Initial results of a phase II trial of 18F-DOPA PET-guided re-irradiation for recurrent high-grade glioma.

PURPOSE: In-field high-grade glioma (HGG) recurrence is a common challenge with limited treatment options, including re-irradiation. The radiotracer 3,4-dihydroxy-6-[18F]-fluoro-L-phenylalanine (18F-DOPA) crosses the blood brain barrier and demonstrates high uptake in tumor, but low uptake in normal tissue. This study investigated whether 18F-DOPA positron emission tomography (PET) and MRI guided re-irradiation for recurrent HGG may improve progression free survival (PFS). METHODS: Adults with recurrent or progressive HGG previously treated with radiation were eligible. The primary endpoint was a 20% improvement from the historical control PFS at 3 months (PFS3) of 20% with systemic therapy alone. Re-RT dose was 35 Gy in 10 fractions. The target volume was MRI T1 contrast-enhancement defined tumor plus 18F-DOPA PET defined tumor. RESULTS: Twenty patients completed treatment per protocol. Diagnosis was most commonly glioblastoma, IDH-wildtype (60%). MRI-defined volumes were expanded by a median 43% (0-436%) by utilizing 18F-DOPA PET. PFS3 was 85% (95% CI 63.2-95.8%), meeting the primary endpoint of PFS3 ≥ 40%. With 9.7 months median follow-up, 17 (85%) had progressed and 15 (75%) had died. Median OS from re-RT was 8.8 months. Failure following re-RT was within both the MRI and PET tumor volumes in 75%, MRI only in 13%, PET only in 0%, and neither in 13%. Four (20%) patients experienced grade 3 toxicity, including CNS necrosis (n = 2, both asymptomatic with bevacizumab initiation for radiographic findings), seizures (n = 1), fatigue (n = 1), and nausea (n = 1). No grade 4-5 toxicities were observed. CONCLUSION: 18F-DOPA PET-guided re-irradiation for progressive high-grade glioma appears safe and promising for further investigation.

Prospective trial evaluating the sensitivity and specificity of 3,4-dihydroxy-6-[18F]-fluoro-L-phenylalanine (18F-DOPA) PET and MRI in patients with recurrent gliomas.

Treatment-related changes can be difficult to differentiate from progressive glioma using MRI with contrast (CE). The purpose of this study is to compare the sensitivity and specificity of 18F-DOPA-PET and MRI in patients with recurrent glioma. Thirteen patients with MRI findings suspicious for recurrent glioma were prospectively enrolled and underwent 18F-DOPA-PET and MRI for neurosurgical planning. Stereotactic biopsies were obtained from regions of concordant and discordant PET and MRI CE, all within regions of T2/FLAIR signal hyperintensity. The sensitivity and specificity of 18F-DOPA-PET and CE were calculated based on histopathologic analysis. Receiver operating characteristic curve analysis revealed optimal tumor to normal (T/N) and SUVmax thresholds. In the 37 specimens obtained, 51% exhibited MRI contrast enhancement (M+) and 78% demonstrated 18F-DOPA-PET avidity (P+). Imaging characteristics included M-P- in 16%, M-P+ in 32%, M+P+ in 46% and M+P- in 5%. Histopathologic review of biopsies revealed grade II components in 16%, grade III in 43%, grade IV in 30% and no tumor in 11%. MRI CE sensitivity for recurrent tumor was 52% and specificity was 50%. PET sensitivity for tumor was 82% and specificity was 50%. A T/N threshold > 2.0 altered sensitivity to 76% and specificity to 100% and SUVmax > 1.36 improved sensitivity and specificity to 94 and 75%, respectively. 18F-DOPA-PET can provide increased sensitivity and specificity compared with MRI CE for visualizing the spatial distribution of recurrent gliomas. Future studies will incorporate 18F-DOPA-PET into re-irradiation target volume delineation for RT planning.

Evaluation of RANO response criteria compared to clinician evaluation in WHO grade III anaplastic astrocytoma: implications for clinical trial reporting and patterns of failure.

The utility of current response criteria has not been established in anaplastic astrocytoma (AA). We retrospectively reviewed MR images for 20 patients with AA and compared RANO-based approaches to clinician impression described as follow: (1) standard RANO-based criteria met by growth of or development of new enhancing lesion (RANO-C), (2) RANO criteria for progression based on significant FLAIR increase (RANO-F) and (3) clinical progression usually resulting in change of treatment (Clinical). Patterns of failure (POF) were analyzed utilizing all proposed progression MRIs fused with the patients' radiotherapy treatment plan. With an overall median survival of 24.3 months, development of new enhancing lesion was the most common determinant of progression (70 % of patients). Median time to RANO-C, RANO-F and Clinical progression was 9.2, 9.2 and 11.76 months respectively. RANO-C and RANO-F preceded Clinical in 70 and 55 % of patients, respectively. In six patients (30 %) Clinical was concurrent with RANO-F; four of six also met RANO-C. POF for FLAIR component differed based on time point used to determine progression. FLAIR POF was more often marginal or distant when progression was defined clinically compared to either RANO-C or RANO-F criteria. Central POF based on FLAIR at Clinical determination of progression was associated with significantly poorer OS (9.8 vs. 34.4 months). Clinical progression occurs later than progression determined by RANO-based criteria. Evaluation of POF based on FLAIR signal abnormality at the time of clinical progression suggests central recurrences are associated with worse survival.

Dose de-intensified 3-day photon, proton, or brachytherapy: a nonrandomized controlled partial breast irradiation trial.

BACKGROUND: The optimal approach for partial breast irradiation (PBI) is unknown. We investigated a novel de-intensified 3-fraction PBI regimen for photons, protons, and brachytherapy. METHODS: A multicenter nonrandomized controlled trial with primary outcome of adverse cosmesis at 3 years versus pre-PBI. Eligibility criteria were ≥ age 50 years treated with breast-conserving surgery for node-negative estrogen receptor positive (ER+) invasive breast cancer or any ductal carcinoma in-situ (DCIS) measuring ≤ 2.5 cm. Photon and proton PBI were prescribed 21.9 Gy (RBE) and brachytherapy 21 Gy in 3 fractions. Radiotherapy technique and use of adjuvant endocrine therapy was selected at physician and patient discretion. RESULTS: Between June 17, 2015 and July 13, 2017, 161 eligible patients were treated with photons (56), protons (49), or brachytherapy (56). Median patient age was 66.8 years. 126 (78.3%) had invasive breast cancer (all ER+) and 35 (21.7%) had DCIS (88.6% ER+). 54.0% of patients with invasive breast cancer and 25.8% of patients with ER+ DCIS initiated and adhered to prescribed endocrine therapy. The proportion of patients with adverse cosmesis (by trained nurse assessment) was 14.5% at baseline, 2.3% at 3 years (difference -12.2%, 95% CI (-100%, -6.4%)). Adverse cosmesis at last-follow-up, with median follow-up 5 years, was 5.7% by nurse assessment, 5.6% by panel assessment of digital photographs, and 5.2% by patient self-report. There were no observed clinically meaningful changes in other patient reported outcomes, and just two grade 2 or higher adverse events, both grade 2, in the brachytherapy cohort. 5-year local recurrence-free and progression-free survival were 98.0% and 95.5%, respectively. There were no local recurrences amongst 60 patients with invasive breast cancer and Ki67 ≤ 13.25%. CONCLUSIONS: De-intensified 3-day PBI provided favorable disease control, tolerability, and cosmetic outcomes, meeting the pre-specified criteria for acceptability. This approach is an attractive option for small node-negative ER+ BC and DCIS patients. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT02453737.

The role of LAT1 in (18)F-DOPA uptake in malignant gliomas.

Positron emission tomography (PET) imaging with the amino acid tracer 6-(18)F-fluoro-L-3,4-dihydroxy-phenylalanine ((18)F-DOPA) may provide better spatial and functional information in human gliomas than CT or MRI alone. The L-type amino acid transporter 1 (LAT1) is responsible for membrane transport of large neutral amino acids in normal cells. This study assessed the relationship between LAT1 expression and (18)F-DOPA uptake in human astrocytomas. Endogenous LAT1 expression was measured in established glioblastoma (GBM) cell lines and primary GBM xenografts using Western blotting and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Uptake of (18)F-DOPA was approximated in vitro using (3)H-L-DOPA as an analog. Uptake of (3)H-L-DOPA was assessed in cells expressing LAT1 shRNA or LAT1 siRNA and compared to non-targeted (NT) control shRNA or siRNA sequences, respectively. To demonstrate the clinical relevance of these findings, LAT1 immunofluorescence staining was compared with corresponding regions of (18)F-DOPA PET uptake in patients with newly diagnosed astrocytomas. LAT1 mRNA and protein expression varies in GBM, and the extent of (3)H-L-DOPA uptake was positively correlated with endogenous LAT1 expression. Stable shRNA-mediated LAT1 knockdown in T98 and GBM28 reduced (3)H-L-DOPA uptake relative to NT shRNA by 57 (P < 0.0001) and 52 % (P < 0.001), respectively. Transient siRNA-mediated LAT1 knockdown in T98 reduced (3)H-L-DOPA uptake relative to NT siRNA up to 68 % (P < 0.01). In clinical samples, LAT1 expression positively correlated with (18)F-DOPA PET uptake (P = 0.04). Expression of LAT1 is strongly associated with (3)H-L-DOPA uptake in vitro and (18)F-DOPA uptake in patient biopsy samples. These results define LAT1 as a key determinant of (18)F-DOPA accumulation in GBM.

Dosimetric patterns of failure in the era of novel chemoradiotherapy in newly-diagnosed glioblastoma patients.

BACKGROUND: Patterns of failure (POF) may provide an alternative quantitative endpoint to overall survival for evaluation of novel chemoradiotherapy regimens with glioblastoma. MATERIALS AND METHODS: POF of 109 newly-diagnosed glioblastoma patients per 2016 WHO classification who received conformal radiotherapy with concomitant and adjuvant temozolomide were reviewed. Seventy-five of those patients also received an investigational chemotherapy agent (everolimus, erlotinib, or vorinostat). Recurrence volumes were defined with MRI contrast enhancement. POF at protocol (POFp), initial (POFi), and RANO (POFRANO) progression timepoints were characterized by the percentage of recurrence volume within the 95% dose region. POFp, POFi, and POFRANO of each patient were categorized (central, non-central, or both). RESULTS: POF of the temozolomide-only control cohort were unchanged (79% central, 12% non-central, and 9% both) across protocol, initial, and RANO progression timepoints. Unlike the temozolomide-only cohort, POF of the collective novel chemotherapy cohort appeared increasingly non-central when comparing POFi with POFp, with a non-central component increasing from 16% to 29% (p = 0.078). POF did not correlate with overall survival or time to progression. CONCLUSION: POF of patients receiving a novel chemotherapy appeared to be influenced by the timepoint of analysis and were increasingly non-central at protocol progression as compared with initial recurrence, suggesting that recurrence originates from the central region. Addition of everolimus and vorinostat appeared to influence POF, despite similar survival outcomes with the temozolomide-only control group. In studies dealing with novel therapeutic agents, robust and properly-timed dosimetric POF analysis may be helpful to evaluate biologic aspects of novel agents.

Single and Multifraction Spine Stereotactic Body Radiation Therapy and the Risk of Radiation Induced Myelopathy.

Purpose: This study reports on the risk of radiation-induced myelitis (RM) of the spinal cord from a large single-institutional experience with 1 to 5 fraction stereotactic body radiation therapy (SBRT) to the spine. Methods and Materials: A retrospective review of patients who received spine SBRT to a radiation naïve level at or above the conus medullaris between 2007 and 2019 was performed. Local failure determination was based on SPIne response assessment in Neuro-Oncology criteria. RM was defined as neurologic symptoms consistent with the segment of cord irradiated in the absence of neoplastic disease recurrence and graded by Common Toxicity Criteria for Adverse Events, version 4.0. Rates of adverse events were estimated and dose-volume statistics from delivered treatment plans were extracted for the planning target volumes and spinal cord. Results: A total of 353 lesions in 277 patients were identified that met the specified criteria, for which 270, 70, and 13 lesions received 1-, 3-, and 5-fraction treatments, respectively, with a median follow-up of 46 months (95% confidence interval [CI], 41-52 months) for all surviving patients. The median overall survival was 33.0 months (95% CI, 29-43). The median D0.03cc to the spinal cord was 11.7 Gy (interquartile range [IQR], 10.5-12.4), 16.7 Gy (IQR, 12.8-20.6), and 26.0 Gy (IQR, 24.1-28.1), for 1-, 3-, 5-fractions. Using an a/b = 2Gy for the spinal cord, the median single-fraction equivalent-dose (SFED2) was 11.7 Gy (IQR, 10.2-12.5 Gy) and the normalized biological equivalent dose (nBED2/2) was 19.9 Gy (IQR, 15.4-22.8 Gy). One patient experienced grade 2 RM after a single-fraction treatment. The cumulative probability of RM was 0.3% (95% CI, 0%-2%). Conclusions: Spine SBRT is safe while limiting the spinal cord (as defined on treatment planning magnetic resonance imaging or computed tomography myelogram) D0.03cc to less than 14 Gy, 21.9 Gy, and 30 Gy, for 1, 3, and 5-fractions, consistent with standard guidelines.

Comparable Efficacy of Reduced Dose Radiation Therapy for the Treatment of Early Stage Gastric Extranodal Marginal Zone Lymphoma of Mucosa-Associated Lymphoid Tissue.

PURPOSE: This study compares reduced (<27 Gy) to standard dose (≥30 Gy) radiation therapy (RT) in the treatment of gastric extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (gMALT lymphoma). METHODS AND MATERIALS: Forty-two patients with stage I or II disease were retrospectively reviewed. Response to RT was assessed with endoscopy after RT. Complete response rate (CR), freedom from treatment failure, and overall survival (OS) were calculated. RESULTS: All patients were stage I (n = 40) or II (n = 2). All patients had residual biopsy proven gMALT lymphoma before RT. Twenty-six patients (61.9%) were treated with standard dose RT, 30 to 36 Gy, and 16 (38.1%) with the reduced dose RT, 23.5 to 27 Gy. The median follow-up was 29.5 months (range, 6-85). Thirty-six patients (86%) achieved complete response (CR), and 6 patients (14%) achieved partial response (PR). The complete response rate (CR) at the first endoscopic assessment, median time of 3 months, was 81% (95% confidence interval, 0.61%-0.93%) for standard RT, and 94% (confidence interval, 0.69%-0.99%) for reduced RT. Among CR patients, one patient had locally relapsed disease at 50 months. The 1-year overall survival (OS) was 100% in both groups. The 1-year freedom from treatment failure (FFTF) was 100% in the reduced RT group and 92% in the standard RT group. The 2-year FFTF and OS of the whole cohort were 92% and 96%, respectively. There was no significant difference in the OS, FFTF, and CR between the 2 treatment groups (P = .38, P = .18, and P = .267, respectively). For toxicity, the mean liver dose and the mean V20 heart dose were significantly lower in the reduced RT group (P <.001 and P = .001, respectively). However, incidence and severity of reported toxicities were similar between the 2 groups. CONCLUSIONS: Reduced dose RT (23.5-27 Gy) achieved excellent complete response rates with minimal toxicity, comparable with standard dose RT (30-36 Gy), for gMALT.

Intracranial motion during frameless Gamma-Knife stereotactic radiosurgery.

PURPOSE/OBJECTIVES: The Gamma-Knife radiosurgery (GKRS) (Elekta AB, Stockholm) platform delivers highly conformal and precise radiation; however, intracranial displacement during treatment allows for the potential of a marginal target-miss. Frameless (mask-based) GKRS using the Gamma Knife Icon system monitors nasal tip motion as a surrogate for intracranial motion by tracking an infrared marker using a high-definition motion management (HDMM) system. To date, there is limited data available regarding the incidence and severity of motion and factors that impact intrafraction motion when treating with frameless GKRS. MATERIALS/METHODS: A retrospective study was performed to evaluate patients with brain tumors who were treated with frameless GKRS using the Gamma Knife Icon between May and December 2018. All patients underwent mask-based immobilization using a thermoplastic mask. Data on patient demographics, mask type, use of bite block, and number of treatments received, use of anxiolytics, treatment time, and whether a physics clearance check was performed prior to treatment were collected. For each treatment session, average displacement (mm), maximum displacement (mm) and total treatment time (min) were recorded and logistic regression analyses were performed. RESULTS: Data was collected for 89 consecutive treatments (38 patients). Of these, an anxiolytic was used in 61 treatments and a physics clearance check was performed for 45 treatments. The median average and maximum displacement was 0.60 mm and 1.22 mm, respectively. An average displacement greater than 0.60 mm was seen with Eastern Cooperative Oncology Group performance status (ECOG) > 1, male gender, and malignant tumors (p < 0.05). Anxiolytic use prior to treatment was associated with a significant reduction in average displacement (p < 0.05). Significantly greater odds of observing a maximum displacement over 1.22 mm was seen with patients with ECOG > 1, male gender, and increased treatment time (p < 0.05). Age > 65 and anxiolytic use were associated with a significant reduction in maximum displacement (p < 0.05). Performance of clearance checks and use of bite block use did not impact average or maximum patient displacement. CONCLUSIONS: This is the first study to evaluate patient and treatment-related factors that influence intrafraction motion during GKRS with mask-based immobilization through HDMM tracking. Increased intracranial displacement during frameless GKRS was associated with higher ECOG, male gender, increased treatment time and malignant tumors, while anxiolytics were shown to mitigate excessive motion. Radiosurgery teams should consider these patient factors when treating patients with mask immobilization.

Prediction of MGMT Status for Glioblastoma Patients Using Radiomics Feature Extraction From 18F-DOPA-PET Imaging.

PURPOSE: Methylation of the O6-methylguanine methyltransferase (MGMT) gene promoter is associated with improved treatment response and survival in patients with glioblastoma (GB), but the necessary pathologic specimen can be nondiagnostic. In this study, we assessed whether radiomics features from pretreatment 18F-DOPA positron emission tomography (PET) imaging could be used to predict pathologic MGMT status. METHODS AND MATERIALS: This study included 86 patients with newly diagnosed GB, split into 3 groups (training, validating, and predicting). We performed a radiomics analysis on 18F-DOPA PET images by extracting features from 2 tumor-based contours: a "Gold" contour of all abnormal uptake per expert nuclear medicine physician and a high-grade glioma (HGG) contour based on a tumor-to-normal hemispheric ratio >2.0, representing the most aggressive components. Feature selection was performed by comparing the weighted feature importance and filtering with bivariate analysis. Optimization of model parameters was explored using grid search with selected features. The stability of the model with increasing input features was also investigated for model robustness. The model predictions were then applied by comparing the overall survival probability of the patients with GB and unknown MGMT status versus those with known MGMT status. RESULTS: A radiomics signature was constructed to predict MGMT methylation status. Using features extracted from HGG contour alone with a random forest model, we achieved 80% ± 10% accuracy for 95% confidence level in predicting MGMT status. The prediction accuracy was not improved with the addition of the Gold contour or with more input features. The model was applied to the patients with unknown MGMT methylation status. The prediction results are consistent with what is expected using overall survival as a surrogate. CONCLUSIONS: This study suggests that 3 features from radiomics modeling of 18F-DOPA PET imaging can predict MGMT methylation status with reasonable accuracy. These results could provide valuable therapeutic guidance for patients in whom MGMT testing is inconclusive or nondiagnostic.

NRG Oncology Survey on Practice and Technology Use in SRT and SBRT Delivery.

PURPOSE: To assess stereotactic radiotherapy (SRT)/stereotactic body radiotherapy (SBRT) practices by polling clinics participating in multi-institutional clinical trials. METHODS: The NRG Oncology Medical Physics Subcommittee distributed a survey consisting of 23 questions, which covered general technologies, policies, and procedures used in the Radiation Oncology field for the delivery of SRT/SBRT (9 questions), and site-specific questions for brain SRT, lung SBRT, and prostate SBRT (14 questions). Surveys were distributed to 1,996 radiotherapy institutions included on the membership rosters of the five National Clinical Trials Network (NCTN) groups. Patient setup, motion management, target localization, prescriptions, and treatment delivery technique data were reported back by 568 institutions (28%). RESULTS: 97.5% of respondents treat lung SBRT patients, 77.0% perform brain SRT, and 29.1% deliver prostate SBRT. 48.8% of clinics require a physicist present for every fraction of SBRT, 18.5% require a physicist present for the initial SBRT fraction only, and 14.9% require a physicist present for the entire first fraction, including set-up approval for all subsequent fractions. 55.3% require physician approval for all fractions, and 86.7% do not reposition without x-ray imaging. For brain SRT, most institutions (83.9%) use a planning target volume (PTV) margin of 2 mm or less. Lung SBRT PTV margins of 3 mm or more are used in 80.6% of clinics. Volumetric modulated arc therapy (VMAT) is the dominant delivery method in 62.8% of SRT treatments, 70.9% of lung SBRT, and 68.3% of prostate SBRT. CONCLUSION: This report characterizes SRT/SBRT practices in radiotherapy clinics participating in clinical trials. Data made available here allows the radiotherapy community to compare their practice with that of other clinics, determine what is achievable, and assess areas for improvement.

Carbon Fiducial Image Guidance Increases the Accuracy of Lumpectomy Cavity Localization in Radiation Therapy for Breast Cancer.

PURPOSE: We investigated the feasibility and accuracy of using carbon fiducials to localize the lumpectomy cavity with 2-dimensional kV imaging for early stage breast cancer radiation therapy. METHODS AND MATERIALS: Carbon fiducials were placed intraoperatively in the periphery of the lumpectomy cavity. Nine patients received whole breast irradiation with a boost, and 2 patients received 3-dimensional conformal partial breast irradiation. A total of 89 fractions were assessed for setup errors relative to a predefined gold standard, cone beam computed tomography (CBCT) match to the lumpectomy cavity, using the following 4 setup methods: (1) Align skin tattoos with lasers; (2) match bone with 2-dimensional-2-dimensional (2D/2D) kV onboard imaging (OBI); (3) match the whole breast with CBCT; and (4) match carbon fiducials with 2D/2D kV OBI. The margin for the planning target volume (PTV) was calculated by 2 standard deviations of the setup errors, and compared among the 4 setup methods. Setup errors for patients treated with free breathing and patients with deep inspiration breath hold were also compared. RESULTS: The carbon fiducials were sufficiently visible on OBI for matching and introduced minimal artifacts. Of the 4 alignment methods, 2D/2D OBI match to fiducials resulted in the smallest setup errors. The PTV margin was 12 mm for aligning skin tattoos using lasers, 9.2 mm for matching bone on OBI, 6.5 mm for matching breast on CBCT, and 3.5 mm for matching fiducials on 2D/2D OBI. Compared with free breathing, deep inspiration breath hold generally reduced the standard deviations of the setup errors, but further investigation would be needed. CONCLUSIONS: Matching to carbon fiducials increased the localization accuracy to the lumpectomy cavity. This reduces residual setup error and PTV margins, facilitating tissue sparing without diminishing treatment efficacy.

Dosimetric impact of amino acid positron emission tomography imaging for target delineation in radiation treatment planning for high-grade gliomas.

BACKGROUND AND PURPOSE: The amino-acid positron emission tomography (PET) tracer 3,4-dihydroxy-6-[18F] fluoro-l-phenylalanine (18F-DOPA) has increased sensitivity for detecting regions of biologically aggressive tumors compared to T1 contrast-enhanced (T1-CE) magnetic resonance imaging (MRI). We performed dosimetric evaluation of treatment plans prepared with and without inclusion of 18F-DOPA-based biological target volume (BTV) evaluating its role in guiding radiotherapy of grade III/IV gliomas. MATERIALS AND METHODS: Eight patients (five T1-CE, three non-contrast-enhancing [NCE]) were included in our study. MRI only-guided anatomic plans and MRI+18FDOPA-PET-guided biologic plans were prepared for each patient, and dosimetric data for target volumes and organs at risk (OAR) were compared. High-dose BTV60Gy was defined as regions with tumor to normal brain (T/N) >2.0, while low-dose BTV51Gy was initially based on T/N >1.3, but refined per Nuclear Medicine expert. RESULTS: For T1-CE tumors, planning target volumes (PTV) were larger than MRI-only anatomic target volumes. Despite increases in size of both gross target volumes and PTV, with volumetric-modulated arc therapy planning, no increase of dose to OAR was observed while maintaining similar target dose coverage. For NCE tumors, MRI+18F-DOPA PET biologic imaging identified a sub-region of the large, T2-FLAIR abnormal signal which may allow a smaller volume to receive the high dose (60 Gy) radiation. CONCLUSIONS: For T1-CE tumors, PTVs were larger than MRI-only anatomic target volumes with no increase of dose to OARs. Therefore, MRI+18F-DOPA PET-based biologic treatment planning appears feasible in patients with high-grade gliomas.

Is the blood-brain barrier really disrupted in all glioblastomas? A critical assessment of existing clinical data.

The blood-brain barrier (BBB) excludes the vast majority of cancer therapeutics from normal brain. However, the importance of the BBB in limiting drug delivery and efficacy is controversial in high-grade brain tumors, such as glioblastoma (GBM). The accumulation of normally brain impenetrant radiographic contrast material in essentially all GBM has popularized a belief that the BBB is uniformly disrupted in all GBM patients so that consideration of drug distribution across the BBB is not relevant in designing therapies for GBM. However, contrary to this view, overwhelming clinical evidence demonstrates that there is also a clinically significant tumor burden with an intact BBB in all GBM, and there is little doubt that drugs with poor BBB permeability do not provide therapeutically effective drug exposures to this fraction of tumor cells. This review provides an overview of the clinical literature to support a central hypothesis: that all GBM patients have tumor regions with an intact BBB, and cure for GBM will only be possible if these regions of tumor are adequately treated.

Initial clinical experience of postmastectomy intensity modulated proton therapy in patients with breast expanders with metallic ports.

PURPOSE: The feasibility of proton postmastectomy radiation therapy in patients reconstructed with expanders has not been previously reported, limiting treatment options. We analyzed the dosimetric impact of the metallic port contained within expanders on intensity modulated proton therapy (IMPT) and report our techniques and quality control for treating patients in this setting. METHODS AND MATERIALS: Twelve patients with the same expander model underwent 2-field IMPT as part of a prospective registry. All planning dosimetry was checked with an in-house graphic processing unit--based Monte Carlo simulation. Proton ranges through the expander were validated using a sample implant. Dosimetric impact of setup metallic port position uncertainty was evaluated. Pre- and posttreatment photographs were obtained and acute toxicity was graded using the Common Terminology Criteria for Adverse Events, version 4.0. RESULTS: Nine patients had bilateral skin-sparing mastectomy with bilateral tissue expander reconstruction, and 3 patients had unilateral skin-sparing mastectomy and reconstruction. The left side was treated in 10 patients and the right side in 2. Target coverage and normal tissue dose uncertainties resulting from the expander were small and clinically acceptable. The maximum physician-assessed acute radiation dermatitis was grade 3 in 1 patient, grade 2 in 5 patients, and grade 1 in 6 patients. CONCLUSIONS: Postmastectomy IMPT in breast cancer patients with expanders is feasible and associated with favorable clinical target volume coverage and normal tissue sparing, even when taking into account treatment uncertainties; therefore, these patients should be eligible to participate in clinical trials studying the potential role of proton therapy in breast cancer. We caution, however, that institutions should carry out similar analyses of the physical properties and dosimetric impact of the particular expanders used in their practice before considering IMPT.

Feasibility and full-course dosimetry of an intraoperatively placed multichannel brachytherapy catheter for accelerated partial breast irradiation.

PURPOSE: Determine feasibility and resultant dosimetry of an intraoperatively placed multichannel intracavitary brachytherapy catheter for accelerated partial breast irradiation (APBI). METHODS: Patients with breast cancer underwent intraoperative brachytherapy catheter placement based on frozen section analysis with immediate postoperative APBI. The planning target volume evaluation (PTVEval) and organs at risk were contoured on daily pretreatment CT scans for each patient, and the original treatment plan was applied to assess full-course dosimetry. RESULTS: Of the first 21 patients consented for intraoperative catheter placement, 20 (95%) were able to proceed with treatment as planned. The mean volume of PTVEval receiving 90% of prescription dose (V90%) and mean percentage of prescription dose to 90% of the PTVEval (D90%) on initial planning were 96.7 (±1.1%) and 100.2 (±2.1%), respectively. Full-course dose coverage remained excellent with a mean PTVEval V90% and D90% of 95.0 (±4.4%) and 100.2 (±9.6%), respectively. Mean full-course maximum dose constraints for chest wall and skin were met by 70% and 95% of patients, respectively. Air accumulation >1 cc during treatment increased the risk of a daily fraction with PTVEval coverage below goal (odds ratio, 9.8; p = 0.05), whereas those with applicators <0.5 cm from the chest wall at planning were at risk of exceeding that organ's maximum dose constraint on a daily fraction (odds ratio, 45; p = 0.02). CONCLUSIONS: Intraoperative catheter placement and early initiation of APBI based on frozen section pathology is feasible, yields acceptable dosimetry, and is an option for completing breast conserving therapy in less than 10 days.

Decreased affinity for efflux transporters increases brain penetrance and molecular targeting of a PI3K/mTOR inhibitor in a mouse model of glioblastoma.

BACKGROUND: Targeting drug delivery to invasive glioma cells is a particularly difficult challenge because these cells lie behind an intact blood-brain barrier (BBB) that can be observed using multimodality imaging. BBB-associated efflux transporters such as P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) influence drug distribution to these cells and may negatively impact efficacy. To test the hypothesis that efflux transporters influence brain pharmacokinetics/pharmacodynamics of molecularly targeted agents in glioma treatment, we assessed region-specific penetrance and molecular-targeting capacity for a PI3K/mTOR kinase inhibitor that has high substrate affinity for efflux transporters (GDC-0980) and an analog (GNE-317) that was purposely designed to have reduced efflux. METHODS: Brain tumor penetrance of GDC-0980 and GNE-317 was compared between FVB/n wild-type mice and Mdr1a/b(-/-)Bcrp(-/-) triple-knockout mice lacking P-gp and BCRP. C57B6/J mice bearing intracranial GL261 tumors were treated with GDC-0980, GNE-317, or vehicle to assess the targeted pharmacokinetic/pharmacodynamic effects in a glioblastoma model. RESULTS: Animals treated with GNE-317 demonstrated 3-fold greater penetrance in tumor core, rim, and normal brain compared with animals dosed with GDC-0980. Increased brain penetrance correlated with decreased staining of activated p-Akt, p-S6, and p-4EBP1 effector proteins downstream of PI3K and mTOR. CONCLUSIONS: GDC-0980 is subject to active efflux by P-gp and BCRP at the BBB, while brain penetrance of GNE-317 is independent of efflux, which translates into enhanced inhibition of PI3K/mTOR signaling. These data show that BBB efflux by P-gp and BCRP is therefore an important determinant in both brain penetrance and molecular targeting efficacy in the treatment of invasive glioma cells.

Analysis of automatic match results for cone-beam computed tomography localization of conventionally fractionated lung tumors.

PURPOSE: To evaluate the dependence of an automatic match process on the size of the user-defined region of interest (ROI), the structure volume of interest (VOI), and changes in tumor volume when using cone-beam computed tomography (CBCT) for tumor localization and to compare these results with a gold standard defined by a physician's manual match. METHODS AND MATERIALS: Daily CBCT images for 11 patients with lung cancer treated with conventionally fractionated radiation therapy were retrospectively matched to a reference CT image using the Varian On Board Imager software (Varian, Palo Alto, CA) and a 3-step automatic matching protocol. Matches were performed with 3 ROI sizes (small, medium, large), with and without a structure VOI (internal target volume [ITV] or planning target volume [PTV]) used in the last step. Additionally, matches were performed using an intensity range that isolated the bony anatomy of the spinal column. All automatic matches were compared with a manual match made by a physician. RESULTS: The CBCT images from 109 fractions were analyzed. Automatic match results depend on ROI size and the structure VOI. Compared with the physician's manual match, automatic matches using the PTV as the structure VOI and a small ROI resulted in differences ≥ 5 mm in 1.8% of comparisons. Automatic matches using no VOI and a large ROI differed by ≥ 5 mm in 30.3% of comparisons. Differences between manual and automatic matches using the ITV as the structure VOI increased as tumor size decreased during the treatment course. CONCLUSIONS: Users of automatic matching techniques should carefully consider how user-defined parameters affect tumor localization. Automatic matches using the PTV as the structure VOI and a small ROI were most consistent with a physician's manual match, and were independent of volumetric tumor changes.

Biopsy validation of 18F-DOPA PET and biodistribution in gliomas for neurosurgical planning and radiotherapy target delineation: results of a prospective pilot study.

BACKGROUND: Delineation of glioma extent for surgical or radiotherapy planning is routinely based on MRI. There is increasing awareness that contrast enhancement on T1-weighted images (T1-CE) may not reflect the entire extent of disease. The amino acid tracer (18)F-DOPA (3,4-dihydroxy-6-[18F] fluoro-l-phenylalanine) has a high tumor-to-background signal and high sensitivity for glioma imaging. This study compares (18)F-DOPA PET against conventional MRI for neurosurgical biopsy targeting, resection planning, and radiotherapy target volume delineation. METHODS: Conventional MR and (18)F-DOPA PET/CT images were acquired in 10 patients with suspected malignant brain tumors. One to 3 biopsy locations per patient were chosen in regions of concordant and discordant (18)F-DOPA uptake and MR contrast enhancement. Histopathology was reviewed on 23 biopsies. (18)F-DOPA PET was quantified using standardized uptake values (SUV) and tumor-to-normal hemispheric tissue (T/N) ratios. RESULTS: Pathologic review confirmed glioma in 22 of 23 biopsy specimens. Thirteen of 16 high-grade biopsy specimens were obtained from regions of elevated (18)F-DOPA uptake, while T1-CE was present in only 6 of those 16 samples. Optimal (18)F-DOPA PET thresholds corresponding to high-grade disease based on histopathology were calculated as T/N > 2.0. In every patient, (18)F-DOPA uptake regions with T/N > 2.0 extended beyond T1-CE up to a maximum of 3.5 cm. SUV was found to correlate with grade and cellularity. CONCLUSIONS: (18)F-DOPA PET SUV(max) may more accurately identify regions of higher-grade/higher-density disease in patients with astrocytomas and will have utility in guiding stereotactic biopsy selection. Using SUV-based thresholds to define high-grade portions of disease may be valuable in delineating radiotherapy boost volumes.