Mutian Zhang

Anesthesia complications of pediatric radiation therapy

PURPOSE Complications of anesthesia for pediatric radiation therapy are imperative for both radiation oncologists and anesthesiologists to clinically assess and manage. We performed the first systematic review to date addressing this important issue. METHODS A systematic search of PubMed and EMBASE was conducted using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Searches were not restricted based on publication date. Nine original investigations were identified, analyzed, and collated for this report. RESULTS General anesthesia has proven superior to conscious sedation with regard to maintaining satisfactory procedural sedation while maintaining low respiratory and cardiovascular complication rates. Although agents such as ketamine (complication rates approaching 23%-24%) have been used in the past, other agents such as propofol and volatile anesthetics have lower complication rates because of improved drug side effect profiles (0.01%-3.5%). Most common complications are respiratory-based (eg, airway obstruction, broncho/laryngospasm, desaturation, apnea), followed by those that are cardiovascular-based (eg, tachy/bradycardia, arrhythmias, hypotension) and nausea/vomiting. Though procedure duration and anesthetic dose can be associated with higher complication risks, prior or concurrent chemotherapy does not confer added risks other than neutropenia-related sepsis. Other potential complications include those with vascular access devices, observed in up to 20% to 25%, with peripherally inserted central catheters having the highest rates of vascular complications and port catheters the lowest. CONCLUSIONS Rates of anesthetic complications encountered in pediatric radiation therapy are similar, if not lower, than rates reported in controlled operating room settings, implying that anesthesia for pediatric radiation therapy is safe, with low complication rates periprocedurally. Propofol infusion and oxygen delivery via nasal cannula offer the lowest immediate anesthetic complication rates and are hence most recommended for use. Though the long-term neurocognitive consequences of multiple anesthetics in pediatric patients have yet to be clearly defined, health care providers should be cognizant of the potentially serious implications.

Anaplastic lymphoma kinase: Role in cancer and therapy perspective

Anaplastic lymphoma kinase (ALK) is correlated with oncogenesis in different types of cancers, such as anaplastic large cell lymphoma, lung cancer, neuroblastoma, and even breast cancer, by abnormal fusion of ALK or non-fusion ALK activation. ALK is a receptor tyrosine kinase, with a single transmembrane domain, that plays an important role in development. Upon ligand binding to the extracellular domain, the receptor undergoes dimerization and subsequent autophosphorylation of the intracellular kinase domain. In recent years, ALK inhibitors have been developed for cancer treatment. These inhibitors target ALK activity and show effectiveness in ALK-positive non-small cell lung cancer. However, acquired treatment resistance makes the future of this therapy unclear; new strategies are underway to overcome the limitations of current ALK inhibitors.

A new variable for SRS plan quality evaluation based on normal tissue sparing: the effect of prescription isodose levels

OBJECTIVE A new dosimetric variable, dose-dropping speed (DDS), was proposed and used to evaluate normal tissue sparing among stereotactic radiosurgery (SRS) plans with different prescription isodose lines. METHODS 40 plans were generated for 8 intracranial SRS cases, prescribing to isodose levels (IDLs) ranging from 50% to 90% in 10% increments. Whilst maintaining similar coverage and conformity, plans at different IDLs were evaluated in terms of normal tissue sparing using the proposed DDS. The DDS was defined as the greater decay coefficient in a double exponential decay fit of the dose drop-off outside the planning target volume (PTV), which models the steep portion of the drop-off. Provided that the prescription dose covers the whole PTV, a greater DDS indicates better normal tissue sparing. RESULTS Among all plans, the DDS was found to be the lowest for the prescription at 90% IDL and the highest for the prescription at 60% or 70%. The beam profile slope change in the penumbra and its field size dependence were explored and given as the physical basis of the findings. CONCLUSION A variable was proposed for SRS plan quality evaluation. Using this measure, prescriptions at 60% and 70% IDLs were found to provide best normal tissue sparing. ADVANCES IN KNOWLEDGE A new variable was proposed based on which normal tissue sparing was quantitatively evaluated, comparing different prescription IDLs in SRS.

Setup uncertainties in linear accelerator based stereotactic radiosurgery and a derivation of the corresponding setup margin for treatment planning.

PURPOSE In the present study, clinical stereotactic radiosurgery (SRS) setup uncertainties from image-guidance data are analyzed, and the corresponding setup margin is estimated for treatment planning purposes. METHODS Patients undergoing single-fraction SRS at our institution were localized using invasive head ring or non-invasive thermoplastic masks. Setup discrepancies were obtained from an in-room x-ray patient position monitoring system. Post treatment re-planning using the measured setup errors was performed in order to estimate the individual target margins sufficient to compensate for the actual setup errors. The formula of setup margin for a general SRS patient population was derived by proposing a correlation between the three-dimensional setup error and the required minimal margin. RESULTS Setup errors of 104 brain lesions were analyzed, in which 81 lesions were treated using an invasive head ring, and 23 were treated using non-invasive masks. In the mask cases with image guidance, the translational setup uncertainties achieved the same level as those in the head ring cases. Re-planning results showed that the margins for individual patients could be smaller than the clinical three-dimensional setup errors. The derivation of setup margin adequate to address the patient setup errors was demonstrated by using the arbitrary planning goal of treating 95% of the lesions with sufficient doses. CONCLUSIONS With image guidance, the patient setup accuracy of mask cases can be comparable to that of invasive head rings. The SRS setup margin can be derived for a patient population with the proposed margin formula to compensate for the institution-specific setup errors.

Estimation of internal organ motion-induced variance in radiation dose in non-gated radiotherapy

In the delivery of non-gated radiotherapy (RT), owing to intra-fraction organ motion, a certain degree of RT dose uncertainty is present. Herein, we propose a novel mathematical algorithm to estimate the mean and variance of RT dose that is delivered without gating. These parameters are specific to individual internal organ motion, dependent on individual treatment plans, and relevant to the RT delivery process. This algorithm uses images from a patients 4D simulation study to model the actual patient internal organ motion during RT delivery. All necessary dose rate calculations are performed in fixed patient internal organ motion states. The analytical and deterministic formulae of mean and variance in dose from non-gated RT were derived directly via statistical averaging of the calculated dose rate over possible random internal organ motion initial phases, and did not require constructing relevant histograms. All results are expressed in dose rate Fourier transform coefficients for computational efficiency. Exact solutions are provided to simplified, yet still clinically relevant, cases. Results from a volumetric-modulated arc therapy (VMAT) patient case are also presented. The results obtained from our mathematical algorithm can aid clinical decisions by providing information regarding both mean and variance of radiation dose to non-gated patients prior to RT delivery.

Technical Note: Fabricating Cerrobend grids with 3D printing for spatially modulated radiation therapy: A feasibility study.

PURPOSE Grid therapy has promising applications in the radiation treatment of large tumors. However, research and applications of grid therapy are limited by the accessibility of the specialized blocks that produce the grid of pencil-like radiation beams. In this study, a Cerrobend grid block was fabricated using the 3D printing technique. METHODS A grid block mold was designed with flared tubes which follow the divergence of the beam. The mold was 3D printed using a resin with the working temperature below 230 °C. The melted Cerrobend liquid at 120 °C was cast into the resin mold to yield a block with a thickness of 7.4 cm. At the isocenter plane, the grid had a hexagonal pattern, with each pencil beam diameter of 1.4 cm; the distance between the beam centers was 2.1 cm. RESULTS The dosimetric properties of the grid block were studied using small field dosimeters: a pinpoint ionization chamber and a stereotactic diode. For a 6 MV photon beam, its valley-to-peak ratio was 20% at dmax and 30% at 10 cm depth; the output factor was 84.9% at dmax and 65.1% at 10 cm depth. CONCLUSIONS This study demonstrates that it is feasible to implement 3D printing technique in applying grid therapy in clinic.

Using weighted power mean for equivalent square estimation

Abstract Purpose Equivalent Square (ES) enables the calculation of many radiation quantities for rectangular treatment fields, based only on measurements from square fields. While it is widely applied in radiotherapy, its accuracy, especially for extremely elongated fields, still leaves room for improvement. In this study, we introduce a novel explicit ES formula based on Weighted Power Mean (WPM) function and compare its performance with the Sterling formula and Vadash/Bjärngards formula. Methods The proposed WPM formula is ESWPMa,b=waα+1−wbα1/α for a rectangular photon field with sides a and b. The formula performance was evaluated by three methods: standard deviation of model fitting residual error, maximum relative model prediction error, and models Akaike Information Criterion (AIC). Testing datasets included the ES table from British Journal of Radiology (BJR), photon output factors (S cp) from the Varian TrueBeam Representative Beam Data (Med Phys. 2012;39:6981–7018), and published S cp data for Varian TrueBeam Edge (J Appl Clin Med Phys. 2015;16:125‐148). Results For the BJR dataset, the best‐fit parameter value α = −1.25 achieved a 20% reduction in standard deviation in ES estimation residual error compared with the two established formulae. For the two Varian datasets, employing WPM reduced the maximum relative error from 3.5% (Sterling) or 2% (Vadash/Bjärngard) to 0.7% for open field sizes ranging from 3 cm to 40 cm, and the reduction was even more prominent for 1 cm field sizes on Edge (J Appl Clin Med Phys. 2015;16:125–148). The AIC value of the WPM formula was consistently lower than its counterparts from the traditional formulae on photon output factors, most prominent on very elongated small fields. Conclusion The WPM formula outperformed the traditional formulae on three testing datasets. With increasing utilization of very elongated, small rectangular fields in modern radiotherapy, improved photon output factor estimation is expected by adopting the WPM formula in treatment planning and secondary MU check.

A feasibility study of applying thermal imaging to assist quality assurance of high-dose rate brachytherapy

Aim: High-dose rate (HDR) brachytherapy poses a special challenge to radiation safety and quality assurance (QA) due to its high radioactivity, and it is thus critical to verify the HDR source location and its radioactive strength. This study explores a new application for thermal imaging, to visualize/locate the HDR source and measure radioactivity using temperature information. A potential application would relate to HDR QA and safety improvement. Methods: Heating effects by an HDR source were studied using finite element analysis (FEA). Thermal cameras were used to visualize an HDR source inside a plastic catheter made of polyvinylidene difluoride (PVDF). Using different source dwell times, relationships between the HDR source strength and heating effects were studied, thus establishing potential daily QA criteria using thermal imaging. Results: For an Ir-192 source with a source radioactivity of 10 Ci, the decay-induced heating power inside the source was about 13.3 mW. After the HDR source was extended into the PVDF applicator and reached thermal equilibrium, thermal imaging visualized the temperature gradient of 10 K/cm along the PVDF catheter surface, which agreed with FEA modeling. For the Ir-192 source strengths ranging from 16.9 to 41.1 kU, thermal imaging could verify source activity with a relative error of 6.3% with a dwell time of 10 s, and a relative error of 2.5% with 100 s. Conclusion: Thermal imaging could be a feasible tool to visualize HDR source dwell positions and verify source integrity. Potentially, patient safety and treatment quality may be improved by integrating thermal measurements into HDR QA procedures.

MO-FG-BRA-02: A Feasibility Study of Integrating Breathing Audio Signal with Surface Surrogates for Respiratory Motion Management

PURPOSE Tracking the surrogate placed on patient skin surface sometimes leads to problematic signals for certain patients, such as shallow breathers. This in turn impairs the 4D CT image quality and dosimetric accuracy. In this pilot study, we explored the feasibility of monitoring human breathing motion by integrating breathing sound signal with surface surrogates. METHODS The breathing sound signals were acquired though a microphone attached adjacently to volunteers nostrils, and breathing curve were analyzed using a low pass filter. Simultaneously, the Real-time Position Management™ (RPM) system from Varian were employed on a volunteer to monitor respiratory motion including both shallow and deep breath modes. The similar experiment was performed by using Calypso system, and three beacons taped on volunteer abdominal region to capture breath motion. The period of each breathing curves were calculated with autocorrelation functions. The coherence and consistency between breathing signals using different acquisition methods were examined. RESULTS Clear breathing patterns were revealed by the sound signal which was coherent with the signal obtained from both the RPM system and Calypso system. For shallow breathing, the periods of breathing cycle were 3.00±0.19 sec (sound) and 3.00±0.21 sec (RPM); For deep breathing, the periods were 3.49± 0.11 sec (sound) and 3.49±0.12 sec (RPM). Compared with 4.54±0.66 sec period recorded by the calypso system, the sound measured 4.64±0.54 sec. The additional signal from sound could be supplement to the surface monitoring, and provide new parameters to model the hysteresis lung motion. CONCLUSION Our preliminary study shows that the breathing sound signal can provide a comparable way as the RPM system to evaluate the respiratory motion. Its instantaneous and robust characteristics facilitate it possibly to be a either independently or as auxiliary methods to manage respiratory motion in radiotherapy.

SU-G-201-16: Thermal Imaging in Source Visualization and Radioactivity Measurement for High Dose Rate Brachytherapy

PURPOSE High Dose Rate (HDR) brachytherapy poses a special challenge to radiation safety and quality assurance (QA) due to its high radioactivity, and it is thus critical to verify the HDR source location and its radioactive strength. This study demonstrates a new method for measuring HDR source location and radioactivity utilizing thermal imaging. A potential application would relate to HDR QA and safety improvement. METHODS Heating effects by an HDR source were studied using Finite Element Analysis (FEA). Thermal cameras were used to visualize an HDR source inside a plastic applicator made of polyvinylidene difluoride (PVDF). Using different source dwell times, correlations between the HDR source strength and heating effects were studied, thus establishing potential daily QA criteria using thermal imaging RESULTS: For an Ir1?2 source with a radioactivity of 10 Ci, the decay-induced heating power inside the source is ∼13.3 mW. After the HDR source was extended into the PVDF applicator and reached thermal equilibrium, thermal imaging visualized the temperature gradient of 10 K/cm along the PVDF applicator surface, which agreed with FEA modeling. For Ir192 source activities ranging from 4.20-10.20 Ci, thermal imaging could verify source activity with an accuracy of 6.3% with a dwell time of 10 sec, and an accuracy of 2.5 % with 100 sec. CONCLUSION Thermal imaging is a feasible tool to visualize HDR source dwell positions and verify source integrity. Patient safety and treatment quality will be improved by integrating thermal measurements into HDR QA procedures.