Asymmetric Jaws Research Articles

Characteristics of rehabilitation for patients with severe asymmetric jaw deformities resulting from temporomandibular joint pathology

Relevance. Temporomandibular joint (TMJ) pathology, along with the resultant facial asymmetry, is a common condition within maxillofacial disorders. Addressing the rehabilitation of these patients within specialised medico-social care is a crucial and challenging task.Purpose. To develop a comprehensive rehabilitation protocol for patients with severe asymmetric jaw deformities caused by TMJ pathology.Materials and methods. From 2018 to 2023, ten patients with defects and deformities of the TMJ condylar process, presenting with severe asymmetric jaw deformities, were treated. An assessment of subjective and objective facial aesthetic parameters was conducted based on photographic protocols, as well as 2D and 3D cephalometric facial measurements. Comprehensive preparation for orthognathic surgery with simultaneous endoprosthesis replacement was performed based on the collected data. A regimen of postoperative therapeutic procedures was prescribed following the surgery.Results. All patients achieved the intended statistically significant outcomes: in the sagittal plane, an improvement in facial profile was noted based on the position of the chin (Pog) relative to the true vertical line passing through the subnasale point. In the frontal plane, alignment of the occlusal plane and normalization of the central line of the upper and lower incisors relative to the midline of the face were observed.Conclusion. The algorithm for the comprehensive preparation of patients with asymmetric jaw deformities, developed during growth, prior to performing orthognathic surgery with simultaneous TMJ endoprosthesis replacement should include: orthodontic treatment aimed at aligning teeth position and dental arches, eliminating rotations and pathological inclinations of teeth using a bracket system, fully restoring interocclusal height with temporary implant-supported structures, using occlusal splints and temporary composite restorations, as well as employing separating orthodontic plates. These stages enabled the achievement of good aesthetic results and improved patients' quality of life.

The anatomy and feeding mechanism of the Japanese giant salamander (Andrias japonicus).

The fully aquatic Japanese giant salamander (Andrias japonicus) is a member of the Cryptobranchidae, and is currently distributed in western Japan, with other members of this group restricted to China and North America. Their feeding behaviour is characterized by a form of suction feeding that includes asymmetric movements of the jaw and hyobranchial apparatus. Previous studies on the North American species, Cryptobranchus alleganiensis, have suggested that this specialized jaw movement is produced by a flexible quadrate-articular joint combined with a loosely connected lower jaw symphysis including two small fibrocartilaginous pads. However, little is known about this feeding behaviour in the Asian species, nor have the three-dimensional asymmetric jaw movements been fully investigated in any member of Cryptobranchidae. In this study, we explore the asymmetric jaw movements in A. japonicus using three methods: (1) dissection of musculoskeletal structures; (2) filming of feeding behaviour to understand in which situations asymmetric feeding is used; (3) analysis of 3D movement of jaws and skull. In the third component, fresh (from frozen) specimens of A. japonicus were manipulated to replicate asymmetric and symmetric jaw movements, with the specimens CT scanned after each step to obtain the 3D morphology of the jaws at different positions. These positions were combined and their Euler angles from resting (closed) jaw position were calculated for asymmetric or symmetric jaw positions. Our filming revealed that asymmetric jaw movements are linked to the position of the prey in relation to the snout, with the jaw closest to the prey opening asymmetrically. Moreover, this action allows the salamander to simultaneously grasp prey in one side of the mouth while ejecting water on the other side, if the first suction attempt fails. The asymmetric jaw movements are performed mainly by rotation of the mandible about its long axis, with very limited lateral jaw movements. During asymmetric and symmetric jaw movements, the posterior ends of the maxilla and quadrate move slightly. The asymmetric jaw movements are permitted by a mobile quadrate-articular joint formed by wide, round cartilages, and by two small fibrocartilage pads within the jaw symphysis that act as cushions during jaw rotation. Some of these soft tissue structures leave traces on the jaws and skull, allowing feeding mode to be reconstructed in fossil taxa. Understanding cryptobranchid asymmetric jaw movement thus requires a comprehensive assessment of not only the symphysial morphology but also that of other cranial and hyobranchial elements.

Gretel

Gretel Hedgie Choi (bio) I called a friend and asked to be picked up from Home Depot, where I’d spent all afternoon pushing my cart through the gardening section, picking up whatever looked sturdy and useful. I saw a spade, which looked a lot like what I had, until now, considered a shovel, and wondered how a shovel and a spade differed in form and function. But I didn’t look for a shovel or search for images of shovels on my phone or ask anyone. I already knew what I needed to know: that the cheapest way to pay for a tomato was with money, not time and labor. I was trying to grow something else. Like intuition. Or connection—to my body, or to dirt, or the cycle of time. I found a brand of dirt called Miracle-Gro. I took this as an encouraging sign. I bought three bags of it, though I already had endless volumes of dirt in my backyard. “Please don’t think I’m having some sort of anarcho-communist phase,” I said as I pulled my bags of Miracle-Gro onto my lap. My friend’s car smelled bitter and had many stains. “What would that even mean!” she said, laughing like someone who knew all about anarcho-communism and felt a mild disdain for it. My friends knew everything; they were very informed. They wanted to change the world by being aware of the many terrible things that were happening in it. Some mornings, there would be a clear, uncontested, single most terrible thing. This signaled a reprieve that would last about a week, in which we could simply think about this single most terrible thing. But then it would fade, shockingly quickly, and other terrible things would compete, and I was often at a loss as to where to turn my attention. But I had my gardening, and I hoped this was an alternative way to do some good in the world, even while knowing nothing. The house I lived in was in a neighborhood that was, aside from my house, mostly mansions. My friend whistled. I said, “I know! It’s crazy!” as I always did when my friends, inevitably, whistled at my mansion neighborhood. I told her my place was the small one, and that rent was surprisingly affordable because the AC unit was broken, and the landlord didn’t want to deal with it—and had, in fact, threatened to kill me if I ever called about the AC unit. This was not true. I’d never met my landlord. I kept telling this story to friends who drove me home, though it never really had the effect I desired. Mostly my friends said, “That’s awful!” and “It must be very hot.” [End Page 25] I’m not really sure what effect I desired. “Oh yes,” my friend said, cutting me off. “The AC. You told me.” We pulled into the driveway. “I would invite you in, but unfortunately, because of Gretel, I can’t,” I said. “God, Gretel!” my friend said. “Gretel do anything crazy lately?” ________ Gretel was a made-up roommate I told my friends about. Gretel was horrible and rude. Gretel was the reason none of them could come inside, which I claimed was badly designed and prone to molding anyway. “My roommate is obscene!” I would say. “She has no sense of boundaries!” Every now and then I made up a new story to tell about her: “Gretel went into my room and ruined my favorite lipstick!” Or “Gretel told me my asymmetric jaw makes me look like an ugly drag queen in photographs!” Gretel was the name my mother had gone by for a short while, when my parents moved to the US from Korea to get their PhDs, but then she soon realized this was not a typical American name and reverted back to Mi-kyung. It was easy to come up with these stories about Gretel because they were true stories of what my mom had said or done. My friends would say, “Wow, Gretel is fucking crazy” or “Gretel sucks, I’m so sorry,” which I...

Fgf8 dosage regulates jaw shape and symmetry through pharyngeal-cardiac tissue relationships.

Asymmetries in craniofacial anomalies are commonly observed. In the facial skeleton, the left side is more commonly and/or severely affected than the right. Such asymmetries complicate treatment options. Mechanisms underlying variation in disease severity between individuals as well as within individuals (asymmetries) are still relatively unknown. Developmental reductions in fibroblast growth factor 8 (Fgf8) have a dosage dependent effect on jaw size, shape, and symmetry. Further, Fgf8 mutants have directionally asymmetric jaws with the left side being more affected than the right. Defects in lower jaw development begin with disruption to Meckel's cartilage, which is discontinuous. All skeletal elements associated with the proximal condensation are dysmorphic, exemplified by a malformed and misoriented malleus. At later stages, Fgf8 mutants exhibit syngnathia, which falls into two broad categories: bony fusion of the maxillary and mandibular alveolar ridges and zygomatico-mandibular fusion. All of these morphological defects exhibit both inter- and intra-specimen variation. We hypothesize that these asymmetries are linked to heart development resulting in higher levels of Fgf8 on the right side of the face, which may buffer the right side to developmental perturbations. This mouse model may facilitate future investigations of mechanisms underlying human syngnathia and facial asymmetry.

Development of a new Hybrid Virtual Source Model to simulate Elekta Synergy MLCi2 linac

Monte Carlo (MC) simulations of medical linear accelerators applying the phase space approach provide excellent results and substantially reduce execution time. This approach becomes impractical because a new complete MC simulation is needed for any new generation of linac heads. To overcome this disadvantage, the investigation exhibits an innovative hybrid Virtual Source Model (VSM) based on a theoretical reconstruction model utilizing the unchangeable parameters of linacs, taking as input the distribution of dose profiles and energy spectra weight. This VSM involves a couple of principal components, virtual source of photons and scattered particle sources from the Virtual Flattening Filter (VFF) and the asymmetric jaws. Extensive calculations and comparisons between the experimental dose distributions and the hybrid VSM are performed to evaluate VSM accuracy. The TOpas and Gate MC codes are utilized to achieve dose computational speedup and memory management optimization. For validation, several regular squared fields of varying sizes ranging from 3 × 3 to 20×20cm2 are considered, as well as two complex IMRT plans based on head&neck and pelvic treatments. Examining the VSM accuracy in the penumbra and the high dose gradient regions, applying gamma index (2%/2mm) criterion confirmed satisfactory results. A two and three dimensional γ index examination demonstrated an excellent agreement concerning the (3%/3mm) criteria for IMRT treatments. Furthermore, the speedup factor reached is 290 when applying this hybrid VSM compared to the entire simulation. Consequently, and according to the results achieved in this task, the hybrid VSM proposed is considered suitable for treatment planning systems (TPS) calculation purposes.

Installation, commissioning, and performance evaluation of Bhabhatron-II TAW – An Indian-made telecobalt unit

Aim: The aim of this study was to report commissioning and performance evaluation of Bhabhatron-II TAW (an Indian made machine). Materials and Methods: Commissioning comprises of following quality assurance (QA) (a) electrical QA, (b) mechanical QA, (c) radiation QA and (d) survey of installation. Electrical QA were done for various components of the unit for its functionality. Mechanical QA were done and the measured data were verified as per guidelines of Atomic Energy Regulatory Board (AERB), India and vendor's specified values. Cylindrical ionization chamber, electrometer, ready pack films, water phantom, thermometer and barometer were used during radiation QA and survey of installation procedures. Moreover, the data so generated were fed to treatment planning system (TPS) for dose calculation and also kept in proper tabular manner for clinical use. Results: Couch and collimator parameters were found to comply the tolerance criteria. Source strength of 172.2 roentgen per minute at 1 meter (RMM) was measured with an absolute dose rate of 225.76 cGy/min at dmax for 10cm x 10cm field size at normal treatment distance (NTD). Shutter timer error of 0.004 min was measured and incorporated in the clinical data. A maximum of 3.66 % variation was noted for 300 (15W × 20) physical wedge transmission factor between measured and vendor specified value. Radiation leakage through beam limiting device (BLD) and outside BLD were found to be within the limits prescribed by AERB. Conclusion: Commissioning is a prerequisite process after installation of a radiation therapy machine for medical purpose. Bhabhatron-II machine has several advantages over other telecobalt machine. Features like high source storage capacity of machine head, one pair of asymmetric jaw, closure of jaws to 0 cm x 0 cm during radiation emergency and presence of one motorized wedge filter makes it unique and yet cost effective telecobalt machine..

Breast telecobalt beam therapy using multi-isocentric technique.

To treat breast cancer patients in telecobalt unit with image based conformal radiotherapy planning using the multi-isocentric technique. Breast cancer is the leading cancer among all the female cancers. With improved screening techniques, many patients are being diagnosed at an early stage and the need for radiotherapy in such patients has increased. The telecobalt machine is still a preferred machine in many of the low income countries as it is cost-effective and can offer uninterrupted treatment to large number of patients. Three hundred patients requiring radiotherapy had a computed tomography based planning. Patients were immobilized using a breast board with a thermoplastic mould. Three dimensional planning was done with the multi-isocentric technique. These patients were then simulated using a Nucletron Simulix digital simulator for field verification and were treated in a Theratron Phoenix telecobalt treatment unit. The doses to the heart, ipsilateral lung and the conformity index were within the recommended values. The homogeneity index was not comparable; however, a section by section qualitative analysis was done and a final plan approved. As per the RTOG toxicity grading system, acute skin reaction grade 3 was observed in 3.6% of treatments to intact breast including nodal regions and in 3.5% of post mastectomy radiation patients. Single isocenter technique was not feasible as the telecobalt unit did not have multileaf collimators and asymmetric jaws. With improved image based planning, a multi-isocentric technique was planned. By evaluating the dose distribution, beam modifications can be made and treatments can be given with acceptable toxicity.

Pretreatment quality control of single isocenter half- beam treatment planning technique using an amorphous silicon electronic portal-imaging device (EPID)

Introduction: Electronic portal imaging devices (EPIDs) are fundamentally used for instantaneous verification of the patient set‐up, block shape, and leaf positions during radiation therapy. In radiotherapy, situations arise in which an inclined PTV must be treated mutually with adjacent nodal regions. This methodology is most widely used for matching tangential/lateral breast/head and neck fields to supraclavicular and axillary nodal fields. The single-isocenter half-beam technique (SIHB) is the commonly used technique for field matching in the three-dimensional radiation therapy (3DCRT) in which abutting fields asymmetrically with no divergence at the central axis are matched. Linear accelerator asymmetric jaw junctioning is used in single isocenter half-beam treatment planning (SIHB) technique. In practice, the major difficulty of the SIHB technique lies in creating the dose accuracy at the central axis and dose homogeneity in the abutting region of half beams with sufficient precision represents. The aim of this work was to investigate the use of amorphous silicon EPIDs for pretreatment quality control of the SIHB-based treatment plans. Materials and Methods: The zero jaw position was studied at the gantry angle of 0o. All measurements were made for 6, 10, and 15MV photon beams. The EPID used in this study was a CCD camera‐based iView EPID mounted to an Elekta synergy platform. The EPID has been calibrated to convert a grayscale EPID image into a two‐dimensional absolute dose distribution. In addition, calculations of the central field dose were performed at a fixed EPID distance of 157.5cm. The double-exposure technique and EPID was used for measuring the junction doses for each asymmetric jaw. The junction dose was obtained as a function of jaw position. Then, the EPID- based junction dose measurements were compared with radiographic film measurements of junction dose. Results: The results, obtained for 6, 10, and 15MV photon beams, showed that there was an approximately linear relationship between doses and gap or overlap. Because of the non- water equivalent EPID scattering properties, there were a different in the junction doses measured with the EPID and film. A correction factor was obtained to convert the EPID measured junction dose to film measured equivalent. Conclusions: The inaccurate abutting junction between the half beams results in under or overdose of the normal tissue between the two volumes. In the present study, we carried out a procedure for daily EPID-based quality assurance of the SIHB technique of treatment planning. The utilization of this method can be significant enough to warrant the accuracy and safety of the SIHB technique in clinical procedures. Conclusion: our study showed that the aSi EPID can be used as a transit dosimeter. The technique to reconstruct the dose delivered in the patient is straightforward, reproducible, and rapid for repeated in vivo dose verification.

Replacing routine film-based linac QC tests with EPID measurements: a method to reduce the time required for machine-specific QC

Increasingly complex radiotherapy techniques require additional machine-specific quality control (QC). The extra time required for such tests is in addition to existing, well-established QC required for standard linac deliveries. Additional time for QC can be in direct conflict with current cost saving driven practice and patient scheduling. One approach to create additional time for machine specific QC is to review current processes and the frequencies of well-established QC tests. In this work, the potential to transfer radiation field size, asymmetric jaw alignment, multi-leaf collimator (MLC) transmission and MLC rotation tests from film analysis to analysis of digital EPID images was investigated. In-house software was developed in MATLAB® and commissioned for each test by comparison to film. Following commissioning, EPID analysis was introduced into routine use and the results and trends for these tests from 10 Varian linacs were analysed over 5 yr. Radiation field size measurements were found to be smaller than film due to the steeper penumbra in EPID profiles. This effect was field size dependent. By correcting for this, EPID and film measurements agreed within 0.0 ± 0.5 mm (mean ± 1SD), with drifts of ≤0.3 mm yr−1 in field size measurements. The EPID profile response also results in overestimation of asymmetric jaw alignment measurements, which when accounted for permitted the junction gap to be maintained within ±2 mm. Junction gap was found to drift at <0.15 mm yr−1. EPID assessment of MLC transmission and MLC rotation were also achievable and maintained within tolerance with trend analysis verifying current recommendations for annual assessment. Overall, a shift from film to EPID analysis for radiation field size, asymmetric jaw alignment, MLC transmission and MLC rotation tests saved 9.5 h machine time and 6.7 h subsequent analysis time annually per linac. This will be further increased as trend analysis over 5 yr has indicated the potential to reduce the frequency of some tests.

A Quality Assurance Approach for Linear Accelerator Mechanical Isocenters with Portal Images

Purpose: With usually a millimeter-level PTV margin, stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) pose a stringent requirement on the isocentricity of the Linac. This requirement is partly fulfilled by routine isocenter quality assurance (QA) test to verify the size and location of the isocenter. The current common QA methods such as spoke shot were developed before SBRT/SRS became popular and when IGRT was largely absent and hence have their limitations. In this work, we describe an isocenter QA approach based on portal imaging to provide the community with a superior alternative. Methods: The proposed approach utilizes a BrainLab ball bearing (BB) phantom in conjunction with an electronic portal imaging devices (EPID) imager. The BB phantom was first aligned with a calibrated room laser system. Portal images were then acquired using 6 MV beam with a 2 × 2 cm2 open field and a 15 mm cone on a Varian TrueBeam STx machine. The gantry, collimator, and table were rotated separately at selected angles to acquire a series of portal images in order to determine the isocenter of each rotating system. The location and diameter of these isocenters were determined by calculating the relative displacement of either BB or open field edge between the acquired EPID images. The demonstration of the reproducibility and robustness of this EPID-based approach was carried out by repeating measurements 10 times independently for each rotating system and simulating clinical scenarios of asymmetric jaws and misalignment of BB phantom, respectively. Results: For our TrueBeam STx machine, the isocenter diameter derived from open-field EPID images was roughly 0.15 mm, 0.18 mm, 0.49 mm for the collimator, table, and gantry, respectively. For the collimator and gantry, images taken with the cone gave considerably smaller isocenter diameter. Results remained almost unchanged despite the presence of simulated BB misalignment and asymmetric jaws error, and between independent measurements. Isocenter location and diameter derived from images obtained at a limited number of angles (≤11) were adequately accurate to represent those derived from images of densely sampled angles. Conclusions: An EPID-based isocenter QA approach is described and demonstrated to be accurate, robust, and reproducible. This approach provides a superior alternative to conventional isocenter QA methods with no additional cost. It can be implemented with convenience for any linear accelerator with an EPID imager.

Specialized movement and laterality of fin-biting behaviour in Genyochoromis mento in Lake Malawi.

Several vertebrates, including fish, exhibit behavioural laterality and associated morphological asymmetry. Laterality may increase individual fitness as well as foraging strength, accuracy and speed. However, little is known about which behaviours are affected by laterality or what fish species exhibit obvious laterality. Previous research on the predatory behaviour of the scale-eating Lake Tanganyika cichlid Perissodus microlepis indicates behavioural laterality that reflects asymmetric jaw morphology. The Lake Malawi cichlid Genyochromis mento feeds on the fins of other fish, a behaviour that G. mento developed independently from the Tanganyikan Perissodini scale eaters. We investigated stomach contents and behavioural laterality of predation in aquarium to clarify the functional roles and evolution of laterality in cichlids. We also compared the behavioural laterality and mouth asymmetry of G. mento and P. microlepis The diet of G. mento mostly includes fin fragments, but also scales of several fish species. Most individual G. mento specimens showed significant attack bias favouring the skew mouth direction. However, there was no difference in success rate between attacks from the preferred side and those from the non-preferred side, and no lateralized kinetic elements in predation behaviour. Genyochromismento showed weaker laterality than P. microlepis, partly because of their different feeding habits, the phylogenetic constraints from their shorter evolutionary history and their origin from ancestor Haplochromini omnivorous/herbivorous species. Taken together, this study provides new insights into the functional roles of behavioural laterality: predatory fish aiming for prey that show escape behaviours frequently exhibit lateralized behaviour in predation.

Sintomatología y patología temporomandibular frecuente en adultos mayores desdentados totales de según criterios diagnósticos (RDC/TMD)

Los trastornos témporomandibulares (TTM) se presentan clínicamente con dolor en los músculos de la masticación, apertura limitada, movimiento mandibular asimétrico, y/o sonidos en la ATM, entre otros. Es motivo de consulta en sujetos de ambos sexos, diversas edades y condiciones oclusales. Objetivo: Determinar la sintomatología y la patología temporomandibular más frecuente en pacientes adultos mayores desdentados totales. Materiales y Métodos: La muestra quedó conformada por 30 sujetos consecutivos, 25 mujeres y cinco hombres mayores de 65 años de edad (70.8±5.7), desdentados totales y portadores de prótesis que cumplían los criterios de inclusión. A todos los sujetos se les aplicó el cuestionario y el procedimiento de examen según el Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) para determinar la sintomatología y patología témporomandibular según eje I y las condiciones conductuales según eje II. Resultados: Del total de los sujetos examinados (30), 28 (93%) presentaron al menos uno o más signos y/o síntomas de TTM no necesariamente diagnosticados con una patología específica. Respecto al eje I de los RDC/TMD, del total de individuos examinados, 2 presentaron patología correspondiente al grupo 1 (7%), 5 al grupo 2 (16%) y 11 al grupo 3 (37%). Respecto al eje II de los RDC/TMD, un 20% de la muestra presentó algún grado de dolor crónico y un 73% de los pacientes mostró algún grado de tendencia a la depresión. Conclusión: Los adultos mayores desdentados totales examinados evidenciaron una alta frecuencia de sintomatología temporomandibular. Esto no es necesariamente indicador de la presencia de una patología disfuncional diagnosticada bajo el contexto del RDC/TMD. El alto indice de tendencia a la depresión no tan solo puede deberse a los TTM sino a la condición de edentulismo u otro.

An MLC-based version for the ecliptic method for the determination of backscatter into the beam monitor chambers in photon beams of medical accelerators.

A very simple method to measure the effect of the backscatter from secondary collimators into the beam monitor chambers in linear accelerators equipped with multi-leaf collimators (MLC) is presented here. The backscatter to the monitor chambers from the upper jaws of the secondary collimator was measured on three beam-matched linacs by means of three methods: this new methodology, the ecliptic method, and assessing the variation of the beam-on time per monitor unit with dose rate feedback disabled. This new methodology was used to assess the backscatter characteristics of asymmetric over-traveling jaws. Excellent agreement between the backscatter values measured using the new methodology introduced here and the ones obtained using the other two methods was established. The experimental values reported here differ by less than 1% from published data. The sensitivity of this novel technique allowed differences in backscatter due to the same opening of the jaws, when placed at different positions on the beam path, to be resolved. The introduction of the ecliptic method has made the determination of the backscatter to the monitor chambers an easy procedure. The method presented here for machines equipped with MLCs makes the determination of backscatter to the beam monitor chambers even easier, and suitable to characterize linacs equipped with over-traveling asymmetric secondary collimators. This experimental procedure could be simply implemented to fully characterize the backscatter output factor constituent when detailed dosimetric modeling of the machine's head is required. The methodology proved to be uncomplicated, accurate and suitable for clinical or experimental environments.

Poster - Thur Eve - 67: Tangential Modulated Arc Therapy (TMAT): A Novel Technique using Megavoltage Photons for the Treatment of Superficial Disease

We propose a new type of treatment that employs a modulated tangential photon field to provide superior coverage of complex superficial targets when compared to other commonly employed methods, and drastically reduce dose to the underlying sensitive structures often present in these cases. TMAT plans were formulated for a set of four representative cases: 1. Scalp sarcoma, 2. Posterior chest-wall sarcoma, 3. Pleural mesothelioma with intact lung, 4. Chest-wall with deep inframammary nodes. For these cases, asymmetric jaw placement, angular limitations, and central isocenter placements were used to force optimization solutions with beam lines tangential to the body surface. When compared with unrestricted modulated arcs, the tangential arc scalp treatment reduced the max and mean doses delivered to the brain by 33Gy (from 55Gy to 22Gy) and 6Gy (from 14Gy to 8Gy), respectively. In the posterior chest wall case, the V10 for the ipsilateral lung was kept below 5% impressively while retaining the 45Gy target prescription coverage by over 97%. For the breast chest-wall case, the TMAT plan achieved reductions in high dose to the ipsilateral lung and heart by a factor of 2–3 when compared to classic, laterally opposed, tangents and reduced the V5 by 40% when compared to standard modulated arcs. TMAT has outperformed the conventional modalities of treatment for superficial lesions used in our clinic. We hope that with the advent of digitally controlled linear accelerators, we can uncover further benefits of this new technique and extend its applicability to a wider section of the patient population.

SU-E-T-404: Simple Field-In-Field Technique for Total Body Irradiation in Large Patients

Purpose: A simple Field-in-Field technique for Total Body Irradiation (TBI) was developed for traditional AP/PA TBI treatments to improve dosimetric uniformity in patients with large separation. Methods: TBI at our institution currently utilizes an AP/PA technique at an extended source-to-surface distance (SSD) of 380cm with patients in left decubitus position during the AP beam and in right decubitus during the PA beam. Patients who have differences in thickness (separation) between the abdomen and head greater than 10cm undergo CT simulation in both left and right decubitus treatment positions. One plan for each CT is generated to evaluate dose to patient midline with both AP and PA fields, but only corresponding AP fields will be exported for treatment for patient left decubitus position and PA fields for patient right decubitus position. Subfields are added by collimating with the x-ray jaws according to separation changes at 5–7% steps to minimize hot regions to less than 10%. Finally, the monitor units (MUs) for the plans are verified with hand calculation and water phantom measurements. Results: Dose uniformity (+/−10%) is achieved with field-in-field using only asymmetric jaws. It is dosimetrically robust with respect to minor setup/patient variations inevitable due to patient conditions. MUs calculated with Pinnacle were verified in 3 clinical cases and only a 2% difference was found compared to homogeneous calculation. In-vivo dosimeters were also used to verify doses received by each patient with and confirmed dose variations less than 10%. Conclusion: We encountered several cases with separation differences that raised uniformity concerns — based on a 1% dose difference per cm separation difference assumption. This could Resultin an unintended hot spot, often in the head/neck, up to 25%. This method allows dose modulation without adding treatment complexity nor introducing radiobiological variations, providing a reasonable solution for this unique TBI situation.

SU‐E‐T‐309: Tangential Modulated Arc Therapy: A Novel Technique for the Treatment of Superficial Disease

Purpose:We propose a new type of treatment that employs a modulated and sliding tangential photon field to provide superior coverage of superficial targets when compared to other commonly employed methods while drastically reducing dose to the underlying sensitive structures often present in these cases.Methods:Modulated treatment plans were formulated for a set of three representative cases. The first was a revised treatment of a scalp sarcoma, while the second was a treatment of a right posterior chest wall sarcoma. For these cases, asymmetric jaw placement, angular limitations, and central isocenter placements were used to force the optimization algorithm into finding solutions with beamlines that were not perpendicular to the body surface. The final case targeted the chest wall of a breast cancer patient, in which standard treatments were compared to the use of modulated fields with multiple isocenters along the chest wall.Results:When compared with unrestricted modulated arcs, the tangential arc scalp treatment reduced the max and mean doses delivered to the brain by 33Gy (from 55 to 22Gy) and 6Gy (from 14Gy to 8Gy), respectively. In the right posterior chest wall case, the V10 in the ipsilateral lung was kept below 5% while retaining a Rx dose (45Gy) target coverage of over 97%. For the breast case, the modulated plan achieved reductions in high dose to the ipsilateral lung and heart by a factor of 2–3 when compared to classic laterally opposed tangents and reduced the V5 by 40% when compared to standard modulated arcs.Conclusion:Tangential modulated arc therapy has outperformed the conventional modalities of treatment for superficial lesions used in our clinic. We hope that with the advent of digitally controlled linear accelerators, we can uncover further benefits of this new technique and extend its applicability to a wider section of the patient population.

Quality assurance of asymmetric jaw alignment using 2D diode array

A method using a 2D diode array is proposed to measure the junction gap (or overlap) and dose with high precision for routine quality assurance of the asymmetric jaw alignment. The central axis (CAX) of the radiation field was determined with a 15 × 15 cm(2) photon field at four cardinal collimator angles so that the junction gap (or overlap) can be measured with respect to the CAX. Two abutting fields having a field size of 15 cm (length along the axis parallel to the junction) × 7.5 cm (width along the axis perpendicular to the junction) were used to irradiate the 2D diode array (MapCHECK2) with 100 MU delivered at the photon energy of 6 MV. The collimator was slightly rotated at 15° with respect to the beam central axis to increase the number of diodes effective on the measurement of junction gap. The junction gap and dose measured in high spatial resolution were compared to the conventional methods using an electronic portal imaging device (EPID) and radiochromic film, respectively. In addition, the reproducibility and sensitivity of the proposed method to the measurements of junction gap and dose were investigated. The junction gap (or overlap) and dose measured by MapCHECK2 agreed well to those measured by the conventional methods of EPID and film (the differences ranged from -0.01 to 0 cm and from -1.34% to 0.6% for the gap and dose, respectively). No variation in the repeat measurements of the junction gap was found whereas the measurements of junction dose were found to vary in quite a small range over the days of measurement (0.21%-0.35%). While the sensitivity of the measured junction gap to the actual junction gap applied was the ideal value of 1 cm∕cm as expected, the sensitivity of the junction dose to the actual junction gap increased as the junction gap (or overlap) decreased (maximum sensitivity: 201.7%∕cm). The initial results suggest that the method is applicable for a comprehensive quality assurance of the asymmetric jaw alignment.

SU-E-T-43: The Impact of Gantry Rotations On the Accuracy of IMRT Dose Measurements Using EPIDs

Purpose: The use of electronic portal imaging device (EPID) in IMRT QA has recently gained popularity. This study is to investigate the effect of gantry rotations on the accuracy of measured dose distributions. Methods: Two Varian LINACs (Clinac-iX and Trilogy) were used to collect EPID data daily over 3-week period. Energy fluencies were measured at gantry angles separated 45° apart (0°,45°,…270°,315°)for both static fields defined by asymmetric jaws and dynamic fields from patient treatment plans. The measured fluencies were converted to 2D dose distributions by EPIDoseTM. The dose distributions obtained at zero gantry angle were used as base lines (BL) for comparison with those measured at non-zero gantry angles. The differences generated from static asymmetric fields were used to identify the mechanical misalignment between the center of EPID and beam axis. These differences were applied as the “shifts” to correct the corresponding IMRT fields. The modified dose distributions were then compared with their BL for error analysis using Gamma Index (1mm/1%). Results: The rotations of gantry and their associated “sagging” have various effects over the accuracy of measured dose distributions. The un-shifted Gamma passing rates were between 34.5% and 100%, dependent on the gantry angles. For both machines, the errors were consistently larger for dose comparisons made between gantry angles 135° −225°,with the lowest average of 44.2% at angle 225°. There have also been consistently high passing rates (>95%) between angles 315°−45°(clockwise). Once the pre-determined “shifts” were applied, all the matching statistics were improved to over 90%. Conclusion: Gantry rotation can exert effect on the accuracy of measured dose distributions. Proper shifts should be used, especially for gantry angles 135° −225°, to reduce the effect caused by the misalignment between EPID/beam axis. Blindly use of “best fit” available from QA software would Result in hiding true errors.

SU-E-P-26: 3-D Treatment Planning Of Chest Wall/Breast, Using Monoisocentric Technique

Purpose: The purpose of this study is to describe the monoisocentric technique followed in Shifa International Hospital. Methods: More than 30 consecutive patients have been treated from Oct 2011 to May 2012 with monoisocentric technique. Methods for treatment planning and irradiation, the methodology for making the isocenter and fields. With precise treatment planning system, linear accelerator — asymmetric four collimator jaws, the longitudinal(Y) jaws beam-split at the match line namely upper and lower border of fields, transverse (X) jaws defined lateral border of the fields. All patients underwent CT planning in the supine position with the ipsilateral arm overhead. The chest wall/breast was treated with a pair of opposing half beam tangential fields with the blockage of upper half of the field and the upper axillary and supraclavicular nodal region were treated with an anterior photon field with the blockage of lower half of the field. A monoisocentric technique was used to match the tangential fields with the anterior field at the isocentre. Multi-leaf collimators were utilized for shielding of normal structures. Results: Various techniques using a half-blocked supraclavicular field with special tangential fields have been introduced to eliminate the junction problem. These are, however complicated involving couch motion & machine isocentre repositioning when changing from the supraclavicular to the tangential fields. Monoisocentric technique is simple and easy to setup; since the same machine's isocentre is used for all treatment fields and no couch movements or patient reposition is required. Another use/advantage of monoisocentric technique is a reduction of treatment time. Conclusion: Treatment technique takes full advantage of dual asymmetric jaws to achieve a perfect match-line, necessitates only one isocenter and setup point. In monoisocentric technique reproducibility of positioning is simple and precise. This setup is technician friendly and the match-line is perfect without overdose and underdose at the junction.

A method for accurate zero calibration of asymmetric jaws in single-isocenter half-beam techniques

To present a practical method for calibrating the zero position of asymmetric jaws that provides higher accuracy at the central axis and improves dose homogeneity in the abutting region of half-beams. Junction doses were measured for each asymmetric jaw using the double-exposure technique and electronic portal imaging devices. The junction dose was determined as a function of jaw position. The shift in the zero jaw position (or in its corresponding potentiometer readout) required to correct for the measured junction dose could thus be obtained. The jaw calibration was then modified to introduce the calculated shift and therefore achieve an accurate zero position in order to provide a relative junction dose that was as close to zero as possible. All the asymmetric jaws from four medical linear accelerators were calibrated with the new calibration procedure. Measured relative junction doses at gantry 0° were reduced from a maximum of ±40% to a maximum of ±8% for all the jaws in the four considered accelerators. These results were valid for 6 MV and 18 MV photon beams and for any combination of asymmetric jaws set to zero. The calibration was stable over a long period of time; therefore, the need for recalibrating is seldom necessary. Accurate calibration of the zero position of the jaws is feasible in current medical linear accelerators. The proposed procedure is fast and it improves dose homogeneity at the junction of half-beams, thus, allowing a more accurate and safer use of these techniques.