Impact of a Centralized Database System on Radiation Therapy Quality Assurance Management at a Large Health Care Network: 5 Years' Experience.

PURPOSE: This study reports the impact of using a centralized database system for major equipment quality assurance (QA) at a large institution. METHODS AND MATERIALS: A centralized database system has been implemented for radiation therapy machine QA in our institution at 6 campuses with 11 computed tomographies and 22 linear accelerators (LINACs). The database system was customized to manage monthly and annual computed tomography and LINAC QA. This includes providing the same set of QA procedures across the enterprise, digitally storing all measurement records, and generating trend analyses. Compared with conventional methods (ie, paper forms), the effectiveness of the database system was quantified by changes in the compliance of QA tests and perceptions of staff to the efficiency of data retrieval and analyses. An anonymized questionnaire was provided to physicists enterprise-wide to assess workflow changes. RESULTS: With the implementation of the database system, the compliance of QA test completion improved from 80% to >99% for the entire institution. This resonates with the 56% of physicists who found the database system helpful in guiding them through QA, and 25% of physicists found the contrary, and 19% reported no difference (n = 16). Meanwhile, 40% of physicists reported longer times needed to record data using the database system compared with conventional methods, and another 40% suggested otherwise. In addition, 87% and 80% found the database more efficient to analyze and retrieve previous data, respectively. This was also reflected by the shorter time taken to generate year-end QA statistics using the software (5 vs 30 min per LINAC). Overall, 94% of physicists preferred the centralized database system over conventional methods and endorsed continued use of the system. CONCLUSIONS: A centralized database system is useful and can improve the effectiveness and efficiency of QA management in a large institution. With consistent data collection and proper data storage using a database, high-quality data can be obtained for failure modes and effects analyses as per TG 100.

Risk Management of Clinical Reference Dosimetry of a Large Hospital Network Using Statistical Process Control.

Managing TG-51 reference dosimetry in a large hospital network can be a challenging task. The objectives of this study are to investigate the effectiveness of using Statistical Process Control (SPC) to manage TG-51 workflow in such a network. All the sites in the network performed the annual reference dosimetry in water according to TG-51. These data were used to cross-calibrate the same ion chambers in plastic phantoms for monthly QA output measurements. An energy-specific dimensionless beam quality cross-calibration factor, k q n S W , was derived to monitor the process across multiple sites. The SPC analysis was then performed to obtain the mean, 〈 k q n S W 〉 , standard deviation, σ k , the Upper Control Limit (UCL) and Lower Control Limit (LCL) in each beam. This process was first applied to 15 years of historical data at the main campus to assess the effectiveness of the process. A two-year prospective study including all 30 linear accelerators spread over the main campus and seven satellites in the network followed. The ranges of the control limits (±3σ) were found to be in the range of 1.7% - 2.6% and 3.3% - 4.2% for the main campus and the satellite sites respectively. The wider range in the satellite sites was attributed to variations in the workflow. Standardization of workflow was also found to be effective in narrowing the control limits. The SPC is effective in identifying variations in the workflow and was shown to be an effective tool in managing large network reference dosimetry.

Couch and multileaf collimator tracking: A clinical feasibility study for pancreas and liver treatment.

PURPOSE: Real-time tumor tracking through active correction by the multileaf collimator or treatment couch offers a promising strategy to mitigate delivery uncertainty due to intrafractional tumor motion. This study evaluated the performance of MLC and couch tracking using the prototype iTools Tracking system in TrueBeam Developer Mode and the application for abdominal cancer treatments. METHODS: Experiments were carried out using a phantom with embedded Calypso transponders and a motion simulation platform. Geometric evaluations were performed using a circular conformal field with sinusoidal traces and pancreatic tumor motion traces. Geometric tracking accuracy was retrospectively calculated by comparing the compensational MLC or couch motion extracted from machine log files to the target motion reconstructed from real-time MV and kV images. Dosimetric tracking accuracy was measured with radiochromic films using clinical abdominal VMAT plans and pancreatic tumor traces. RESULTS: Geometrically, the root-mean-square errors for MLC tracking were 0.5 and 1.8 mm parallel and perpendicular to leaf travel direction, respectively. Couch tracking, in contrast, showed an average of 0.8 mm or less geometric error in all directions. Dosimetrically, both MLC and couch tracking reduced motion-induced local dose errors compared to no tracking. Evaluated with five pancreatic tumor motion traces, the average 2%/2 mm global gamma pass rate of eight clinical abdominal VMAT plans was 67.4% (range: 26.4%-92.7%) without tracking, which was improved to 86.0% (range: 67.9%-95.6%) with MLC tracking, and 98.1% (range: 94.9%-100.0%) with couch tracking. In 16 out of 40 deliveries with different plans and motion traces, MLC tracking did not achieve clinically acceptable dosimetric accuracy with 3%/3mm gamma pass rate below 95%. CONCLUSIONS: This study demonstrated the capability of MLC and couch tracking to reduce motion-induced dose errors in abdominal cases using a prototype tracking system. Clinically significant dose errors were observed with MLC tracking for certain plans which could be attributed to the inferior MLC tracking accuracy in the direction perpendicular to leaf travel, as well as the interplay between motion tracking and plan delivery for highly modulated plans. Couch tracking outperformed MLC tracking with consistently high dosimetric accuracy in all plans evaluated, indicating its clinical potential in the treatment of abdominal cancers.

Utilizing historical MLC performance data from trajectory logs and service reports to establish a proactive maintenance model for minimizing treatment disruptions.

PURPOSE: This study proposes a proactive maintenance model utilizing historical Multileaf collimator (MLC) performance data to predict potential MLC dysfunctions, promote preemptive maintenance and thereby reduce treatment disruptions. METHODS: MLC failures were assumed to correlate with MLC performance quantitation from trajectory logs. A cohort of data from service reports and trajectory logs was used to establish a model for predicting MLC dysfunctions. Specifically, the service reports logged by our in-house engineers recorded failure status, including service date, service reason and actions taken, while trajectory logs recorded the ordered/actual leaf positions in 20-ms intervals. Leaf performance from trajectory logs was quantified, where an event was defined as detecting a leaf's position deviation ≥a mm. Three a values, 0.05, 0.1, and 0.5 mm, were used as candidates to determine the appropriate threshold for deviation event quantitation. Logged MLC failures from service reports were retrieved and classified into two categories based on the patterns of their deviation events calculated from trajectory logs: (a) failures with continuous deviations: deviation events lasted several days before failure, and (b) failures with a burst of deviations: deviation events only lasted 1 or 2 days and then MLC failed suddenly. The proposed proactive model focused on the failures with continuous deviations since abnormal trends in their deviation events lasted couple of days, allowing preventive maintenance. The model was predefined with three parameters (x, y, z): if a leaf scored ≥x deviation events per day in any y days within up to a z-day window, the leaf was marked as a "potential failure." The distributions of the deviation events as functions of time (days or weeks) and leaves using the found a-value were then associated with logged failures to find model parameters. In a retrospective demonstration, a total of 28 logged failures with continuous deviations and 66 397 trajectory logs from two TBs' 3-yr records were used to determine the model parameters (x, y, z). The established model was then applied to a third TB for validation. RESULTS: Deviation event threshold, a, was determined to be 0.1 mm, and the resulting model parameters were (x = 20, y = 6, z = 10). When validating the third TB's 3-yr record with 12 logged continuous deviation failures, the model predicted 16 failures: seven were confirmed from the records with a hit rate of 58.3%, while nine were not; further investigation of each unconfirmed failure convinced that some could be actual failures, but somehow not recorded. CONCLUSION: The model offers an addition to preemptive maintenance for reducing treatment disruptions.

Intraoperative implantation of a mesh of directional palladium sources (CivaSheet): Dosimetry verification, clinical commissioning, dose specification, and preliminary experience.

PURPOSE: To present the clinical commissioning of a novel 103Pd directional brachytherapy device (CivaSheet) for intraoperative radiation therapy. METHODS AND MATERIALS: Clinical commissioning for the CivaSheet consisted of establishing: (1) source strength calibration capabilities, (2) experimental verification of TG-43 dosimetry parameters, (3) treatment planning system validation, and (4) departmental practice for dose specification and source ordering. Experimental verification was performed in water with radiochromic film calibrated with a 37 kVp X-ray beam. Percentage difference ([measurements - calculation]/calculation) and distance to agreement (difference between film-to-source distance and distance that minimized the percentage difference) were calculated. Nomogram values (in U/100 Gy) for all configurations (up to 20 × 20 sources) were calculated for source ordering. Clinical commissioning was used on patients enrolled in an ongoing Institutional Review Board-approved protocol. RESULTS: A source calibration procedure was established, and the treatment planning system was commissioned within standard clinical uncertainties. Percentage dose differences (distances to agreement) between measured and calculated doses were 8.6% (-0.12 mm), 0.6% (-0.01 mm), -6.4% (0.22 mm), and -10.0% (0.44 mm) at depths of 2.3, 5.1, 8.0, and 11.1 mm, respectively. All differences were within the experimental uncertainties. Nomogram values depended on sheet size and spatial extent. A value of 2.4U/100 Gy per CivaDot was found to satisfy most cases, ranging from 2.3 to 3.3U/100 Gy. Nomogram results depended on elongation of the treatment area with a higher variation observed for smaller treatment areas. Postimplantation dose evaluation was feasible. CONCLUSIONS: Commissioning and clinical deployment of CivaSheet was feasible using BrachyVision for postoperative dose evaluation. Experimental verification confirmed that the available TG-43 dosimetry parameters are accurate for clinical use.

Dose calculation for hypofractionated volumetric-modulated arc therapy: approximating continuous arc delivery and tongue-and-groove modeling.

Hypofractionated treatments generally increase the complexity of a treatment plan due to the more stringent constraints of normal tissues and target coverage. As a result, treatment plans contain more modulated MLC motions that may require extra efforts for accurate dose calculation. This study explores methods to minimize the differences between in-house dose calculation and actual delivery of hypofractionated volumetric-modulated arc therapy (VMAT), by focusing on arc approximation and tongue-and-groove (TG) modeling. For dose calculation, the continuous delivery arc is typically approximated by a series of static beams with an angular spacing of 2°. This causes significant error when there is large MLC movement from one beam to the next. While increasing the number of beams will minimize the dose error, calculation time will increase significantly. We propose a solution by inserting two additional apertures at each of the beam angle for dose calculation. These additional apertures were interpolated at two-thirds' degree before and after each beam. Effectively, there were a total of three MLC apertures at each beam angle, and the weighted average fluence from the three apertures was used for calculation. Because the number of beams was kept the same, calculation time was only increased by about 6%-8%. For a lung plan, areas of high local dose differences (> 4%) between film measurement and calculation with one aperture were significantly reduced in calculation with three apertures. Ion chamber measurement also showed similar results, where improvements were seen with calculations using additional apertures. Dose calculation accuracy was further improved for TG modeling by developing a sampling method for beam fluence matrix. Single element point sampling for fluence transmitted through MLC was used for our fluence matrix with 1 mm resolution. For Varian HDMLC, grid alignment can cause fluence sampling error. To correct this, transmission volume averaging was applied. For three paraspinal HDMLC cases, the average dose difference was greatly reduced in film and calculation comparisons with our new approach. The gamma (3%, 3 mm) pass rates have improved significantly from 74.1%, 90.0%, and 90.4% to 99.2%, 97.9%, and 97.3% for three cases, for calculation without volume averaging and calculation with volume averaging, respectively. Our results indicate that more accurate MLC leaf position and transmission sampling can improve accuracy and agreement between calculation and measurement, and are particularly important for hypofractionated VMAT that consists of large MLC movement.

32P brachytherapy conformal source model RIC-100 for high-dose-rate treatment of superficial disease: Monte Carlo calculations, diode measurements, and clinical implementation.

PURPOSE: A novel (32)P brachytherapy source has been in use at our institution intraoperatively for temporary radiation therapy of the spinal dura and other localized tumors. We describe the dosimetry and clinical implementation of the source. METHODS AND MATERIALS: Dosimetric evaluation for the source was done with a complete set of MCNP5 Monte Carlo calculations preceding clinical implementation. In addition, the depth dose curve and dose rate were measured by use of an electron field diode to verify the Monte Carlo calculations. Calibration procedures using the diode in a custom-designed phantom to provide an absolute dose calibration and to check dose uniformity across the source area for each source before treatment were established. RESULTS: Good agreement was established between the Monte Carlo calculations and diode measurements. Quality assurance measurements results are provided for about 100 sources used to date. Clinical source calibrations were usually within 10% of manufacturer specifications. Procedures for safe handling of the source are described. DISCUSSION: Clinical considerations for using the source are discussed.

IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119.

AAPM Task Group 119 has produced quantitative confidence limits as baseline expectation values for IMRT commissioning. A set of test cases was developed to assess the overall accuracy of planning and delivery of IMRT treatments. Each test uses contours of targets and avoidance structures drawn within rectangular phantoms. These tests were planned, delivered, measured, and analyzed by nine facilities using a variety of IMRT planning and delivery systems. Each facility had passed the Radiological Physics Center credentialing tests for IMRT. The agreement between the planned and measured doses was determined using ion chamber dosimetry in high and low dose regions, film dosimetry on coronal planes in the phantom with all fields delivered, and planar dosimetry for each field measured perpendicular to the central axis. The planar dose distributions were assessed using gamma criteria of 3%/3 mm. The mean values and standard deviations were used to develop confidence limits for the test results using the concept confidence limit = /mean/ + 1.96sigma. Other facilities can use the test protocol and results as a basis for comparison to this group. Locally derived confidence limits that substantially exceed these baseline values may indicate the need for improved IMRT commissioning.

Commissioning and quality assurance of RapidArc radiotherapy delivery system.

PURPOSE: The Varian RapidArc is a system for intensity-modulated radiotherapy (IMRT) treatment planning and delivery. RapidArc incorporates capabilities such as variable dose-rate, variable gantry speed, and accurate and fast dynamic multileaf collimators (DMLC), to optimize dose conformality, delivery efficiency, accuracy and reliability. We developed RapidArc system commissioning and quality assurance (QA) procedures. METHODS AND MATERIALS: Tests have been designed that evaluate RapidArc performance in a stepwise manner. First, the accuracy of DMLC position during gantry rotation is examined. Second, the ability to vary and control the dose-rate and gantry speed is evaluated. Third, the combined use of variable DMLC speed and dose-rate is studied. RESULTS: Adapting the picket fence test for RapidArc, we compared the patterns obtained with stationary gantry and in RapidArc mode, and showed that the effect of gantry rotation on leaf accuracy was minimal (< or =0.2 mm). We then combine different dose-rates (111-600 MU/min), gantry speeds (5.5-4.3 degrees /s), and gantry range (Deltatheta = 90-12.9 degrees ) to give the same dose to seven parts of a film. When normalized to a corresponding open field (to account for flatness and asymmetry), the dose of the seven portions show good agreement, with a mean deviation of 0.7%. In assessing DMLC speed (0.46, 0.92, 1.84, and 2.76 cm/s) during RapidArc, the analysis of designed radiation pattern indicates good agreement, with a mean deviation of 0.4%. CONCLUSIONS: The results of these tests provide strong evidence that DMLC movement, variable dose-rates and gantry speeds can be precisely controlled during RapidArc.

IMRT delivery performance with a varian multileaf collimator.

The use of a multileaf collimator (MLC) for intensity-modulated radiotherapy poses unique dosimetric issues. The nature of intensity-modulated radiotherapy dosimetry, centered on leaf position accuracy, is common to all MLCs. However, the mechanical and software designs of MLCs from the different manufacturers distinguish them. This report focused on the Varian Millennium 120, although the concepts are applicable to the earlier Varian Mark series as well. The factors that affect dose delivery in clinical fields (i.e., mechanical tolerances, motor fatigue, and latency effects) have been quantified. Moreover, inadequate modeling of the MLC in the planning system can be perceived as erratic performance. Individually, some problems have been shown to be insignificant; others are correctable using software. If these problems are rectified or at least understood by the physicist, quality assurance can be simplified.

TG-69: radiographic film for megavoltage beam dosimetry.

TG-69 is a task group report of the AAPM on the use of radiographic film for dosimetry. Radiographic films have been used for radiation dosimetry since the discovery of x-rays and have become an integral part of dose verification for both routine quality assurance and for complex treatments such as soft wedges (dynamic and virtual), intensity modulated radiation therapy (IMRT), image guided radiation therapy (IGRT), and small field dosimetry like stereotactic radiosurgery. Film is convenient to use, spatially accurate, and provides a permanent record of the integrated two dimensional dose distributions. However, there are several challenges to obtaining high quality dosimetric results with film, namely, the dependence of optical density on photon energy, field size, depth, film batch sensitivity differences, film orientation, processing conditions, and scanner performance. Prior to the clinical implementation of a film dosimetry program, the film, processor, and scanner need to be tested to characterize them with respect to these variables. Also, the physicist must understand the basic characteristics of all components of film dosimetry systems. The primary mission of this task group report is to provide guidelines for film selection, irradiation, processing, scanning, and interpretation to allow the physicist to accurately and precisely measure dose with film. Additionally, we present the basic principles and characteristics of film, processors, and scanners. Procedural recommendations are made for each of the steps required for film dosimetry and guidance is given regarding expected levels of accuracy. Finally, some clinical applications of film dosimetry are discussed.

Pencil beam approach for correcting the energy dependence artifact in film dosimetry for IMRT verification.

The higher sensitivity to low-energy scattered photons of radiographic film compared to water can lead to significant dosimetric error when the beam quality varies significantly within a field. Correcting for this artifact will provide greater accuracy for intensity modulated radiation therapy (IMRT) verification dosimetry. A procedure is developed for correction of the film energy-dependent response by creating a pencil beam kernel within our treatment planning system to model the film response specifically. Film kernels are obtained from EGSnrc Monte Carlo simulations of the dose distribution from a 1 mm diameter narrow beam in a model of the film placed at six depths from 1.5 to 40 cm in polystyrene and solid water phantoms. Kernels for different area phantoms (50 x 50 cm2 and 25 x 25 cm2 polystyrene and 30 x 30 cm2 solid water) are produced. The Monte Carlo calculated kernel is experimentally verified with film, ion chamber and thermoluminescent dosimetry (TLD) measurements in polystyrene irradiated by a narrow beam. The kernel is then used in convolution calculations to, predict the film response in open and IMRT fields. A 6 MV photon beam and Kodak XV2 film in a polystyrene phantom are selected to test the method as they are often used in practice and can result in large energy-dependent artifacts. The difference in dose distributions calculated with the film kernel and the water kernel is subtracted from film measurements to obtain a practically film artifact free IMRT dose distribution for the Kodak XV2 film. For the points with dose exceeding 5 cGy (11% of the peak dose) in a large modulated field and a film measurement inside a large polystyrene phantom at depth of 10 cm, the correction reduces the fraction of pixels for which the film dose deviates from dose to water by more than 5% of the mean film dose from 44% to 6%.

Do metallic ports in tissue expanders affect postmastectomy radiation delivery?

PURPOSE: Postmastectomy radiation therapy (PMRT) is often delivered to patients with permanent breast implants. On occasion, patients are irradiated with a tissue expander (TE) in place before their permanent implant exchange. Because of concern of potential under-dosing in these patients, we examined the dosimetric effects of the Magna-Site (Santa Barbara, CA) metallic port that is present in certain TEs. METHODS AND MATERIALS: We performed ex vivo film dosimetry with single 6-MV and 15-MV photon beams on a water phantom containing a Magna-Site disc in two orientations. Additionally, using in vivo films, we measured the exit dose from 1 patient's TE-reconstructed breast during chest wall treatment with 15-MV tangent beams. Finally, we placed thermoluminescent dosimeters (TLDs) on 6 patients with TEs who received PMRT delivered with 15-MV tangent beams. RESULTS: Phantom film dosimetry revealed decreased transmission in the region of the Magna-Site, particularly with the magnet in the parallel orientation (at 22 mm: 78% transmission with 6 MV, 84% transmission with 15 MV). The transmission measured by in vivo films during single beam treatment concurred with ex vivo results. TLD data showed acceptable variation in median dose to the skin (86-101% prescription dose). CONCLUSION: Because of potential dosimetric effects of the Magna-Site, it is preferable to treat PMRT patients with permanent implants. However, it is not unreasonable to treat with a TE because the volume of tissue affected by attenuation from the Magna-Site is small. In this scenario, we recommend using 15 MV photons with compensating bolus.

Influence of phantom material and phantom size on radiographic film response in therapy photon beams.

The energy dependence of radiographic film can introduce dosimetric errors when evaluating photon beams. The variation of the film response, which is attributed to the changing photon spectrum with depth and field size, has been the subject of numerous publications in recent years. However, these data show large unexplained differences in the magnitude of this variation among independent studies. To try to resolve this inconsistency, this study assesses the dependence of radiographic film response on phantom material and phantom size using film measurements and Monte Carlo calculations. The relative dose measured with film exposed to 6 MV x rays in various phantoms (polystyrene, acrylic, Solid Water, and water; the lateral phantom dimensions vary from 25 to 50 cm square; backscatter thickness varies from 10 to 30 cm) is compared with ion chamber measurements in water. Ranges of field size (5 x 5 to 40 x 40 cm2) and depth (dmax to 20 cm) are studied. For similar phantom and beam configurations, Monte Carlo techniques generate photon fluence spectra from which the relative film response is known from an earlier study. Results from film response measurements agree with those derived from Monte Carlo calculations within 3%. For small fields (< or = 10 x 10 cm2) and shallow depths (< or = 10 cm) the film response variation is small, less than 4%, for all phantoms. However, for larger field sizes and depths, the phantom material and phantom size have a greater influence on the magnitude of the film response. The variation of film response, over the ranges of field sizes and depths studied, is 50% in polystyrene compared with 30% in water. Film responses in Solid Water and water phantoms are similar; acrylic is between water and polystyrene. In polystyrene the variation of film response for a 50 cm square phantom is nearly twice that observed in a 25 cm square phantom. This study shows that differences in the configuration of the phantoms used for film dosimetry can explain much of the inconsistency for film response reported in the literature.

Predicting energy response of radiographic film in a 6 MV x-ray beam using Monte Carlo calculated fluence spectra and absorbed dose.

The advantage of radiographic film is that it allows two-dimensional, high-resolution dose measurement. While there is concern over its photon energy dependence, these problems are considered acceptable within small fields, where the scatter component is small. The application of film dosimetry to intensity modulated radiotherapy (IMRT) raises additional concern since the primary fluence may vary significantly within the field. The varying primary fluence in combination with a large scatter fraction, present for large fields and large depths, causes the spectrum at various points within the IMRT field to differ from the spectrum in the uniform fields typically used for calibrating the film. As a result, significant artifacts are introduced in the measured dose distribution. The purpose of this work is to quantify and develop a method to correct for these artifacts. Two approaches based on Monte Carlo (MC) simulations are examined. In the first method, the film artifact, as quantified by film and ion chamber output measurements in uniform square fields, is derived from the MC calculated ratio of absorbed doses to film and to water. In the second method, the measured film artifact is correlated with MC calculated photon spectra, revealing a strong correlation between the measured artifact and the "scatter"-to-"primary" ratio, defined by the ratio of the number of photons below to the number of photons above 0.1 MeV, independent of field size and depth. These methods are evaluated in high- and low-dose regions of a large intensity-modulated field created with a central block. The spectral approach is also tested with a clinical IMRT field. The absorbed dose method accurately corrects the measured film dose in the open part of the field and in points under the block and outside the field. The dose error is reduced from as much as 16% of the open field dose to less than 1%, as verified with an ion chamber. The spectral method accurately corrects the measured film dose in the open region of the centrally blocked field, but does not fully correct for the film artifact for points under the block and outside the field, where the spectrum is substantially different. Applied to the clinical field, the corrected film measurement shows good agreement with data obtained with a two-dimensional diode array.

Intensity-modulated radiotherapy.

Intensity-modulated radiotherapy represents a recent advancement in conformal radiotherapy. It employs specialized computer-driven technology to generate dose distributions that conform to tumor targets with extremely high precision. Treatment planning is based on inverse planning algorithms and iterative computer-driven optimization to generate treatment fields with varying intensities across the beam section. Combinations of intensity-modulated fields produce custom-tailored conformal dose distributions around the tumor, with steep dose gradients at the transition to adjacent normal tissues. Thus far, data have demonstrated improved precision of tumor targeting in carcinomas of the prostate, head and neck, thyroid, breast, and lung, as well as in gynecologic, brain, and paraspinal tumors and soft tissue sarcomas. In prostate cancer, intensity-modulated radiotherapy has resulted in reduced rectal toxicity and has permitted tumor dose escalation to previously unattainable levels. This experience indicates that intensity-modulated radiotherapy represents a significant advancement in the ability to deliver the high radiation doses that appear to be required to improve the local cure of several types of tumors. The integration of new methods of biologically based imaging into treatment planning is being explored to identify tumor foci with phenotypic expressions of radiation resistance, which would likely require high-dose treatments. Intensity-modulated radiotherapy provides an approach for differential dose painting to selectively increase the dose to specific tumor-bearing regions. The implementation of biologic evaluation of tumor sensitivity, in addition to methods that improve target delineation and dose delivery, represents a new dimension in intensity-modulated radiotherapy research.