Incorporating intensity modulated total body irradiation into a Children's Oncology Group trial: Rationale, techniques, and safeguards.

Historically, total body irradiation (TBI) has been delivered using static, parallel opposed photon beams (2D-TBI). Recently, centers have increasingly used intensity-modulated radiation therapy (IMRT) techniques for TBI. Relative to 2D-TBI, IMRT can reduce doses to critical organs (i.e., lungs and kidneys) while delivering myeloablative doses to the rest of the body, so it may decrease the risk of toxicity while maintaining oncologic outcomes. Despite these potential benefits, delivering TBI using IMRT introduces new challenges in treatment planning and delivery. We describe the extensive experience with IMRT-based TBI at Stanford University and City of Hope Cancer Center. These groups, and others, have reported favorable clinical outcomes and have developed methods to optimize treatment planning and delivery. A critical next step is to evaluate the broader adoption of this approach. Therefore, IMRT-based TBI will be incorporated into a prospective, multi-institutional Children's Oncology Group study with careful procedures and safeguards in place.

Health Impact of a Mobile-Delivered Diabetes Intervention to Control Blood Pressure in Older Adults.

Introduction: Patient education is an effective modality to reinforce self-care practices for chronic disease management. The purpose of this study was twofold: (1) to assess the health impact of a phone-delivered diabetes intervention and (2) to identify predictors of telehealth message use among adults aged 18-65 years with diabetes in a primary care setting using the Technology Acceptance Model theoretical framework. Methods: A pretest-posttest experimental study design was employed. Participants were randomized to receive 7 weeks of telehealth self-care messages or to the routine care group. Outcome measures included (1) telehealth use among patients who received weekly telehealth messages, (2) self-care behavior management derived from the Behavior Score Instrument, and (3) clinical outcomes measures. Results: The study team enrolled 150 patients, and of these, 138 (aged 18-65 years) completed the study. Participants aged 53±9.6 (mean±SD) years were mainly females (n=93; 76%), and the majority received government-sponsored health insurance (n=75; 54%). Age was a strong predictor of telehealth use (p<0.001). Among patients who received telehealth messages, systolic and diastolic blood pressure measures (140/78 mmHg vs 134/74 mmHg) were statistically significant at follow-up (p=0.001 and p=0.007, respectively). Conclusions: Digital support tools can play a valuable role in supporting lifestyle modification changes and reinforcing good diabetes self-care practices in older adults. Providing accessible tools and resources empowers adults to take an active role in their own health.

Lessons learned from an intercalibration exercise on the quantification and characterisation of microplastic particles in sediment and water samples.

An intercalibration exercise on the characterisation of microplastics in marine sediment and water samples was carried out among five laboratories involved in the implementation of the Marine Strategy Framework Directive (MSFD) in their country. The samples were prepared by mixing cleaned natural sediment and sea water with microplastics sets made of particles of various polymers, shapes and colours. Overall, the errors on total counts were under 25% in absolute value. The risk of non-detection and loss of particles is greater than the risk of contamination during sample analysis. Significant differences are observed among particle types. It appears difficult to obtain reliable and comparable data on the colour of microplastics. A comparison of the errors with regards to the protocols used led to recommend NaCl [1.2 g/cm3] density separation for sediment and one filtering step (200 µm). The operators' experience appears as a key factor for the quality of the results.

Low-Dose Image-Guided Pediatric CNS Radiation Therapy: Final Analysis From a Prospective Low-Dose Cone-Beam CT Protocol From a Multinational Pediatrics Consortium.

BACKGROUND: Lower-dose cone-beam computed tomography protocols for image-guided radiotherapy may permit target localization while minimizing radiation exposure. We prospectively evaluated a lower-dose cone-beam protocol for central nervous system image-guided radiotherapy across a multinational pediatrics consortium. METHODS: Seven institutions prospectively employed a lower-dose cone-beam computed tomography central nervous system protocol (weighted average dose 0.7 mGy) for patients ≤21 years. Treatment table shifts between setup with surface lasers versus cone-beam computed tomography were used to approximate setup accuracy, and vector magnitudes for these shifts were calculated. Setup group mean, interpatient, interinstitution, and random error were estimated, and clinical factors were compared by mixed linear modeling. RESULTS: Among 96 patients, with 2179 pretreatment cone-beam computed tomography acquisitions, median age was 9 years (1-20). Setup parameters were 3.13, 3.02, 1.64, and 1.48 mm for vector magnitude group mean, interpatient, interinstitution, and random error, respectively. On multivariable analysis, there were no significant differences in mean vector magnitude by age, gender, performance status, target location, extent of resection, chemotherapy, or steroid or anesthesia use. Providers rated >99% of images as adequate or better for target localization. CONCLUSIONS: A lower-dose cone-beam computed tomography protocol demonstrated table shift vector magnitude that approximate clinical target volume/planning target volume expansions used in central nervous system radiotherapy. There were no significant clinical predictors of setup accuracy identified, supporting use of this lower-dose cone-beam computed tomography protocol across a diverse pediatric population with brain tumors.

Quality of life following salvage surgery for squamous cell carcinoma of the anus.

INTRODUCTION: Squamous cell carcinoma of the anus is a rare condition. First line treatment is combined chemo-radio therapy. As many as a third of patients undergoing chemo-radiotherapy will experience recurrence. These patients often undergo salvage surgery with an extended abdominoperineal excision. The aim of this study was to examine the quality of life in disease free survivors following salvage surgery for squamous cell carcinoma of the anus. MATERIAL AND METHODS: Patients undergoing salvage surgery for SCCA at Copenhagen University Hospital Herlev between 1st of January 2011 and 31st December 2016 were identified and quality of life was assessed with EORTC QLQ-C30 and EORTC QLQ-CR29 questionnaires. RESULTS: 47 patients underwent salvage surgery for relapse or residual tumor in the period. From this cohort 25 disease-free survivors were identified. Fourteen (56%) patients returned a completed questionnaire. Overall median global health status was 75(range 20-100). Functional scores were generally high. In General, symptom scores were low, however all men reported impotence with a median symptom score of 100(range 67-100) and half the women reported dyspareunia. Urinary impairment was present in half the patients. Abdominal and buttock pain scores were low. CONCLUSION: Quality of life following salvage surgery for squamous cell carcinoma of the anus is affected but at an acceptable level. However, there are considerable side-affects in the form of impotence, dyspareunia and urinary impairment.

Clinical breast concerns in low-risk pediatric patients: practice review with proposed recommendations.

BACKGROUND: Fibroadenoma is overwhelmingly the most common pediatric breast lesion. Breast malignancy is quite uncommon in children, most frequently metastatic or hematological malignancy. Core biopsy has largely replaced excision for diagnosis of breast masses in adults. OBJECTIVE: The purpose of this study is two-fold: (1) compare utilization at our institution of interventional procedures vs. surgery for breast mass diagnosis in patients ≤18 years and (2) propose guidelines for breast imaging and biopsy in this population. MATERIALS AND METHODS: We extracted data for all patients ≤18 who, between 2004 and 2016, underwent either (a) imaging and/or intervention procedure, or (b) breast surgery, from the Radiology Information System and Pathology Data System, respectively. We recorded age, gender, imaging, procedure, lesion size and histopathology. RESULTS: We found 1,050 pediatric patients ≤18 years who underwent diagnostic breast ultrasound between 2004 and 2016. Of these, 168 patients underwent 199 interventional procedures. One hundred thirty patients underwent 160 core biopsies of solid lesions. Core biopsy pathology diagnosed benign lesions in 99%, of which 84.3% were fibroadenomas (n=135). One malignancy was diagnosed, B cell lymphoma. Two hundred three patients underwent surgical excision for 266 discrete lesions, and 89% were fibroadenomas. Seven benign phyllodes tumors were surgically diagnosed. No malignancies were diagnosed. CONCLUSION: Core biopsy in patients 18 years and younger is well-tolerated, has few risks, and is preferable to surgery in developing breasts, but the goal is to avoid any breast procedure whenever possible. We propose guidelines for pediatric breast imaging, follow-up, core biopsy and excisions.

GLIOMA CELL PROLIFERATION MEDIATED BY COENZYME Q10 AT SERUM DEPRIVATION IN VITRO.

Mechanisms of coenzyme Q10 effect on serum-deprived glioma cell proliferation have been studied. Our results have shown that the addition of coenzyme Q10 into serum-free culture medium leads to increase in cell viability, stimulation of cell growth, as well as restoration of mitochondrial potential and increase of quantity of energized mitochondria. It has been found out that coenzyme Q10-induced glioma cell proliferation under serum deficiency is a result of intracellular reduced glutathione concentration decrease with subsequent activation of proteinkinase C, ERK1/2 and phosphoinositol-3-kinase.

Impact of the New Jersey Breast Density Law on Imaging and Intervention Volumes and Breast Cancer Diagnosis.

PURPOSE: Increased breast density is acknowledged as an independent risk factor for breast cancer and may obscure malignancy on mammography. Approximately half of all mammograms depict dense breasts. Legislation related to mandatory breast density notification was first enacted in Connecticut in 2009. On May 1, 2014, New Jersey joined other states with similar legislation. The New Jersey breast density law (NJBDL) mandates that mammography reports acknowledge the relevance and masking effect of mammographic breast density. The aim of this study was to assess the impact of the NJBDL at one of the state's largest ACR-accredited breast centers. METHODS: A retrospective chart review was performed to determine changes in imaging and intervention utilization and modality of cancer diagnosis after enactment of the legislation. Data for the present study were extracted from a review of all patients with core biopsy-proven malignancy at a large outpatient breast center between November 1, 2012, and October 31, 2015. Data were divided into the 18-month period before the implementation of the NJBDL (November 1, 2012 to April 30, 2014) and the 18-month period after passage of the law (May 1, 2014 to October 31, 2015). RESULTS: Screening ultrasound increased significantly after the implementation of the NJBDL, by 651% (1,530 vs 11,486). MRI utilization increased by 59.3% (2,595 vs 4,134). A total of 1,213 cancers were included in the final analysis, 592 in the first time period and 621 after law implementation. Breast cancer was most commonly detected on screening mammography, followed by diagnostic mammography with ultrasound for palpable concern, in both time periods. Of the 621 cancers analyzed, 26.1% (n = 162) were found in patients 50 years of age or younger. Results demonstrated that with respect to how malignancies were detected, age and average mammographic density were both statistically significant (P = .002). CONCLUSIONS: The NJBDL succeeded in publicizing the masking effect of dense breasts. The number of supplemental screening ultrasound and MRI examinations increased after the implementation of this legislation. An efficacy analysis affirmed the high sensitivity of screening MRI compared with other modalities. The use of MRI increased core biopsy efficiency and reduced the number of biopsies needed per cancer diagnosed.

Diagnostics and treatment of insulinoma.

Insulinomas are the most common functioning pancreatic neuroendocrine neoplasms (pNENs), developed mainly from pancreatic islet cells. More than 90% of insulinomas are sporadic, benign and small sized. Autonomous production of insulin results in neuroglycopenic and adrenergic symptomatology with potential lethality. Surgery remains the only curative treatment with a high success rate. Preoperative tumor localization is challenging, but important for appropriate surgical approach. Metastatic forms represent a challenge, mainly on the field of therapy, with the need of tumor burden reduction and glycemia stabilization. The rarity of malignant forms limits reports on therapeutic strategies and outcome. Authors present in this article a summarized overview of epidemiology, clinic, diagnostics and treatment of benign and malign forms of insulinomas.

Physician attitudes and practices related to voluntary error and near-miss reporting.

PURPOSE: Incident learning systems are important tools to improve patient safety in radiation oncology, but physician participation in these systems is poor. To understand reporting practices and attitudes, a survey was sent to staff members of four large academic radiation oncology centers, all of which have in-house reporting systems. METHODS: Institutional review board approval was obtained to send a survey to employees including physicians, dosimetrists, nurses, physicists, and radiation therapists. The survey evaluated barriers to reporting, perceptions of errors, and reporting practices. The responses of physicians were compared with those of other professional groups. RESULTS: There were 274 respondents to the survey, with a response rate of 81.3%. Physicians and other staff agreed that errors and near-misses were happening in their clinics (93.8% v 88.7%, respectively) and that they have a responsibility to report (97% overall). Physicians were significantly less likely to report minor near-misses (P = .001) and minor errors (P = .024) than other groups. Physicians were significantly more concerned about getting colleagues in trouble (P = .015), liability (P = .009), effect on departmental reputation (P = .006), and embarrassment (P < .001) than their colleagues. Regression analysis identified embarrassment among physicians as a critical barrier. If not embarrassed, participants were 2.5 and 4.5 times more likely to report minor errors and major near-miss events, respectively. CONCLUSIONS: All members of the radiation oncology team observe errors and near-misses. Physicians, however, are significantly less likely to report events than other colleagues. There are important, specific barriers to physician reporting that need to be addressed to encourage reporting and create a fair culture around reporting.

Expression of PIK3CA mutant E545K in the mammary gland induces heterogeneous tumors but is less potent than mutant H1047R.

The phosphoinositide 3-kinase (PI3K) signaling cascade is a key mediator of cellular growth, survival and metabolism and is frequently subverted in human cancer. The gene encoding for the alpha catalytic subunit of PI3K (PIK3CA) is mutated and/or amplified in ∼30% of breast cancers. Mutations in either the kinase domain (H1047R) or the helical domain (E545K) are most common and result in a constitutively active enzyme with oncogenic capacity. PIK3CA(H1047R) was previously demonstrated to induce tumors in transgenic mouse models; however, it was not known whether overexpression of PIK3CA(E545K) is sufficient to induce mammary tumors and whether tumor initiation by these two types of mutants differs. Here, we demonstrate that expression of PIK3CA(E545K) in the mouse mammary gland induces heterogenous mammary carcinomas but with a longer latency than PIK3CA(H1047R)-expressing mice. Our results suggest that the helical domain mutant PIK3CA(E545K) is a less potent inducer of mammary tumors due to less efficient activation of downstream Akt signaling.

3D inpatient dose reconstruction from the PET-CT imaging of 90Y microspheres for metastatic cancer to the liver: feasibility study.

PURPOSE: The introduction of radioembolization with microspheres represents a significant step forward in the treatment of patients with metastatic disease to the liver. This technique uses semiempirical formulae based on body surface area or liver and target volumes to calculate the required total activity for a given patient. However, this treatment modality lacks extremely important information, which is the three-dimensional (3D) dose delivered by microspheres to different organs after their administration. The absence of this information dramatically limits the clinical efficacy of this modality, specifically the predictive power of the treatment. Therefore, the aim of this study is to develop a 3D dose calculation technique that is based on the PET imaging of the infused microspheres. METHODS: The Fluka Monte Carlo code was used to calculate the voxel dose kernel for 90Y source with voxel size equal to that of the PET scan. The measured PET activity distribution was converted to total activity distribution for the subsequent convolution with the voxel dose kernel to obtain the 3D dose distribution. In addition, dose-volume histograms were generated to analyze the dose to the tumor and critical structures. RESULTS: The 3D inpatient dose distribution can be reconstructed from the PET data of a patient scanned after the infusion of microspheres. A total of seven patients have been analyzed so far using the proposed reconstruction method. Four patients underwent treatment with SIR-Spheres for liver metastases from colorectal cancer and three patients were treated with Therasphere for hepatocellular cancer. A total of 14 target tumors were contoured on post-treatment PET-CT scans for dosimetric evaluation. Mean prescription activity was 1.7 GBq (range: 0.58-3.8 GBq). The resulting mean maximum measured dose to targets was 167 Gy (range: 71-311 Gy). Mean minimum dose to 70% of target (D70) was 68 Gy (range: 25-155 Gy). Mean minimum dose to 90% of target (D90) was 53 Gy (range: 13-125 Gy). CONCLUSIONS: A three-dimensional inpatient dose reconstruction method has been developed that is based on the PET/CT data of a patient treated with 90Y microspheres. It allows for a complete description of the absorbed dose by the tumor and critical structures. It represents the first step in building predictive models for treatment outcomes for patients receiving this therapeutic modality as well as it allows for better analysis of patients' dose response and will ultimately improve future treatment administration.

SU-E-T-594: Dosimetric Evaluation of Different Treatment Techniques for Prostate Cancer.

PURPOSE: To evaluate the Volumetric Modulated Arc Therapy (VMAT, RapidArc) and IMRT plan quality for prostate deliveries conducted by two different treatment planning systems: Oncentra Masterplan (Nucletron inc.) and Eclipse (Varian inc.). METHODS: We investigated ten prostate treatment delivery plans. For a given case studied we created a RapidArc plan (Eclipse), a VMAT and an IMRT plan (Oncentra) by using both treatment planning systems. The rotational therapy plans consisted of 2 to 3 arcs and the IMRT fields consisted of 7 to 9 fields. The prescription dose was 200 cGy X 40 fx using a Varian Trilogy with 10 MV beams. The treatment parameters were used to evaluate the plan quality: the minimal, mean and maximal doses to the target (PTV) and the volumes received 65Gy and 40 Gy, respectively, for the rectum and bladder, V65 and V40. In addition, we calculated the conformity index (CI) and the heterogeneity index (HI) for each delivery type. RESULTS: No significant difference was found between RapidArc, VMAT and IMRT, regarding the minimal and average PTV dose value. The rectum and bladder constraints showed no significant variation as well. The PTV hot spot was significantly higher for the VMAT plan compared to the RapidArc plan (p=0.007). The target CI for VMAT (0.55±0.05) and IMRT (0.71±0.08) was found to be smaller than the RapidArc (0.82±0.04) and the difference is statistically significant (p=0). The HI, value was found to have no significant difference between RapidArc, VMAT and IMRT plan deliveries. CONCLUSIONS: Two TPS are capable of producing high-quality treatment plans for prostate cancer. The quality is associated with the degree of intensity modulation and the number of incident angles. Overall, the RapidArc plans with 2-3 arcs showed better dosimetric qualities than the VMAT and IMRT plans.

SU-E-T-383: Pulsed Low Dose Rate Radiotherapy Using Advanced Treatment Methods: A Novel Technique for Patient Re-Irradiation.

PURPOSE: Pulsed low dose-rate radiotherapy (PLDR) re-irradiation has the potential to reduce late normal tissue toxicity while still providing significant tumor control for recurrent cancers. In contrast to conventional treatments delivered at dose-rates of 400-600cGy/min, PLDR treatments deliver 20cGy pulses separated by 3-minute intervals to achieve an effective-dose-rate of 6.7cGy/min. This work aims to investigate the planning strategy and delivery quality of PLDR treatment using IMRT and RapidArc techniques. METHODS: Twenty cases (10 treated with PLDR IMRT, 10 for evaluation purposes) were recruited in this study including prostate, pancreas, lung, head-and-neck, breast and pelvis. IMRT and the RapidArc treatment plans were generated using the Eclipse TPS. For IMRT treatment, each plan consisted of 10 fields to achieve a daily dose of 200cGy. The breast IMRT and the RapidArc plans consisted of two fields/arcs, respectively (40cGy/plan) and were delivered 5 times. The dose contribution from each field to the planning target volume (PTV) was analyzed to evaluate the feasibility for PLDR treatment. Machine-operation- dose-rate and plan quality was also investigated. Dose delivery accuracy was assessed using a cylindrical diode array. RESULTS: Throughout the six treatment sites, the mean PTV dose ranged from 16.1 to 26.1cGy/arc for RapidArc plans and 10.3 to 36.7cGy/field for IMRT plans. For IMRT, the PTV dose contribution from each field strongly depends on the beam arrangement and optimization parameters. With very low dose for a full rotation (∼ 20cGy/arc), the machine-operation-dose-rate of RapidArc plans significantly affects plan quality and deliverability. A machine-operation-dose-rate of 100 MU/min results in superior delivery accuracy (>97.7% gamma-passing-rate for 3%/3mm criteria) for both IMRT and RapidArc plans. CONCLUSIONS: PLDR radiotherapy using IMRT and RapidArc techniques Result in both dosimetric and radiobiological benefits, which may have great potential for those previously-irradiated patients who have historically done poorly.

SU-E-T-279: A Novel Electron-Beam Combined with Magnetic Field Application for Radiotherapy.

PURPOSE: The new beam and delivery system consists of an electron accelerator and a system of magnets (one or more). Introducing a transverse magnetic field in and near the tumor, causes the electrons to spiral in this region, thereby producing an effective peak in the depth dose distribution, within the tumor volume. Although the basic idea is not new, we suggest here for the first time, a viable as well as a workable, magnetic field configuration, which in addition to focusing the beam does not interfere with its propagation to the target. METHODS: The electron accelerator: can be a linear accelerator or any other type electron accelerator, capable of producing different electron energies for different depths and dose absorption accumulation. The Field size can be as small as a pencil beam and as big as any of the other standard field sizes that are used in radiotherapy. The scatter filter can be used or removed. The dose rate accumulation can be as higher as possible.The magnets are able to produce magnetic fields. The order, direction, width, place, shape and number of the magnetic fields define the shape and the Percentage Depth Dose (PDD) curve of the electron beam. Prototypes were successfully tested by means of computer simulation, using:COMSOL-Multiphsics for magnetic fields calculations. FLUKA package, for electron beam MC simulation. RESULTS: Our results suggest that by using an electron beam at different energies, combined with magnetic fields, we could modify the delivered dose. This is caused by manipulating the electron motion via the Lorentz force. The applied magnetic field, will focus the electron beam at a given depth and deposit the energy in a given volume and depth, where otherwise the electron energy will have spread deeper. The direction and magnitude of the magnetic fields will prevent the scattering of the electron beam and its absorption in remote volumes. In practice, we get a pseudo Bragg peak depth dose distribution, applying a relatively low cost system. The therapeutic efficiency induced by the system is of similar efficiency as the ion beam therapy techniques. CONCLUSIONS: Our novel concept demonstrates treatment that is almost similar to proton therapy and in some parameters even better performance.Unlike the current high-energy electron therapy, our system's beam deposit almost all of its energy on its target, with a low amount of radiation deposited in tissues from the surface of the skin to the front of tumor, and almost no "exit dose" beyond the tumor. This property will enables to hit tumors with higher, potentially more effective radiation doses, while being considerably less expensive.

SU-E-T-638: Treatment Margins Expansion for CyberKnife Treatment Plans.

PURPOSE: The CyberKnife uses an online prediction model to track moving targets. The system works well if patients can breathe regularly. However, some patients cannot maintain a regular breathing pattern, which means a larger PTV margin is necessary for these patients to ensure sufficient CTV dose coverage. However, it is very difficult to predict a patient's breathing pattern in advance. The purpose of this study is to investigate a quick and easy way to adapt the treatment plan if extra margins are needed. METHODS: Multiple algorithms have been developed to calculate the adjustment. Generally, if a larger target region requires coverage by the prescription dose, the size of the beams will be larger and they should move in a peripheral direction for a certain distance to avoid hot spots. Dose is recalculated and renormalized consistently after the adjustment. If the dose distribution of the new plan covers the new PTV with acceptable conformality and coverage, the plan will be used for treatment. Otherwise, more iterations of the adjustment are performed. Dose calculations are limited to a small region surrounding the target to reduce calculation time. RESULTS: 5 clinical cases (3 lungs, 1 liver and 1 adrenal) have been tested in this study. The dose margin can be extended up to 10 mm without changing dose distributions around the target region dramatically. The average PTV coverage is 98.7% compared to 99.1% in the original plans and the average CI is 1.22, which is slightly less than the 1.24 in the original plans. CONCLUSIONS: Treatment margins can be sufficiently expanded resulting in satisfactory plan quality for patients with breathing irregularities.

SU-E-T-554: PTV to Skin Proximity for Head and Neck IMRT Treatment Planning.

PURPOSE: The goal of this work was to evaluate measured vs. calculated surface dose as a function of PTV-to-skin proximity and calculation matrix oxel size, determine effects on plan quality, and provide parameters and levels of uncertainty for clinical use. METHODS: A right-sided CTV with the lateral border 5mm from the surface was delineated on the CT data of a head and neck phantom. A 5mm PTV was generated except laterally where distances of 0-5mm were used. A 7-field IMRT plan was generated using the Eclipse TPS. Optimization was performed where 95% of the PTV receives the prescription dose using a matrix size of 2mm3 . Dose calculations were repeated for grid sizes of 1, 3 and 5mm3 . For each plan nine point dose values were obtained just inside the phantom surface, corresponding to a 2cm2 grid near the central target region. Nine ultra-thin TLDs were placed on the phantom surface corresponding to the grid. Measured and calculated dose values were compared. Conformality, homogeneity and target coverage were compared. RESULTS: Surface dose is over-estimated by the TPS by 21 and 8% for 5 and 3mm3 voxels, respectively and accurately predicted for 2mm3 voxels. A voxel size of 1mm3 results in underestimation of 13%. Conformality improves with increasing PTV to skin distance and a CI of unity results for grid sizes of 1-3mm3 between 4 and 4.5mm. Hot spot decreases as the PTV moves away from the surface and falls below 110% at 4mm. Underdosage worsens as the PTV approaches the skin. CONCLUSIONS: For decreasing PTV-to-skin distance with this TPS, isodose conformality decreases, 'hot spot' increases, and target coverage degrades. Surface dose is accurately predicted for a 2mm3 voxel size, while choosing a finer or coarser grid results in underestimation or overestimation, respectively. All of the above appear to hold for VMAT.

TU-E-BRB-06: Best in Physics (Therapy) - Development and Experimental Validation of EPID-Based 4D Dose Reconstruction.

PURPOSE: To develop and validate an EPID-based 4D patient dose reconstruction framework accounting for linac delivery uncertainties, interfractional and intrafractional motions, and interplay effect. METHODS: Patients with fiducial markers were scanned with 4D-CT for SBRT planning. Before treatment, in-room 4D-CT was performed. Both the MLC and the tumor movements were tracked by continuously acquiring EPID images during treatment. Instead of directly using the heterogeneous transit photon fluence measured by the EPID, this method reconstructed the incident beam fluence based on the MLC apertures measured by the EPID and the delivered MU recorded by the linac. To account for the time-dependent-geometry, the incident fluence distributions were sorted into their corresponding phases based on the tumor motion pattern detected by the EPID and accumulated as the incident fluence map for each phase. Together with 4D-CT, it was then used for Monte Carlo dose calculation. Deformable registration was performed to sum up the phase doses for treatment assessment. The feasibility of using the transit EPID images for incident fluence reconstruction was evaluated against EPID in-air measurements. The accuracy of 3D- and 4D-dose reconstruction was validated by a motordriven cylindrical diode array for six clinical SBRT plans. RESULTS: The average difference between the measured and reconstructed fluence maps is within 0.16%. The reconstructed 3D-dose shows 1.4% agreement in the CAX-dose and >98.5% gamma-passing-rate (2%/2mm) in the peripheral-dose. A distorted dose distribution is observed in the measurement for the moving ArcCheck-phantom. The comparison between the measured and the reconstructed 4D-dose without considering interplay fails the gammaevaluation (59%-88.9% gamma-passing-rate). In contrast, when the interplay is considered, the dose distortion phenomena is successfully represented in the reconstructed dose (>97.6% gamma-passing-rate). CONCLUSIONS: The experimental validation demonstrates that the proposed method provides a practical way to reconstruct the fractional 4D-doses received by the patient and enables adaptive SBRT strategy.

WE-G-BRB-09: CyberKnife Patient Specific QA Using a 4D Cylindrical Diode Array System.

PURPOSE: To examine and facilitate the feasibility of the ArcCheck cylindrical diode array system as a patient specific QA device for CyberKnife radiosurgery delivery. METHODS: There is an obvious necessity for CyberKnife robotic radiosurgery patient QA procedures for hypofractionated treatment of larger planned treatment volumes (PTV), e.g. prostate. This need will increase when the future CyberKnife MLC is introduced. The small unflattened CyberKnife fields, along with the variation of beam-to-detector spatial angles, pose a significant detection challenge for dosimetric systems. The feasibility of the ArcCheck (Sun Nuclear Inc.) cylindrical diode array system for patient-specific QA on the CyberKnife is demonstrated using a beam-to-diode specific angular correction that was developed and has been applied. For localization and tracking, four gold seed fiducial markers were embedded in the system's central plug. We used a Monte Carlo 1% uncertainty for the dose calculation. RESULTS: By disabling the Linac based corrections and applying the custom CyberKnife correction that we developed, the passing rate increased from 39.6% to 99.8% using a 3%3mm gamma criteria for a given lung case. An additional lung case passed 98.5%. In both cases, a 10% dose threshold was used. In addition, brain, trigeminal nerve and lung cases with synchrony tracking are being investigated. CONCLUSIONS: We demonstrated the ArcCheck feasibility for CyberKnife patient specific QA performance. The custom CK angular correction that we developed and applied showed a high passing rate for the lung cases. A verification of the polar angle response should be conducted, in addition to the azimuthal angle that was verified for Linacs. Any data that is being retrieved is additional data to the current chamber point measurement procedures.

Correlated cerebral events between physically and sensory isolated pairs of subjects exposed to yoked circumcerebral magnetic fields.

In three different experiments pairs of unrelated people sitting in two different rooms were exposed simultaneously to different rates of circumcerebral rotations of weak, complex magnetic fields in order to produce "dynamic similarity". Quantitative electroencephalographic (QEEG) measurements were taken for one member of each pair in one room while the other sat in a closed chamber in another room and intermittently observed 5Hz, 8Hz, 10Hz, or 15Hz flashing lights. Reliable increases in QEEG power within specific frequencies over the right parietal region were observed during the similar-frequency light flashes when the shared temporal-spatial complexity of the circumcerebral rotating fields was based on 100ms, the average duration of normal microstates. The development of this experimental procedure could facilitate rational understanding of this class of "coincidence" phenomena.