Patient Immobilization Devices Research Articles

MRgFUS ablation of a recurrent tenosynovial giant cell tumor in the foot using ExAblate 2100 system in combination with patient immobilization device

IntroductionMagnetic Resonance–guided Focused Ultrasound (MRgFUS) treatment for certain anatomy locations can be extremely challenging due to patient positioning and potential motion. This present study describes the treatment of a recurrent tenosynovial giant cell tumor of the plantar forefoot using the ExAblate 2100 system in combination with patient immobilization device. MethodsPrior to the treatment, several patient immobilization devices were investigated. Vacuum cushions were selected and tested for safety and compatibility with the treatment task and the MR environment. ResultsDuring the treatment, one vacuum cushion immobilized the patient's right leg in knee flexion and allowed the bottom of the foot to be securely positioned on the treatment window. Another vacuum cushion supported the patient upper body extended outside the scanner bore. 19 sonications were successfully executed. The treatment was judged to be successful. No immediate complications were observed. ConclusionsMRgFUS treatment of a recurrent tenosynovial giant cell tumor of the right plantar forefoot was successful with the use of patient immobilization vacuum cushions. Implications for practiceThe immobilization system could be utilized to aid future MRgFUS treatment of lesions in challenging anatomic locations. Various sizes of the vacuum cushions are available to potentially better accommodate other body parts and treatment configurations.

Effectiveness of the barcode certification system in preventing incorrect use of patient immobilization device in radiotherapy

The present study showed that using a barcode system could reduce the improper use of immobilization devices in patient positioning, by reviewing the incident/accident (IA) reports before and after the introduction of the barcode system. A barcode system is an effective tool to eliminate human error, which is essential for patient safety. In our institution, approximately 1700 patients were treated using external irradiation. We introduced a barcode system for patient immobilization devices used in external irradiation of radiation therapy. Radiation therapy cannot be performed until each immobilization device is authenticated by a barcode. The IA reports from 2010 to 2019, before and after the barcode system was introduced, were compared. During this period of time, 271 IA reports were submitted from our department, of which 16 reports concerned with patient setup. Analysis was performed using R, comparing the IA report before and after the barcode system was introduced. The number of the IA reports concerning patient positioning and immobilization decreased from 12 to 4 after the barcode system was introduced. We have also investigated the time efficiency of barcode certification system. The average treatment time per patient was 7 min both before and after the barcode certification was introduced, showing no significant change in time efficiency. In conclusion, an authentication system of patient’s individual therapeutic devices using barcode is a necessary tool to avoid the improper use of immobilization devices, misplacement of bolus, and improper couch shape.

Clinical experience in the use of 3D printing as a rapid replacement of traditional radiation therapy immobilization materials.

Patient positioning and immobilization devices are commonly employed in radiation therapy. Unfortunately, cases can arise where the devices need to be reconstructed or improved. This work describes clinical processes to use a planning CT, to design and 3D print immobilization devices for reproducible patient positioning within a clinically feasible time frame when traditional methods can no longer be used or are insufficient. Three clinical cases required rapid 3D printing of an immobilization device mid-treatment due to the following: (1) a lost headrest cushion, (2) needed improvement in lumbar spine positioning, and (3) a partially deflated vacuum immobilization mattress. In the three cases, the 3D printed immobilization devices were clinically implemented successfully; two of the devices were fully designed and printed in 1 day. The 3D printed immobilization devices achieved a positioning accuracy sufficient to avoid the necessity to repeat the simulation and planning process. If traditional immobilization devices fail or are misplaced, it is feasible to have a 3D printed replacement within the time span of 1 day. The design and fabrication methods, as well as the experiences gained, are described in detail to assist clinicians to implement 3D printing for similar situations.

A Feasibility Study of LiDAR-Enhanced Augmented Reality on a Handheld Device for Collision Detection and Patient Positioning

<h3>Purpose/Objective(s)</h3> This study investigates the feasibility of using a commercially available handheld device with augmented reality (AR) cameras, enhanced by light detection and ranging (LiDAR), for pre-treatment collision detection and patient positioning. The on-device LiDAR scanner detects object depths with direct time-of-flight (ToF) measurements, thus improving the accuracy of contrast-based visual depth estimation. Our proposed approach leverages AR for near-real-time reconstruction of patient external contour during simulation and setup. This is advantageous compared with conventional laser-tattoo alignment and photo-based patient position, by providing an intuitive 3D rendering of the patient's body and immobilization devices at arbitrary angles. <h3>Materials/Methods</h3> Two possible modes for AR-assisted positioning were investigated: mesh and point-cloud mode. In mesh mode, surface mesh of a mock pediatric phantom (50 × 40 × 15 cm³) was rapidly reconstructed via the default meshing algorithm from the software development kit (SDK). Resulting 3D contours were manually registered to a computerized tomography (CT) scan of the phantom in a third-party open source image processing suite. For point cloud mode, surface anchor points of the phantom and its supporting devices were detected and placed in the real-world frame of reference, which were subsequently overlaid on the real-time color image. Each handheld scanning session was kept at 30 seconds. The native pulse intervals of 0.2 – 0.5 nsec of the LiDAR scanner were used; depth map was updated at 60 frames per second (fps). Scanning method was kept consistent and mimicked CT scans, with the device camera rotated about the superior-inferior axis pointing towards the phantom. The resolution of the resulting surface mesh and point cloud was quantified. Extent of the volume reconstructed was estimated. <h3>Results</h3> The scan and on-device real-time reconstruction were completed within 30 seconds. We successfully extracted the reconstructed mesh and registered that to a CT scan of the phantom. A mean distance of 1.5 ± 1.0 cm between each adjacent vertex was achieved. The point cloud density was on an average 20.9 ± 0.9 points/cm², with decreased point density 35cm superior to the phantom midpoint (10.0 points/cm²). Both modes captured approximately 4 × 4 × 4m³ volume of the phantom and its supporting structures. <h3>Conclusion</h3> AR has emerged as a promising modality for surface guided patient positioning, yet several previous studies have found a lack of sufficient mesh resolution and/or accuracy. LiDAR improves both aspects with directly measured depth information. We demonstrated that sub-cm full 3D rendering of the patient body contour and supporting device is achievable with a handheld device in under 30 seconds, which could provide a viable option for improved guidance on collision check and patient positioning.

Challenges of Irradiation on Extrathoracic and Non-thoracic Organs in Portable Neonatal Chest Radiography: Do We Need Mandatory Protective Rules?

Background: Chest X-ray (CXR) is known as the most common radiography used for adult and pediatric patients worldwide. Improper X-ray field collimation can result in excessive radiation dose on non-thoracic organs in chest radiographs. Objectives: This study was to investigate X-ray field collimation quality in neonatal chest radiography. Methods: A total of 213 chest radiographs of neonates from three hospitals were analyzed for collimation quality assessment in a retrospective study. Accordingly, ideal imaging field (IIF) and current imaging field (CIF) were initially defined. The margins of the IIF included acromioclavicular (AC) level to lower costal margin (i.e. top to bottom) and one centimeter beyond the broadest area of the chest on each side (that is, right to left). The CIF size was also defined as the square borders of collimators. Results: The findings revealed that the area of the CIF was 1.65 ± 0.39 times to the ideal imaging firlddd (IIF) for three hospitals, suggesting that collimation quality in neonatal chest radiographs was not accurate and it had defects. According to the results, acceptable collimation percentage (36.6%) in Hospital A was more than that in two other centers, and the given center also provided the lowest radiation due to the exposure of non-thoracic structures to primary beams. Conclusions: It was concluded that training radiographers and using patient immobilization devices and stabilizers were important points that could reduce radiation exposure to non-thoracic organs in pediatric CXR.

4DMRI-based analysis of inter— and intrafractional pancreas motion and deformation with different immobilization devices

Time-resolved magnetic resonance imaging (4DMRI) provides spatial motion information with high soft-tissue contrast. This study exploits the potential of 4DMRI by investigation of inter- and intrafractional pancreas motion and deformation with different patient immobilization devices. In total, 150 4DMRI scans were acquired for a cohort of 5 volunteers, each was scanned in 10 imaging sessions using three different positioning modes (flat table top (FTT), vacuum bag (VB), abdominal corset (AC)), respectively, to simulate repeated 4DMR imaging sessions of patients during fractionated radiotherapy. Large pancreatic motion variations were observed throughout the volunteers with mean inferior-superior (IS) motion amplitudes up to 28.5/21.9 mm for FTT/VB measurements, which were reduced by 48%/34%, respectively, by using abdominal corsets. Small IS motion reductions were present for vacuum bag measurements, compared to flat table top measurements. Corset measurements additionally showed an improved motion reproducibility between different days by more than 60% compared to FTT and VB. In anterior-posterior direction, motion amplitudes were reduced by 69%/60% for corset measurement, compared to FTT/VB, and their day-to-day fluctuations were reduced by approximately 130%. With respect to respiration-induced pancreas deformations, the pancreas showed the lowest deformation and highest reproducibility for corset measurements in 4 out of 5 volunteers. Moreover, both, the VB and AC setup showed a generally improved setup reproducibility compared to the non-immobilized flat table top setting. All in all, in this study, abdominal corsets showed to reduce both pancreatic motion and deformations. Moreover, by using corsets it is possible to improve the reproducibility of both pancreatic motion and deformation, which are important factors in radiotherapy treatments. Therefore, radiotherapy treatments of pancreatic cancer patients with abdominal corsets may be a viable option for patients with large internal organ motion amplitudes and may lead to a better consistency of the treatment planning and delivery situation.

Combifix or Vacloc Bags, Which One Is Better for Prostate Patient Setup and Immobilization?

Compared to traditional used VacLoc bags, Combifix is a new patient setup and immobilization device for pelvic region treatment. It has adjustable kneefix and feetfix cushions. This study is to evaluate and compare these two device performance by analyzing patient pre-treatment setup and post-treatment radiographs from prostate patients treated with proton. Total 22 prostate patients were selected for the study, with 11 using Combifix and 11 using VacLoc bags for patient immobilization and setup. Pre-treatment setup radiographs and post-treatment radiographs were obtained to evaluate the setup residual errors and prostate intrafraction motion errors for both cohorts of patients. The systematic and random components of the residual errors and intrafraction motion errors were calculated and compared. Therapists were interviewed about their experiences using Combifix. For Combifix patients, the setup residual systematic errors are 0.02, 0.03 and 0.02cm in lateral (LR), longitudinal (SI) and Vertical (AP) directions, respectively. The residual random errors are 0.05, 0.07 and 0.07cm in LR, SI and AP directions, respectively. For VacLoc patients, the setup residual systematic errors are 0.0, 0.01 and 0.01cm in LR, SI and AP directions, respectively. The residual random errors are 0.02, 0.04 and 0.04cm in LR, SI and AP directions, respectively. The intrafraction motion errors are slightly larger than residual errors. For Combifix patients, the setup residual systematic errors are 0.04, 0.07 and 0.05cm in LR, SI and AP directions, respectively. The residual random errors are 0.08, 0.15 and 0.15cm in LR, SI and AP directions, respectively. For VacLoc patients, the setup residual systematic errors are 0.02, 0.05 and 0.05cm in LR, SI and AP directions, respectively. The residual random errors are 0.05, 0.12 and 0.11cm in LR, SI and AP directions, respectively. Therapists observed that there were less rotation errors but slightly more pitching errors at the beginning of patient setup. But after 1 or 2 corrections, the residual errors are very similar between the two immobilization devices. However, if multiple consecutive patients treated with Combifix device, it improves clinical flow. The error analyses of the patient initial setup and intrafraction motion showed that similar characteristics between the two patient immobilization devices. Nevertheless, improved clinical flow can be achieved by treating consecutive patients with Combifix devices.

A framework for clinical commissioning of 3D-printed patient support or immobilization devices in photon radiotherapy.

PurposeThe objective of this work is to outline a framework for dosimetric characterization that will comprehensively detail the clinical commissioning steps for 3D‐printed materials applied as patient support or immobilization devices in photon radiotherapy. The complex nature of 3D‐printed materials with application to patient‐specific configurations requires careful consideration. The framework presented is generalizable to any 3D‐printed object where the infill and shell combinations are unknown.MethodsA representative cylinder and wedge were used as test objects to characterize devices that may be printed of unknown, patient‐specific dimensions. A case study of a 3D‐printed CSI immobilization board was presented as an example of an object of known, but adaptable dimensions and proprietary material composition. A series of measurements were performed to characterize the material's kV radiologic properties, MV attenuation measurements and calculations, energy spectrum water equivalency, and surface dose measurements. These measurements complement the recommendations of the AAPM's TG176 to characterize the additional complexity of 3D‐printed materials for use in a clinical radiotherapy environment.ResultsThe dosimetric characterization of 3D‐printed test objects and a case study device informed the development of a step‐by‐step template that can easily be followed by clinicians to accurately and safely utilize 3D‐printed materials as patient‐specific support or immobilization devices.ConclusionsA series of steps is outlined to provide a formulaic approach to clinically commission 3D‐printed materials that may possess varying material composition, infill patterns, and patient‐specific dimensions.

Comparison of Interfractional Setup Reproducibility between Two Types of Patient Immobilization Devices in Image-Guided Radiation Therapy for Prostate Cancer.

Purpose:The aim of this study is to compare the interfractional setup reproducibility of two types of patient immobilization devices for prostate cancer receiving image-guided radiation therapy (IGRT).Materials and Methods:The MOLDCARE (MC) involves hydraulic fixation, whereas the BlueBAG (BB) and Vac-Lock (VL) involve vacuum fixation. For 72 patients, each immobilization device was individually customized during computed tomography (CT) simulation. Before the treatment, bony registration was performed using orthogonal kV images and digitally reconstructed radiographs. The shift of the treatment couch was recorded as a benchmark in the first session. In subsequent sessions, the shifts from the benchmark were measured and analyzed. Soft-tissue registration was performed weekly by cone-beam CT and CT images, and the shifts were measured and analyzed.Results:In the superior-inferior and left-right directions, there were nearly no changes in the overall mean among the immobilization devices. In the anterior-posterior (AP) direction, the overall mean for the MC, BB, and VL were 0.34 ± 1.33, −0.47 ± 1.27, and −1.82 ± 1.65 mm, respectively. The mean shifts along the AP direction were approximately 1 mm more in patients immobilized on the BB and 2.5 mm more in those on the VL, compared to those on the MC, after the twentieth treatment. No significant changes were observed among the patients immobilized on those devices, respectively, in soft-tissue registration.Conclusion:It can be concluded that the settling of the vacuum fixation was caused by air leakage in the latter-half treatment, and the immobilization device type has no effect on the treatment-position reproducibility in IGRT.

EP-1821: Air gap between patient surface and immobilization devices: dosimetric impact on H&N IMRT plans

EP-1821: Air gap between patient surface and immobilization devices: dosimetric impact on H&N IMRT plans

Long-term outcomes of stereotactic body radiation therapy (SBRT) with fiducial tracking for inoperable stage I non-small cell lung cancer (NSCLC).

BackgroundStereotactic body radiation therapy (SBRT) for stage I non-small cell lung cancer (NSCLC) is considered standard of care in the medically inoperable patient population. Multiple methods of SBRT delivery exist including fiducial-based tumor tracking, which allows for smaller treatment margins and avoidance of patient immobilization devices. We explore the long-term clinical outcomes of this novel fiducial-based SBRT method.MethodsIn this single institutional retrospective review, we detail the outcomes of medically inoperable pathologically confirmed stage I NSCLC. Patients were treated with the Cyberknife SBRT system using a planning target volume (PTV) defined as a 5-mm expansion from gross tumor volume (GTV) without creation of an internal target volume (ITV). Dose was delivered in three or five equal fractions of 10 to 20 Gy. Pretreatment and posttreatment pulmonary function test (PFT) changes and evidence of late radiological rib fractures were analyzed for the majority of patients. Actuarial local control, locoregional control, distant control, and overall survival were calculated using the Kaplan-Meier method.ResultsSixty-one patients with a median age of 75 years were available for analysis. The majority (80 %) of patients were deemed to be medically inoperable due to underlying pulmonary dysfunction. Eleven patients (18 %) developed symptomatic pneumothoraces secondary to fiducial placement under CT guidance, which precipitously dropped to 0 % following transition to bronchoscopic fiducial placement. The 2-year rib fracture risk was 21.4 % with a median time to rib fracture of 2.9 years. PFTs averaged over all patients and parameters demonstrated small absolute declines, 5.7 % averaged PFT decline, at approximately 1 year of follow-up, but only the diffusing capacity of lung for carbon monoxide (DLCO) demonstrated a statistically significant decline (10.29 vs. 9.01 mL/min/mmHg, p = 0.01). Five-year local control, locoregional control, and overall survival were 87.6, 71.8, and 39.3 %, respectively.ConclusionsDespite reduced treatment margins and lack of patient immobilization, SBRT with fiducial-based tumor tracking achieves clinically comparable long-term outcomes to other linac-based SBRT approaches.

Comprehensive MRI simulation methodology using a dedicated MRI scanner in radiation oncology for external beam radiation treatment planning.

The use of magnetic resonance imaging (MRI) in radiation oncology is expanding rapidly, and more clinics are integrating MRI into their radiation therapy workflows. However, radiation therapy presents a new set of challenges and places additional constraints on MRI compared to diagnostic radiology that, if not properly addressed, can undermine the advantages MRI offers for radiation treatment planning (RTP). The authors introduce here strategies to manage several challenges of using MRI for virtual simulation in external beam RTP. A total of 810 clinical MRI simulation exams were performed using a dedicated MRI scanner for external beam RTP of brain, breast, cervix, head and neck, liver, pancreas, prostate, and sarcoma cancers. Patients were imaged in treatment position using MRI-optimal immobilization devices. Radiofrequency (RF) coil configurations and scan protocols were optimized based on RTP constraints. Off-resonance and gradient nonlinearity-induced geometric distortions were minimized or corrected prior to using images for RTP. A multidisciplinary MRI simulation guide, along with window width and level presets, was created to standardize use of MR images during RTP. A quality assurance program was implemented to maintain accuracy and repeatability of MRI simulation exams. The combination of a large bore scanner, high field strength, and circumferentially wrapped, flexible phased array RF receive coils permitted acquisition of thin slice images with high contrast-to-noise ratio (CNR) and image intensity uniformity, while simultaneously accommodating patient setup and immobilization devices. Postprocessing corrections and alternative acquisition methods were required to reduce or correct off-resonance and gradient nonlinearity induced geometric distortions. The methodology described herein contains practical strategies the authors have implemented through lessons learned performing clinical MRI simulation exams. In their experience, these strategies provide robust, high fidelity, high contrast MR images suitable for external beam RTP.

Clinical Outcomes of Patients Undergoing Radiation Therapy for Head-and-Neck Cancer During Superstorm Sandy: Definitive Management of Head-and-Neck Squamous Cell Carcinoma

Radiation therapy (RT) interruptions have been shown to compromise local control in the definitive treatment of head and neck cancer (HNC). Superstorm Sandy (SS) brought the destruction of treatment units, patient immobilization devices, as well as the loss of electrical power at our hospital, resulting in treatment interruptions. Here, we review the clinical outcomes of patients nearly one year after the start of treatment. All patients undergoing RT for HNC during SS were included. Duration of treatment interruptions were recorded for all patients. Alterations in fraction number and schedule to address breaks in an attempt to mitigate their effect on tumor control were calculated by each treating physician and recorded for all patients. Clinical status at most recent follow up was recorded. Twelve patients were actively undergoing RT for HNC during SS. Seven patients had their immobilization device destroyed and required re-simulation and re-planning. Of these, six patients were treated through weekends without breaks and 3 patients had fractions added; the median prolongation of RT course was 12 days. Five patients' immobilization devices were not destroyed, 4 of them continued RT through weekends without breaks, one received an extra fraction of RT; the median prolongation of RT course was 5 days. At a median follow up of 9.6 months, 9 patients were alive with no evidence of disease, 1 developed metastatic disease, 1 was lost to follow up and 1 patient committed suicide. Ten of eleven patients (91%) achieved a clinical complete response (cCR), 7 had cCR at the time of first imaging following RT, one patient had cCR by physical exam but committed suicide prior to imaging, and two patients had persistent FDG uptake on follow up PET-CT, which was biopsied and was negative for persistent or recurrent cancer. Nearly one year following SS, HNC patients who underwent RT have not developed a high number of early local recurrences and had an excellent cCR rate. Alterations in RT scheduling and additional fractions may have compensated for prolongation of RT course. Longer follow up is required to determine if this population will suffer higher rates of recurrence compared to historical standards.

Prevention of gross setup errors in radiotherapy with an efficient automatic patient safety system

Treatment of the wrong body part due to incorrect setup is among the leading types of errors in radiotherapy. The purpose of this paper is to report an efficient automatic patient safety system (PSS) to prevent gross setup errors. The system consists of a pair of charge‐coupled device (CCD) cameras mounted in treatment room, a single infrared reflective marker (IRRM) affixed on patient or immobilization device, and a set of in‐house developed software. Patients are CT scanned with a CT BB placed over their surface close to intended treatment site. Coordinates of the CT BB relative to treatment isocenter are used as reference for tracking. The CT BB is replaced with an IRRM before treatment starts. PSS evaluates setup accuracy by comparing real‐time IRRM position with reference position. To automate system workflow, PSS synchronizes with the record‐and‐verify (R&V) system in real time and automatically loads in reference data for patient under treatment. Special IRRMs, which can permanently stick to patient face mask or body mold throughout the course of treatment, were designed to minimize therapist's workload. Accuracy of the system was examined on an anthropomorphic phantom with a designed end‐to‐end test. Its performance was also evaluated on head and neck as well as abdominalpelvic patients using cone‐beam CT (CBCT) as standard. The PSS system achieved a seamless clinic workflow by synchronizing with the R&V system. By permanently mounting specially designed IRRMs on patient immobilization devices, therapist intervention is eliminated or minimized. Overall results showed that the PSS system has sufficient accuracy to catch gross setup errors greater than 1 cm in real time. An efficient automatic PSS with sufficient accuracy has been developed to prevent gross setup errors in radiotherapy. The system can be applied to all treatment sites for independent positioning verification. It can be an ideal complement to complex image‐guidance systems due to its advantages of continuous tracking ability, no radiation dose, and fully automated clinic workflow.PACS number: 87.55.Qr

Dose prediction accuracy of collapsed cone convolution superposition algorithm in a multi-layer inhomogenous phantom

Purpose: Dose prediction accuracy of dose calculation algorithms is important in external beam radiation therapy. This study investigated the effect of air gaps on depth dose calculations computed by collapsed cone convolution superposition (CCCS) algorithm. Methods : A computed tomography (CT) scan of inhomogenous phantom (30 × 30 × 30 cm 3 ) containing rectangular solid-water blocks and two 5 cm air gaps was used for central axis dose calculations computed by CCCS in Pinnacle treatment planning system. Depth dose measurements were taken using a cylindrical ionization chamber for identical beam parameters and monitor units as in the depth dose computations. The calculated and the measured percent depth dose (PDDs) were then compared. The data presented in this study included 6 MV photon beam and field sizes of 3 × 3 cm 2 , 5 × 5 cm 2 , 10 × 10 cm 2 , and 15 × 15 cm 2 . Results: The results of CCCS were within ±1.4% in the first water medium. However, upon traversing the first air gap and re-entering the water medium, in comparison to the measurements, the CCCS under-predicted the dose, with difference ranged from -1.6% to -3.3% for 3 × 3 cm 2 , from -2.4% to -4.2% for 5 × 5 cm 2 , from -2.4% to -6.7% for 10 × 10 cm 2 , and from -1.6% to -6.3% for 15 × 15 cm 2 . After the second air gap, the CCCS continued to under-predict the dose, and the difference ranged from -3.2% to -3.9% for 3× 3cm 2 , from -2.4% to -5.6% for 5 × 5 cm 2 , from -2.3% to -6.0% for 10 × 10 cm 2 , and from -1.5% to -5.6% for 15 × 15 cm 2 . Conclusion : The CCCS under-predicted the dose in water medium after the photon beam traversed the air gap. Special attention must be given during the patient set-up since large air gap between the patient body and immobilization devices may lead to unacceptable dose prediction errors. ---------------------------------------------- Cite this article as: Oyewale S. Dose prediction accuracy of collapsed cone convolution superposition algorithm in a multi-layer inhomogenous phantom. Int J Cancer Ther Oncol 2013; 1 (1):01016. DOI: http://dx.doi.org/10.14319/ijcto.0101.6

SU-E-T-576: Dosimetric Evaluation of Collapsed Cone Convolution (CCC) Algorithm in Predicting Dose Beyond Air Gap

Purpose: To investigate the effect of air gaps on depth dose calculations computed by collapsed cone convolution (CCC) algorithm Methods: A computed tomography scan of inhomogenous phantom (30×30×30 cm3) containing rectangular solid‐water blocks and two 5 cm air gaps was used for central axis dose calculations computed by CCC in Pinnacle treatment planning system. Central axis depth dose measurements were taken by a cylindrical ionization chamber for identical beam parameters and monitor units as in the depth dose computations. The calculated and the measured percent depth dose (PDDs) were then compared. The data presented in this study included 6 mega‐voltage (MV) X‐ray and field sizes of 3×3, 5×5, 10×10, and 15×15 cm2. Results: The results of CCC were within ±1.5% in the first water medium. However, upon traversing the first air gap and re‐entering the water medium, in comparison to the measurements, the CCC under‐predicted the dose, with difference ranged from 1.6 to 3.3% for 3×3 cm2, 2.4 to 4.2% for 5×5 cm2, 2.4 to 6.7% for 10×10 cm2, and 1.6 to 6.3% for 15×15 cm2. After the second air gap, the CCC continued to under‐predict the dose, and the difference ranged from 3.2 to 3.9% for 3×3 cm2, 2.4 to 5.6% for 5×5 cm2, 2.3 to 6.0% for 10×10 cm2, and 1.5 to 5.6% for 15×15 cm2. Conclusion: The CCC had good agreement with the measurements in the first water medium before the air gap. However, the CCC under‐predicted the dose in water‐medium after the photon beam traversed the air gap. These effects should be considered in treatment planning of lung cancer where lesion is at the center of the lung. Furthermore, special attention must be given during the patient set up since large air gaps between the patient body and immobilization devices are often encountered.

REPEATABILITY OF A PLANNING TARGET VOLUME EXPANSION PROTOCOL FOR RADIATION THERAPY OF REGIONAL LYMPH NODES IN CANINE AND FELINE PATIENTS WITH HEAD TUMORS

For canine and feline patients with head tumors, simultaneous irradiation of the primary tumor and mandibular and retropharyngeal lymph nodes (LNs) is often indicated. The purpose of this study was to assess the repeatability of a planning target volume (PTV) expansion protocol for these LNs. Two CT image sets from 44 dogs and 37 cats that underwent radiation therapy for head tumors were compared to determine LN repositioning accuracy and precision; planning-CT (for radiation therapy planning) and cone-beam CT (at the time of actual treatment sessions). Eleven percent of dogs and 65% of cats received treatment to their LNs. In dogs, the mandibular LNs were positioned more caudally (P=0.0002) and the right mandibular and right retropharyngeal LNs were positioned more to the left side of the patient (P=0.00015 and P=0.003, respectively). In cats, left mandibular LN was positioned higher (toward roof) than the planning-CT (P=0.028). In conclusion, when the patient immobilization devices and bony anatomy matching are used to align the primary head target and these LNs are treated simultaneously, an asymmetrical PTV expansion that ranges 4-9mm (dogs) and 2-4mm (cats), depending on the directions of couch movement, should be used to include the LNs within the PTV at least 95% of the time.

Patient Positioning, Immobilization Devices, and Fiducial Markers in Positron Emission Tomography-Computed Tomgraphy Scanner-Based Radiation Therapy Simulation

Positron emission tomography-computed tomography (PET-CT)-based radiation therapy (RT) treatment planning has become widely available in many RT practices. This broad acceptance has been facilitated by the RT specific features which are now commonly available on practically all modern PET-CT scanners. The quality and usability of PET-CT studies for RT treatment planning purposes strongly depends on patient positioning and immobilization during image acquisition. A well-developed clinical process and understanding of special needs for this type of imaging is crucial for successful use of PET-CT in radiation therapy planning and treatment. This article describes some of the important considerations in this process and provides several observations based on clinical experience with use of PET-CT imaging in radiation therapy planning and treatment. The use of fiducial markers in this process is also discussed.

Evaluation of two‐dimensional bolus effect of immobilization/support devices on skin doses: A radiochromic EBT film dosimetry study in phantom

In this study, the authors have quantified the two-dimensional (2D) perspective of skin dose increase using EBT film dosimetry in phantom in the presence of patient immobilization devices during conventional and IMRT treatments. For 6 MV conventional photon field, the authors evaluated and quantified the 2D bolus effect on skin doses for six different common patient immobilization/support devices, including carbon fiber grid with Mylar sheet, Orfit carbon fiber base plate, balsa wood board, Styrofoam, perforated AquaPlast sheet, and alpha-cradle. For 6 and 15 MV IMRT fields, a stack of two film layers positioned above a solid phantom was exposed at the air interface or in the presence of a patient alpha-cradle. All the films were scanned and the pixel values were converted to doses based on an established calibration curve. The authors determined the 2D skin dose distributions, isodose curves, and cross-sectional profiles at the surface layers with or without the immobilization/support device. The authors also generated and compared the dose area histograms (DAHs) and dose area products from the 2D skin dose distributions. In contrast with 20% relative dose [(RD) dose relative to dmax on central axis] at 0.0153 cm in the film layer for 6 MV 10 x 10 cm2 open field, the average RDs at the same depth in the film layer were 71%, 69%, 55%, and 57% for Orfit, balsa wood, Styrofoam, and alpha-cradle, respectively. At the same depth, the RDs were 54% under a strut and 26% between neighboring struts of a carbon fiber grid with Mylar sheet, and between 34% and 56% for stretched perforated AquaPlast sheet. In the presence of the alpha-cradle for the 6 MV (15 MV) IMRT fields, the hot spot doses at the effective measurement depths of 0.0153 and 0.0459 cm were 140% and 150%, (83% and 89%), respectively, of the isocenter dose. The enhancement factor was defined as the ratio of a given DAH parameter (minimum dose received in a given area) with and without the support device. For 6 MV conventional 10 x 10 cm2 field, the enhancement factor was the highest (3.4) for the Orfit carbon fiber plate. As for the IMRT field, the enhancement factors varied with the size of the area of interest and were as high as 3.8 (4.3) at the hot spot of 5 cm2 area in the top film layer (0.0153 cm) for 6 MV (15 MV) beams. Significant 2D bolus effect on skin dose in the presence of patient support and immobilization devices was confirmed and quantified with EBT film dosimetry. Furthermore, the EBT film has potential application for in vivo monitoring of the 2D skin dose distributions during patient treatments.

The Impact of Patient Immobilization Devices on Skin Dose during IMRT: A Radiochromic EBT Film Dosimetry Study in Phantom

The Impact of Patient Immobilization Devices on Skin Dose during IMRT: A Radiochromic EBT Film Dosimetry Study in Phantom