Intensity-modulated Radiation Therapy Delivery Research Articles

Intra-fraction motion prediction in MRI-guided radiation therapy using Markov processes

Internal organ motion during radiation delivery may lead to underdosing of cancer cells or overdosing of normal tissue, potentially causing treatment failure or normal-tissue toxicity. Organ motion is of particular concern in the treatment of lung and abdominal cancers, where breathing induces large tumor displacement and organ deformation. A new generation of radiotherapy devices is equipped with on-board MRI scanners to acquire a real-time movie of the patient’s anatomy during radiation delivery. The goal of this research is to develop, calibrate, and test motion predictive models that employ real-time MRI images to provide the short-term trajectory of respiration-induced anatomical motion during radiation delivery. A semi-Markov model predicts transitions between the phases of a respiratory cycle, and a Markov model predicts transitions to future respiratory cycles, leading to accurate motion forecasting over longer-term horizons. The intended application for this work is real-time tracking and re-optimization of intensity-modulated radiation delivery.

Early prediction of acute xerostomia during radiation therapy for nasopharyngeal cancer based on delta radiomics from CT images.

Acute xerostomia is the most common side effect of radiation therapy (RT) for head and neck (H&N) malignancies. Investigating radiation-induced changes of computed tomography (CT) radiomics in parotid glands (PGs) and saliva amount (SA) can predict acute xerostomia during the RT for nasopharyngeal cancer (NPC). CT and SA data from 35 patients with stages I-IVB were randomly collected from an NPC clinical trial registered on the clinicaltrials.gov (ID: NCT01762514). All patients received radical treatment based on intensity-modulated RT (IMRT) with a prescription dose of 68.1 Gy in 30 fractions. The patients' ages ranged 24-72 years, and each patient had five CT sets acquired at treatment position: at the 0th, 10th, 20th, 30th fractions during the RT, and at 3-month later after the RT. The PGs for each CT set were delineated by a radiation oncologist and verified independently by another. Patients' saliva was collected every other 10 days during the RT. Acute xerostomia was evaluated based on the RTOG acute toxicity scoring and the SA. In total, 1,703 radiomics features were calculated for PGs from each CT set, including feature value at 0th fraction (FV0F), FV10F, and delta FV (ΔFV10F-0F), respectively. Extensive experiments were conducted to achieve the optimal results. RidgeCV and Recursive Feature Elimination (RFE) were used for feature selection, while linear regression was used for predicting SA30F. Four more patients were added for independent testing. Substantial changes in various radiomics metrics of PGs were observed during the RT. Eight normalized feature value (NFV), selected from NFV0F, predicted SA10F with a mean square error (MSE) of 0.9042 and a R2 score of 0.7406. Fourteen NFV, selected from ΔNFV10F-0F, NFV0F, and NFV10F to predict SA30F, showed the best predictive ability with an MSE of 0.0569. The model predicted the level of acute xerostomia with a precision of 0.9220 and a sensitivity of 100%, compared to the clinical observed SA. For the independent test, the MSE of PSA30F was 0.0233. This study demonstrated that radiation-induced acute xerostomia level could be early predicted based on the SA and radiomics changes of the PGs during IMRT delivery. SA, NFV0F, NFV10F, and especially ΔNFV10F-0F provided the best performance on acute xerostomia prediction for individual patient based on RidgeCV_RFE_LinearRegression method of delta radiomics.

Quantifying institutional resource utilization of adjuvant brachytherapy and intensity-modulated radiation therapy for endometrial cancer via time-driven activity-based costing

PurposeThe purpose of this study was to quantify the cost of resources required to deliver adjuvant radiation therapy (RT) for high- to intermediate-risk endometrial cancer using time-driven activity-based costing (TDABC). Methods and MaterialsComparisons were made for three and five fractions of vaginal cuff brachytherapy (VCB), 28 fractions of intensity-modulated radiation therapy (IMRT), and combined modality RT (25-fraction IMRT followed by 2-fraction VCB). Process maps were developed representing each phase of care. Salary and equipment costs were obtained to derive capacity cost rates, which were multiplied by process times and summed to calculate total costs. Costs were compared with 2018 Medicare physician fee schedule reimbursement. ResultsFull cycle costs for 5-fraction VCB, IMRT, and combined modality RT were 42%, 61%, and 93% higher, respectively, than for 3-fraction VCB. Differences were attributable to course duration and number of fractions/visits. Accumulation of cost throughout the cycle was steeper for VCB, rising rapidly within a shorter time frame. Personnel cost was the greatest driver for all modalities, constituting 76% and 71% of costs for IMRT and VCB, respectively, with VCB requiring 74% more physicist time. Total reimbursement for 5-fraction VCB was 40% higher than for 3-fractions. Professional reimbursement for IMRT was 31% higher than for 5-fraction VCB, vs. IMRT requiring 43% more physician TDABC than 5-fraction VCB. ConclusionsTDABC is a feasible methodology to quantify the cost of resources required for delivery of adjuvant IMRT and brachytherapy and produces directionally accurate costing data as compared with reimbursement calculations. Such data can inform institution-specific financial analyses, resource allocation, and operational workflows.

Evaluation of the plan delivery accuracy of intensity-modulated radiation therapy by texture analysis using fluence maps

PurposeThe aim of this study is to evaluate the plan delivery accuracy of intensity-modulated radiation therapy (IMRT) by using textural features calculated from fluence maps. MethodsIn total, 202 IMRT plans were generated with the Trilogy (C-series linac) and TrueBeam STx systems. Fluence maps were obtained for each IMRT plan. With the fluence map, six textural features were calculated, namely angular second moment (ASM), inverse difference moment (IDM), contrast, variance, correlation, and entropy (particular displacement distances, d = 1, 5, and 10). To evaluate performances of textural features in predicting IMRT delivery accuracy, Spearman’s rank correlation coefficients (rs) were calculated between textural feature values and measures of conventional methods. ResultsFor Trilogy, correlation (d = 1) showed rs values of −0.764 (p < 0.001) with gamma passing rates of 2%/1 mm and 0.863 (p < 0.001) with multi-leaf collimator (MLC) errors. For TrueBeam STx, variance (d = 10) showed rs values of 0.691 (p < 0.001) with gamma passing rates of 1%/2 mm and −0.585 (p < 0.001) with MLC errors. ConclusionCorrelation (d = 1) for Trilogy and variance (d = 10) for TrueBeam STx demonstrated the potential in predicting IMRT delivery accuracy with high correlations to conventional IMRT delivery accuracy measures.

Plan quality comparison for cervical carcinoma treated with Halcyon and Trilogy intensity-modulated radiotherapy.

Purpose: Varian Halcyon is a novel machine with dual-layer leaves, single flattening filter free (FFF) energy and an enclosed bore. The purpose of this study was to compare the differences in dosimetry and plan parameters of intensity-modulated radiation therapy (IMRT) plans between the Halcyon and Trilogy accelerators.Methods and Materials: A total of 30 IMRT plans from cervical carcinoma patients were retrospectively analyzed on the Trilogy and Eclipse v13.5 treatment planning systems (TPSs). For each patient, a new plan based on Halcyon was created with the same planning parameters and optimization constraints using the Eclipse Version 15.1 TPS. To compare plan qualities, dosimetry parameters regarding planning target volume (PTV), organs at risk (OARs), monitor unit (MU) efficiency, segment size and treatment time were evaluated. Evaluation of the helical diode array system was performed with gamma-index analysis.Results: The dose distribution of the target volume of the Halcyon and Trilogy plans showed no significant difference (p > 0.05). The mean doses of rectum and both femoral heads for Halcyon plans were significantly reduced compared to those for Trilogy plans (p < 0.05). Compared to Trilogy, Halcyon increased the number of MUs from 1542.9±248.3 MU to 2514.9±328.2 MU (p = 0.00) and decreased the delivery time from 11.28±1.36 min to 3.26±0.26 min (p = 0.00). The average segment areas of Halcyon plans for proximal and distal multileaf collimators (MLCs) were 42.1 ± 31.2 cm2 and 28.4 ± 23.7 cm2, respectively, and that of Trilogy plans was 27.3 ± 16.9 cm2. The mean gamma index (3 mm/3%) results for the Halcyon and Trilogy plans were 99.41±0.26 and 99.76±0.32 (p > 0.05), respectively.Conclusions: All Halcyon treatment plans were recognized as clinically acceptable and had statistically better OAR sparing with higher delivery efficiency. The Halcyon system exhibited fast treatment delivery of IMRT with good dosimetric agreement using ArcCHECK.

Dosimetric evaluation of the compass program for patient dose analysis in IMRT delivery quality assurance.

A practical method was designed to verify the accuracy of dose distributions calculated using Compass, which can reconstruct the dose distribution inside a patient’s body during intensity-modulated radiation therapy (IMRT). Twelve virtual IMRT treatment plans were developed using an ArcCHECK diode detector array, and then the recalculated and reconstructed doses in Compass were compared with the actual measurements to assess the dosimetric accuracy. Based on the results of gamma evaluation for the 12 plans, Compass achieved average pass rates higher than 98%, which confirmed proper dosimetric accuracy in the IMRT quality assurance process. The validity of Compass for clinical applications was also confirmed through an additional comparison with the results calculated using 3DVH, another dose reconstruction program. It is necessary to verify the accuracy of the dose calculated using the program in advance before the commercialized dose reconstruction program is applied in clinical practice. This study has limitations in that it did not provide a real scientific contribution such as an introduction of new algorithm for dose calculation and the development of new measurement tools. However, the method based on the comparative analysis with the actual measured dose values as devised in this study seems to be useful in that it can be applied effectively to verify the dosimetric accuracy of the dose reconstruction program before first using it in the clinical cases.

Assessment of the modulation degrees of intensity-modulated radiation therapy plans

BackgroundTo evaluate the modulation indices (MIs) for predicting the plan delivery accuracies of intensity-modulated radiation therapy (IMRT) plans.MethodsA total of 100 dynamic IMRT plans that used TrueBeam STx and 102 dynamic IMRT plans that used Trilogy were selected. For each plan, various MIs were calculated, which included the modulation complexity score (MCS), plan-averaged beam area (PA), plan-averaged beam irregularity (PI), plan-averaged beam modulation (PM), MI quantifying multi-leaf collimator (MLC) speeds (MIs), MI quantifying MLC acceleration (MIa), and MI quantifying MLC acceleration and segment aperture irregularity (MIc,IMRT). To determine plan delivery accuracy, global gamma passing rates, MLC errors of log files, and dose-volumetric parameter differences between original and log file-reconstructed IMRT plans were obtained. To assess the ability of each MI for predicting plan delivery accuracy, Spearman’s rank correlation coefficients (rs) between MIs and plan delivery accuracy measures were calculated.ResultsPI showed moderately strong correlations with gamma passing rates in MapCHECK2 measurements of both TrueBeam STx and Trilogy (rs = − 0.591 with p < 0.001 and − 0.427 with p < 0.001 to with gamma criterion of 2%/2 mm, respectively). For ArcCHECK measurements, PI also showed moderately strong correlations with the gamma passing rates in the ArcCHECK measurements of TrueBeam STx and Trilogy (rs = − 0.545 with p < 0.001 and rs = − 0.581 with p < 0.001 with gamma criterion of 2%/2 mm, respectively). The PI showed the second strongest correlation with MLC errors in both TrueBeam STx and Trilogy (rs = 0.861 with p < 0.001 and rs = 0.767 with p < 0.001, respectively). In general, the PI showed moderately strong correlations with every plan delivery accuracy measure.ConclusionsThe PI showed moderately strong correlations with every plan delivery accuracy measure and therefore is a useful predictor of IMRT delivery accuracy.

Clinical experience using Delta 4 phantom for pretreatment patient-specific quality assurance in modern radiotherapy

AbstractPurposeIn advanced radiotherapy techniques such as intensity-modulated radiation therapy (IMRT), the quality assurance (QA) process is essential. The aim of the study was to assure the treatment planning dose delivered during delivery of complex treatment plans. The QA standard is to perform patient-specific comparisons between planned doses and doses measured in a phantom.Materials and methodThe Delta 4 phantom (Scandidos, Uppsala, Sweden) has been used in this study. This device consists of diode matrices in two orthogonal planes inserted in a cylindrical acrylic phantom. Each diode is sampled per beam pulse so that the dose distribution can be evaluated on segment-by-segment, beam-by-beam, or as a composite plan from a single set of measurements. Ninety-five simple and complex radiotherapy treatment plans for different pathologies, planned using a treatment planning system (TPS) were delivered to the QA device. The planned and measured dose distributions were then compared and analysed. The gamma index was determined for different pathologies.ResultsThe evaluation was performed in terms of dose deviation, distance to agreement and gamma index passing rate. The measurements were in excellent agreement between with the calculated dose of the TPS and the QA device. Overall, good agreement was observed between measured and calculated doses in most cases with gamma values above 1 in &gt;95% of measured points. Plan results for each test met the recommended dose goals.ConclusionThe delivery of IMRT and volumetric-modulated arc therapy (VMAT) plans was verified to correspond well with calculated dose distributions for different pathologies. We found the Delta 4 device is accurate and reproducible. Although Delta4 appears to be a straightforward device for measuring dose and allows measure in real-time dosimetry QA, it is a complex device and careful quality control is required before its use.

Dosimetric and Radiobiological Evaluation of Delivered Dose Distribution with Intra-Fractional Motion in Prostate Stereotactic Radiation Therapy Treatments Using VMAT and Helical Tomotherapy

The implementation of motion-management techniques during intensity modulated radiation therapy (IMRT) is still under challenging issue. Moreover, the dose-per-fraction regime and beam-delivery methods affect the dose distribution owing to the interplay effect. Hypofractionation may be a uniquely appropriate treatment for prostate cancer because of a lower α/β ratio. Several prospective studies support the safety of moderate hypofractionation; however, extreme fractionation may lead to greater toxicity. It has been reported that respiratory motion during IMRT delivery of stereotactic body radiation therapy (SBRT) can lead to dosimetric errors in the target of up to ±20%. Therefore, intra-fractional prostate motion may occur unpredictably during IMRT and lead to under-treatment of the target. In this study, we evaluated the dosimetric and radiobiological effects of the SBRT dose distributions with patient-specific intra-fractional motion in prostate cancer for volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) using a commercially available six-dimensional (6D) motion system. Dose distributions with patient-specific prostate intra-fractional motion were evaluated using the 6D-motion simulator system, which was coupled to a biplanar diode array detector phantom. These bidirectional prostate motions were acquired from magnetic resonance (MR)-cine images. Then, these motions were continuously generated for approximately 4 min, and dose measurements were repeated 5 times to measure the uncertainty of prostate motion during irradiation. We tested two typical motion patterns: large (over 2.0 mm) and small (under 1.0 mm). The SBRT plan was created in VMAT and HT with a prescription of 36.25 Gy/5 fractions to D95% of the PTV. We compared dose distributions with static irradiations using the 3 dimensional gamma (3D-γ) analysis. Moreover, the equivalent uniform dose (EUD)-based tumor control probability (TCP) and normal tissue complication probability (NTCP) of the rectum were compared with 76 Gy/38 fractions, which is the standard prostate fractionation plan. In the results of the dosimetric evaluation, the pass rate of the γ-analysis (criterion of 2 mm, 3%) was degraded by 9.5% and 22.7% in VMAT and HT plans in the large motion patterns and 3.0% and 8.7% in the small motion patterns, respectively. However, degradation of the D99 for CTV was only 0.7% and 1.8% in VMAT and HT plans, respectively, even in the large motion patterns. Moreover, these errors were negligible in small motion patterns. For the radiobiological evaluation, no significant differences in TCP and NTCP degradations were found in VMAT and HT SBRT plans compared with the standard fractionation plan. SBRT dose distributions with intra-fractional motion over 2.0 mm in prostate cancer were more degraded in HT than those observed in VMAT; however, these dosimetric errors might not be clinically significant degradation for TCP and/or NTCP.

Impact of Medicare Advantage Enrollment on Utilization of Intensity-Modulated Radiation Therapy and Cost of Care for Cancer Treatment

Intensity-modulated radiation therapy (IMRT) is an important driver of rising costs in oncology care, but the level of evidence supporting its routine use varies across disease sites, including breast, lung, and prostate. While Medicare Advantage (MA) plans have incentives to reduce health care spending, the effect of MA enrollment on utilization of high-cost medical services and quality of care is unclear, especially for cancer patients. We examined differences in IMRT utilization and health care spending between MA and traditional fee-for-service (FFS) Medicare for patients receiving radiation therapy (RT) across these disease sites. We performed a retrospective cohort study using 2009-2012 health insurance claims data from the Health Care Cost Institute (HCCI) and the Centers for Medicare and Medicaid Services (CMS). We identified 2,571 MA and 6,062 FFS Medicare beneficiaries from the HCCI and CMS databases, respectively, who were newly diagnosed with non-metastatic breast, lung, or prostate cancer in 2011 and were treated with external beam RT within 12 months of diagnosis. We measured utilization rate of IMRT, unit price of RT delivery, and RT-specific spending among patients within each cancer-type cohort. Outcomes were adjusted for differences in patient characteristics (age, sex, and Charlson co-morbidity index) and geography between MA and FFS beneficiaries. Statistical significance of the differences between groups was assessed using two-sample t tests. In both MA and FFS Medicare, the adjusted rate of IMRT utilization was highest among prostate patients and lowest among breast patients. Across all three disease sites, IMRT utilization was lower in MA than FFS Medicare, but the difference was statistically significant only for the prostate cohort (18.0 vs. 20.2%, p=0.149 for breast; 32.8 vs. 36.0%, p=0.385 for lung; 94.0 vs. 98.5%, p<0.001 for prostate). Average unit price of IMRT delivery was not significantly different in MA versus FFS Medicare. However, per patient RT-related costs were lower among MA patients in the breast and prostate cancer cohorts ($12,630 vs. $13,214 and $25,990 vs. $27,685, respectively; p=0.005 and p<0.001), but not significantly different among lung cancer patients ($15,653 vs. $15,024; p=0.301). IMRT utilization rates in both MA and FFS Medicare were consistent with the relative level of evidence supporting its use in each disease site. MA enrollment was associated with modestly lower IMRT utilization for all patients, with no evidence of a differential impact based on cancer type. The unit price of IMRT delivery was similar in MA versus FFS Medicare. We found no evidence that MA plans adopted utilization management tools that more effectively targeted high-cost therapies based on clinical evidence than in traditional Medicare.

Intensity-modulated radiotherapy for prostate cancer.

Radiation therapy (RT) is a curative treatment modality for localized prostate cancer. Over the past two decades, advances in technology and imaging have considerably changed RT in prostate cancer treatment. Treatment has evolved from 2-dimensional (2D) planning using X-ray fields based on pelvic bony landmarks to 3-dimensional (3D) conformal RT (CRT) which uses computed tomography (CT) based planning. Despite improvements with 3D-CRT, dose distributions often remained suboptimal with portions of the rectum and bladder receiving unacceptably high doses. In more recent years, intensity-modulated radiation therapy (IMRT) has become the standard of care to deliver external beam RT. IMRT uses multiple radiation beams of different shapes and intensities delivered from a wide range of angles to ‘paint’ the radiation dose onto the tumor. IMRT allows for a higher dose of radiation to be delivered to the prostate while reducing dose to surrounding organs. Multiple clinical trials have demonstrated improved cancer outcomes with dose escalation, but toxicities using 3D-CRT and escalated doses have been problematic. IMRT is a method to deliver dose escalated RT with more conformal dose distributions than 3D-CRT and has been associated with improved toxicity profiles. IMRT also appears to be the safest method to deliver hypofractionated RT and pelvic lymph node radiation. The purpose of this review is to summarize the technical aspects of IMRT planning and delivery, and to review the literature supporting the use of IMRT for prostate cancer.

Utilization of Intensity-Modulated Radiation Therapy for Malignant Pleural Mesothelioma in the United States

BackgroundAlthough postoperative radiotherapy (RT) for malignant pleural mesothelioma (MPM) has historically been delivered using 3-dimensional conformal RT (3DCRT) techniques, multiple reports show noteworthy safety and efficacy of the more advanced intensity-modulated RT (IMRT). To our knowledge, this is the only known study to evaluate national practice patterns of IMRT utilization for MPM. Materials and MethodsThe National Cancer Data Base was queried for newly-diagnosed MPM patients who underwent definitive surgery (extrapleural pneumonectomy [EPP] or extended pleurectomy/decortication [P/D]) followed by adjuvant RT. Patients with metastatic disease, non-EPP or P/D surgical techniques, and lack of RT receipt (or without specified RT technique) were excluded. Statistics included multivariable logistic regression, Kaplan–Meier overall survival (OS) analysis, and Cox proportional hazards modeling. ResultsOverall, 286 patients met criteria (181 [63%] IMRT and 105 [37%] 3DCRT). Temporal trends revealed that although 3DCRT was more common at initial time periods, IMRT utilization rose from 2004 to 2007 and stayed as a relatively constant majority thereafter. This was also present when substratifying the cohort according to EPP versus P/D approaches. IMRT was more often delivered at academic centers, along with institutions in the Southern United States, whereas 3DCRT was more frequently utilized in community facilities and in the Northeast (P ≤ .05 for all). RT technique did not affect OS (P > .05 for all comparisons). ConclusionIn the United States, IMRT is now the most commonly utilized adjuvant RT technique for MPM. Facility and regional differences might associate with IMRT delivery. The findings of this investigation have implications for insurance coverage, clinical referral patterns, and ongoing and future prospective trial design.

Remote Cherenkov imaging-based quality assurance of a magnetic resonance image-guided radiotherapy system.

Tools to perform regular quality assurance of magnetic resonance image-guided radiotherapy (MRIgRT) systems should ideally be independent of interference from the magnetic fields. Remotely acquired optical Cherenkov imaging-based dosimetry measurements in water were investigated for this purpose, comparing measures of dose accuracy, temporal dynamics, and overall integrated IMRT delivery. A 40×30.5×37.5cm3 water tank doped with 1g/L of quinine sulfate was imaged using an intensified charge-coupled device (ICCD) to capture the Cherenkov emission while being irradiated by a commercial MRIgRT system (ViewRay™). The ICCD was placed down-bore at the end of the couch, 4m from treatment isocenter and behind the 5-Gauss line of the 0.35-T MRI. After establishing optimal camera acquisition settings, square beams of increasing size (4.2×4.2cm2 , 10.5×10.5cm2 , and 14.7×14.7cm2 ) were imaged at 0.93 frames per second, from an individual cobalt-60 treatment head, to develop projection measures related to percent depth dose (PDD) curves and cross beam profiles (CPB). These Cherenkov-derived measurements were compared to ionization chamber (IC) and radiographic film dosimetry data, as well as simulation data from the treatment planning system (TPS). An intensity-modulated radiotherapy (IMRT) commissioning plan from AAPM TG-119 (C4:C-Shape) was also imaged at 2.1 frames per second, and the single linear sum image from 509s of plan delivery was compared to the dose volume prediction generated by the TPS using gamma index analysis. Analysis of standardized test target images (1024×1024pixels) yielded a pixel resolution of 0.37mm/pixel. The beam width measured from the Cherenkov image-generated projection CBPs was within 1mm accuracy when compared to film measurements for all beams. The 502 point measurements (i.e., pixels) of the Cherenkov image-based projection percent depth dose curves (pPDDs) were compared to pPDDs simulated by the treatment planning system (TPS), with an overall average error of 0.60%, 0.56%, and 0.65% for the 4.2, 10.5, and 14.7cm square beams, respectively. The relationships between pPDDs and central axis PDDs derived from the TPS were used to apply a weighting factor to the Cherenkov pPDD, so that the Cherenkov data could be directly compared to IC PDDs (average error of -0.07%, 0.10%, and -0.01% for the same sized beams, respectively). Finally, the composite image of the TG-119 C4 treatment plan achieved a 95.1% passing rate using 4%/4mm gamma index agreement criteria between Cherenkov intensity and TPS dose volume data. This is the first examination of Cherenkov-generated pPDDs and pCBPs in an MR-IGRT system. Cherenkov imaging measurements were fast to acquire, and minimal error was observed overall. Cherenkov imaging also provided novel real-time data for IMRT QA. The strengths of this imaging are the rapid data capture ability providing real-time, high spatial resolution data, combined with the remote, noncontact nature of imaging. The biggest limitation of this method is the two-dimensional (2D) projection-based imaging of three-dimensional (3D) dose distributions through the transparent water tank.

Intensity-modulated radiation therapy: a review with a physics perspective.

Intensity-modulated radiation therapy (IMRT) has been considered the most successful development in radiation oncology since the introduction of computed tomography into treatment planning that enabled three-dimensional conformal radiotherapy in 1980s. More than three decades have passed since the concept of inverse planning was first introduced in 1982, and IMRT has become the most important and common modality in radiation therapy. This review will present developments in inverse IMRT treatment planning and IMRT delivery using multileaf collimators, along with the associated key concepts. Other relevant issues and future perspectives are also presented.

Retrospective dosimetry study of intensity-modulated radiation therapy for nasopharyngeal carcinoma: measurement-guided dose reconstruction and analysis

BackgroundConventional phantom-based planar dosimetry (2D-PBD) quality assurance (QA) using gamma pass rate (GP (%)) is inadequate to reflect clinically relevant dose error in intensity-modulated radiation therapy (IMRT), owing to a lack of information regarding patient anatomy and volumetric dose distribution. This study aimed to evaluate the dose distribution accuracy of IMRT delivery for nasopharyngeal carcinoma (NPC), which passed the 2D-PBD verification, using a measurement-guided 3D dose reconstruction (3D-MGR) method.MethodsRadiation treatment plans of 30 NPC cases and their pre-treatment 2D-PBD data were analyzed. 3D dose distribution was reconstructed on patient computed tomography (CT) images using the 3DVH software and compared to the treatment plans. Global and organ-specific dose GP (%), and dose-volume histogram (DVH) deviation of each structure was evaluated. Interdependency between GP (%) and the deviation of the volumetric dose was studied through correlation analysis.ResultsThe 3D-MGR achieved global GP (%) similar to conventional 2D-PBD in the same criteria. However, structure-specific GP (%) significantly decreased under stricter criteria, including the planning target volume (PTV). The average deviation of all inspected dose volumes (DV) and volumetric dose (VD) parameters ranged from − 2.93% to 1.17%, with the largest negative deviation in V100% of the PTVnx of − 15.66% and positive deviation in D1cc of the spinal cord of 6.66%. There was no significant correlation between global GP (%) of 2D-PBD or 3D-MGR and the deviation of the most volumetric dosimetry parameters (DV or VD), when the Pearson’s coefficient value of 0.8 was used for correlation evaluation.ConclusionEven upon passing the pre-treatment phantom based dosimetric QA, there could still be risk of dose error like under-dose in PTVnx and overdose in critical structures. Measurement-guided 3D volumetric dosimetry QA is recommended as the more clinically efficient verification for the complicated NPC IMRT.

Treatment plan quality and delivery accuracy assessments on 3 IMRT delivery methods of stereotactic body radiotherapy for spine tumors

Stereotactic body radiotherapy (SBRT) for spine tumors has demonstrated clinical effectiveness. The treatment planning and delivery techniques have evolved from dynamic conformal arc therapy, to fixed gantry angle intensity modulated radiotherapy (IMRT), and most recently to volumetric modulated arc therapy (VMAT). A hybrid-arc (HARC) planning and delivery method combining dynamic conformal arc therapy delivery with a number of equally spaced IMRT beams is proposed. In this study we investigated plan quality, delivery accuracy, and efficiency of 3 delivery techniques: IMRT, HARC, and VMAT. Patients who underwent spine SBRT treatments were randomly selected from an Institutional Review Board-approved registry. For each patient, the prescription dose was 14 to 16 Gy in a single fraction to cover >90% of the tumor (without planning margin) while constraining V10Gy ≤ 10% of the spinal cord and the maximum point dose (MPD) of the spinal cord ≤ 14 Gy. All cases were clinically treated with fixed gantry step-shoot IMRT plans and then re-planned with VMAT using Pinnacle 9.0 and with HARC using Brainlab iPlan 4.5. Student t-test was used to compare the dosimetric end points, including V16Gy to the planning target volume, homogeneity index, MPDPTV, the conformity index, V10Gy of the spinal cord, and MPDcord. To compare the accuracy of delivery, we delivered all plans on a phantom and conducted gamma index (GI) comparisons with 3 mm/3% and 2 mm/2% criteria. All plans met our clinical requirements. Among 3 techniques, there were no differences on dose coverage to the tumor volume, maximum dose to the spinal cord, and plan homogeneity index (p > 0.05). The average V10Gy of the spinal cord was 6.66 ± 0.03%, 5.49 ± 0.03%, and 4.76 ± 0.02% for IMRT, HARC, and VMAT plans, respectively. Accordingly, the conformity indices were 1.30 ± 0.11 and 1.29 ± 0.20, 1.53 ± 0.29, respectively. VMAT plans were significantly (p < 0.05) less conformal but significantly (p < 0.05) lower V10Gy of the spinal cord than those from HARC and IMRT plans. With delivery accuracy measured by GIs, the average GIs of 3%/3 mm were 92.6 ± 1.1%, 96.5 ± 2.7%, 99.0 ± 1.1% for IMRT, HARC, and VMAT plans, respectively. The differences were significant (p < 0.05). Accordingly, the average monitor units were 9238 ± 2242, 9853 ± 2548 and 5091 ± 910. The plan quality created from the 3 planning techniques can meet the clinical requirement. Adding arc beams in delivery such as in HARC and VMAT plans improves the delivery accuracy. VMAT is the most efficient delivery method.

Clinical efficacy and safety of a highly conformal, supine, hybrid forward and inverse planned intensity modulated radiation therapy technique for craniospinal irradiation

Purpose: To demonstrate the clinical efficacy and safety of a highly conformal, supine, hybrid forward and inverse planned intensity modulated radiation therapy (IMRT) technique for photon craniospinal irradiation (CSI).Methods: Patients who received supine, hybrid IMRT CSI from 2009 to 2014 were included in this retrospective review. Clinical target volume (CTV) was defined as intracranial contents and thecal sac, including nerve roots. Dose was prescribed such that >99% of CTV received >99% of prescription and >95% of the planning target volume received >95% of prescription, with no attempt to include vertebral bodies. Lateral fields were utilized at the cranium and upper cervical spine. Spine fields were either single posterior or 2–3 obliques. Plans were generated with a hybrid of forward and inverse planned IMRT. Inferior borders of the cranium fields and superior border of the lower spine field were designed with 6–15 cm long, gradual dose gradients by sequential closing of multileaf collimator leaves using forward planned multiple static segment IMRT delivery. The sliding window upper spine IMRT field was created by the inverse planning system to match gradients of the brain and lower spine fields. The lower spine field gradient was similarly completed.Results: The cohort consisted of 34 patients. Median CSI dose was 36 Gy (range: 18–39.6 Gy). With a median follow up of 59.4 months, there were no isolated recurrences or spinal myelopathies at CTV margins or field gradients. Eleven patients had recurrence, all of which were intracranial.Conclusions: Our hybrid forward and inverse planned IMRT supine CSI technique did not result in any isolated recurrences or myelopathies at CTV margins or field gradients. This suggests our target volumes and blended gradients are appropriate for highly conformal three-dimensional planning.

MS 06.05 The Use of Adjuvant IMRT after Pleurectomy/Decortication

MS 06.05 The Use of Adjuvant IMRT after Pleurectomy/Decortication

Evaluation of Intensity Modulated Radiation Therapy Delivery System using a Volumetric Phantom on the Basis of the Task Group 119 Report of American Association of Physicists in Medicine.

The current work describes the implementation of the American Association of Physicists in Medicine (AAPM)'s Task Group 119 report on a volumetric phantom (Delta4, Scandidos, Uppsala, Sweden) following the stated dose goals, to evaluate the step-and-shoot intensity modulated radiation therapy (IMRT) system. Delta4 consists of diode detectors, lying on two crossed planes, measuring the delivered dose, and providing two-dimensional dosimetric information. Seven plans of different goals and complexity were performed, with individual structure sets. TG199 structure sets and plans were transferred and implemented on the Delta4 phantom taking into account its cylindrical geometry. All plans were delivered with a 6 MV linear accelerator equipped with multileaf collimator of 1 cm thickness. Plan results for each test met the recommended dose goals. The evaluation was performed in terms of dose deviation, distance to agreement, and gamma index passing rate. In all test cases, the gamma index passing rate was measured >90%. Delta4 phantom has proven to be fast, applicable, and reliable for the step-and-shoot IMRT commissioning following TG119's recommended tests. Although AAPM's TG119 report is referring to the implementation of test plans that do not correspond to patient plans, it could be used as an evaluation tool of various IMRT systems, considering the local treatment planning system and the delivery system.

Verification of Dosimetric Commissioning Accuracy of Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy Delivery using Task Group-119 Guidelines.

Aim:The purpose of this study is to verify the accuracy of the commissioning of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) based on the recommendation of the American Association of Physicists in Medicine Task Group 119 (TG-119).Materials and Methods:TG-119 proposes a set of clinical test cases to verify the accuracy of IMRT planning and delivery system. For these test cases, we generated two sets of treatment plans, the first plan using 7–9 IMRT fields and a second plan utilizing two-arc VMAT technique for both 6 MV and 15 MV photon beams. The template plans of TG-119 were optimized and calculated by Varian Eclipse Treatment Planning System (version 13.5). Dose prescription and planning objectives were set according to the TG-119 goals. The point dose (mean dose to the contoured chamber volume) at the specified positions/locations was measured using compact (CC-13) ion chamber. The composite planar dose was measured with IMatriXX Evaluation 2D array with OmniPro IMRT Software (version 1.7b). The per-field relative gamma was measured using electronic portal imaging device in a way similar to the routine pretreatment patient-specific quality assurance.Results:Our planning results are compared with the TG-119 data. Point dose and fluence comparison data where within the acceptable confident limit.Conclusion:From the obtained data in this study, we conclude that the commissioning of IMRT and VMAT delivery were found within the limits of TG-119.