By collecting photons scattered out of the therapy beam, scatter imaging creates images of the treated volume. Two phantoms were used to assess the possible application of scatter imaging for markerless tracking of lung tumors during stereotactic body radiation therapy (SBRT) treatment. A scatter-imaging camera was assembled with a CsI flat-panel detector and a 5 mm diameter pinhole collimator. Scatter images were collected during the irradiation of phantoms with megavoltage photons. To assess scatter image quality, spherical phantom lung tumors of 2.1-2.8 cm diameters were placed inside a static, anthropomorphic phantom. To show the efficacy of the technique with a moving target (3 cm diameter), the position of a simulated tumor was tracked in scatter images during sinusoidal motion (15 mm amplitude, 0.25 Hz frequency) in a dynamic lung phantom in open-field, dynamic conformal arc (DCA), and volumetric modulated arc therapy (VMAT) deliveries. Anatomical features are identifiable on static phantom scatter images collected with 10 MU of delivered dose (2.1 cm diameter lung tumor contrast-to-noise ratio of 4.4). The contrast-to-noise ratio increases with tumor size and delivered dose. During dynamic motion, the position of the 3.0 cm diameter lung tumor was identified with a root-mean-square error of 0.8, 1.2, and 2.9 mm for open field (0.3 s frame integration), DCA (0.5 s), and VMAT (0.5 s), respectively. Based on phantom studies, scatter imaging is a potential technique for markerless lung tumor tracking during SBRT without additional imaging dose. Quality scatter images may be collected at low, clinically relevant doses (10 MU). Scatter images are capable of sub-millimeter tracking precision, but modulation decreases accuracy.

PURPOSE:The purpose of this study was to provide guidance on quality management for electronic brachytherapy. MATERIALS AND METHODS:The task group used the risk-assessment approach of Task Group 100 of the American Association of Physicists in Medicine. Because the quality management program for a device is intimately tied to the procedure in which it is used, the task group first designed quality interventions for intracavitary brachytherapy for both commercial electronic brachytherapy units in the setting of accelerated partial-breast irradiation. To demonstrate the methodology to extend an existing risk analysis for a different application, the task group modified the analysis for the case of post-hysterectomy, vaginal cuff irradiation for one of the devices. RESULTS:The analysis illustrated how the TG-100 methodology can lead to interventions to reduce risks and improve quality for each unit and procedure addressed. CONCLUSION:This report provides a model to guide facilities establishing a quality management program for electronic brachytherapy.

Acoustic-based proton range verification (protoacoustics) is a potential in vivo technique for determining the Bragg peak position. Previous measurements and simulations have been restricted to homogeneous water tanks. Here, a CT-based simulation method is proposed and applied to a liver and prostate case to model the effects of tissue heterogeneity on the protoacoustic amplitude and time-of-flight range verification accuracy. For the liver case, posterior irradiation with a single proton pencil beam was simulated for detectors placed on the skin. In the prostate case, a transrectal probe measured the protoacoustic pressure generated by irradiation with five separate anterior proton beams. After calculating the proton beam dose deposition, each CT voxel's material properties were mapped based on Hounsfield Unit values, and thermoacoustically-generated acoustic wave propagation was simulated with the k-Wave MATLAB toolbox. By comparing the simulation results for the original liver CT to homogenized variants, the effects of heterogeneity were assessed. For the liver case, 1.4 cGy of dose at the Bragg peak generated 50 mPa of pressure (13 cm distal), a 2×  lower amplitude than simulated in a homogeneous water tank. Protoacoustic triangulation of the Bragg peak based on multiple detector measurements resulted in 0.4 mm accuracy for a δ-function proton pulse irradiation of the liver. For the prostate case, higher amplitudes are simulated (92-1004 mPa) for closer detectors (<8 cm). For four of the prostate beams, the protoacoustic range triangulation was accurate to  ⩽1.6 mm (δ-function proton pulse). Based on the results, application of protoacoustic range verification to heterogeneous tissue will result in decreased signal amplitudes relative to homogeneous water tank measurements, but accurate range verification is still expected to be possible.

By collimating the photons scattered when a megavoltage therapy beam interacts with the patient, a Compton-scatter image may be formed without the delivery of an extra dose. To characterize and assess the potential of the technique, an analytical model for simulating scatter images was developed and validated against Monte Carlo (MC). For three phantoms, the scatter images collected during irradiation with a 6 MV flattening-filter-free therapy beam were simulated. Images, profiles, and spectra were compared for different phantoms and different irradiation angles. The proposed analytical method simulates accurate scatter images up to 1000 times faster than MC. Minor differences between MC and analytical simulated images are attributed to limitations in the isotropic superposition/convolution algorithm used to analytically model multiple-order scattering. For a detector placed at 90° relative to the treatment beam, the simulated scattered photon energy spectrum peaks at 140-220 keV, and 40-50% of the photons are the result of multiple scattering. The high energy photons originate at the beam entrance. Increasing the angle between source and detector increases the average energy of the collected photons and decreases the relative contribution of multiple scattered photons. Multiple scattered photons cause blurring in the image. For an ideal 5 mm diameter pinhole collimator placed 18.5 cm from the isocenter, 10 cGy of deposited dose (2 Hz imaging rate for 1200 MU min-1 treatment delivery) is expected to generate an average 1000 photons per mm2 at the detector. For the considered lung tumor CT phantom, the contrast is high enough to clearly identify the lung tumor in the scatter image. Increasing the treatment beam size perpendicular to the detector plane decreases the contrast, although the scatter subject contrast is expected to be greater than the megavoltage transmission image contrast. With the analytical method, real-time tumor tracking may be possible through comparison of simulated and acquired patient images.

Functional imaging such as magnetic resonance spectroscopy (MRS) and positron emission tomography (PET) can identify the biology and characteristics of tumor cells. This facilitates design of personalized treatment plans that deliver escalated dose to these tumor pockets. Biological information of a patient including the location of the tumor pockets, their shape and vicinity to critical organs, may play an important role in the resulting tumor control probability (TCP) of an optimized treatment plan. In this study, we apply machine learning to uncover the relationship between a patient's biological information and TCP value of an optimized treatment plan.

PURPOSE:Lung stereotactic body radiation therapy (SBRT) requires delivering large radiation doses with millimeter accuracy, making image guidance essential. An approach to forming images of patient anatomy from Compton-scattered photons during lung SBRT is presented. METHODS:To investigate the potential of scatter imaging, a pinhole collimator and flat-panel detector are used for spatial localization and detection of photons scattered during external beam therapy using lung SBRT treatment conditions (6 MV FFF beam). MCNP Monte Carlo software is used to develop a model to simulate scatter images. This model is validated by comparing experimental and simulated phantom images. Patient scatter images are then simulated from 4DCT data. RESULTS:Experimental lung tumor phantom images have sufficient contrast-to-noise to visualize the tumor with as few as 10 MU (0.5 s temporal resolution). The relative signal intensity from objects of different composition as well as lung tumor contrast for simulated phantom images agree quantitatively with experimental images, thus validating the Monte Carlo model. Scatter images are shown to display high contrast between different materials (lung, water, bone). Simulated patient images show superior (~double) tumor contrast compared to MV transmission images. CONCLUSIONS:Compton scatter imaging is a promising modality for directly imaging patient anatomy during treatment without additional radiation, and it has the potential to complement existing technologies and aid tumor tracking and lung SBRT image guidance.

PURPOSE: The Xoft Axxent Electronic Brachytherapy System (Xoft, Inc., San Jose, CA) is a viable option for intraoperative radiation therapy (TORT) treatment of early-stage breast cancer. The low-energy (50-kVp) X-ray source simplifies shielding and increases relative biological effectiveness but increases dose distribution sensitivity to medium composition. Treatment planning systems typically assume homogenous water for brachytherapy dose calculations, including precalculated atlas plans for Xoft IORT. However, Xoft recommends saline for balloon applicator filling. This study investigates dosimetric differences due to increased effective atomic number (Z(eff)) for saline (Z(eff) = 7.56) versus water (Z(eff) = 7.42). METHODS: Balloon applicator diameters range from 3 to 6 cm. Monte Carlo N-Particle software is used to calculate dose at the surface (D-s) of and 1 cm away (D-1cm) from the water-/saline-filled balloon applicator using a single dwell at the applicator center as a simple estimation of the dosimetry and multiple dwells simulating the clinical dose distributions for the atlas plans. RESULTS: Single-dwell plans show a 4.4-6.1% decrease in D-s for the 3- to 6-cm diameter applicators due to the saline. Multidwell plans show similar results: 4.9% and 6.4% D-s decrease, for 4-cm and 6-cm diameter applicators, respectively. For the single-dwell plans, D-1cm decreases 3.6-5.2% for the 3- to 6-cm diameter applicators. For the multidwell plans, D-1cm decreases 3.3% and 5.3% for the 4-cm and 6-cm applicators, respectively. CONCLUSIONS: The dosimetric effect introduced by saline versus water filling for Xoft balloon applicator based IORT treatments is similar to 5%. Users should be aware of this in the context of both treatment planning and patient outcome studies. (C) 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

PURPOSE:To identify policy and system related weaknesses in treatment planning and plan check work-flows.METHODS:The authors' web deployed plan check automation solution, PlanCheck, which works with all major planning and record and verify systems (demonstrated here for mosaiq only), allows them to compute violation rates for a large number of plan checks across many facilities without requiring the manual data entry involved with incident filings. Workflows and failure modes are heavily influenced by the type of record and verify system used. Rather than tackle multiple record and verify systems at once, the authors restricted the present survey to mosaiq facilities. Violations were investigated by sending inquiries to physicists running the program.RESULTS:Frequent violations included inadequate tracking in the record and verify system of total and prescription doses. Infrequent violations included incorrect setting of patient orientation in the record and verify system. Peaks in the distribution, over facilities, of violation frequencies pointed to suboptimal policies at some of these facilities. Correspondence with physicists often revealed incomplete knowledge of settings at their facility necessary to perform thorough plan checks.CONCLUSIONS:The survey leads to the identification of specific and important policy and system deficiencies that include: suboptimal timing of initial plan checks, lack of communication or agreement on conventions surrounding prescription definitions, and lack of automation in the transfer of some parameters.

Small bowel (SB) is an organ at risk (OAR) that may potentially develop toxicity after radiotherapy for cervix cancer. However, its dose from brachytherapy (BT) is not systematically reported as in other OARs, even with image-guided brachytherapy (IGBT). This study aims to introduce consideration of quantified objectives for SB in BT plan optimization and to evaluate the feasibility of sparing SB while maintaining adequate target coverage. In all, 13 patients were included in this retrospective study. All patients were treated with external beam radiotherapy (EBRT) 45Gy in 25 fractions followed by high dose rate (HDR)-BT boost of 28Gy in 4 fractions using tandem/ring applicator. Magnetic resonance imaging (MRI) and computed tomographic (CT) images were obtained to define the gross tumor volume (GTV), high-risk clinical target volume (HR-CTV) and OARs (rectum, bladder, sigmoid colon, and SB). Treatment plans were generated for each patient using GEC-ESTRO recommendations based on the first CT/MRI. Treatment plans were revised to reduce SB dose when the [Formula: see text] dose to SB was > 5Gy, while maintaining other OAR constraints. For the 7 patients with 2 sets of CT and MRI studies, the interfraction variation of the most exposed SB was analyzed. Plan revisions were done in 6 of 13 cases owing to high [Formula: see text] of SB. An average reduction of 19% in [Formula: see text] was achieved. Meeting SB and other OAR constraints resulted in less than optimal target coverage in 2 patients (D90 of HR-CTV < 77Gyαβ10). The highest interfraction variation was observed for SB at 16 ± 59%, as opposed to 28 ± 27% for rectum and 21 ± 16% for bladder. Prospective reporting of SB dose could provide data required to establish a potential correlation with radiation-induced late complication for SB.

Three-dimensional measurement arrays are an efficient means of acquiring a distribution of data for patient plan delivery QA. However, the tie between plan integrity and traditional gamma-based analysis of these data are not clear. This study explores the sensitivity of such analysis by creating errors in Helical Tomotherapy delivery and measuring the passing rates with an ArcCHECK cylindrical diode array. Errors were introduced in each of the couch speed, leaf open time, and gantry starting position in increasing magnitude while the resulting gamma passing rates were tabulated. The error size required to degrade the gamma passing rate to 90% or below was on average a 3% change in couch speed, 5° in gantry synchronization, or a 5 ms in leaf closing speed for a 3%/3 mm Van Dyk gamma analysis. This varied with plan type, with prostate plans exhibiting less sensitivity than head and neck plans and with gamma analysis criteria, but in all cases the error magnitudes were large compared to actual machine tolerances. These findings suggest that the sensitivity of ArcCHECK-based gamma analysis to single-mode errors in tomotherapy plans is dependent upon plan and analysis type and at traditional passing thresholds unable to detect small defects in the plan.

PURPOSE: To validate an in-house optimization program that uses adaptive simulated annealing (ASA) and gradient descent (GD) algorithms and investigate features of physical dose and generalized equivalent uniform dose (gEUD)-based objective functions in high-dose-rate (HDR) brachytherapy for cervical cancer.METHODS: Eight Syed/Neblett template-based cervical cancer HDR interstitial brachytherapy cases were used for this study. Brachytherapy treatment plans were first generated using inverse planning simulated annealing (IPSA). Using the same dwell positions designated in IPSA, plans were then optimized with both physical dose and gEUD-based objective functions, using both ASA and GD algorithms. Comparisons were made between plans both qualitatively and based on dose-volume parameters, evaluating each optimization method and objective function. A hybrid objective function was also designed and implemented in the in-house program.RESULTS: The ASA plans are higher on bladder V-75% and D-2cc (p = 0.034) and lower on rectum V75% and D-2cc (p = 0.034) than the IPSA plans. The ASA and GD plans are not significantly different. The gEUD-based plans have higher homogeneity index (p = 0.034), lower overdose index (p = 0.005), and lower rectum gEUD and normal tissue complication probability (p = 0.005) than the physical dose-based plans. The hybrid function can produce a plan with dosimetric parameters between the physical dose-based and gEUD-based plans. The optimized plans with the same objective value and dose-volume histogram could have different dose distributions.CONCLUSIONS: Our optimization program based on ASA and GD algorithms is flexible on objective functions, optimization parameters, and can generate optimized plans comparable with IPSA. (C) 2014 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

Cervical cancer has a high mortality rate (approximately 35 percent) in the United States and is difficult to treat successfully. One promising treatment is high-dose-rate brachytherapy, which entails delivering high-dose radiation to the tumor via the temporary implantation of radioactive seeds. This treatment promises to be particularly effective in eradicating tumors while preserving the organs. Yet, major obstacles to successful treatment remain, especially (1) determining the best seed type, spatial configuration of seeds, and seed dwelling time, and (2) improving the probability that the treatment will eliminate all malignant cells. We developed an advanced planning model to simultaneously address both of these issues. To permit taking advantage of the best available information, our model works with inputs from positron emission tomography. We begin with a multiobjective, nonlinear, mixed-integer programming model that is initially intractable. To solve the model, we introduce an original branch-and-cut and local-search approach that couples new polyhedral cuts with matrix reduction and intelligent geometric heuristics. The result has been accurate solutions that are obtained rapidly. Clinical trials at Rush University Medical Center demonstrated superior medical outcomes. These analytical techniques are applicable not only to cervical cancer, but also to other types of cancer, including breast, lung, and prostate cancer.

The purpose was to study the dosimetric characteristics of the small diameter (≤ 10.0 mm) BrainLAB cones used for stereotactic radiosurgery (SRS) treatments in conjunction with a Varian Trilogy accelerator. Required accuracy and precision in dose delivery during SRS can be achieved only when the geometric and dosimetric characteristics of the small radiation fields is completely understood. Although a number of investigators have published the dosimetric characteristics of SRS cones, to our knowledge, there is no generally accepted value for the relative output factor (ROF) for the 5.0 mm diameter cone. Therefore, we have investigated the dosimetric properties of the small (≤ 10.0 mm) diameter BrainLAB SRS cones used in conjunction with the iPlan TPS and a Trilogy linear accelerator with a SRS beam mode. Percentage depth dose (PDD), off-axis ratios (OAR), and ROF were measured using a SRS diode and verified with Monte Carlo (MC) simulations. The dependence of ROF on detector material response was studied. The dependence of PDD, OAR, and ROF on the alignment of the beam CAX with the detector motion line was also investigated using MC simulations. An agreement of 1% and 1 mm was observed between measurements and MC for PDD and OAR. The calculated ROF for the 5.0 mm diameter cone was 0.692 ± 0.008--in good agreement with the measured value of 0.683 ± 0.007 after the diode response was corrected. Simulations of the misalignment between the beam axis and detector motion axis for angles between 0.5°-1.0° have shown a deviation > 2% in PDD beyond a certain depth. We have also provided a full set of dosimetric data for BrainLAB SRS cones. Monte Carlo calculated ROF values for cones with diameters less than 10.0 mm agrees with measured values to within 1.8%. Care should be exercised when measuring PDD and OAR for small cones. We recommend the use of MC to confirm the measurement under these conditions.

Skin toxicity is a ubiquitous side effect in radiotherapy and can be difficult to predict. Moist desquamation in cancer patients can decrease quality of life and occasionally demand unplanned treatment breaks thus worsening outcome. In breast cancer patients, moist desquamation occurs approximately one-third of the time, and while avenues such as intensity-modulated radiation therapy exist to decrease skin side effects, they may be prohibitively expensive to distribute widely. To selectively target patients who are at risk for high skin toxicity, toxicity prediction beyond heuristics is required. This study presents 3D thermal tomography, a translation technology that employs active thermal imaging to map the thermal effusivity of skin. Irradiated mice were imaged throughout reaction development to establish a correlation between effusivity changes and eventual toxicity severity. Female hairless mice (n = 11) were anesthetized and irradiated to 40 Gy in one fraction using a 1 cm Leipzig brachytherapy applicator with an Ir-192 source. After irradiation, thermal imaging was conducted daily with a flash lamp and infrared camera. Effusivity was calculated using custom software and tracked within irradiated and contralateral control regions. Mice were retrospectively grouped into high-grade (moist desquamation present, n = 6) and low-grade (n = 5). All mice showed an increase in the relative average effusivity difference among the treated and control regions between irradiation and peak reaction between 12 and 15 days after irradiation. The high-grade group showed an earlier increase in relative average effusivity difference (mean 1.7 days after irradiation versus 4.4 days after irradiation) than the low-grade group, and had a significantly greater relative average effusivity difference between 2–5 days after irradiation. We concluded that 3D thermal tomography is quick, non-invasive, non-ionizing and exhibited a correlative difference between mice that eventually developed moist desquamation and those that only presented dry desquamation. With further development, it may prove to be a useful tool in the clinic for differentiating patients who require preventative measures to reduce skin toxicity.

An effective screening technology is needed to triage individuals at the time of radiation incidents involving a large population. Three-dimensional thermal tomography is a relatively new development in active thermal imaging technology that produces cross-sectional images based on the subject's ability to transfer heat-thermal effusivity-at the voxel level. This noninvasive imaging modality has been used successfully in nondestructive examination of complex materials; also it has been shown to predict the severity of radiation-induced skin injuries several days before the manifestation of severe moist desquamations or blister formation symptoms in mice at 40 Gy. If these results are confirmed at lower dose levels in human subjects, a thermal tomography imaging device may be an ideal screening tool in radiation emergencies. This imaging method is non-invasive, relatively simple, easily adaptable for field use, and when properly deployed, it will enhance public emergency preparedness for incidents involving unexpected radiation exposure.

Purpose:Total body irradiation (TBI) with megavoltage photon beams has been accepted as an important component of management for a number of hematologic malignancies, generally as part of bone marrow conditioning regimens. The purpose of this paper is to present and discuss the authors' TBI technique, which both simplifies the treatment process and improves the treatment quality.Methods:An AP/PA TBI treatment technique to produce uniform dose distributions using sequential collimator reductions during each fraction was implemented, and a sample calculation worksheet is presented. Using this methodology, the dosimetric characteristics of both 6 and 18 MV photon beams, including lung dose under cerrobend blocks was investigated. A method of estimating midplane lung doses based on measured entrance and exit doses was proposed, and the estimated results were compared with measurements.Results:Whole body midplane dose uniformity of ±10% was achieved with no more than two collimator‐based beam modulations. The proposed model predicted midplane lung doses 5% to 10% higher than the measured doses for 6 and 18 MV beams. The estimated total midplane doses were within ±5% of the prescribed midplane dose on average except for the lungs where the doses were 6% to 10% lower than the prescribed dose on average.Conclusions:The proposed TBI technique can achieve dose uniformity within ±10%. This technique is easy to implement and does not require complicated dosimetry and/or compensators.

Identification of source positions after implantation is an important step in brachytherapy planning. Reconstruction is traditionally performed from films taken by conventional simulators, but these are gradually being replaced in the clinic by computed tomography (CT) simulators. The present study explored the use of a scout image–based reconstruction algorithm that replaces the use of traditional film, while exhibiting low sensitivity to metal-induced artifacts that can appear in 3D CT methods. In addition, the accuracy of an in-house graphical software implementation of scout-based reconstruction was compared with seed location reconstructions for 2 phantoms by conventional simulator and CT measurements. One phantom was constructed using a planar fixed grid of 1.5-mm diameter ball bearings (BBs) with 40-mm spacing. The second was a Fletcher-Suit applicator embedded in Styrofoam (Dow Chemical Co., Midland, MI) with one 3.2-mm-diameter BB inserted into each of 6 surrounding holes. Conventional simulator, kilovoltage CT (kVCT), megavoltage CT, and scout-based methods were evaluated by their ability to calculate the distance between seeds (40 mm for the fixed grid, 30–120 mm in Fletcher-Suit). All methods were able to reconstruct the fixed grid distances with an average deviation of <1%. The worst single deviations (approximately 6%) were exhibited in the 2 volumetric CT methods. In the Fletcher-Suit phantom, the intermodality agreement was within approximately 3%, with the conventional sim measuring marginally larger distances, with kVCT the smallest. All of the established reconstruction methods exhibited similar abilities to detect the distances between BBs. The 3D CT-based methods, with lower axial resolution, showed more variation, particularly with the smaller BBs. With a software implementation, scout-based reconstruction is an appealing approach because it simplifies data acquisition over film-based reconstruction without requiring any specialized equipment and does not carry risk of misreads caused by artifacts.

Purpose: PET studies can provide information related to tumor metabolic activities. This information may facilitate targeted dose delivery to improve local tumor control. In this study, we perform feasibility tests on PET-image guided dose escalation in high-dose-rate brachytherapy (HDR). Robustness of the planning is tested, and plan quality and potential outcome significance are evaluated. Materials and Methods: CT and 18F-fluorodeoxyglucose based-PET images are obtained for patients with cervical cancer. Planning target volumes (PTV) and critical structures are delineated from CT images. Enhanced PET signal defines boost target volume (BTV). In addition, we have outlined additional hypothetical BTVs of various sizes to test the optimization algorithm. HDR plans are optimized to deliver 35 Gy to PTV and 37-40 Gy to BTV following 45 Gy external beam radiotherapy. Each dwell location is modeled via two variables: a binary decision variable to indicate whether a radioactive seed will be deposited and a continuous variable to denote the associated dwell time. The treatment planning model ensures a coverage of 95% to the PTV. In the escalated case, the PET-identified region is delivered escalated dose over the prescribed dose. The objective function seeks rapid overall dose fall-off from the prescribed dose. Specifically, to gauge the feasibility, characteristics, and potential benefit of PET-image guided dose escalation, we compare 3 alternative plans for the above patient cases: 1) standard HDR plan with no escalation, 2) escalation with same PTV prescription dose, and 3) escalation with reduced PTV prescription dose. Results: For dose escalation, an escalated dose of >= 37 Gy is placed on PET-identified tumor pockets. When the BTV is less than 15% of the PTV, the dose escalation can be delivered with virtually identical dose profiles to PTV, bladder and rectum as in the standard plan. When the BTV occupies 30% of the PTV, dose escalation to PET intrinsically increases dose to the other structures by about 5%. In both cases, over 99% of the PET-region receives over 40 Gy. When PTV is prescribed 33 Gy (reduced dose), independent of the size of the BTV, escalation can be achieved while dose to PTV, bladder and rectum are simultaneously reduced. Conclusions: With advances in biological and functional imaging, there is an urgent need to incorporate radiobiological parameters within the planning process. The presented treatment planning algorithm allows for PET-enhanced treatment, which facilitates targeted delivery of escalated dose and the potential to improve overall clinical outcome. Expected improvements in tumor control, and organs-at-risk dose reduction can be significant. Clinical studies are in progress to test its feasibility, to validate its importance, and to measure potential gain in clinical outcome.

PET studies can provide information related to tumor metabolic activities. This information may facilitate targeted dose delivery to improve local tumor control. In this study, we perform feasibility tests on PET-image guided dose escalation in high-dose rate brachytherapy (HDR). Robustness of the planning is tested, and plan quality and potential outcome significance are evaluated. CT and 18F-fluorodeoxyglucose based-PET images are obtained for patients with cervical cancer. Planning target volumes (PTV) and critical structures are delineated from CT images. Enhanced PET signal defines boost target volume (BTV). In addition, we have outlined additional hypothetical BTVs of various sizes to test the optimization algorithm. HDR plans are optimized to deliver 35 Gy to PTV and 37-40 Gy to BTV following 45 Gy external beam radiotherapy. Each dwell location is modeled via two variables: a binary decision variable to indicate whether a radioactive seed will be deposited and a continuous variable to denote the associated dwell time. The treatment planning model ensures a coverage of 95% to the PTV. In the escalated case, the PET-identified region is delivered escalated dose over the prescribed dose. The objective function seeks rapid overall dose fall-off from the prescribed dose. Specifically, to gauge the feasibility, characteristics, and potential benefit of PET-image guided dose escalation, we compare 3 alternative plans for the above patient cases: 1) standard HDR plan with no escalation, 2) escalation with same PTV prescription dose, and 3) escalation with reduced PTV prescription dose. For dose escalation, an escalated dose of >= 37 Gy is placed on PET-identified tumor pockets. When the BTV is less than 15% of the PTV, the dose escalation can be delivered with virtually identical dose profiles to PTV, bladder and rectum as in the standard plan. When the BTV occupies 30% of the PTV, dose escalation to PET intrinsically increases dose to the other structures by about 5%. In both cases, over 99% of the PET-region receives over 40Gy. When PTV is prescribed 33Gy (reduced dose), independent of the size of the BTV, escalation can be achieved while dose to PTV, bladder and rectum are simultaneously reduced. With advances in biological and functional imaging, there is an urgent need to incorporate radiobiological parameters within the planning process. The presented treatment planning algorithm allows for PET-enhanced treatment, which facilitates targeted delivery of escalated dose and the potential to improve overall clinical outcome. Expected improvements in tumor control, and organs-at-risk dose reduction can be significant. Clinical studies are in progress to test its feasibility, to validate its importance, and to measure potential gain in clinical outcome.