A script-enabled interactive checklist document for efficient management of electronic devices in a busy multimodality radiotherapy clinic

PURPOSE

Develop an efficient, interactive, and instructive checklist document for the management of implanted electronic medical devices in a multimodality radiotherapy clinic.

METHODS

The built-in scripting and interactivity of a popular commercial word processor was used to develop an interactive document that changes the information presented to the user based on drop-down selections. The interactivity and scripting were compatible with the radiation oncology information system (ROIS) which allows the document to be accessible by all team members and serve as a permanent record in a patient's electronic chart.

RESULTS

The final interactive document, which was clinically deployed after beta testing with a group consisting of nurses and medical physicists, presents information and action plans to the user based on multiple departmental medical device decision trees that are specific to the combination of device, treatment modality, rhythm-pacing dependence for cardiac devices, and distance from the device to the treatment volume.

CONCLUSION

A script-enabled interactive document was developed for a busy multimodality clinic, condensing multiple comprehensive departmental guidelines spanning multiple device types and treatment modalities into a single interactive checklist accessible within the ROIS. Given the wide accessibility of the commercial word processor, this approach could be adopted by other clinics to streamline their own respective workflows.

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.

Local Control after Re-Irradiation of Spinal Metastases with Stereotactic Body Radiation Therapy

PURPOSE/OBJECTIVE(S)

Determine local control (LC) rate and risk of vertebral compression fractures (VCFs) and radiation myelitis (RM) for patients receiving re-irradiation of spinal metastases (SMs) using stereotactic body radiation therapy (SBRT) from large single-institutional experience with long follow-up.

MATERIALS/METHODS

Retrospectively identified patients receiving re-irradiation SBRT (rSBRT, 1, 3, or 5 fractions) to SMs previously treated with radiation therapy (RT) and having follow up imaging to assess local control. 1 fraction patients typically received 20-24 Gy and 16-18 Gy to the high- and low-risk planning target volumes (PTVs), respectively, and 27-39 Gy and 21-24 Gy for the 3 fraction patients, with a single level of 50 Gy for 5 fractions. Patient and treatment characteristics for previous RT (pRT) and rSBRT were collected, including histology and dose-volume histogram statistics (DVH). Kaplan-Meier estimates of overall survival (OS), and cumulative incidence (competing with death) of local failure with death as a competing risk was computed for the whole cohort and stratified by radioresistance of histology, and risk of VCF for RM (for treatments at L1 and above) and 95% confidence intervals. Equivalent dose in 2 Gy fractions (EQD2) for PTV and spinal cord (SC) DVH statistics was computed for each individual course and cumulatively, using a/b = 10 Gy for tumor and 2 Gy for SC.

RESULTS

Identified 107 lesions in 91 patients. 48 (45%) had radioresistant histologies. For all patients, at 1 and 2 years, respectively OS was 64% (55-74%) and 43% (34-55%), LC was 88% (81-94%) and 85% (78-91%) with median follow-up of 52 months (Table 1). OS and LC were not significantly different between radiosensitivity groups (p>0.05). Risk of VCF at 1 and 2 years was 7% (3-13%) and 9% (4-16%). RM was identified in 1 patient, who received 30 Gy in 5 fractions to T1, and had 1-fraction rSBRT 21 months later. SC Dmax was 31.5 Gy for pRT and 10.4 Gy, for rSBRT, resulting in total SC EQD2 of 73 Gy. RM was confirmed on MRI 8 months after rSBRT. Cumulative RM risk at 8 months after rSBRT was estimated at 1% (0-4%). Median EQD2 for the minimum dose to the high and low risk PTVs were 17.7 Gy (interquartile range, IQR, 13.0-27.6 Gy) and 13.7 Gy (IQR, 10.8-19.3 Gy) for rSBRT, and maximum EQD to SC for previous RT, rSBRT, and cumulatively was 38 Gy (IQR, 30-41 Gy), 27 Gy (IQR, 22-36 Gy), and 65 Gy (IQR, 54-73 Gy).Re-irradiation of spinal metastasis with SBRT can be delivered safely and provide high rates of local control, including for radioresistant tumors, as demonstrated with the longest reported follow-up in this setting.

CONCLUSION

Re-irradiation of SM with SBRT provides high rates of LC even for radioresistant tumors, and low risk of VCF and RM, based on the longest reported follow-up in this setting.

Evaluation of a New, Highly Flexible Radiofrequency Coil for MR Simulation of Patients Undergoing External Beam Radiation Therapy

PURPOSE

To evaluate the performance of a new, highly flexible radiofrequency (RF) coil system for imaging patients undergoing MR simulation.

METHODS

Volumetric phantom and in vivo images were acquired with a commercially available and prototype RF coil set. Phantom evaluation was performed using a silicone-filled humanoid phantom of the head and shoulders. In vivo assessment was performed in five healthy and six patient subjects. Phantom data included T1-weighted volumetric imaging, while in vivo acquisitions included both T1- and T2-weighted volumetric imaging. Signal to noise ratio (SNR) and uniformity metrics were calculated in the phantom data, while SNR values were calculated in vivo. Statistical significance was tested by means of a non-parametric analysis of variance test.

RESULTS

At a threshold of p = 0.05, differences in measured SNR distributions within the entire phantom volume were statistically different in two of the three paired coil set comparisons. Differences in per slice average SNR between the two coil sets were all statistically significant, as well as differences in per slice image uniformity. For patients, SNRs within the entire imaging volume were statistically significantly different in four of the nine comparisons and seven of the nine comparisons performed on the per slice average SNR values. For healthy subjects, SNRs within the entire imaging volume were statistically significantly different in seven of the nine comparisons and eight of the nine comparisons when per slice average SNR was tested.

CONCLUSIONS

Phantom and in vivo results demonstrate that image quality obtained from the novel flexible RF coil set was similar or improved over the conventional coil system. The results also demonstrate that image quality is impacted by the specific coil configurations used for imaging and should be matched appropriately to the anatomic site imaged to ensure optimal and reproducible image quality.

Phase II Evaluation of Stereotactic Ablative Radiotherapy (SABR) and Immunity in 11C-Choline-PET/CT-Identified Oligometastatic Castration-Resistant Prostate Cancer

PURPOSE

Outcomes for resistant metastatic castration-resistant prostate cancer (CRPC) are poor. Stereotactic ablative radiotherapy (SABR) induces antitumor immunity in clinical and preclinical studies, but immunologic biomarkers are lacking.

PATIENTS AND METHODS

Eighty-nine patients with oligometastatic CRPC were identified by ¹¹C-Choline-PET (Choline-PET) from August 2016 to December 2019 and treated with SABR. Prespecified coprimary endpoints were 2-year overall survival (OS) and PSA progression. Secondary endpoints included 2-year SABR-treated local failure and 6-month adverse events. Correlative studies included peripheral blood T-cell subpopulations before and after SABR.

RESULTS

128 lesions in 89 patients were included in this analysis. Median OS was 29.3 months, and 1- and 2-year OS were 96% and 80%, respectively. PSA PFS was 40% at 1 year and 21% at 2 years. Local PFS was 84.4% and 75.3% at 1 and 2 years, respectively, and no grade ≥3 AEs were observed. Baseline high levels of tumor-reactive T cells (T_TR; CD8⁺CD11a^high) predicted superior local, PSA, and distant PFS. Baseline high levels of effector memory T cells (T_EM; CCR7^-CD45RA^-) were associated with improved PSA PFS. An increase in T_TR at day 14 from baseline was associated with superior OS.

CONCLUSIONS

This is the first comprehensive effector T-cell immunophenotype analysis in a phase II trial before and after SABR in CRPC. Results are favorable and support the incorporation of immune-based markers in the design of future randomized trials in patients with oligometastatic CRPC treated with SABR.

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.

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.

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 BTV_60Gy was defined as regions with tumor to normal brain (T/N) >2.0, while low-dose BTV_51Gy 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.

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.

Treatment planning for metals using an extended CT number scale

Metal implants which saturate the CT number scale may require dosimetrist and physicist involvement to manually contour and assign an appropriate value to the metal for accurate dose calculation. This study investigated dose calculation based directly on extended CT scale images for different metals and geometries. The aim was to evaluate extended CT accuracy as a suitable alternative to standard CT methods in the presence of high‐Z materials and artifacts, despite the reduced HU resolution of extended CT. Gafchromic film measurements were made for comparison to calculated doses. The method of direct dose calculation on extended CT scale was compared to our institution's standard method of manually contouring and assigning metal values on saturated CT images for each of the metal samples. Clinical patient plans with metal implants were investigated and DVHs were compared between standard CT and extended CT dose calculations. Dose calculations showed agreement within 2% between the two methods of metal characterization and the film measurement in the case of the strongest metal attenuator, cobalt‐chromium. In the clinical treatment plans, the greatest dose discrepancy between the two methods was 1.2%. This study suggests that direct dose calculation on an extended scale CT image in the presence of metal implants can produce accurate clinically viable treatment plans, thereby improving efficiency of clinical workflow and eliminating a potential source of human error by manual CT number assignment.

PACS number(s): 87.55.dk

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.

The addition of SPECT/CT lymphoscintigraphy to breast cancer radiation planning spares lymph nodes critical for arm drainage

BACKGROUND

This prospective cohort study was designed to determine whether the amount of radiation delivered to the nonpathological lymph nodes (LNs) that drain the arm can be significantly reduced by integrating single-photon emission computed tomography (SPECT)/computed tomography (CT) scans into radiation treatment planning.

METHODS

SPECT-CT scans were acquired for the 28 patients with stage I or II breast cancer and fused with the routinely obtained radiation oncology planning CT scans. Arm-draining LNs were contoured with 0.5-cm margins automatically using a threshold of 50% maximum intensity. Two treatment plans were generated: 1 per routine clinical practice (standard; STD) and the second (modified; MOD) with treatment fields modified to minimize dose to the arm-draining LNs visible on SPECT/CT images without interfering with the dosage delivered to target tissues. Participants were treated per the MOD plans. Arm volumes were measured prior to radiation and thereafter at least three subsequent 6-month intervals.

RESULTS

Sixty-eight level I-III arm-draining LNs were identified, 57% of which were inside the STD plan fields but could be blocked in the MOD plan fields. Sixty-five percent of arm-draining LNs in the STD versus 16% in the MOD plans received a mean of ≥10 Gy, and 26% in the STD versus 4% in the MOD plans received a mean of ≥40 Gy. Mean LN radiation exposure was 23.6 Gy (standard deviation 18.2) with the STD and 7.7 Gy (standard deviation 11.3) with the MOD plans (P<.001). No participant developed lymphedema.

CONCLUSIONS

The integration of SPECT/CT scans into breast cancer radiation treatment planning reduces unnecessary arm-draining LN radiation exposure and may lessen the risk of lymphedema.

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.

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.

An investigation of temporal resolution parameters in cine-mode four-dimensional computed tomography acquisition

The accuracy of four‐dimensional computed tomography (4DCT) imaging depends on temporal characteristics of the acquisition protocol—for example, the temporal spacing of the reconstructed images (also known as cine duration between images) and the gantry rotation speed. These parameters affect the temporal resolution of 4DCT images, and a single default acquisition protocol, as commonly used in most clinics, may be suboptimal for a subset of respiratory motion characteristics. It could lead to substantial inaccuracies in target delineation. The aim of the present study was to evaluate the interplay between parameters affecting temporal resolution and the accuracy of the resulting images.

We acquired 4DCT images of cylindrical phantoms under repetitive motion induced by a translation platform. Acquisition settings varied with respect to temporal spacing, gantry rotation speed, and motion period of the phantoms. Reconstructed images were sorted into 10 phase bins and were compared to static phantom images acquired at corresponding positions of the respiration phase. Acquisitions with different temporal spacing did not play a significant role in the amount of motion observed in full‐cycle maximum intensity projection images. Target delineation accuracy at end‐of‐inhalation phase was observed to be constant up to a threshold in the value of the reconstruction interval, beyond which it varied arbitrarily. This threshold was found to be correlated with the number of phase bins and the motion period. No observable variations were noted with images from the end of exhalation when temporal spacing was varied. Target delineation accuracy was observed to be enhanced in acquisitions using faster gantry rotation speeds. An evaluation of the acquisition parameters needs to be performed depending on the period of the motion and limiting factors such as the availability of acquisition settings, X‐ray tube workload, image storage, and processing power.

PACS numbers: 87.53.Xd, 87.57.‐s, 87.57.Gg, 87.59.Fm

The impact of temporal inaccuracies on 4DCT image quality

Accurate delineation of target volumes is one of the critical components contributing to the success of image-guided radiotherapy treatments and several imaging modalities are employed to increase the accuracy in target identification. Four-dimensional (4D) techniques are incorporated into existing radiation imaging techniques like computed tomography (CT) to account for the mobility of the target volumes. However, these methods in some cases introduce further inaccuracies in the target delineation when further quality assurance measures are not implemented. A source of commonly observed inaccuracy is the misidentification of the respiration cycles and resulting respiration phase assignments used in the construction of the 4D patient model. The aim of this work is to emphasize the importance of optimal respiration phase assignment during the 4DCT image acquisition process and to perform a quantitative assessment of the effect of inaccurate phase assignments on the overall image quality. The accuracy of the phase assignment was assessed by comparison with an independent calculation of the respiration phases. Misplaced phase assignments manifest themselves as deformations and artifacts in reconstructed images. These effects are quantified as volumetric discrepancies in the localization of target objects represented by spherical phantoms. Measurements are performed using a fully programmable motion phantom designed and built at Mayo Clinic (Rochester, MN). Implementation of a case based independent check and correction procedure is also demonstrated with emphasis on the use of this procedure in the clinical environment. Review of clinical 4D scans performed in this institution showed discrepancies in the phase assignments in about 40% of the cases when compared to our independent calculations. It is concluded that for improved image reconstruction, an independent check of the sorting procedure should be performed for each clinical 4DCT case.

Incidence of radiation pneumonitis after thoracic irradiation: Dose-volume correlates

PURPOSE

To define clinical and dosimetric parameters correlated with the risk of clinically relevant radiation pneumonitis (RP) after thoracic radiotherapy.

METHODS AND MATERIALS

Records of consecutive patients treated with definitive thoracic radiotherapy were retrospectively reviewed for the incidence of RP of Grade 2 or greater by the Common Toxicity Criteria. Dose-volume histograms using total lung volume (TL) and TL minus gross tumor volume (TL-G) were created with and without heterogeneity corrections. Mean lung dose (MLD), effective lung volume (V(eff)), and percentage of TL or TL-G receiving greater than or equal to 10, 13, 15, 20, and 30 Gy (V10-V30, respectively) were analyzed by logistic regression. Receiver operating characteristic (ROC) curves were generated to estimate RP predictive values.

RESULTS

Twelve cases of RP were identified in 92 eligible patients. Mean lung dose, V10, V13, V15, V20, and V(eff) were significantly correlated to RP. Combinations of MLD, V(eff), V20, and V30 lost significance using TL-G and heterogeneity corrections. Receiver operating characteristic analysis determined V10 and V13 as the best predictors of RP risk, with a decrease in predictive value above those volumes.

CONCLUSIONS

Intrathoracic radiotherapy should be planned with caution when using radiotherapy techniques delivering doses of 10 to 15 Gy to large lung volumes.

Selective identification of different brachytherapy sources, ferromagnetic seeds, and fiducials in the prostate using an automated seed sorting algorithm

PURPOSE

Routine permanent prostate brachytherapy (PPB) includes CT-based postimplant dosimetry (PID). A method of identifying different source types from CT data in the same implant volume is described.

METHODS AND MATERIALS

A previously described automatic method for seed localization using CT data is used in this study. Two cases were analyzed: a PPB case with (103)Pd followed by salvage (125)I implantation, both performed at another institution, and a cadaver case where 4 different seed types, including ferromagnetic seeds, and fiducials were implanted.

RESULTS

Automatic segregation of different seed types with minimal manual correction is demonstrated using the described localization algorithm. The process is confirmed accurate by comparison of plain film radiographs to CT data and digitally reconstructed radiographs.

CONCLUSION

Unique identification of different source types, including PPB seeds, fiducial markers, and ferromagnetic seeds in permanent implants is possible and permits dosimetric analyses that are spatially coincident.

Automated seed localization from CT datasets of the prostate

With the increasing utilization of permanent brachytherapy implants for treating carcinoma of the prostate, the importance of accurate post-treatment dose calculation also increases for assessing patient outcome and planning future treatments. An automatic method for seed localization of permanent brachytherapy implants, using CT datasets of the prostate, has been developed and tested on a phantom using an actual patient planned seed distribution. This method was also compared to results with the three-film technique for three patient datasets. The automatic method is as accurate or more accurate than the three film technique for 1 mm, 3 mm, and 5 mm contiguous CT slices, and eliminates the inter- and intra-observer variability of the manual methods. The automated method improves the localization of brachytherapy seeds while reducing the time required for the user to input information, and is demonstrated to be less operator dependent, less time consuming, and potentially more accurate than the three-film technique.