaplan-Meier method was used for survival analysis and log-rank test for intergroup comparisons. Results: Overall, 118 patients underwent 124 courses of LINAC-based SRS. The median number of lesions treated per course was 20 (range, 15-94). Most patients received fractionated SRS to a dose of 24 Gy in 3 fractions (81.5%). At the time of SRS, 19.4% patients had received prior WBRT, and 24.2% had received prior SRS. The rate of any grade radiation necrosis (RN) and grade ≥3 RN were 15.3% and 3.2%, respectively. When evaluating longitudinal PROMIS score trends, 25 of 31 patients had a stable/improved PROMIS score. Patients who did not receive prior brain RT had a longer median survival (7.4 months vs 4.6 months, P = .034). The 12m local control was 97.6%, and the cumulative incidence of distant intracranial failure, with death as a competing event, was 46% (95% CI, 36%, 55%). One year freedom from neurologic death, leptomeningeal disease, and salvage WBRT were 89%, 94.6%, and 84%, respectively. Conclusion: We present here one of the largest studies evaluating SRS for patients with ≥15 BMs. SRS was safe, had favorable cognitive outcomes, and had comparable survival outcomes to contemporary studies evaluating WBRT in this population. Treatment-naïve patients had a median survival of >6 months, long enough to benefit from cognitive sparing with SRS. Our study supports randomized studies comparing SRS and hippocampal avoidance WBRT approaches for these patients.

The application of radiation therapy to the Pediatric Preclinical Testing Program (PPTP): results of a pilot study in rhabdomyosarcoma.

BACKGROUND: The Pediatric Preclinical Testing Program (PPTP) has been successfully used to determine the efficacy of novel agents against solid tumors by testing them within a mouse-flank in vivo model. To date, radiation therapy has not been applied to this system. We report on the feasibility and biologic outcomes of a pilot study using alveolar and embryonal rhabdomyosarcoma xenograft lines. PROCEDURES: We developed a high-throughput mouse-flank irradiation device that allows the safe delivery of radiotherapy in clinically relevant doses. For our pilot study, two rhabdomyosarcoma xenograft lines from the PPTP, Rh30 (alveolar) and Rh18 (embryonal) were selected. Using established methods, xenografts were implanted, grown to appropriate volumes, and were subjected to fractionated radiotherapy. Tumor response-rates, growth kinetics, and event-free survival time were measured. RESULTS: Once optimized, the rate of acute toxicity requiring early removal from study in 93 mice was only 3%. During the optimization phase, it was observed that the alveolar Rh30 xenograft line demonstrated a significantly greater radiation resistance than embryonal Rh18 in vivo. This finding was validated within the standardized 30 Gy treatment phase, resulting in overall treatment failure rates of 10% versus 60% for the embryonal versus alveolar subtype, respectively. CONCLUSIONS: Our pilot study demonstrated the feasibility of our device which enables safe, clinically relevant focal radiation delivery to immunocompromised mice. It further recapitulated the expected clinical radiobiology.

Targeting Squalene Epoxidase Interrupts Homologous Recombination via the ER Stress Response and Promotes Radiotherapy Efficacy.

Over 50% of all patients with cancer are treated with radiotherapy. However, radiotherapy is often insufficient as a monotherapy and requires a nontoxic radiosensitizer. Squalene epoxidase (SQLE) controls cholesterol biosynthesis by converting squalene to 2,3-oxidosqualene. Given that SQLE is frequently overexpressed in human cancer, this study investigated the importance of SQLE in breast cancer and non-small cell lung cancer (NSCLC), two cancers often treated with radiotherapy. SQLE-positive IHC staining was observed in 68% of breast cancer and 56% of NSCLC specimens versus 15% and 25% in normal breast and lung tissue, respectively. Importantly, SQLE expression was an independent predictor of poor prognosis, and pharmacologic inhibition of SQLE enhanced breast and lung cancer cell radiosensitivity. In addition, SQLE inhibition enhanced sensitivity to PARP inhibition. Inhibition of SQLE interrupted homologous recombination by suppressing ataxia-telangiectasia mutated (ATM) activity via the translational upregulation of wild-type p53-induced phosphatase (WIP1), regardless of the p53 status. SQLE inhibition and subsequent squalene accumulation promoted this upregulation by triggering the endoplasmic reticulum (ER) stress response. Collectively, these results identify a novel tumor-specific radiosensitizer by revealing unrecognized cross-talk between squalene metabolites, ER stress, and the DNA damage response. Although SQLE inhibitors have been used as antifungal agents in the clinic, they have not yet been used as antitumor agents. Repurposing existing SQLE-inhibiting drugs may provide new cancer treatments. SIGNIFICANCE: Squalene epoxidase inhibitors are novel tumor-specific radiosensitizers that promote ER stress and suppress homologous recombination, providing a new potential therapeutic approach to enhance radiotherapy efficacy.

Accelerators, Gantries, Magnets and Imaging Systems for Particle Beam Therapy: Recent Status and Prospects for Improvement.

The paper begins by emphasizing the clinical and commercial importance of proton or other charged particle such as carbon ion therapy, refers to the manufacturers of such systems of which more than 120 are installed or under construction worldwide by April 2021. A general review of charged particle therapy systems refers to six manufacturers and provides in tabular form some details of systems installed in the US, Europe, Asia, and elsewhere. In a description of the principles of particle beam therapy a comparison is made of the properties of photons (x-rays) versus protons and protons versus carbon ions. A brief discussion of accelerators in general is followed by descriptions of cyclotrons (including the isosynchronous cyclotron and the synchrocyclotron) and synchrotrons. An interesting case study describes the evolution of a normal-conducting 220 ton cyclotron into an iron-free synchrocyclotron weighing only 5 tons. The general principles of beam handling and gantry design are described. Subsequent sections describe gantry magnets in detail - normal conducting gantry magnets, superconducting gantry magnets for proton- and carbon therapy. Mention is made of a novel CERN-designed superconducting toroidal gantry for hadron therapy, GaToroid. This device, operating under steady state current and magnetic field, is able to deliver a beam at discrete angles over a range of treatment energies. Also considered are low temperature superconducting (LTS) and high temperature superconducting (HTS) magnet windings, and the choice of REBCO conductors for cryogen-free carbon-ion gantries. Finally, the paper mentions an important "Prospect for Improvement", viz: the introduction of MRI image guidance. A well-known property of the particle beam as it passes through tissue is its energy dependent absorption that rises to a pronounced peak (the Bragg peak) at the end of its range. In order to take advantage of this effect the exact targeting of the tumor and positioning of the patient should be guided by imaging visualization using X-ray, CT, and hopefully advanced MRI. Unlike MRI-guided photon therapy the direct interaction of the magnetic field with the charged particle beam presents a huge challenge such that MRI image-guided proton/particle therapy has not yet been available in clinical practice. Modeling studies have been undertaken on the general topic of beam-line/magnetic field interaction using, for example, the software GEANT4 (GEometry And Tracking) a platform for simulating the passage of charged particles through matter using a Monte Carlo method.

Using Endoscopic Optical Coherence Tomography to Detect and Treat Early-Stage Pancreatic Cancers.

We developed a novel technology capable of detecting early-stage pancreatic cancers using high-resolution three-dimensional endoscopic optical coherence tomography (Endo-OCT), and treating them using high dose rate brachytherapy (HDR) under the Endo-OCT image guidance. This technology integrates our custom-built ultra-high resolution endoscopic three-dimensional OCT diagnostic imaging device with a commercial high dose rate brachytherapy system (HDR), resulting in a compact, portable, easy-to-operate, and low-cost Endo-OCT image-guided high dose rate brachytherapy (OCT-IGHDR) system. The system has the dual functions of diagnosis and treatment that can precisely detect and measure the location and size of the early-stage pancreatic cancer or premalignant lesions and then treat them from the inside of the pancreatic duct with an accurate and focused dose while greatly reducing the radiation toxicity to the neighboring tissues and organs. This minimally-invasive treatment technology could avoid the potential complications from surgery and reduces the high operation cost. This technology could also be applied to treat diseases of the esophagus, rectum, bronchus, and other aerodigestive organs that are suitable for use with an endoscopic device. In this article, we describe the concept of this technology and the preliminary experiments that could demonstrate the concept by using this homemade Endo-OCT machine to image the pancreatic duct for diagnosis of early-stage pancreatic cancer or premalignant lesions and to perform Endo-OCT image-guided brachytherapy.

Two-miRNA-based finger-stick assay for estimation of absorbed ionizing radiation dose.

Nuclear radiation and radioactive fallouts resulting from a nuclear weapon detonation or reactor accidents could result in injuries affecting multiple sensitive organs, defined as acute radiation syndrome (ARS). Rapid and early estimation of injuries to sensitive organs using markers of radiation response is critical for identifying individuals who could potentially exhibit ARS; however, there are currently no biodosimetry assays approved for human use. We developed a sensitive microRNA (miRNA)-based blood test for radiation dose reconstruction with ±0.5 Gy resolution at critical dose range. Radiation dose-dependent changes in miR-150-5p in blood were internally normalized by a miRNA, miR-23a-3p, that was nonresponsive to radiation. miR-23a-3p was not highly expressed in blood cells but was abundant in circulation and was released primarily from the lung. Our assay showed the capability for dose estimation within hours to 1 week after exposure using a drop of blood from mice. We tested this biodosimetry assay for estimation of absorbed ionizing radiation dose in mice of varying ages and after exposure to both improvised nuclear device (IND)-spectrum neutrons and gamma rays. Leukemia specimens from patients exposed to fractionated radiation showed depletion of miR-150-5p in blood. We bridged the exposure of these patients to fractionated radiation by comparing responses after fractionated versus single acute exposure in mice. Although validation in nonhuman primates is needed, this proof-of-concept study suggests the potential utility of this assay in radiation disaster management and clinical applications.

Single-Isocenter Multitarget Stereotactic Radiosurgery Is Safe and Effective in the Treatment of Multiple Brain Metastases.

PURPOSE: Multiple studies have reported favorable outcomes for stereotactic radiosurgery (SRS) in the treatment of limited brain metastases. An obstacle of SRS in the management of numerous metastases is the longer treatment time using traditional radiosurgery. Single-isocenter multitarget (SIMT) SRS is a novel technique that permits rapid therapy delivery to multiple metastases. There is a lack of clinical evidence regarding its efficacy and safety. We report the outcomes of patients treated with this technique. METHODS AND MATERIALS: We reviewed the records of patients with intact or resected brain metastases treated with SRS in 1 to 5 fractions using SIMT technique at our institution, with at least 1 available follow-up brain magnetic resonance imaging. Survival, disease control, and toxicity were evaluated using Cox regression, logistic regression, and Kaplan-Meier analysis. RESULTS: We identified 173 patients with 1014 brain metastases. Median follow up was 12.7 months. Median beam-on time was 4.1 minutes. The median dose to the brain was 219.4 cGy. Median overall survival and freedom from intracranial progression were 13.2 and 6.3 months, respectively. Overall survival did not differ between patients treated with greater than or less than 4 lesions (hazard ratio, 1.03; 95% confidence interval 0.66-1.61; P = .91). Actuarial 1- and 2-year local control were 99.0% and 95.1%, respectively. Rates of grade 2 and grade 3 or higher radionecrosis were 1.4% and 0.9%, respectively. CONCLUSIONS: SIMT radiosurgery delivered in 1 to 5 fractions offers excellent local control and acceptable toxicity in the treatment of multiple intact and postoperative brain metastases. This technique should be evaluated prospectively.

IL-27 gene therapy induces depletion of Tregs and enhances the efficacy of cancer immunotherapy.

Tumor-induced expansion of Tregs is a significant obstacle to cancer immunotherapy. However, traditional approaches to deplete Tregs are often inefficient, provoking autoimmunity. We show here that administration of IL-27-expressing recombinant adeno-associated virus (AAV-IL-27) significantly inhibits tumor growth and enhances T cell responses in tumors. Strikingly, we found that AAV-IL-27 treatment causes rapid depletion of Tregs in peripheral blood, lymphoid organs, and - most pronouncedly - tumor microenvironment. AAV-IL-27-mediated Treg depletion is dependent on IL-27 receptor and Stat1 in Tregs and is a combined result of CD25 downregulation in Tregs and inhibition of IL-2 production by T cells. In combination with a GM-CSF vaccine, AAV-IL-27 treatment not only induced nearly complete tumor rejection, but also resulted in amplified neoantigen-specific T cell responses. AAV-IL-27 also dramatically increased the efficacy of anti-PD-1 therapy, presumably due to induction of PD-L1 in T cells and depletion of Tregs. Importantly, AAV-IL-27 therapy did not induce significant adverse events, partially due to its induction of IL-10. In a plasmacytoma mouse model, we found that IL-10 was required for AAV-IL-27-mediated tumor rejection. Thus, our study demonstrates the potential of AAV-IL-27 as an independent cancer therapeutic and as an efficient adjuvant for cancer immunotherapy.

Effects of Ionizing Irradiation on Mouse Diaphragmatic Skeletal Muscle.

Undesirable exposure of diaphragm to radiation during thoracic radiation therapy has not been fully considered over the past decades. Our study aims to examine the potential biological effects on diaphragm induced by radiation. One-time ionizing irradiation of 10 Gy was applied either to the diaphragmatic region of mice or to the cultured C2C12 myocytes. Each sample was then assayed for muscle function, oxidative stress, or cell viability on days 1, 3, 5, and 7 after irradiation. Our mouse model shows that radiation significantly reduced muscle function on the 5th and 7th days and increased reactive oxygen species (ROS) formation in the diaphragm tissue from days 3 to 7. Similarly, the myocytes exhibited markedly decreased viability and elevated oxidative stress from days 5 to 7 after radiation. These data together suggested that a single dose of 10-Gy radiation is sufficient to cause acute adverse effects on diaphragmatic muscle function, redox balance, and myocyte survival. Furthermore, using the collected data, we developed a physical model to formularize the correlation between diaphragmatic ROS release and time after irradiation, which can be used to predict the biological effects of radiation with a specific dosage. Our findings highlight the importance of developing protective strategies to attenuate oxidative stress and prevent diaphragm injury during radiotherapy.

Conformal Nanoencapsulation of Allogeneic T Cells Mitigates Graft-versus-Host Disease and Retains Graft-versus-Leukemia Activity.

Allogeneic transplantation of hematopoietic stem cells (HSC) in combination with T cells has a curative potential for hematopoietic malignancies through graft-versus-leukemia (GVL) effects, but is often compromised by the notorious side effect of graft-versus-host disease (GVHD) resulting from alloreactivity of the donor T cells. Here, we tested if temporary immunoisolation achieved by conformally encapsulating the donor T cells within a biocompatible and biodegradable porous film (∼450 nm in thickness) of chitosan and alginate could attenuate GVHD without compromising GVL. The nanoencapsulation was found not to affect the phenotype of T cells in vitro in terms of size, viability, proliferation, cytokine secretion, and cytotoxicity against tumor cells. Moreover, the porous nature of the nanoscale film allowed the encapsulated T cells to communicate with their environment, as evidenced by their intact capability of binding to antibodies. Lethally irradiated mice transplanted with bone marrow cells (BMCs) and the conformally encapsulated allogeneic T cells exhibited significantly improved survival and reduced GVHD together with minimal liver damage and enhanced engraftment of donor BMCs, compared to the transplantation of BMCs and non-encapsulated allogeneic T cells. Moreover, the conformal nanoencapsulation did not compromise the GVL effect of the donor T cells. These data show that conformal nanoencapsulation of T cells within biocompatible and biodegradable nanoscale porous materials is a potentially safe and effective approach to improve allogeneic HSC transplantation for treating hematological malignancies and possibly other diseases.

Using NanoDot dosimetry to study the RS 2000 X-ray biological irradiator.

PURPOSE: To use NanoDot dosimeters to study the RS 2000 X-ray Biological Irradiator dosimetry characteristics and perform in vivo dosimetry for cell or small animal experiments. METHODS AND MATERIALS: We first calibrated the Landauer NanoDot(™) Reader by irradiating some NanoDot dosimeters with a set of known doses at specific positions defined by the irradiator. A group of five NanoDot dosimeters were placed at five specific positions where the dose rates were known and provided by the irradiator. Each group was irradiated for a set of times respectively. By correlating the readings of dosimeters with the given irradiated doses, we established the dose-reading relationship for the irradiator under the specific running condition. The established calibration curve was validated by exposing arbitrary known doses to a set of dosimeters, using the Landauer NanoDot(™) Reader to measure the doses, and then making the comparison between the two doses. To study the dose gradient of the X-ray inside the irradiated target (dose variation/cm), we placed dosimeters under different thicknesses of water-equivalent bolus and irradiated them, then measured the doses to determine the dose gradient. RESULTS: Using the method described above, we were able to calibrate the Landauer InLight NanoDot(™) Reader and use NanoDot dosimeters to measure the actual doses delivered to the targets for the cell/small animal experiments that use the RS 2000 X-ray Biological Irradiator. CONCLUSIONS: NanoDots are ideal dosimeters to use for in vivo dosimetry for cell/small animal irradiation experiments. The dose decrease inside the animal tissue is about 20% per cm.

Translating response during therapy into ultimate treatment outcome: a personalized 4-dimensional MRI tumor volumetric regression approach in cervical cancer.

PURPOSE: To assess individual volumetric tumor regression pattern in cervical cancer during therapy using serial four-dimensional MRI and to define the regression parameters' prognostic value validated with local control and survival correlation. METHODS AND MATERIALS: One hundred and fifteen patients with Stage IB(2)-IVA cervical cancer treated with radiation therapy (RT) underwent serial MRI before (MRI 1) and during RT, at 2-2.5 weeks (MRI 2, at 20-25 Gy), and at 4-5 weeks (MRI 3, at 40-50 Gy). Eighty patients had a fourth MRI 1-2 months post-RT. Mean follow-up was 5.3 years. Tumor volume was measured by MRI-based three-dimensional volumetry, and plotted as dose(time)/volume regression curves. Volume regression parameters were correlated with local control, disease-specific, and overall survival. RESULTS: Residual tumor volume, slope, and area under the regression curve correlated significantly with local control and survival. Residual volumes >or=20% at 40-50 Gy were independently associated with inferior 5-year local control (53% vs. 97%, p <0.001) and disease-specific survival rates (50% vs. 72%, p = 0.009) than smaller volumes. Patients with post-RT residual volumes >or=10% had 0% local control and 17% disease-specific survival, compared with 91% and 72% for <10% volume (p <0.001). CONCLUSION: Using more accurate four-dimensional volumetric regression analysis, tumor response can now be directly translated into individual patients' outcome for clinical application. Our results define two temporal thresholds critically influencing local control and survival. In patients with >or=20% residual volume at 40-50 Gy and >or=10% post-RT, the risk for local failure and death are so high that aggressive intervention may be warranted.

Predicting outcomes in cervical cancer: a kinetic model of tumor regression during radiation therapy.

Applications of mathematical modeling can improve outcome predictions of cancer therapy. Here we present a kinetic model incorporating effects of radiosensitivity, tumor repopulation, and dead-cell resolving on the analysis of tumor volume regression data of 80 cervical cancer patients (stages 1B2-IVA) who underwent radiation therapy. Regression rates and derived model parameters correlated significantly with clinical outcome (P < 0.001; median follow-up: 6.2 years). The 6-year local tumor control rate was 87% versus 54% using radiosensitivity (2-Gy surviving fraction S(2) < 0.70 vs. S(2) > or = 0.70) as a predictor (P = 0.001) and 89% vs. 57% using dead-cell resolving time (T(1/2) < 22 days versus T(1/2) > or = 22 days, P < 0.001). The 6-year disease-specific survival was 73% versus 41% with S(2) < 0.70 versus S(2) > or = 0.70 (P = 0.025), and 87% vs. 52% with T(1/2) < 22 days versus T(1/2) > or = 22 days (P = 0.002). Our approach illustrates the promise of volume-based tumor response modeling to improve early outcome predictions that can be used to enable personalized adaptive therapy.

Longitudinal changes in tumor perfusion pattern during the radiation therapy course and its clinical impact in cervical cancer.

PURPOSE: To study the temporal changes of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) perfusion patterns during the radiation therapy (RT) course and their influence on local control and survival in cervical cancer. METHODS AND MATERIALS: DCE-MRI was performed in 98 patients with Stage IB(2)-IVA cervical cancer before RT (pre-RT) and during early RT (20-25 Gy) and mid-RT (45-50 Gy). Signal intensity (SI) from the DCE-MRI time-SI curve was derived for each tumor voxel. The poorly perfused low-DCE tumor subregions were quantified as lower 10th percentiles of SI (SI10). Local control, disease-specific survival, and overall survival were correlated with DCE parameters at pre-RT, early RT, and mid-RT. Median follow-up was 4.9 (range, 0.2-9.0) years. RESULTS: Patients (16/98) with initial pre-RT high DCE (SI10 >or=2.1) had 100% 5-year local control, 81% disease-specific survival, and 81% overall survival, compared with only 79%, 61%, and 55%, respectively, in patients with pre-RT low DCE. Conversion from pre-RT low DCE to high DCE in early RT (28/82 patients) was associated with higher local control, disease-specific survival, and overall survival (93%, 74%, and 67%, respectively). In comparison with all other groups, outcome was worst in patients with persistently low DCE from pre-RT throughout the mid-RT phase (66%, 44%, and 43%; p = 0.003, 0.003, and 0.020; respectively). CONCLUSION: Longitudinal tumor perfusion changes during RT correlate with treatment outcome. Persistently low perfusion in pre-RT, early RT, and mid-RT indicates a high risk of treatment failure, whereas outcome is favorable in patients with initially high perfusion or subsequent improvements of initially low perfusion. These findings likely reflect reoxygenation and may have potential for noninvasive monitoring of intra-treatment radio-responsiveness and for guiding adaptive therapy.