Routine Intensity Modulated Radiation Therapy Research Articles

Feasibility of omitting the clinical target volume under PET-CT guidance in unresectable stage III non-small-cell lung cancer: A phase II clinical trial

BackgroundThis clinical trial aims at investigate the feasibility of CTV-omitted, positron-emission tomography computed tomography (PET-CT) combined with intensity-modulated radiation therapy (IMRT) for unresectable stage III NSCLC. Methods and MaterialsThis was a single-center, phase II clinical trial initiated in July 2016. Patients with unresectable stage III NSCLC undergoing routine IMRT were randomly enrolled into the study group (CTV-omitted under PET-CT guidance) and the control group (CTV-delineated). Patients received platinum-based dual-drug concurrent chemoradio therapy. In the study group, the PGTV dose was 60 Gy given in 30 daily 2 Gy fractions; in the control group, the PCTV dose was 54 Gy given in 30 daily 1.8 Gy fractions, and the PGTV dose was 60 Gy given in 30 daily 2 Gy fractions. The primary endpoint was the incidence of radiation respiratory events or esophagitis with grade 3 or higher. The secondary endpoints included objective response rate (ORR), locate control rate, progression-free survival (PFS), failure pattern and overall survival (OS). ResultsA total of 90 patients were enrolled between July 2016 and March 2019. The incidence of radiation respiratory events or esophagitis with grade 3 or higher was 11.1 % in the study group, significantly lower than the rate of 28.9 % in the control group (P = 0.035), basically due to the reduced irradiated volumes of the lungs and esophagus in the study group. The median PFS was 9.0 months versus 10.0 months (P = 0.597), and the median OS 31.0 months versus 26.0 months (P = 0.489) in the study group and the control group, respectively. The failure pattern was not significantly different between the two groups (P = 0.826). ConclusionOmitting the CTV under PET-CT guidance has high feasibility to reduce severe radiation associated toxicity in IMRT for unresectable stage III NSCLC, without compromising the efficacy.

Feasibility of Omitting Clinical Target Volume under PET-CT Guidance in Unresectable Stage III Non-Small-Cell Lung Cancer, a Phase II Clinical Trial

<h3>Purpose/Objective(s)</h3> This clinical trial aims to investigate the feasibility of CTV-omitted, positron-emission tomography computed tomography (PET-CT) combined with intensity-modulated radiation therapy (IMRT) for unresectable stage III NSCLC. <h3>Materials/Methods</h3> This was a single-center, phase II clinical trial initiated in July 2016. Patients with unresectable stage III NSCLC undergoing routine IMRT were randomly enrolled into the study group (CTV-omitted under PET-CT guidance) and the control group (CTV-delineated). The primary endpoint was the incidence of radiation respiratory events or esophagitis with grade 3 or higher. The secondary endpoints included objective response rate (ORR), locate control rate, progression-free survival (PFS), failure pattern and overall survival (OS). <h3>Results</h3> A total of 62 patients were enrolled between July 2016 and October 2018. The incidence of radiation respiratory events or esophagitis with grade 3 or higher was 6.5 % in the study group, significantly lower than the rate of 25.8 % in the control group (P = 0.04), basically due to the reduced irradiated volumes of the lungs and esophagus in the study group. The median PFS was 11.0 months versus 9.0 months (P = 0.374), and the median OS 31.0 months versus 24.0 months (P = 0.186) in the study group and the control group, respectively. The failure pattern was not significantly different between the two groups (P = 0.464). <h3>Conclusion</h3> Omitting the CTV under PET-CT guidance has high feasibility to reduce severe radiation associated toxicity in IMRT for unresectable stage III NSCLC, without compromising the efficacy.

Outcomes of Routine Intensity Modulated Radiation Therapy Quality Assurance in a Large Head and Neck Cancer Center

The primary endpoint was to ascertain whether the percentage of major changes implemented from our routine intensity modulated radiation therapy (IMRT) quality assurance (QA) process was more than 10%. The secondary endpoints were to document the percentage of minor changes, ascertain the time taken to perform the IMRT QA process, evaluate potential predictors for major changes, and ascertain the perceived value of the program by the compliance of radiation oncologists (ROs) treating head and neck cancer (HNC). This was a retrospective analysis of a prospective database for all radically treated HNC patients. Recommended changes were predefined with criteria as either "major changes" or "minor changes." Of 595 patients treated radically between May 21, 2012, and May 21, 2014, 548 patients were entered, giving a compliance of 92.1%. The vast majority were treated with IMRT (470/548, 89%), 49.3% treated definitively and 50.7% treated adjuvantly; overall, 63% had stage IV disease. Eighty-one patients (14.8%) had 1 or more major changes recommended and implemented, and 21 patients (3.8%) had major changes recommended but not implemented because of a lack of consensus. Of minor recommendations, in 115 patients (21%) they were implemented and in 13 patients (2.4%) they were not implemented. No changes were recommended in the remaining 324 patients (59.1%). The only factor correlating with the likelihood of a major change was treatment with IMRT (P=.001). In the vast majority of cases (85%), the time taken for IMRT QA was less than 20minutes. Our routine HNC IMRT QA program resulted in the implementation of a significant number of major changes. The high compliance with the program is indicative of the belief in its clinical value. This study can inform discussion on optimal RT QA processes in routine clinical practice.

Quick, efficient and effective patient-specific intensity-modulated radiation therapy quality assurance using log file and electronic portal imaging device.

The aim of work is to explore a quick, efficient, and effective patient-specific intensity-modulated radiation therapy (IMRT) quality assurance (QA). Software tools were developed to extract and analyze the multi-leaf collimator (MLC) leaf positions (LPs) from electronic portal imaging device (EPID) images for Varian C-series machine and TrueBeam, to extract useful data from MLC log file of C-series linear accelerator (LINAC), to extract useful information from the trajectory log binary file of TrueBeam LINAC, to compare LPs derived from EPID images with log file/trajectory log data, and to analyze IMRT treatment files using the MATLAB programming language. The difference in LP determined from the trajectory log and EPID images was proposed for patient-specific QA. It was found that the differences in LP for regular radiation fields generated using stationary leaves are <0.5 mm for all the field sizes while for regular radiation fields generated using the moving leaves are more but <2 mm. The differences in LPs for IMRT field were also determined and found to be <2 mm. The methodology demonstrated can be used for establishing the accuracy of trajectory log data and for independent routine IMRT QA by generating single number like gamma index to indicate pass or fail of an IMRT treatment plan. The QA indices such as numbers of occurrences of ≥2 mm error in LPS are found more than 5% of total number of occurrences; the dosimetric review of planned treatment is advisable.

Proton therapy for early stage prostate cancer: is there a case?

Proton-beam therapy (PBT) for prostate cancer has been in used for several decades, with its technique evolving significantly over this period. A growing number of centers now routinely utilize pencil-beam scanning as an advanced technique of PBT. Interest and controversy concerning its use have recently come under scrutiny. While the past decade has produced an assemblage of evidence suggesting that PBT is safe and effective for early stage prostate cancer, it is still unknown whether the theoretical dosimetric advantages of PBT translate into meaningful clinical improvements over routine intensity-modulated radiation therapy, which is commonly used for these patients. Outcomes from early trials using whole courses of PBT have shown mixed results when compared with routine intensity-modulated radiation therapy. Therefore, randomized trials comparing these two techniques should be undertaken, as this would help in defining the role of PBT for this patient group. This article aims to describe the basics of PBT, review the reasons for the growing interest in PBT, review the evidence for PBT, review the controversy surrounding PBT, and inquire about PBT’s future in the treatment of prostate cancer, with attention to its physical properties, comparative clinical and cost-effectiveness, and advances in its delivery.

IMRT QA: Selecting gamma criteria based on error detection sensitivity.

The gamma comparison is widely used to evaluate the agreement between measurements and treatment planning system calculations in patient-specific intensity modulated radiation therapy (IMRT) quality assurance (QA). However, recent publications have raised concerns about the lack of sensitivity when employing commonly used gamma criteria. Understanding the actual sensitivity of a wide range of different gamma criteria may allow the definition of more meaningful gamma criteria and tolerance limits in IMRT QA. We present a method that allows the quantitative determination of gamma criteria sensitivity to induced errors which can be applied to any unique combination of device, delivery technique, and software utilized in a specific clinic. A total of 21 DMLC IMRT QA measurements (ArcCHECK®, Sun Nuclear) were compared to QA plan calculations with induced errors. Three scenarios were studied: MU errors, multi-leaf collimator (MLC) errors, and the sensitivity of the gamma comparison to changes in penumbra width. Gamma comparisons were performed between measurements and error-induced calculations using a wide range of gamma criteria, resulting in a total of over 20 000 gamma comparisons. Gamma passing rates for each error class and case were graphed against error magnitude to create error curves in order to represent the range of missed errors in routine IMRT QA using 36 different gamma criteria. This study demonstrates that systematic errors and case-specific errors can be detected by the error curve analysis. Depending on the location of the error curve peak (e.g., not centered about zero), 3%/3 mm threshold = 10% at 90% pixels passing may miss errors as large as 15% MU errors and ±1 cm random MLC errors for some cases. As the dose threshold parameter was increased for a given %Diff/distance-to-agreement (DTA) setting, error sensitivity was increased by up to a factor of two for select cases. This increased sensitivity with increasing dose threshold was consistent across all studied combinations of %Diff/DTA. Criteria such as 2%/3 mm and 3%/2 mm with a 50% threshold at 90% pixels passing are shown to be more appropriately sensitive without being overly strict. However, a broadening of the penumbra by as much as 5 mm in the beam configuration was difficult to detect with commonly used criteria, as well as with the previously mentioned criteria utilizing a threshold of 50%. We have introduced the error curve method, an analysis technique which allows the quantitative determination of gamma criteria sensitivity to induced errors. The application of the error curve method using DMLC IMRT plans measured on the ArcCHECK® device demonstrated that large errors can potentially be missed in IMRT QA with commonly used gamma criteria (e.g., 3%/3 mm, threshold = 10%, 90% pixels passing). Additionally, increasing the dose threshold value can offer dramatic increases in error sensitivity. This approach may allow the selection of more meaningful gamma criteria for IMRT QA and is straightforward to apply to other combinations of devices and treatment techniques.

Clinical validation of an in-house EPID dosimetry system for IMRT QA at the Prince of Wales Hospital

In this study a simple method using standard flood-field corrected Electronic Portal Imaging Device (EPID) images for routine Intensity Modulated Radiation Therapy (IMRT) Quality Assurance (QA) was investigated. The EPID QA system was designed and tested on a Siemens Oncor Impression linear accelerator with an OptiVue 1000ST EPID panel (Siemens Medical Solutions USA, Inc, USA) and an Elekta Axesse linear accelerator with an iViewGT EPID (Elekta AB, Sweden) for 6 and 10 MV IMRT fields with Step-and-Shoot and dynamic-MLC delivery. Two different planning systems were used for patient IMRT field generation for comparison with the measured EPID fluences. All measured IMRT plans had >95% agreement to the planning fluences (using 3 cGy / 3 mm Gamma Criteria) and were comparable to the pass-rates calculated using a 2-D diode array dosimeter.

Quality correction factors of composite IMRT beam deliveries: Theoretical considerations

In the scope of intensity modulated radiation therapy (IMRT) dosimetry using ionization chambers, quality correction factors of plan-class-specific reference (PCSR) fields are theoretically investigated. The symmetry of the problem is studied to provide recommendable criteria for composite beam deliveries where correction factors are minimal and also to establish a theoretical limit for PCSR delivery k(Q) factors. The concept of virtual symmetric collapsed (VSC) beam, being associated to a given modulated composite delivery, is defined in the scope of this investigation. Under symmetrical measurement conditions, any composite delivery has the property of having a k(Q) factor identical to its associated VSC beam. Using this concept of VSC, a fundamental property of IMRT k(Q) factors is demonstrated in the form of a theorem. The sensitivity to the conditions required by the theorem is thoroughly examined. The theorem states that if a composite modulated beam delivery produces a uniform dose distribution in a volume V(cyl) which is symmetric with the cylindrical delivery and all beams fulfills two conditions in V(cyl): (1) the dose modulation function is unchanged along the beam axis, and (2) the dose gradient in the beam direction is constant for a given lateral position; then its associated VSC beam produces no lateral dose gradient in V(cyl), no matter what beam modulation or gantry angles are being used. The examination of the conditions required by the theorem lead to the following results. The effect of the depth-dose gradient not being perfectly constant with depth on the VSC beam lateral dose gradient is found negligible. The effect of the dose modulation function being degraded with depth on the VSC beam lateral dose gradient is found to be only related to scatter and beam hardening, as the theorem holds also for diverging beams. The use of the symmetry of the problem in the present paper leads to a valuable theorem showing that k(Q) factors of composite IMRT beam deliveries are close to unity under specific conditions. The theoretical limit k(Q(pcsr),Q(msr) ) (f(pcsr),f(msr) )=1 is determined based on the property of PCSR deliveries to provide a uniform dose in the target volume. The present approach explains recent experimental observations and proposes ideal conditions for IMRT reference dosimetry. The result of this study could potentially serve as a theoretical basis for reference dosimetry of composite IMRT beam deliveries or for routine IMRT quality assurance.

SU-E-T-788: DICOM-Based Electronic Patient Record (ePR) System with Computer-Aided Evaluation (CAE) of Intensity Modulated Radiation Therapy (IMRT) Plans

Purpose: To develop a DICOM‐based electronic patient record system with computer‐aided evaluation (CAE) of intensity modulated radiation therapy(IMRT) plans and to assess the technical aspects of the system and its performance. Methods: The system was developed using the WampServer version 2.0, a package of Apache web server 2.2, PHP 5.2 and MySQL 5.1 to facilitate evaluation of IMRT plans in any Web browser. After tracing the clinical workflow, a set of routines were written to parse key data items from the DICOM‐RT objects. To save planners from tedious manual evaluation, the direct relationships between the DVH curve to the corresponding CTimages, RT dose data and ROI contours were visualized. Extraction of both overdose and underdose regions was based on the edge‐based approach. Followed by reconstruction of ROI contours, the grid doses were constructed by multiplying each pixel value stored in the Image pixel module with the Dose Grid Scaling attribute in the RT Dose module. Graphic User Interfaces (GUIs) were created to allow planners to establish customized plan acceptance criteria and query for evaluation results. Thirty IMRT plans were collected for technical verification and performance validation. Results: The CAE system was successfully developed, allowing better appreciation of resultant plans. There was no statistical difference between CAE results and those obtained manually by experienced planners on all datasets. With prompt problem detection feature, the direct relationship between the DVH data to the corresponding inhomogeneity regions on CT slices could be shown within an average of 20 seconds. Conclusions: The CAE system will represent a breakthrough in the routine IMRT planning workflow by eliminating all tedious manual evaluation steps and introducing remote plan evaluation across multiple locations by the local area network and Internet. The concept could also be adopted in the evaluation of plans other than IMRT.

Evaluation of IMRT QA Point Measurement Rocesses Using a Commercial Heterogeneous Phantom

Intensity Modulated Radiation Therapy (IMRT) has the potential to deliver a highly conformal dose distribution to the target volume compared to conventional radiotherapy. However, the use of IMRT introduces complexities in dose delivery and veri fi cation. Routine IMRT QA is typically performed in a homogeneous solid water phantom and does not verify the accuracy of a treatment planning system’s handling of the heterogeneity correction algorithm, which is particularly important in a low density lung medium. The purpose of this work is to evaluate common IMRT QA point measurement processes that take advantage of a commercial heterogeneous phantom [CIRS IMRT thorax phantom (CIRS, Inc., Norfolk, Virginia, USA)]. Dose calculated with Monte Carlo (MC) methods and pencil beam (PB) methods are used. IMRT QA using the CIRS phantom with the MC and PB algorithms was retrospectively analyzed using control charts and a capability index. Fifteen actual IMRT treatment plans of lung cancer patients were used for this study. The dose was measured in the phantom at points located in lung, bone, and tissue with an ion chamber (IC) for 15 cases and thermoluminescent dosimeters (TLDs) for 5 cases. Measurements and calculations in each heterogeneity (e.g., TLD/MC in bone) were considered as separate processes. Control charts and the capability index Cpm were used to evaluate the following processes using the CIRS phantom: IC/MC, PB/MC, TLD/MC for measurements in the lung, tissue and bone. The processes PB/IC and MC/IC using conventional homogeneous water-equivalent slab geometry were also evaluated. In total, 11 IMRT QA processes were considered. Comparison of the data showed that the dose inside the lung calculated with PB was overestimated by 6% on average relative to the MC calculations. On average, MC calculations in bone and tissue agree within 3% with PB calculations and IC measurements. Process capability values (Cpm) greater than 1.33 indicate a well performing process. Using the CIRS phantom, Cpm ranged from 0.25 for the PB/ MC process in lung to 1.41 for the TLD/MC process in tissue. By comparison, the process using the conventional water- equivalent slab phantom showed the PB/IC and MC/IC Cpm values of 1.36 and 1.21, respectively. Nine of the 11 IMRT QA processes studied were not able to meet the clinical speci fi cations of 5%. However, we found the CIRS phantom is versatile to compare both homogeneous and heterogeneous IMRT QA measurements to calculations. Our results indicate that additional re fi nements of the IMRT QA processes are required. This is especially true for calculations and measurements in lung-equivalent media. The capability index is a simple and useful quantitative tool for comparing different approaches to lung IMRT QA.

SU-FF-T-206: Evaluation of a Computed Radiography System for Verification of Intensity Modulated Radiation Therapy

Purpose: There has been great interest recently in replacing conventional film with computed radiography(CR) systems. However, the study of its dosimetric applications has been limited. This work presents a detailed evaluation of its performance in quality assurance (QA) for intensity modulated radiation therapy(IMRT).Method and Materials: A CR system comprised of a Kodak ACR‐2000i laser scanner, an Agfa CR plate, and a PC was used for IMRT verification. Both the scanner and the CR plate were calibrated by following the Kodak‐provided instructions. A dosecalibration curve for the CR plate was generated in the dose range of 0.5cGy to 400cGy. In the IMRT verification experiment, the CR plate with 6cm solid water build‐up was irradiated to a clinical 6‐field IMRT treatment plan (Varian Eclipse) of 6MV photons. Gantry angles were set to 0° for the dose delivery. The CR plate was scanned right after irradiation. An independent EDR2 film measurement of the delivered dose was also conducted. A 3‐way comparison of dose information between the Eclipse calculations, film measurements, and CR measurements was performed. Dose maps, profiles, isodose lines, and Gamma maps were utilized for analysis. Results: The CR results show excellent agreement with both Eclipse calculations and film measurements within the 3% dose difference and 3mm distance to agreement criteria except in penumbra regions or just outside field edges. CR and film measurements agree with each other better than with Eclipse calculations in the regions outside field edges, indicating possible limitations of calculation algorithms in those regions. Conclusion: The CR system can provide comparable accuracy in relative dose measurements to conventional film. The CR system, having the advantages of digital nature, environmental cleanliness, reusability, and high convenience, is a feasible and reliable tool for routine IMRT QA.

An intercomparison between film dosimetry and diode matrix for IMRT quality assurance

The evaluation of the agreement between measured and calculated dose plays an essential role in the quality assurance (QA) procedures for intensity modulated radiation therapy (IMRT). Film dosimetry has been widely adopted for this purpose due to excellent film characteristics in terms of spatial resolution; unfortunately, it is a time-consuming procedure and requires great care if film has to be used as an absolute dosimeter. If this is not the case, then an independent ionimetric measurement is mandatory to assess the absolute dose agreement. Arrays of detectors are now replacing films for routine IMRT QA, since they permit very simple verification procedures. They show excellent characteristics in terms of linearity, repeatability, and independence of the response from the dose rate, but at the same time present a poor spatial resolution, due to the limited number of detectors available. In our institution, a diode matrix (MapCHECK, provided by Sun Nuclear) is adopted for routine QA. The aim of this work is to compare the performances of absolute film dosimetry with this matrix in QA procedures and to investigate the origin of possible discrepancies between the two methods. The results we present show a very good agreement between the two detectors when used to assess the mean dose deviation between calculated and measured doses (in both cases 0.2%). If the y matrix method is adopted, MapCHECK response shows a slightly better agreement with computed dose distribution than film dosimetry (mean percentage of points satisfying the constraint y < or = 1: 96% versus 94%). This difference is shown not to depend on the different field sampling, but on the detectors' capabilities. Moreover, we show that the diode matrix is able to identify eventual delivery errors as well as film. Our conclusion is that the diode matrix may effectively replace both film dosimetry and ionimetric measurements in routine IMRT QA.

Routine IMRT verification by means of an automated Monte Carlo simulation system

Purpose A tool to simulate complete intensity-modulated radiation therapy (IMRT) treatments with the Monte Carlo (MC) method has been developed. This application is based on a distribution model to employ as short processing times as possible for an operative verification. Methods and materials The Clinical Primus-Siemens Linac beam was simulated with MC, using the EGS4 OMEGA-BEAM code package. An additional home-made program prepares the appropriate parameters for the code, using as input the file sent from the planning system to the linac. These parameters are adapted to the simulation code, making physical and clinical subdivisions of the global simulation of the treatment. Each resultant partition is ordered to a client personal computer in a cluster with 47 machines under a Linux environment. The verification procedure starts delivering the treatment on a plastic phantom containing an ionization chamber. If differences are less than 2%, films are inserted at selected planes in the phantom and the treatment is delivered again to evaluate the relative doses. When matching between treatment planning system (TPS), film, and MC is acceptable, a new evaluation of the patient is then performed between TPS and MC. Three different cases are shown to prove the applicability of the verification model. Results Acceptable agreement between the three methods used was obtained. The results are presented using different analysis tools. The actual time employed to simulate the total treatment in each case was no more than 5 h, depending on the number of segments. Conclusions The MC model presented is fully automated, and results can be achieved within the operative time limits. The procedure is a reliable tool to verify any IMRT treatment.