Quality of Radiotherapy Workforce Training within the USA

The training, competency requirements and scope of practice of professionals within a radiation oncology department vary across countries. The purpose of this review is to shed light on the current status of radiotherapy training in the USA by discussing current benchmarks for medical residency, physics residency, radiation therapy and dosimetry training programmes. Although there are notable strengths, the US radiotherapy workforce training system also faces several challenges when it comes to standardising education to develop a competent workforce that meets societal needs. Continued efforts are needed at a systemic level to improve training in areas such as brachytherapy and proton therapy, promote research involvement and develop trainees who are equipped to form a competent radiation therapy workforce.

Contouring Analysis on Synthetic Contrast-Enhanced MR from GRMM-GAN and Implications on MR-Guide Radiation Therapy

PURPOSE/OBJECTIVE(S)

MR-guided linear accelerators have been commercialized making MR-only planning and adaptation an appealing alternative circumventing MR-CT registration. However, obtaining daily contrast-enhanced MR images can be prohibitive due to the increased risk of side effects from repeated contrast injections. In this work, we evaluate the quality of contrast-enhanced multi-modal MR image synthesis network GRMM-GAN (gradient regularized multi-modal multi-discrimination sparse-attention fusion generative adversarial network) for MR-guided radiation therapy.

MATERIALS/METHODS

With IRB approval, we trained the GRMM-GAN based on 165 abdominal MR studies from 65 patients. Each study included T2, T1 pre-contrast (T1pre), and T1 contrast enhanced (T1ce) images. The two pre-contrast MR modalities, T2 and T1pre images were adopted as inputs for GRMM-GAN, and the T1ce image at the portal venous phase was used as an output. Ten MR scans containing 21 liver tumors were selected for contouring analysis. A Turing test was first given to six radiation oncologists, in which 100 real T1ce and synthetic T1ce image slices are randomly given to the radiation oncologists to determine the authenticity of the synthesis. We then invited two radiation oncologists (RadOnc 1 and RadOnc2) to manually contour the 21 liver tumors independently on the real T1ce images. RadOnc2 then performed contouring on the respective synthetic T1ce MRs. DICE coefficient (defined as the intersection over the average of two volumes) and Hausdorff distance (HD, measuring how far two volumes are from each other) were used as analysis metrics. The DICE coefficients were calculated from the two radiation oncologists' contours on the real T1ce MR for each tumor. The DICE coefficients were also calculated from RadOnc 2's contours on real and synthetic MRs. Besides, tumor center shifts were extracted. The tumor center of mass coordinates was extracted from real and synthetic volumes. The difference in the coordinates indicated the shifts in the superior-inferior (SI), right-left (RL), and anterior-posterior (AP) directions between real and synthetic tumor volumes.

RESULTS

An average of 52.3% test score was achieved from the six radiation oncologists, which is close to random guessing. RadOnc 1 and RadOnc 2, who had participated in the contouring analysis, achieved an average DICE of 0.91±0.02 from tumor volumes drawn on the real T1ce MRs. This result sets the inter-operator uncertainty baseline in the real clinical setting. RadOnc 2 achieved an average DICE (real vs. synth) of 0.90±0.04 and HD of 4.76±1.82 mm. Only sub-millimeter (SI: 0.67 mm, RL: 0.41 mm, AP: 0.39 mm) tumor center shifts were observed in all three directions.

CONCLUSION

The GRMM-GAN method has the potential for MR-guided liver radiation when contrast agents cannot be administered daily and provide synthetic contrast-enhanced MR for better tumor targeting. The network can produce synthetic MR images with satisfactory contour agreement and geometric integrity.

Single projection driven real-time multi-contrast (SPIDERM) MR imaging using pre-learned spatial subspace and linear transformation

Objective. To develop and test the feasibility of a novel Single ProjectIon DrivEn Real-time Multi-contrast (SPIDERM) MR imaging technique that can generate real-time 3D images on-the-fly with flexible contrast weightings and a low latency. Approach. In SPIDERM, a ‘prep’ scan is first performed, with sparse k-space sampling periodically interleaved with the central k-space line (navigator data), to learn a subject-specific model, incorporating a spatial subspace and a linear transformation between navigator data and subspace coordinates. A ‘live’ scan is then performed by repeatedly acquiring the central k-space line only to dynamically determine subspace coordinates. With the ‘prep’-learned subspace and ‘live’ coordinates, real-time 3D images are generated on-the-fly with computationally efficient matrix multiplication. When implemented based on a multi-contrast pulse sequence, SPIDERM further allows for data-driven image contrast regeneration to convert real-time contrast-varying images into contrast-frozen images at user’s discretion while maintaining motion states. Both digital phantom and in-vivo experiments were performed to evaluate the technical feasibility of SPIDERM. Main results. The elapsed time from the input of the central k-space line to the generation of real-time contrast-frozen 3D images was approximately 45 ms, permitting a latency of 55 ms or less. Motion displacement measured from SPIDERM and reference images showed excellent correlation ( R 2 ≥ 0.983 ). Geometric variation from the ground truth in the digital phantom was acceptable as demonstrated by pancreas contour analysis (Dice ≥ 0.84, mean surface distance ≤ 0.95 mm). Quantitative image quality metrics showed good consistency between reference images and contrast-varying SPIDREM images in in-vivo studies (mean NMRSE = 0.141 , PSNR = 3 0.12 , SSIM = 0.88 ). Significance. SPIDERM is capable of generating real-time multi-contrast 3D images with a low latency. An imaging framework based on SPIDERM has the potential to serve as a standalone package for MR-guided radiation therapy by offering adaptive simulation through a ‘prep’ scan and real-time image guidance through a ‘live’ scan.

Definitive chemoradiation or radiation therapy alone for the management of vulvar cancer

Vulvar cancer is rare, and unresectable disease provides a therapeutic conundrum. Although definitive surgery remains the mainstay for curative treatment of vulvar cancer, a minority of patients present with advanced disease for which surgical resection would be extraordinarily morbid. Pre-operative and definitive radiation with radiosensitizing systemic therapy allows such patients an opportunity for cure. In this review, we explore the origins of pre-operative radiation, current treatment standards for pre-operative and definitive chemoradiation, and future directions.

Initial Data Pooling for Radiation Dose-Volume Tolerance for Carotid Artery Blowout and Other Bleeding Events in Hypofractionated Head and Neck Retreatments

PURPOSE

Dose-volume data for injury to carotid artery and other major vessels in stereotactic body radiation therapy (SBRT)/SABR head and neck reirradiation were reviewed, modeled, and summarized.

METHODS AND MATERIALS

A PubMed search of the English-language literature (stereotactic and carotid and radiation) in April 2018 found 238 major vessel maximum point doses in 6 articles that were pooled for logistic modeling. Two subsequent studies with dose-volume major vessel data were modeled separately for comparison. Attempts were made to separate carotid blowout syndrome from other bleeding events (BE) in the analysis, but we acknowledge that all except 1 data set has some element of BE interspersed.

RESULTS

Prior radiation therapy (RT) dose was not uniformly reported per patient in the studies included, but a course on the order of conventionally fractionated 70 Gy was considered for the purposes of the analysis (with an approximately ≥6-month estimated interval between prior and subsequent treatment in most cases). Factors likely associated with reduced risk of BE include nonconsecutive daily treatment, lower extent of circumferential tumor involvement around the vessel, and no surgical manipulation before or after SBRT.

CONCLUSIONS

Initial data pooling for reirradiation involving the carotid artery resulted in 3 preliminary models compared in this Hypofractionated Treatment Effects in the Clinic (HyTEC) report. More recent experiences with alternating fractionation schedules and additional risk-reduction strategies are also presented. Complications data for the most critical structures such as spinal cord and carotid artery are so limited that they cannot be viewed as strong conclusions of probability of risk, but rather, as a general guideline for consideration. There is a great need for better reporting standards as noted in the High Dose per Fraction, Hypofractionated Treatment Effects in the Clinic introductory paper.

Physician-Predicted Prognosis and Palliative Radiotherapy Treatment Utilization at the End of Life: An Audit of a Large Cancer Center Network

CONTEXT

At our institution, clinical pathways capture physicians' prognostication of patients being evaluated for palliative radiotherapy. We hypothesize a low utilization rate of long-course radiotherapy (LCRT) and stereotactic ablative radiotherapy (SAbR) among patients seen at the end of life, especially those with physician-predicted poor prognosis.

OBJECTIVE

To analyze utilization rates and predictors of LCRT and SAbR at the end of life.

METHODS

A retrospective review was conducted on patients who were evaluated for palliative radiotherapy between January 2017 and August 2019 and died within 90 days of consultation. Binary logistic regression was used to identify predictors for utilization of LCRT (≥10 fractions) and SAbR.

RESULTS

A total of 1608 patients were identified, of which 1038 patients (64.6%) were predicted to die within a year. Six hundred ninety-three patients (66.8%) out of 1038 were prescribed LCRT or SAbR. On a multivariate analysis, patients were less likely to be prescribed LCRT if treated at an academic site (odds ratio [OR], 0.30; 95% confidence interval [CI], 0.23-0.39; P < 0.01) and treated for bone metastases (OR, 0.08; 95% CI, 0.05-0.11; P < 0.01) or other nonbrain/nonbone metastases (OR, 0.19; 95% CI, 0.13-0.30; P < 0.01). SAbR was less likely to be prescribed among patients predicted to die within a year (OR, 0.09; 95% CI, 0.06-0.16; P < 0.01), treated for bone metastases (OR, 0.13; 95% CI, 0.07-0.22; P < 0.01), with poor performance status (OR, 0.51; 95% CI, 0.31-0.85; P = 0.01), and with a breast primary (OR, 0.35; 95% CI, 0.15-0.82; P = 0.02).

CONCLUSION

Although most patients were predicted to have a limited prognosis, LCRT and SAbR were commonly prescribed at the end of life.

Hypofractionated Prostate Radiation Therapy: Adoption and Dosimetric Adherence Through Clinical Pathways in an Integrated Oncology Network

PURPOSE

Updates to consensus guidelines in October 2018 recommending moderately hypofractionated external beam radiotherapy (mHF-EBRT) in prostate cancer lagged several years after publication of evidence supporting its efficacy. In January 2018, we amended our prostate cancer clinical pathway (CP) to facilitate adoption of mHF-EBRT. Herein, we analyze patterns of care and changes in mHF-EBRT use after the CP modification.

METHODS

Our prostate CP was amended in January 2018 to make mHF-EBRT the recommended treatment for patients with low- and intermediate-risk prostate cancer pursuing curative EBRT monotherapy. Normal-tissue dose constraints accompanied the CP modification to guide planning. Use of mHF-EBRT from 2015 to 2017 was compared with use in 2018 after the CP modification, using the Cochran-Armitage test for trend. Predictors of mHF-EBRT use and adherence to dose constraints were analyzed with binary logistic regression.

RESULTS

In 560 patients treated with EBRT monotherapy, mHF-EBRT use increased from 3.7% in 2015-2017 to 85.6% in 2018 (P < .001), whereas conventionally fractionated EBRT (CF-EBRT) use decreased from 96.3% to 14.4% (P < .001). Consultation year of 2018 (odds ratio [OR], 214.6; 95% CI, 94.5 to 484.6; P < .001), treatment at an academic facility (OR, 4.5; 95% CI, 1.8 to 11.3; P = 0.001), and having a smaller prostate (OR, 0.99; 95% CI, 0.97 to 1.00; P = .028) predicted for mHF-EBRT use. At least five of six recommended bladder and rectal dose constraints were met in 89.4% of patients.

CONCLUSION

Modification of our prostate cancer CP, in concert with institutional policies to monitor and audit CP compliance, facilitated rapid adoption of mHF-EBRT in our large, integrated cancer center with good adherence to dosimetric constraints.

Dose-escalated intensity modulated radiation therapy in patients with locally-advanced vulvar cancer - does it increase response rate?

PURPOSE

GOG 205 safely increased clinical (cCR) and pathologic complete response (pCR) in locally-advanced vulvar cancer through dose escalation using three-dimensional radiotherapy (RT). The aim of this study is to assess the response of dose-escalated intensity modulated radiotherapy (IMRT) in locally-advanced vulvar cancer.

METHODS

A retrospective review of patients treated with dose-escalated (≥ 55Gy) IMRT from 2012 to 2018 for locally-advanced vulvar cancer was performed. Patients treated with preoperative or definitive intent were included. Rates of cCR and pCR were assessed, and predictors of disease-free survival (DFS) were analyzed using the Kaplan Meier method with log rank test between groups and a parsimonious multivariate Cox model.

RESULTS

Median dose to the vulva was 66.0 Gy (Interquartile Range [IQR]: 66.0-68.0) for definitive and 59.4 Gy (IQR: 58.0-59.4) for preoperative IMRT. The overall rates of cCR and pCR were 76% and 70%, respectively. DFS at two years was 65% (95% Confidence Interval [CI] 50-80%) for all patients, 81% (95% CI 63% - 98%) for definitive IMRT, and 55% (95% CI 35% - 76%) for preoperative IMRT. On multivariate analysis, cCR predicted for disease-free survival (HR 0.21; 95% CI 0.06-0.76; p = 0.02), and pCR predicted for OS (HR 0.12; 95% CI 0.02-0.60; p = 0.01). Grade 3 acute and late RT toxicity was seen in 14 (29%) and 3 (6%) of patients, respectively.

CONCLUSION

Dose-escalated IMRT for locally-advanced vulvar cancer is well tolerated, with rates of cCR and pCR that compare favorably with published data.

Quality of Regional Nodal Irradiation Plans in Breast Cancer Patients Across a Large Network-Can We Translate Results From Randomized Trials Into the Clinic?

PURPOSE

Regional nodal irradiation (RNI) improved disease-free survival by 3% to 5% in 2 large randomized trials, but this small absolute advantage relies on accurate contouring and dose delivery. We audited our network to determine compliance on regional nodal coverage, contouring, and dosimetric parameters with respect to accepted guidelines.

METHODS AND MATERIALS

In our network, we have established a clinical pathway for patients with node-positive breast cancer that guides indications for RNI and dosimetric goals. We reviewed records of 183 patients with nodal macrometastases after upfront surgery or involved nodes of any size after neoadjuvant chemotherapy. Radiation treatment plans were examined to determine lymph node volumes treated, whether nodes were contoured, quality of nodal contours, and whether target coverage and normal organ dosimetric constraints were met when RNI was delivered.

RESULTS

Despite the presence of macrometastases on sentinel lymph node biopsy, no lymph nodes were treated in 2.2% (4 of 183). Of 179 patients who received nodal irradiation, 18 received radiation to axillary levels 1 and 2 only, and 161 patients received RNI. Overall, regional nodes were not treated despite strong indications in 7.6% (14 of 183). Treated nodes were not contoured for 2.2% (4 of 179), and lymph node contours were unacceptable in 15.4% (27 of 175). Of patients receiving RNI, 14.9% (24 of 161) did not have adequate nodal target volume coverage, mean heart dose was >4 Gy for 3.1% (5 of 161), and lung V20 Gy was >35% for 8.7% (14 of 161).

CONCLUSIONS

Adherence to indications for regional nodal treatment was high, but nodes were either not contoured or had unacceptable contour quality in 18% of plans, and coverage was inadequate in 15%. Because the small disease-free survival advantage seen in trials may be decreased with these deviations, routine clinical practice requires detailed peer review to fully translate results of clinical trials.

External validation of life expectancy prognostic models in patients evaluated for palliative radiotherapy at the end-of-life

Background

The TEACHH and Chow models were developed to predict life expectancy (LE) in patients evaluated for palliative radiotherapy (PRT). We sought to validate the TEACHH and Chow models in patients who died within 90 days of PRT consultation.

Methods

A retrospective review was conducted on patients evaluated for PRT from 2017 to 2019 who died within 90 days of consultation. Data were collected for the TEACHH and Chow models; one point was assigned for each adverse factor. TEACHH model included: primary site of disease, ECOG performance status, age, prior palliative chemotherapy courses, hospitalization within the last 3 months, and presence of hepatic metastases; patients with 0‐1, 2‐4, and 5‐6 adverse factors were categorized into groups (A, B, and C). The Chow model included non‐breast primary, site of metastases other than bone only, and KPS; patients with 0‐1, 2, or 3 adverse factors were categorized into groups (I, II, and III).

Results

A total of 505 patients with a median overall survival of 2.1 months (IQR: 0.7‐2.6) were identified. Based on the TEACHH model, 10 (2.0%), 387 (76.6%), and 108 (21.4%) patients were predicted to live >1 year, >3 months to ≤1 year, and ≤3 months, respectively. Utilizing the Chow model, 108 (21.4%), 250 (49.5%), and 147 (29.1%) patients were expected to live 15.0, 6.5, and 2.3 months, respectively.

Conclusion

Neither the TEACHH nor Chow model correctly predict prognosis in a patient population with a survival <3 months. A better predictive tool is required to identify patients with short LE.

Cost-Effectiveness Analysis of Upfront SBRT for Oligometastatic Stage IV Non-Small Cell Lung Cancer Based on Mutational Status

OBJECTIVES

Current National Comprehensive Cancer Network (NCCN) guidelines support systemic therapy based on mutational status in stage IV non-small cell lung cancer (NSCLC), with stereotactic body radiation therapy (SBRT) reserved for oligoprogression. We aimed to evaluate the cost-effectiveness of the routine addition of SBRT to upfront therapy in stage IV NSCLC by mutational subgroup.

MATERIALS AND METHODS

A Markov state transition model was constructed to perform a cost-effectiveness analysis comparing SBRT plus maintenance therapy with maintenance therapy alone for oligometastatic NSCLC. Three hypothetical cohorts were analyzed: epidermal growth factor receptor or anaplastic lymphoma kinase mutation-positive, programmed death ligand-1 expressing, and mutation-negative group. Clinical parameters were obtained largely from clinical trial data, and cost data were based on 2018 Medicare reimbursement. Strategies were compared using the incremental cost-effectiveness ratio with effectiveness in quality-adjusted life years (QALYs) and evaluated with a willingness to pay threshold of $100,000 per QALY gained.

RESULTS

SBRT plus maintenance therapy was not cost-effective at a $100,000/QALY gained threshold, assuming the same survival for both treatments, resulting in an incremental cost effectiveness ratio of $564,186 and $299,248 per QALY gained for the epidermal growth factor receptor or anaplastic lymphoma kinase positive and programmed death ligand-1 positive cohorts, respectively. Results were most sensitive to the cost of maintenance therapy. A large overall survival gain with SBRT could potentially result in upfront SBRT becoming cost-effective. For the mutation-negative cohort, upfront SBRT was nearly cost-effective, costing $128,424 per QALY gained.

CONCLUSION

Adding SBRT to maintenance therapy is not a cost-effective strategy for oligometastatic NSCLC compared with maintenance therapy alone for mutation-positive groups. However, this should be validated via randomized trials.

Dose-response model for severe late laryngeal toxicity after stereotactic body radiation therapy for previously-irradiated head and neck cancer

We sought to evaluate the association between larynx dose and risk of severe late laryngeal toxicity in patients undergoing re-irradiation SBRT for recurrent HNC. Fifty-five patients with an intact larynx underwent re-irradiation SBRT to a median dose of 44 Gy in 5 fractions. Five (41.7%) patients treated for a laryngeal/hypopharyngeal recurrence experienced late grade ≥3 laryngeal toxicity, compared to 0.0-7.1% for other sites. Logistic dose-response models were created to predict risk of severe late laryngeal toxicity, including dysphagia and airway compromise. According to the model, the risk of severe laryngeal toxicity with a larynx D5cc of 5 Gy is 5.8% (95% CI 2.9-9.9%) and rises to 11.4% with a D5cc of 20 Gy and 25.3% with a D5cc of 40 Gy. In patients with a laryngeal/hypopharyngeal recurrence, SBRT planning should carefully assess the dose to laryngeal structures given these dose findings, and SBRT should be approached with significant caution in such patients.

Regional Recurrence Rates With or Without Complete Axillary Dissection for Breast Cancer Patients with Node-Positive Disease on Sentinel Lymph Node Biopsy after Neoadjuvant Chemotherapy

Purpose

Current standard of care for patients with breast cancer with a positive node on sentinel lymph node biopsy (SLNB) after neoadjuvant chemotherapy is axillary dissection with irradiation of the regional nodes, but it is unknown whether axillary lymph node dissection (ALND) can be safely omitted if complete axillary radiation is delivered instead.

Methods and Materials

We identified 161 patients found to have a positive sentinel lymph node on SLNB after neoadjuvant chemotherapy for breast cancer between December 2006 and October 2017, who were treated with or without completion ALND. Local, regional, and distant recurrence and overall survival were analyzed using the Kaplan-Meier method. Patient, disease, and treatment factors potentially predictive of each outcome were entered into Cox regression analysis.

Results

Median follow-up was 28.8 months (range, 2.5-137.0). The 3-year regional control rate did not differ according to extent of axillary surgery (92.6% for SLNB alone vs 96.4% for SLNB with ALND, P = .616). Regional recurrence occurred as part of first recurrence in 9 patients (5.6%). Five patients failed in axillary levels 1 or 2, 6 failed in axillary level 3 or supraclavicular nodes, and 2 failed in internal mammary nodes, with some patients failing in multiple regional nodal areas. Extent of axillary dissection (SLNB only vs SLNB plus ALND) did not predict for disease control or survival. Patients who underwent ALND were significantly more likely to have lymphedema (25.0% vs 9.4%, P = .021).

Conclusions

Careful selection of patients with a positive sentinel node on SLNB after neoadjuvant chemotherapy for omission of completion ALND in favor of irradiation of the undissected axilla does not compromise local, regional, or distant control or overall survival and results in lower rates of lymphedema.

Salvage Curative-Intent Reirradiation Stereotactic Body Radiation Therapy for Isolated Pelvic and/or Paraortic Recurrences of Gynecologic Malignancies

PURPOSE

To determine the feasibility of stereotactic body radiation therapy (SBRT) for isolated nodal recurrences of gynecologic malignancies within a previously irradiated area.

METHODS AND MATERIALS

A retrospective review was performed on 20 patients who underwent 21 curative-intent reirradiation SBRT treatments for locoregional recurrences of gynecologic malignancies. Disease control and survival outcomes were analyzed with the Kaplan-Meier method and log-rank test. Treatment toxicities were graded according to Common Terminology Criteria for Adverse Events version 4.03.

RESULTS

All patients had an isolated pelvic, paraortic, or intra-abdominal nodal recurrence, with the exception of 1 patient who had a concurrent paraortic and right acetabulum metastasis, both of which were irradiated with SBRT. Primary sites included cervix (30.0%), uterus (55.0%), vulva (5.0%), vagina (5.0%), and ovary (5.0%). Median prior external beam radiation therapy dose was 45 Gy. Recurrences were in field in 14 (66.7%) and marginal in 7 (33.3%). SBRT was directed to the pelvis in 13 cases (61.9%) and to paraortic or celiac nodes in 8 (38.1%). The most common SBRT regimen was 40 to 45 Gy in 5 fractions (n = 12). At a median follow-up of 31.2 months, 3-year actuarial in-field local control, distant progression-free survival, and overall survival were 61.4%, 44.0%, and 51.9%, respectively. At the time of last follow-up, 9 (45.0%) patients remained alive without evidence of disease. Actuarial 3-year risk of grade ≥2 and grade ≥3 late toxicities was 38.1% and 14.3%, respectively.

CONCLUSIONS

SBRT for isolated pelvic or intra-abdominal recurrences of gynecologic malignancies within a previously irradiated field is feasible with an acceptable toxicity rate. With this approach, about half of patients achieved durable disease-free survival.

Is Multifocal Regression a Risk Factor for Ipsilateral Breast Tumor Recurrence in the Modern Era After Neoadjuvant Chemotherapy and Breast Conservation Therapy?

PURPOSE

Multifocal pattern of regression after neoadjuvant chemotherapy has been identified as a risk factor for ipsilateral breast tumor recurrence (IBTR). We aimed to determine the significance of multifocal regression as a predictor of IBTR after neoadjuvant chemotherapy and breast conservation therapy in the modern era.

METHODS AND MATERIALS

We retrospectively reviewed 346 patients treated between November 2009 and June 2017. Pattern of regression was categorized as pathologic complete response (pCR), unifocal (tumor present as a cohesive mass), limited multifocal (single cells or clusters of cells concentrated in 1 portion of the fibrotic area), or diffuse multifocal (cells spread over entire fibrotic area). IBTR was defined as new ipsilateral invasive or noninvasive breast tumor after breast conservation therapy. Predictive factors were analyzed using Cox regression.

RESULTS

Incidence of multifocal regression was 25.7% for the overall cohort and 12.2% for estrogen receptor (ER) negative/progesterone receptor (PR) negative/human epidermal growth factor receptor 2 (HER2) positive, 17.5% for triple-negative, 36.9% for ER+ or PR+/HER2-, and 38.5% for triple-positive (P < .001). With a median follow-up of 41.1 months, 4-year IBTR-free survival after pCR or unifocal regression versus multifocal regression was 94.1% versus 90.9% (P = .411). Pattern of regression (P = .010; compared to pCR, hazard ratio [HR] of 11.2 for diffuse multifocal regression, 1.65 for limited multifocal regression, and 3.81 for unifocal regression), phenotype (P = .001; compared to ER+ or PR+/HER2-, HR of 30.67 for ER-/PR-/HER2+, 25.30 for triple-negative, and 1.60 for triple-positive), and lack of nodal pCR (P = .004; HR of 3.78) predicted for IBTR on multivariate Cox regression. On multivariate subset analysis, pattern of regression and lymphovascular space invasion predicted for IBTR in hormone receptor-negative patients, but pattern of regression was not associated with IBTR for hormone receptor-positive patients.

CONCLUSIONS

Multifocal regression, hormone receptor-negative phenotype, and lack of nodal pCR predict for increased risk of IBTR after neoadjuvant chemotherapy. Although more common in hormone receptor-positive disease, multifocal regression was associated with worse outcome only in hormone receptor-negative patients.

Dose-response modeling the risk of carotid bleeding events after stereotactic body radiation therapy for previously irradiated head and neck cancer

Given the lack of clear dose constraints for the carotid artery, we created dose-response models to better quantify the risk of carotid bleeding events following re-irradiation stereotactic body radiation therapy (SBRT) for head and neck cancer (HNC). We performed a retrospective analysis on 75 patients treated with SBRT for recurrent, previously irradiated HNC. Logistic dose-response models were created to predict the risk of a carotid bleeding event, defined as any mucosal bleeding event or bleeding resulting from rupture of the carotid artery or its major branches in the setting of controlled disease. According to the models, the risk of a carotid bleeding event with a cumulative D_0.1cc of 20 Gy from SBRT is 0.8% (95% CI 0.1%-3.9%), and rises to 5.0% with a D_0.1cc of 50 Gy. No patient experienced a carotid bleeding event with D_0.1cc < 39.4 Gy, and none experienced carotid blowout syndrome with a cumulative D_0.1cc < 47.6 Gy.

Hypofractionated Whole-Breast Irradiation in Large-Breasted Women-Is There a Dosimetric Predictor for Acute Skin Toxicities?

PURPOSE

Underutilization of hypofractionated whole-breast irradiation (HF-WBI) in large-breasted women may be partially explained by concerns about dose heterogeneity. Although modern planning may mitigate this issue, validated dosimetric guidelines are lacking. Our clinical pathway mandates hypofractionation, guided by institutional dosimetric criteria for plan evaluation. We examined acute radiation dermatitis rates with HF-WBI in large-breasted patients when our guidelines are followed and evaluated factors predictive for dermatitis.

METHODS AND MATERIALS

Patients with whole-breast clinical target volumes (WB-CTV) of ≥1000 cm3 treated with HF-WBI were reviewed. WB-CTV V105, V107, and V110 were assessed. Our guidelines recommend limiting V105 to <10% to 15% and V110 to 0%. The highest grade of acute dermatitis was recorded. Potential clinical and dosimetric predictors of dermatitis were analyzed using logistic regression.

RESULTS

From 2012 to 2017, 505 breasts in 502 patients were treated with HF-WBI. The median WB-CTV was 1261.3 cm3 (interquartile range [IQR], 1115.3-1510.0). Most plans (99%) delivered 42.56 Gy in 16 fractions. A cavity boost of 10 Gy in 4 fractions was delivered in 99% of plans. Electrons were used in 69% of boost plans. Three-dimensional field-in-field technique was used in 68% of plans and inverse-planned intensity modulated radiation therapy in 32%. The median WB-CTV V105 was 9.7% (IQR, 5.6%-13.3%); the median WB-CTV V107 was 0.8% (IQR, 0.0%-2.5%). The WB-CTV V110 was 0% in 97.4% of plans (median, 0.0%; IQR, 0.0%-0.0%). Grade 1, 2, and 3 dermatitis rates were 55.0%, 40.8%, and 3.4%, respectively. On multivariate analysis, age >64 years (P = .016; odds ratio [OR] 4.0; 95% confidence interval [CI], 1.3-12.3), WB-CTV >1500 cm3 (P = .006; OR, 4.3; 95% CI, 1.5-12.3), body mass index ≥34 (P = .044; OR, 3.9; 95% CI, 1.0-14.5), and WB-CTV V105 >10% (P = .011; OR, 5.3; 95% CI, 1.5-19.3) predicted for grade 3 dermatitis.

CONCLUSIONS

With our institutional dosimetric guidelines, grade 3 dermatitis rates with HF-WBI in large-breasted women was <5%. WB-CTV V105 should be optimized to <10% to keep grade 3 dermatitis rates <2%.

Outcomes after definitive re-irradiation with 3D brachytherapy with or without external beam radiation therapy for vaginal recurrence of endometrial cancer

BACKGROUND

Limited outcome data exists on salvage re-irradiation for vaginal relapse of previously-irradiated endometrial cancer. We report our 10-year experience with management of vaginal recurrence using definitive intent re-irradiation brachytherapy with or without EBRT.

METHODS

A retrospective review was performed on 22 patients treated with definitive-intent re-irradiation brachytherapy ± EBRT for vaginal recurrence of endometrial cancer. The cumulative rectosigmoid and bladder D2cc (EQD2) were limited to <75 Gy and <90 Gy, respectively. Kaplan-Meier and Cox proportional hazards modeling were used to estimate survival. Severe (grade 3 or higher) radiation-related toxicities, defined according to CTCAE v4, were recorded.

RESULTS

Prior radiation therapy consisted of vaginal brachytherapy (54.5%), pelvic EBRT (22.7%), or combination pelvic EBRT and brachytherapy (22.7%). Median re-irradiation interval was 26.6 months. Salvage re-irradiation consisted of EBRT with brachytherapy in 50.0% and brachytherapy alone in 50.0%. Median HR-CTV D90 (EQD2) was 64.5 Gy (IQR: 49.6-75.8). Median cumulative D2cc for bladder, rectum, and sigmoid were 72.1 Gy (range: 30.3-81.8), 70.6 Gy (range: 32.0-80.5), and 52.7 Gy (range: 29.6-75.3), respectively. At a median follow-up of 27.6 months, 3-year local control, regional control, disease-free survival, and overall survival rates were 65.8%, 76.6%, 40.8%, and 68.1%, respectively. There were no grade ≥ 3 acute or late rectosigmoid or bladder toxicities.

CONCLUSION

Re-irradiation with 3D conformal brachytherapy for vaginal recurrence is feasible and safe as long as cumulative dose to surrounding normal organs is limited, and offers a chance to potentially salvage 40% of patients presenting with vaginal recurrence in the setting of prior pelvic radiation.

Lag Time Between Evidence and Guidelines: Can Clinical Pathways Bridge the Gap?

PURPOSE:

The 2018 American Society for Radiation Oncology guidelines state that hypofractionated whole-breast irradiation (HF-WBI) may be used for early-stage breast cancer regardless of age, although evidence to support this became available years ago. Before guideline publication, we sought to change the practice pattern within an integrated, comprehensive radiation oncology network using clinical pathways.

METHODS:

The breast clinical pathway was amended in January 2016 to allow HF-WBI as a pathway-concordant option for women younger than 50 years of age. In December 2016, the pathway was amended to mandate HF-WBI as the only pathway-concordant option. Women younger than 50 years of age treated for stage 0 to IIA breast cancer, without irradiation of regional nodes, were included. Potential predictors of hypofractionation use were analyzed using binary logistic regression.

RESULTS:

We identified 305 patients treated between 2013 and 2017. From 2013 to December 2015, HF-WBI use was 4.2%. After the first and second amendments, use increased to 53.1% ( P < .001) and 96.5% ( P < .001), respectively. Before amendment 1, there was no difference in use of hypofractionation at academic (2.6%) versus community (4.7%) sites ( P = .568). After amendment 1, academic practices were more likely to use hypofractionation (72.0% v 44.6%; P = .026). After amendment 2, there was, again, no difference between academic (100.0%) and community (95.3%) practices ( P = .999).

CONCLUSION:

With implementation of a clinical pathway that mandated use of HF-WBI regardless of age, HF-WBI use for women younger than 50 years of age rapidly increased from 4.2% to greater than 95%. Clinical pathways effectively standardize patterns of care to reflect the most up-to-date clinical evidence, independently of guideline publication.

Role of Immunotherapy in Head and Neck Cancer

Immune system dysfunction plays a role in both the development and progression of head and neck squamous cell carcinoma (HNSCC), highlighting the potential role for immunotherapy to improve outcomes in this disease. The application of anti-PD-1 therapies for recurrent or metastatic HNSCC has found promising results. This has led to interest in combining immunotherapy with radiation therapy (RT) for the primary treatment of locally advanced HNSCC. RT with concurrent cetuximab is an option for patients who are medically unfit to receive cisplatin, and ongoing trials seek to determine to role of cetuximab-RT in treatment de-intensification for HPV+ oropharyngeal HNSCC. Other ongoing trials are evaluating the use of anti-PD-1 and anti-PD-L1 therapies in the upfront setting for newly diagnosed high-risk, locally advanced HNSCC, in an effort to improve disease control. Finally, early phase I studies are now investigating the use of anti-PD-1 therapy in conjunction with RT for refractory recurrent or metastatic HNSCC.

Risk of Severe Toxicity According to Site of Recurrence in Patients Treated With Stereotactic Body Radiation Therapy for Recurrent Head and Neck Cancer

PURPOSE

To report a 10-year update of our institutional experience with stereotactic body radiation therapy (SBRT) for reirradiation of locally recurrent head and neck cancer, focusing on predictors of toxicity.

METHODS AND MATERIALS

A retrospective review was performed on 291 patients treated with SBRT for recurrent, previously irradiated head and neck cancer between April 2002 and March 2013. Logistic regression analysis was performed to identify predictors of severe acute and late toxicity. Patients with <3 months of follow-up (n=43) or who died within 3 months of treatment (n=21) were excluded from late toxicity analysis.

RESULTS

Median time to death or last clinical follow-up was 9.8 months among the entire cohort and 53.1 months among surviving patients. Overall, 33 patients (11.3%) experienced grade ≥3 acute toxicity and 43 (18.9%) experienced grade ≥3 late toxicity. Compared with larynx/hypopharynx, treatment of nodal recurrence was associated with a lower risk of severe acute toxicity (P=.03), with no significant differences in severe acute toxicity among other sites. Patients treated for a recurrence in the larynx/hypopharynx experienced significantly more severe late toxicity compared with those with oropharyngeal, oral cavity, base of skull/paranasal sinus, salivary gland, or nodal site of recurrence (P<.05 for all). Sixteen patients (50%) with laryngeal/hypopharyngeal recurrence experienced severe late toxicity, compared with 6-20% for other sites.

CONCLUSIONS

Salvage SBRT is a safe and effective option for most patients with previously irradiated head and neck cancer. However, patients treated to the larynx or hypopharynx experience significantly more late toxicity compared with others and should be carefully selected for treatment, with consideration given to patient performance status, pre-existing organ dysfunction, and goals of care. Treatment toxicity in these patients may be mitigated with more conformal plans to allow for increased sparing of adjacent normal tissues.

Locoregional Recurrent or Second Primary Head and Neck Cancer: Management Strategies and Challenges

Treatment of patients with locoregional recurrent or second primary head and neck squamous cell cancer (HNSCC) has been guided by well-reasoned principles and informed by carefully tested chemotherapy and radiation regimens. However, clinical decision making for this population is complicated by many factors. Although surgery is generally considered the treatment of choice for patients with HNSCC with recurrent disease or new second primary disease in a previously irradiated field, operability of cases is not always straightforward. Postoperative treatment is frequently warranted but carries significant risk. In addition, the rapid rise in the incidence of HPV-associated HNSCC raises the question of whether established treatment paradigms should be re-examined in this population of patients with a much better prognosis than the non-HPV population. Furthermore, new radiation techniques and new systemic agents show early promising results in recent clinical studies, suggesting potential for practice-changing effects in the future management of this disease. This article examines each of the treatment modalities used in the care of patients with HNSCC with recurrent or new second primary disease and provides a perspective to aid clinicians in the management of this disease.

Underutilization of radiation therapy in early-stage marginal zone lymphoma negatively impacts overall survival

PURPOSE

Multiple population-based studies have suggested increasing omission of radiation therapy in favor of alternative treatment strategies in lymphomas, with an associated negative impact on survival. Radiation therapy has long been considered the standard management for many mucosa-associated lymphoid tissue lymphomas. Thus, we aimed to evaluate patterns of treatment utilization and survival.

METHODS AND MATERIALS

A retrospective analysis based on the National Cancer Database was performed on 22,378 patients with splenic, nodal, or extranodal stage I-II marginal zone lymphoma diagnosed between 1998 and 2012. A logistic regression model was used to assess the association between sociodemographic, tumor, and treatment characteristics and the utilization of radiation therapy. Multivariate propensity score-adjusted Cox proportional hazards models were performed to identify factors independently associated with overall survival (OS).

RESULTS

Of 22,378 patients, 82% had stage I disease, 77% had extranodal mucosa-associated lymphoid tissue lymphoma, 5% had splenic marginal zone lymphoma, and 64% were older than 60 years. Radiation therapy utilization decreased from a peak of 39% in 2007 to 33% in 2011 (P < .001), with a corresponding significant increase in systemic therapy utilization. Radiation therapy was associated with a 5- and 10-year OS of 86.7% and 68.8% compared with 78.3% and 54.3% for no radiation therapy (P < .001). On multivariate propensity score-adjusted survival analysis, radiation therapy remained independently associated with improved OS (hazard of death, 0.75; 95% confidence interval, 0.65-0.85; P < .001).

CONCLUSIONS

Although clinical guidelines endorse radiation therapy as the preferred initial therapy for early-stage nongastric and Helicobacter pylori-negative gastric mucosa-associated lymphoid tissue lymphoma, radiation therapy is underused. Radiation therapy with or without systemic therapy was associated with a significant improvement in OS and should remain standard of care.

Comparison of Toxicity Between Intensity-Modulated Radiotherapy and 3-Dimensional Conformal Radiotherapy for Locally Advanced Non-small-cell Lung Cancer

BACKGROUND

The role of intensity-modulated radiotherapy (IMRT) in reducing treatment-related toxicity for locally advanced non-small-cell lung cancer (NSCLC) remains incompletely defined. We compared acute toxicity and oncologic outcomes in a large cohort of patients treated with IMRT or 3-dimensional conformal radiotherapy (3-DCRT), with or without elective nodal irradiation (ENI).

METHODS

A single-institution retrospective review was performed evaluating 145 consecutive patients with histologically confirmed stage III NSCLC treated with definitive chemoradiotherapy. Sixty-five (44.8%) were treated with 3-DCRT using ENI, 43 (30.0%) with 3-DCRT using involved-field radiotherapy (IFRT), and 37 (25.5%) with IMRT using IFRT. All patients received concurrent chemotherapy. Comparison of acute toxicities by treatment technique (IMRT vs. 3-DCRT) and extent of nodal irradiation (3-DCRT-IFRT vs. 3-DCRT-ENI) was performed for grade 2 or higher esophagitis or pneumonitis, number of acute hospitalizations, incidence of opioid requirement, percutaneous endoscopic gastrostomy utilization, and percentage weight loss during treatment. Local control and overall survival were analyzed by the Kaplan-Meier method.

RESULTS

We identified no significant differences in any measures of acute toxicity by treatment technique or extent of nodal irradiation. There was a trend toward lower rates of grade 2 or higher pneumonitis among IMRT patients compared to 3-DCRT patients (5.4% vs. 23.0%; P = .065). Local control and overall survival were similar between cohorts.

CONCLUSION

Acute and subacute toxicities were similar for patients treated with IMRT and with 3-DCRT with or without ENI, with a nonsignificant trend toward a reduction in pneumonitis with IMRT. Larger studies are needed to better define which patients will benefit from IMRT.

Incidence of hospitalization in patients with head and neck cancer treated with intensity-modulated radiation therapy

BACKGROUND

Patients with primary head and neck cancer managed with radiation therapy (RT) +/- chemotherapy may experience significant treatment-related toxicities. We assessed hospitalization as a metric for severe treatment-related toxicities and evaluated patient and treatment factors for possible association.

METHODS

A retrospective review was performed on 147 patients with head and neck cancer treated with definitive or adjuvant intensity-modulated radiation therapy (IMRT) +/- chemotherapy. Multiple Poisson regression model was used to analyze relationships between patient or treatment factors and number of hospital stays during RT and within 8 weeks after RT.

RESULTS

Multivariate analysis showed preexisting diabetes or pulmonary disease, primary carcinoma of oral cavity, and prescribed radiation dose (p < .05) were associated with increased number of patient hospital stays during or shortly after RT.

CONCLUSION

We found that 34.7% of patients experienced a chemoradiation toxicity-related hospitalization during or shortly after treatment. Prior pulmonary disease, diabetes, and increasing prescribed radiation dose were associated with increased hospital stays.

Postoperative stereotactic radiosurgery to the resection cavity for large brain metastases: clinical outcomes, predictors of intracranial failure, and implications for optimal patient selection

BACKGROUND

Postoperative stereotactic radiosurgery for brain metastases potentially offers similar local control rates and fewer long-term neurocognitive sequelae compared to whole brain radiation therapy, although patients remain at risk for distant brain failure (DBF).

OBJECTIVE

To describe clinical outcomes of adjuvant stereotactic radiosurgery for large brain metastases and identify predictors of intracranial failure and their implications on optimal patient selection criteria.

METHODS

We performed a retrospective review on 100 large (>3 cm) brain metastases in 99 patients managed by resection followed by postoperative stereotactic radiosurgery to a median dose of 22 Gy (range, 10-28) in 1 to 5 fractions (median, 3). Primary histology was nonsmall cell lung in 40%, breast cancer in 18%, and melanoma in 17%. Forty (40%) patients had uncontrolled systemic disease.

RESULTS

With a median follow-up of 12.2 months (range, 0.6-87.4), the 1-year Kaplan-Meier local control was 72%, DBF 64%, and overall survival 55%. Nine patients (9%) developed evidence of radiation injury, and 6 (6%) developed leptomeningeal disease. Uncontrolled systemic disease (P=.03), melanoma histology (P=.04), and increasing number of brain metastases (P<.001) were significant predictors of DBF on Cox multivariate analysis. Patients with <4 metastases, controlled systemic disease, and nonmelanoma primary (n=47) had a 1-year DBF of 48.6% vs 80.1% for all others (P=.01).

CONCLUSION

Postoperative stereotactic radiosurgery to the resection cavity safely and effectively augments local control of large brain metastases. Patients with <4 metastases and controlled systemic disease have significantly lower rates of DBF and are ideal treatment candidates.

Oncologic Outcomes in Patients with Oropharyngeal Squamous Cell Carcinoma Treated with TORS versus Definitive CRT

Objectives:

It has been postulated that treatment outcomes are similar between transoral robotic surgery (TORS) and definitive chemoradiation (CRT) for patients with oropharyngeal squamous cell carcinomas (OPSCC). We compared oncologic outcomes between OPSCC patients treated with definitive CRT and those treated with TORS only.

Methods:

An observational comparison study was performed on 23 patients treated with TORS without adjuvant therapy and 33 patients treated with definitive CRT between July 2005 and December 2013. All patients had early stage disease with T0-T2 and N0-N2. Median age was 57 (range: 36-82) years and 80.4% of patients were male, which was similar between groups. Human papillomavirus (HPV)+ disease was present in 70.0% of TORS and 33.3% of CRT patients, although HPV status was not tested in 63.6% of the CRT patients.

Results:

Median follow-up was 22.5 months (range, 0.33-83.4 months). Local failure rate for the entire cohort was 7.1% (9.1% for definitive CRT, 4.3% for TORS, P = .85). Overall regional failure rate was 3.6% (3.0% for definitive CRT, 4.3% for TORS, P = .48). Overall distant failure rate was 5.4% (9.1% for definitive CRT, 0.0% for TORS, P = .24). Two-year actuarial disease-free survival (DFS) was 86.7% for definitive CRT patients and 80.0% for patients treated with TORS alone ( P = .69).

Conclusions:

Definitive CRT and TORS alone offer similar rates of locoregional control, distant control, and DFS in patients with early stage OPSCC. Further studies are needed to assess the effect of CRT and TORS on quality of life in this patient population.

An interchangeable scanning Hall probe/scanning SQUID microscope

We have constructed a scanning probe microscope for magnetic imaging, which can function as a scanning Hall probe microscope (SHPM) and as a scanning SQUID microscope (SSM). The scanning scheme, applicable to SHPM and SSM, consists of a mechanical positioning (sub) micron-XY stage and a flexible direct contact to the sample without a feedback control system for the Z-axis. With the interchangeable capability of operating two distinct scanning modes, our microscope can incorporate the advantageous functionalities of the SHPM and SSM with large scan range up to millimeter, high spatial resolution (⩽4 μm), and high field sensitivity in a wide range of temperature (4.2 K-300 K) and magnetic field (10(-7) T-1 T). To demonstrate the capabilities of the system, we present magnetic images scanned with SHPM and SSM, including a RbFeB magnet and a nickel grid pattern at room temperature, surface magnetic domain structures of a La(2/3)Ca(1/3)MnO3 thin film at 77 K, and superconducting vortices in a striped niobium film at 4.2 K.

Stereotactic body radiotherapy in the treatment of pancreatic adenocarcinoma in elderly patients

Background

Treatment of pancreatic adenocarcinoma in the elderly is often complicated by comorbidities that preclude surgery, chemotherapy and/or conventional external beam radiation therapy (EBRT). Stereotactic body radiotherapy (SBRT) has thus garnered interest in this setting.

Methods

A retrospective review of 26 patients of age ≥ 80 with pancreatic adenocarcinoma treated with definitive SBRT+/-chemotherapy from 2007–2011 was performed. Twenty-seven percent of patients were stage I, 38% were stage II, 27% were stage III and 8% were stage IV. Patients most commonly received 24 Gy/1 fraction or 30-36 Gy/3 fractions. Kaplan-Meier was used to estimate overall survival (OS), local control (LC), cause specific survival (CSS) and freedom-from-metastatic disease (FFMD).

Results

The median age was 86 (range 80–91), and median follow-up was 11.6 months (3.5-24.6). The median planning target volume was 21.48 cm³ (6.1-85.09). Median OS was 7.6 months with 6/12 month OS rates of 65.4%/34.6%, respectively. Median LC was 11.5 months, 6-month and 12-month actuarial LC rates were 60.1% and 41.2%, respectively. There were no independent predictors for LC, but there was a trend for improved LC with prescription dose greater than 20 Gy (p = 0.063). Median CSS was 6.3 months, and 6-month and 12-month actuarial CSS were 53.8% and 23.1%, respectively. Median FFMD was 8.4 months, and 6-month and 12-month actuarial rates were 62.0% and 41.4%, respectively. Nine patients (47%) had local failures, 11 (58%) had distant metastasis, and 7 (37%) had both. There were no acute or late grade 3+ toxicities.

Conclusions

Definitive SBRT is feasible, safe and effective in elderly patients who have unresectable disease, have comorbidities precluding surgery or decline surgery.

Correlation between magnetic properties and the electronic structures of soft magnetic ternary Fe(78-x)Y(x)B(22) (x = 4-9) bulk metallic glasses

Fe and Y K-edge extended x-ray absorption fine structure, Fe(Y) L(3,2)-edge (L(3)-edge) x-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VB-PES) measurements have been carried out to study soft magnetic ternary Fe(78-x)Y(x)B(22) bulk metallic glasses (BMGs). The combined XANES and VB-PES results do not show broadening of the Fe 3d band to support the previous interpretation of the reduction of the magnetic moment in BMGs by Y-induced decrease of exchange splitting of Fe 3d orbitals. Instead, the density of delocalized/itinerant Fe 3d states in the vicinity of the Fermi level is found to be reduced by Y substitution, which reduces the strength of itinerant-states-mediated ferromagnetic coupling between local spins on the Fe ions and the total magnetic moment of the Fe-based BMGs.

Structural and optical studies of high dielectric constant (Na(0.5)A(0.5))Cu(3)Ti(4)O(12) (A = La and Bi)

We report x-ray powder diffraction and temperature-dependent infrared reflectivity measurements of (Na(0.5)La(0.5))Cu(3)Ti(4)O(12) and (Na(0.5)Bi(0.5))Cu(3)Ti(4)O(12) in order to investigate the origin of their lower room-temperature dielectric constants in comparison with the giant value of CaCu(3)Ti(4)O(12). Substituting Ca with Na/La or Na/Bi is found to decrease all Ti-O-Ti angles by the TiO(6) octahedra tilts, resulting in an increase of the local structural disorder on the Na/La and Na/Bi compounds. Further, several infrared-active phonon modes show a broadening in their linewidths, reflecting that the coherency in these vibrational modes is degraded by disorder. Additionally, the lowest-frequency mode of the Ca material is observed to strengthen dramatically at low temperatures, but to a lesser extent in the Na/La and Na/Bi compounds. These results suggest the important role of the local structural disorder on the anomalous low-frequency dielectric response in these materials.

Charge-orbital ordering and Verwey transition in magnetite measured by resonant soft X-ray scattering

We report experimental evidence for the charge-orbital ordering in magnetite below the Verwey transition temperature T(V). Measurements of O K-edge resonant x-ray scattering on magnetite reveal that the O 2p states in the vicinity of the Fermi level exhibit a charge-orbital ordering along the c axis with a spatial periodicity of the doubled lattice parameter of the undistorted cubic phase. Such a charge-orbital ordering vanishes abruptly above T(V) and exhibits a thermal hysteresis, correlating closely with the Verwey transition in magnetite.

A cost-based index of anther culture response in diverse wheat-breeding germplasm

Anther culture response in a diverse range of Australian wheat-breeding genotypes was tested and expressed as a 'culturability index' based on the actual costs of the various laboratory procedures. When the delay from harvest to plating was up to 12 h, the use of low dose gamma irradiation did not increase the anther culture response in this array of genotypes. This is in contrast to previous findings for which spike harvesting, irradiation, and plating was completed within 3 h and the irradiation treatment increased the anther culture response. Internal contamination of immature spike explants with Fusarium poae caused significant loss of cultures and may be a persistent problem for cereal anther culture. For the genotypes producing green regenerants, costs ranged from $A1.40 to $85/green regenerant.