Intensity-modulated Radiation Therapy Treatment Delivery Research Articles

Longitudinal Remote IMRT Training in Africa: A Prospective Cohort Study

<h3>Purpose/Objective(s)</h3> Intensity-modulated radiation therapy (IMRT) can significantly enhance patient outcomes compared to 3D-conformal radiotherapy (3D-CRT), yet African patients' access to IMRT is sparse. Limited opportunities for continuing education and training for radiation oncology professionals has been identified as a significant problem. We aimed to evaluate a telehealth training curriculum for clinicians and medical physicists in low- and middle- income countries in Africa. <h3>Materials/Methods</h3> A 30-session remote training program on transitioning from 3D to IMRT was provided at no cost to radiation oncology centers in Africa and one sister institution in Pakistan. The program consisted of twice weekly 1-hour live video conferencing sessions for 4 months with interactive didactics and case-based learning utilizing a cloud-based contouring platform. 15 radiation oncology centers across Africa were invited to participate, of which 13 were transitioning to, or had recently began, IMRT programs. A Likert scale (1-5) confidence evaluation on 7 foundational domains of IMRT treatment planning and delivery, 8 physics-specific domains, and 3 physician-specific domains was electronically administered to enrolled individuals pre- and post- curriculum. Participation was tracked for each session. <h3>Results</h3> A total of 12 centers (9 public, 2 private, and 1 semi-private) formally enrolled in training. Of these, 4 began IMRT in the last 3 years and 8 had plans to transition from 3D-CRT to IMRT. 128 individuals participated: 47 medical physicists (36.7%), 21 radiation oncologists (16.4%), 16 radiation therapists (12.5%), 30 residents (23.4%), 9 medical physics trainees (7.0%), and 5 other staff (3.9%). Average participation per session was 31 (range 17–83, SD = 16.6), and 36 individuals attended 10 sessions or more. 30 respondents, who attended 12/30 sessions on average (range 4 to 21, SD = 5.2), completed both pre- and post- surveys and were eligible for paired analysis. Overall pre- and post-curriculum mean self-confidence scores were 2.51 (n = 142) and 4.1 (n = 30), respectively, out of a possible 5. Paired pre- vs. post- analysis for 30 individuals revealed statistically significantly (<i>P</i> < 0.05) higher scores for 7 of 7 foundational domains (n = 30), 5 of 8 physics-specific domains (n = 15), and 3 of 3 physician-specific domains (n = 13). Higher attendance rates significantly correlated with larger gains in confidence scores (<i>P</i> = 0.047). <h3>Conclusion</h3> Longitudinal telehealth training integrating cloud-based tools for radiation oncology professionals is a viable and efficient method for continuing education in Africa. Despite low attendance rates, this program significantly and comprehensively improved confidence in IMRT across multiple training domains, with confidence improving with greater course participation. Future work remains to facilitate and explore the efficacy of similar programs and to assess concordance of participant confidence with clinical knowledge and skill.

A critical literature review on the use of bellyboard devices to control small bowel dose for pelvic radiotherapy.

Delivering curative radiotherapy doses for rectal and gynaecological tumours has historically been complicated by the dose tolerance of the small bowel. Acute radiation-induced small bowel toxicity includes side effects such as abdominal pain, nausea and diarrhoea. With the advent of new treatment delivery modalities, such as IMRT (Intensity modulated radiotherapy) and VMAT (Volumetric modulated Arc radiotherapy), there has been an expectation that small bowel doses can be better controlled with the use of these technologies. These capabilities enable the creation of treatment plans that can better avoid critical radiosensitive organs. The purpose of this review is to look beyond advances in linear accelerator technology in seeking improvements to small bowel dose and toxicity. This review examines whether an alternative prone patient positioning approach using a bellyboard device in conjunction with IMRT and VMAT treatment delivery can reduce small bowel doses further than using these technologies with the patient in a traditional supine position.

Radiation Oncology-External-Beam Radiation Therapy.

The application of structural shielding design techniques and goals as outlined in the National Council on Radiation Protection and Measurements Report 151, Structural Shielding Design and Evaluation for Megavoltage X- and Gamma-Ray Radiotherapy Facilities (2005), continues to be the basis for treatment vault design in 2018 with some updated information. Treatment techniques have changed significantly with the dominant usage of intensity-modulated radiation therapy techniques today based on concurrent imaging. Some of the developments in linear accelerator technology over the past 15 y include flattening filter-free modes, which enable higher instantaneous dose rates; three-dimensional conformal radiation therapy resulting in potentially higher workloads since healthy tissue is spared; improved intensity-modulated radiation therapy treatment delivery systems with lower monitor units per centigray delivered than traditional step and shoot intensity-modulated radiation therapy; stereotactic body radiation therapy with higher treatment fractions and increased workloads; and increased use of stereotactic radiosurgery with conventional linear accelerators as well as robotic arm-mounted linear accelerators with higher treatment fractions. These new treatment units also incorporate multiple-energy x-ray beams (2 to 5 MV typical), which require a significant change in the specification of a workload to be used in each vault. As the equipment in radiation oncology departments has evolved to state-of-the-art modalities, the requirements for adequate radiation shielding for these modalities has become more rigorous. Architectural designs no longer depend on standard maze design rectangular rooms. Innovative layouts and utilization of multiple layers of shielding materials allow much greater flexibility in room designs. Maze-less rooms with direct-shielded doors are part of these challenging designs and are very common today. Use of multiple-density concrete blocks allows quicker construction of vaults and requires less space for the equivalent shielding provided. Combinations of high-density or normal-density concrete, steel, and lead are used in designs to make optimum use of available space and cost. Additional shielding needed at the edges of these single- or bi-parting sliding doors as well as baffle designs for heating, ventilation, and air conditioning systems and communication cable penetrations require detailed calculations. Examples of these designs will be given in this presentation. Consideration of the radiation levels around the planned vault must also include adjacent multistory buildings.

SU‐E‐T‐693: Should We Use RapidArc (VMAT) for Breast Treatments? A Dosimetric Comparison of IMRT Versus VMAT Optimization in Whole Breast Irradiation of Early Stage Breast Cancer

Purpose:The purpose of this study is to compare the dose‐volumetric results of intensity modulated radiation therapy (IMRT) with RapidArc (RA Varian Medical Systems, Palo Alto, CA) for whole breast irradiation.Methods:25 whole left breast patient's plans (either RapidArc plan or IMRT) previously treated were the subjects of this study. Eclipse v 11.0.47 was used to create the alternative plans for each case using the same CT images, contours, energy, Linac and normalization. The prescription dose to the planning target volume was 50 Gy in 25 fractions. All plans were normalized such that 100% of the dose covered 95% of planning target volume (PTV).Results:V10, V20 and Dmean Gy of left lung differ significantly between the two plans (p‐value &lt;0.0001, =0.0473 and &lt;0.0001 respectively). However, V30 Gy does not (p‐value 0.463). V25, D33 and Dmean Gy of heart differ significantly between the two plans (p‐value =0.034, &lt;0.0001 and 0.01 respectively). However V10 Gy does not (p‐value 0.058). V5 of both right breast and right lung differs significantly between the two plans (p‐value &lt;0.0007 and =0.0112, respectively). Dmean of both right breast and right lung differs significantly between the two plans (p‐value &lt;0.0001 for both). The mean conformity index did not differ significantly, p‐value 0.142. There was a significant difference between the mean MUs of the two plans as well, p‐value &lt;0.0001.Conclusion:Mean doses to left lung, heart, right lung and right breast were significantly different in RapidArc than IMRT plans. IMRT treatment delivery was faster than RapidArc in terms of the total monitor units used (mean of 382 vs 707 respectively). In fact, since it was observed that both plans have the same mean of conformity index, IMRT is not only faster but also safer regarding not irradiating the organs at risk.

Impact of dose rate on accuracy of intensity modulated radiation therapy plan delivery using the pretreatment portal dosimetry quality assurance and setting up the workflow at hospital levels.

The aim of this study was to examine the impact of dose rate on accuracy of intensity modulated radiation therapy (IMRT) plan delivery by comparing the gamma agreement between the calculated and measured portal doses by pretreatment quality assurance (QA) using electronic portal imaging device dosimetry and creating a workflow for the pretreatment IMRT QA at hospital levels. As the improvement in gamma agreement leads to increase in the quality of IMRT treatment delivery, gamma evaluation was carried out for the calculated and the measured portal images for the criteria of 3% dose difference and 3 mm distance-to-agreement (DTA). Three gamma parameters: Maximum gamma, average gamma, and percentage of the field area with a gamma value>1.0 were analyzed. Three gamma index parameters were evaluated for 40 IMRT plans (315 IMRT fields) which were calculated for 400 monitor units (MU)/min dose rate and maximum multileaf collimator (MLC) speed of 2.5 cm/s. Gamma parameters for all 315 fields are within acceptable limits set at our center. Further, to improve the gamma results, we set an action level for this study using the mean and standard deviation (SD) values from the 315 fields studied. Forty out of 315 IMRT fields showed low gamma agreement (gamma parameters>2 SD as per action level of the study). The parameters were recalculated and reanalyzed for the dose rates of 300, 400 and 500 MU/min. Lowering the dose rate helped in getting an enhanced gamma agreement between the calculated and measured portal doses of complicated fields. This may be attributed to the less complex motion of MLC over time and the MU of the field/segment. An IMRT QA work flow was prepared which will help in improving the quality of IMRT delivery.

American College of Radiology (ACR) and American Society for Radiation Oncology (ASTRO) Practice Guideline for Intensity-modulated Radiation Therapy (IMRT)

Intensity-modulated radiation therapy (IMRT) is a complex technique for the delivery of radiation therapy preferentially to target structures while minimizing doses to adjacent normal critical structures. It is widely utilized in the treatment of a variety of clinical indications in radiation oncology, including tumors of the central nervous system, head and neck, breast, prostate, gastrointestinal tract, and gynecologic organs, as well as in situations where previous radiation therapy has been delivered, and has allowed for significant therapeutic advances in many clinical areas. IMRT treatment planning and delivery is a complex process. Safe and reliable delivery of IMRT requires appropriate process design and adherence to quality assurance (QA) standards. A collaborative effort of the American College of Radiology and American Society for Therapeutic Radiation Oncology has produced a practice guideline for IMRT. The guideline defines the qualifications and responsibilities of all the involved personnel, including the radiation oncologist, physicist, dosimetrist, and radiation therapist. Factors with respect to the QA of the treatment planning system, treatment-planning process, and treatment-delivery process are discussed, as are issues related to the utilization of volumetric modulated arc therapy. Patient-specific QA procedures are presented. Successful IMRT programs involve integration of many processes: patient selection, patient positioning/immobilization, target definition, treatment plan development, and accurate treatment delivery. Appropriate QA procedures, including patient-specific QA procedures, are essential to ensure quality in an IMRT program and to assure patient safety.

Quantifying the Trade-off Between IMRT Treatment Plan Quality and Delivery Efficiency Using Direct Aperture Optimization

Beam-on time is an important measure of the delivery efficiency in intensity-modulated radiation therapy (IMRT). Traditionally, minimizing beam-on time has been postponed until the leaf sequencing stage, where the treatment plan quality is already determined and fixed. However, there is a trade-off between the beam-on time and the treatment plan quality. The aim of this study is to incorporate the beam-on time into the treatment plan optimization stage using a direct aperture optimization approach that allows for explicitly quantifying the trade-off. The proposed approach can provide clinicians with valuable information for each patient case so that they can design clinically attractive yet efficient treatment plans. Using the special structure of the problem, we propose an exact solution approach that sequentially characterizes segments of the Pareto-efficient frontier. In addition, an approximate solution technique that is applicable to more classes of evaluation criteria is developed. Our approximate technique is tested on clinical cancer cases, and its performance is compared with the general approximation techniques that are available for convex bicriteria optimization problems. The results of our experiments validate that our approach can achieve a more accurate representation of the Pareto-efficient frontier with less computational effort.

TU-F-BRCD-01: Tolerance Levels and Methodologies for IMRT Verification QA.

1. To discuss commonly employed IMRT measurement methods and discuss the pros and cons of each method. 2. To review methodologies for absolute dose verification (single small-volume, 1D, 2D methods), and review dose-difference, DTA, and Gamma analysis techniques including the variability of vendors implementation 3. To review IMRT QA passing rates for given tolerances and action levels, and discuss the clinical relevance of failed IMRT QA.

Multi-center Intensity Modulated Radiotherapy Quality Assurance Program for the Province of Ontario, Canada

Multi-center Intensity Modulated Radiotherapy Quality Assurance Program for the Province of Ontario, Canada

COMPARISON OF IMRT DELIVERY TECHNIQUES AND HELICAL TOMOTHERAPY USING PARETO FRONT EVALUATION

Purpose: The purpose of this work was to explore the possibility to compare treatment-planning- and treatment-delivery systems for intensity modulated radiation therapy (IMRT) using an objective approach. The approach investigated was the Pareto front concept. An additional aim was to adequately compare three different IMRT treatment planning and delivery systemsMaterials and methods: In IMRT treatment planning the goal is to find an optimal compromise between organ at risk (OAR) sparing and target coverage. During the optimization process objectives are chosen for each OAR and for the planning target volume (PTV). For a Pareto optimal plan one objective cannot be improved without worsening another objective. This makes IMRT optimization suitable for Pareto front evaluation. A set of Pareto optimal plans form a Pareto front. By using Pareto front evaluation the influence of individual plans is suppressed and the whole range of plans with the chosen objectives can be evaluated at the same time. Pareto fronts from different treatment planning systems (TPSs) are expected to differ from each other. In this study, different head and neck cases were used. Several plans with varying importance concerning the sparing of a specific OAR were created for each case using different TPSs. The importance of the PTV coverage was held constant for all plans. The TPSs used in the study were Oncentra Masterplan (OMP) (Nucletron B.V.), Eclipse (Varian Medical Systems) and TomoTherapy (Tomotherapy inc.) planning system. A Pareto front was obtained for each TPS by plotting the average OAR dose as a function of underdosed volume of the PTV. The underdosed volume was defined as the relative volume that receives less than 95% of the prescribed dose. Each plan fulfilled the dose restrictions for OARs according to the clinical protocol used apart from the OAR chosen for the trade-off.Results: The TomoTherapy Pareto front is situated below both the OMP front and the Eclipse front indicating that for the same target coverage, the sparing of the parotid is always favourable for this technology. For low priority OAR sparing, however, the Eclipse and the TomoTherapy fronts exhibit almost equal target coverage. As the importance of the OAR increases the target coverage decreases faster for the Eclipse front compared to the TomoTherapy front and is approaching the same coverage as OMP.Conclusion: The results clearly indicate that the approach of using Pareto fronts for different systems is a feasible way to compare different methods and technologies for advanced radiotherapy. For the particular cases studied, TomoTherapy seems to be superior to OMP and Eclipse regarding target coverage and sparing of the parotid gland.

An Analysis of Intrafraction Prostate Motion in the Prone vs. Supine Treatment Positions for Intensity-Modulated Radiation Therapy

To analyze prostate intrafraction motion in the prone vs. supine treatment positions for intensity-modulated radiation therapy (IMRT). Between December 2007 and March 2008, 15 consecutive prostate cancer patients underwent implantation of 5 fiducial gold seeds in their prostate. Patients were subsequently treated with high dose-rate brachytherapy to 22.0 Gy in 4 fractions followed by IMRT to 50.4 Gy in 28 fractions. Patients were immobilized using a Styrofoam wedge and a Velcro strap. Patients underwent CT simulation and IMRT in the prone position. For the first 5 IMRT treatments, a gantry-mounted digital kilovoltage imaging system was used to acquire anterior-posterior (AP) and lateral localization images pre and post treatment. Immediately following treatment, each patient was positioned supine. Two sets of AP and lateral images were obtained in the supine position. The first image set was taken immediately after repositioning. The second image set was acquired 11 minutes later in order to simulate the 9-field IMRT treatment delivery time, resulting in a total of 600 images. A commercially available image analysis program was used to assess prostate displacement. Mean values for the magnitude of prostate motion in the prone vs. supine position were compared using a 2-sided paired samples t test. The Pearson correlation was used to determine if the direction of prostate motion in the prone vs. supine position was consistent across patients. Patients were asked if they were more comfortable in the prone vs. supine position. Mean ± standard deviation AP intrafraction prostate motion was 2.1 ± 2.1 mm and 1.7 ± 1.4 mm in the prone and supine positions, respectively (p = 0.18). In the prone position, AP motion >2 mm occurred in 35% of treatments and AP motion >5 mm occurred in 8% of treatments. In the supine position, AP motion >2 mm occurred in 25% of cases and AP motion >5 mm occurred in 4% of cases. The largest displacement in the AP direction was 8 mm and 6 mm in the prone and supine positions, respectively. In the prone position, prostate motion was typically in the anterior direction. In contrast, in the supine position, prostate motion was typically in the posterior direction (p = 0.008). Patients usually stated that they were more comfortable in the supine position. The prone and supine positions resulted in a similar mean magnitude of intrafraction prostate motion (2 mm). Since there was no significant difference in the magnitude of prostate motion prone vs. supine and patients were more comfortable in the supine position, patients now undergo IMRT at our center in the supine position.

Investigating the Temporal Effects of Respiratory-Gated and Intensity-Modulated Radiotherapy Treatment Delivery on In Vitro Survival: An Experimental and Theoretical Study

To experimentally and theoretically investigate the temporal effects of respiratory-gated and intensity-modulated radiotherapy (IMRT) treatment delivery on in vitro survival. Experiments were designed to isolate the effects of periodic irradiation (gating), partial tumor irradiation (IMRT), and extended treatment time (gating and IMRT). V79 Chinese hamster lung fibroblast cells were irradiated to 2 Gy with four delivery methods and a clonogenic assay performed. Theoretical incomplete repair model calculations were performed using the incomplete repair model. Treatment times ranged from 1.67 min (conformal radiotherapy, CRT) to 15 min (gated IMRT). Survival fraction calculations ranged from 68.2% for CRT to 68.7% for gated IMRT. For the same treatment time (5 min), gated delivery alone and IMRT delivery alone both had a calculated survival fraction of 68.3%. The experimental values ranged from 65.7% +/- 1.0% to 67.3% +/- 1.3%, indicating no significant difference between the experimental observations and theoretical calculations. The theoretical results predicted that of the three temporal effects of radiation delivery caused by gating and IMRT, extended treatment time was the dominant effect. Care should be taken clinically to ensure that the use of gated IMRT does not significantly increase treatment times, by evaluating appropriate respiratory gating duty cycles and IMRT delivery complexity.

Prostate intrafraction motion evaluation using kV fluoroscopy during treatment delivery: A feasibility and accuracy study

Margin reduction for prostate radiotherapy is limited by uncertainty in prostate localization during treatment. We investigated the feasibility and accuracy of measuring prostate intrafraction motion using kV fluoroscopy performed simultaneously with radiotherapy. Three gold coils used for target localization were implanted into the patient's prostate gland before undergoing hypofractionated online image-guided step-and-shoot intensity modulated radiation therapy (IMRT) on an Elekta Synergy linear accelerator. At each fraction, the patient was aligned using a cone-beam computed tomography (CBCT), after which the IMRT treatment delivery and fluoroscopy were performed simultaneously. In addition, a post-treatment CBCT was acquired with the patient still on the table. To measure the intrafraction motion, we developed an algorithm to register the fluoroscopy images to a reference image derived from the post-treatment CBCT, and we estimated coil motion in three-dimensional (3D) space by combining information from registrations at different gantry angles. We also detected the MV beam turning on and off using MV scatter incident in the same fluoroscopy images, and used this information to synchronize our intrafraction evaluation with the treatment delivery. In addition, we assessed the following: the method to synchronize with treatment delivery, the dose from kV imaging, the accuracy of the localization, and the error propagated into the 3D localization from motion between fluoroscopy acquisitions. With 0.16 mAs/frame and a bowtie filter implemented, the coils could be localized with the gantry at both 0 degrees and 270 degrees with the MV beam off, and at 270 degrees with the MV beam on when multiple fluoroscopy frames were averaged. The localization in two-dimensions for phantom and patient measurements was performed with submillimeter accuracy. After backprojection into 3D the patient localization error was (-0.04 +/- 0.30) mm, (0.09 +/- 0.36)mm, and (0.03 +/- 0.68)mm in the right-left (RL), anterior-posterior (AP), and superior-inferior (SI) axes, respectively. Simulations showed that while oscillating (stationary) motion cannot be effectively represented in 3D, linearly drifting (nonstationary) motion is detectable with good accuracy. These results show that measuring prostate intrafraction motion using a single kV imager during radiotherapy is feasible and can be performed with acceptable accuracy.

Quality Assurance of Intensity-Modulated Radiation Therapy

The current paradigm for the quality assurance (QA) program for intensity-modulated radiation therapy (IMRT) includes QA of the treatment planning system, QA of the delivery system, and patient-specific QA. Although the IMRT treatment planning and delivery system is the same as for conventional three-dimensional conformal radiation therapy, it has more parameters to coordinate and verify. Because of complex beam intensity modulation, each IMRT field often includes many small irregular off-axis fields, resulting in isodose distributions for each IMRT plan that are more conformal than those from conventional treatment plans. Therefore, these features impose a new and more stringent set of QA requirements for IMRT planning and delivery. The generic test procedures to validate dose calculation and delivery accuracy for both treatment planning and IMRT delivery have to be customized for each type of IMRT planning and delivery strategy. The rationale for such an approach is that the overall accuracy of IMRT delivery is incumbent on the piecewise uncertainties in both the planning and delivery processes. The end user must have well-defined evaluation criteria for each element of the planning and delivery process. Such information can potentially be used to determine a priori the accuracy of IMRT planning and delivery.

1007: Six Year Institutional Review of Clinical Treatment Delivery Efficiency for Intensity-Modulated Radiation Therapy (IMRT)

Introduction of new technology such as IMRT typically results in more manpower and time requirements for the clinical staff. Further, IMRT treatments take more time to deliver than their conventional counterparts due to their increased complexity. We have previously described the learning curve associated with IGRT. This study describes measurements of implementation and efficiency using our IMRT delivery systems within the clinic over the past six years. Custom software was developed (IMRTAnalyzer) to mine the record-and-verify (R&V) database and automatically perform a chart review on our IMRT patients. Over the past six years, our institution has implemented IMRT on eight linear accelerators. IMRTAnalyzer software extracted 1,700 IMRT patients (> 36,000 treatment fractions) treated from 2000-2005. The software calculated the clinical treatment times (excluding patient immobilization and localization times) for these IMRT patients and categorized by disease site. The analysis software used the timestamps in the R&V database for treatment field history to calculate the time the patient was on the treatment table for actual treatment and portal images. The measurements were normalized for number of treatment fields per plan and dose rates per treatment field. Data shown in figure 1 reveal an improvement in clinical treatment times from 2000 to 2005 after normalizing for the number of treatment fields per plan. Over this time period, head-and-neck (H&N) and prostate cancer patients’ average IMRT treatment time per field decreased by ∼ 45% (97 sec to 44 sec) and ∼ 50% (85 sec to 43 sec), respectively. The improvements in efficiency can partly be attributed to enhancements in the software and hardware upgrades to the treatment console. One R&V software upgrade which improved the user interface for the treatment console resulted in a 10-15% improvement in IMRT treatment times over the subsequent few months. Using the IMRTAnalyzer software, the automated chart review required ∼ 3 hours mining and extracting the data. A comparable chart review by a clinician (30 minutes per chart review) would require > 850 hours (∼21 work weeks) to perform. This study quantifies the clinical efficiency of IMRT treatment delivery as it evolved over a six year period at our institution. R&V software and delivery hardware enhancements have resulted in lower IMRT treatment times which improve the overall IMRT efficiency process and increase patient throughput.

Impact of geometric uncertainties on dose distribution during intensity modulated radiotherapy of head-and-neck cancer: the need for a planning target volume and a planning organ-at-risk volume.

We assessed the effect of geometric uncertainties on target coverage and on dose to the organs at risk (OARS) during intensity-modulated radiotherapy (IMRT) for head-and-neck cancer, and we estimated the required margins for the planning target volume (PTV) and the planning organ-at-risk volume (PRV). For eight head-and-neck cancer patients, we generated IMRT plans with localization uncertainty margins of 0 mm, 2.5 mm, and 5.0 mm. The beam intensities were then applied on repeat computed tomography (CT) scans obtained weekly during treatment, and dose distributions were recalculated.The dose-volume histogram analysis for the repeat ct scans showed that target coverage was adequate (V(100) >/= 95%) for only 12.5% of the gross tumour volumes, 54.3% of the upper-neck clinical target volumes (CTVS), and 27.4% of the lower-neck CTVS when no margins were added for PTV. The use of 2.5-mm and 5.0-mm margins significantly improved target coverage, but the mean dose to the contralateral parotid increased from 25.9 Gy to 29.2 Gy. Maximum dose to the spinal cord was above limit in 57.7%, 34.6%, and 15.4% of cases when 0-mm, 2.5-mm, and 5.0-mm margins (respectively) were used for prv.Significant deviations from the prescribed dose can occur during IMRT treatment delivery for head-and-neck cancer. The use of 2.5-mm to 5.0-mm margins for PTV and PRV greatly reduces the risk of underdosing targets and of overdosing the spinal cord.

Impact of Geometric Uncertainties on Dose Distribution During Intensity Modulated Radiotherapy of Head-and-neck Cancer: The Need for a Planning Target Volume and A Planning Organ-at-Risk Volume

We assessed the effect of geometric uncertainties on target coverage and on dose to the organs at risk (OARS) during intensity-modulated radiotherapy (IMRT) for head-and-neck cancer, and we estimated the required margins for the planning target volume (PTV) and the planning organ-at-risk volume (PRV). For eight headand- neck cancer patients, we generated IMRT plans with localization uncertainty margins of 0 mm, 2.5 mm, and 5.0 mm. The beam intensities were then applied on repeat computed tomography (CT) scans obtained weekly during treatment, and dose distributions were recalculated. The dose–volume histogram analysis for the repeat CT scans showed that target coverage was adequate (V100 ≥ 95%) for only 12.5% of the gross tumour volumes, 54.3% of the upper-neck clinical target volumes (CTVS), and 27.4% of the lower-neck CTVS when no margins were added for PTV. The use of 2.5-mm and 5.0-mm margins significantly improved target coverage, but the mean dose to the contralateral parotid increased from 25.9 Gy to 29.2 Gy. Maximum dose to the spinal cord was above limit in 57.7%, 34.6%, and 15.4% of cases when 0-mm, 2.5-mm, and 5.0-mm margins (respectively) were used for PRV. Significant deviations from the prescribed dose can occur during IMRT treatment delivery for headand- neck cancer. The use of 2.5-mm to 5.0-mm margins for PTV and PRV greatly reduces the risk of underdosing targets and of overdosing the spinal cord.

The Dosimetric Impact of Respiration Motion on 3D, IMRT, and Tomotherapy Treatment Delivery

Purpose/Objective: The accuracy of delivered dose distributions in patients is sensitive to respiration motion during treatment delivery. First and foremost, motion during treatment delivery blurs the edges of the delivered dose distribution. For intensity modulated radiation therapy (IMRT), there is an additional error that arises from the interplay between the motion of the target and the motion of the multileaf collimator sequence. This error could potentially be larger in helical tomotherapy treatment delivery where the treatment is delivered slice-by-slice.

A clinical application of an automated phantom-film QA procedure for validation of IMRT treatment planning and delivery

To quantify the correlation between planned and delivered intensity-modulated radiation therapy (IMRT) dose distributions, IMRT plans for 37 prostate carcinoma patients were analyzed. IMRT treatment plans were converted into hybrid phantom plans using a commercially available treatment planning system and delivered to a specialized film phantom via a static-tomotherapy technique. The films were analyzed using a commercial film dosimetry system. Hybrid phantom axial dose maps and film images were normalized, registered to one another, and subtracted to calculate the overall relative dose difference throughout the entire film area on a pixel-by-pixel basis. The average percentage of pixels with dose-difference values greater than ± 3% among analyzed hybrid patient plans was 8.6% ± 3%. The average percentage of pixels with dose differences greater than ± 5% was 1.7% ± 1.0%. The number of pixels with more than ± 10% dose differences was negligible. An initial subset of hybrid plans was used to develop a quantitative criterion to verify for positional accuracy based on dosimetric verification of intensity map of IMRT plans for prostate patients in our institution. Plans with less than 5% of the pixels outside the ± 5% dose-difference range were accepted. This method could be implemented for other anatomical sites or treatment planning and delivery systems. © 2003 American Association of Medical Dosimetrists.

SIFT: a method to verify the IMRT fluence delivered during patient treatment using an electronic portal imaging device.

Radiotherapy patients are increasingly treated with intensity-modulated radiotherapy (IMRT) and high tumor doses. As part of our quality control program to ensure accurate dose delivery, a new method was investigated that enables the verification of the IMRT fluence delivered during patient treatment using an electronic portal imaging device (EPID), irrespective of changes in patient geometry. Each IMRT treatment field is split into a static field and a modulated field, which are delivered in sequence. Images are acquired for both fields using an EPID. The portal dose image obtained for the static field is used to determine changes in patient geometry between the planning CT scan and the time of treatment delivery. With knowledge of these changes, the delivered IMRT fluence can be verified using the portal dose image of the modulated field. This method, called split IMRT field technique (SIFT), was validated first for several phantom geometries, followed by clinical implementation for a number of patients treated with IMRT. The split IMRT field technique allows for an accurate verification of the delivered IMRT fluence (generally within 1% [standard deviation]), even if large interfraction changes in patient geometry occur. For interfraction radiological path length changes of 10 cm, deliberately introduced errors in the delivered fluence could still be detected to within 1% accuracy. Application of SIFT requires only a minor increase in treatment time relative to the standard IMRT delivery. A new technique to verify the delivered IMRT fluence from EPID images, which is independent of changes in the patient geometry, has been developed. SIFT has been clinically implemented for daily verification of IMRT treatment delivery.