[(18)F]Fluoro-2-deoxy-2-d-glucose versus 3'-deoxy-3'-[(18)F]fluorothymidine for defining hematopoietically active pelvic bone marrow in gynecologic patients

Feasibility of identifying proliferative active bone marrow with fat fraction MRI and multi-energy CT

Objective.Active bone marrow (ABM) can serve as both an organ at risk and a target in external beam radiotherapy.18F-fluorothymidine (FLT) PET is the current gold standard for identifying proliferative ABM but it is not approved for human use, and PET scanners are not always available to radiotherapy clinics. Identifying ABM through other, more accessible imaging modalities will allow more patients to receive treatment specific to their ABM distribution. Multi-energy CT (MECT) and fat-fraction MRI (FFMRI) show promise in their ability to characterize bone marrow adiposity, but these methods require validation for identifying proliferative ABM.Approach.Six swine subjects were imaged using FFMRI, fast-kVp switching (FKS) MECT and sequential-scanning (SS) MECT to identify ABM volumes relative to FLT PET-derived ABM volumes. ABM was contoured on FLT PET images as the region within the bone marrow with a SUV above the mean. Bone marrow was then contoured on the FFMRI and MECT images, and thresholds were applied within these contours to determine which threshold produced the best agreement with the FLT PET determined ABM contour. Agreement between contours was measured using the Dice similarity coefficient (DSC).Main results.FFMRI produced the best estimate of the PET ABM contour. Compared to FLT PET ABM volumes, the FFMRI, SS MECT and FKS MECT ABM contours produced average peak DSC of 0.722 ± 0.080, 0.619 ± 0.070, and 0.464 ± 0.080, respectively. The ABM volume was overestimated by 40.51%, 97.63%, and 140.13% by FFMRI, SS MECT and FKS MECT, respectively.Significance.This study explored the ability of FFMRI and MECT to identify the proliferative relative to ABM defined by FLT PET. Of the methods investigated, FFMRI emerged as the most accurate approximation to FLT PET-derived active marrow contour, demonstrating superior performance by both DSC and volume comparison metrics. Both FFMRI and SS MECT show promise for providing patient-specific ABM treatments.

Staging of Cervical Cancer: A Practical Approach Using MRI and FDG PET

This review provides a practical approach to the imaging evaluation of patients with cervical cancer (CC), from initial diagnosis to restaging of recurrence, focusing on MRI and FDG PET. The primary updates to the International Federation of Gynecology and Obstetrics (FIGO) CC staging system, as well as these updates' relevance to clinical management, are discussed. The recent literature investigating the role of MRI and FDG PET in CC staging and image-guided brachytherapy is summarized. The utility of MRI and FDG PET in response assessment and posttreatment surveillance is described. Important findings on MRI and FDG PET that interpreting radiologists should recognize and report are illustrated. The essential elements of structured reports during various phases of CC management are outlined. Special considerations, including the role of imaging in patients desiring fertility-sparing management, differentiation of CC and endometrial cancer, and unusual CC histologies, are also described. Finally, future research directions including PET/MRI, novel PET tracers, and artificial intelligence applications are highlighted.

Differential Response of Pelvic Bone Marrow Fluorodeoxyglucose Uptake in Patients Receiving Concurrent Chemoradiotherapy

AIMS

Irradiation of pelvic bone marrow (PBM) at the level of the typical low dose bath of intensity-modulated radiotherapy delivery (10-20 Gy) is associated with an increased risk of haematological toxicity, particularly when combined with concurrent chemotherapy. Although sparing of the whole of the PBM at a 10-20 Gy dose level is unachievable, it is known that PBM is divided into haematopoietically active and inactive regions that are identifiable based on the threshold uptake of [18F]-fluorodeoxyglucose (FDG) seen on positron emission tomography-computed tomography (PET-CT). In published studies to date, the definition of active PBM widely used is that of a standardised uptake value (SUV) greater than the mean SUV of the whole PBM prior to the start of chemoradiation. These studies include those looking at developing an atlas-based approach to contouring active PBM. Using baseline and mid-treatment FDG PET scans acquired as part of a prospective clinical trial we sought to determine the suitability of the current definition of active bone marrow as representative of differential underlying cell physiology.

MATERIALS AND METHODS

Active and inactive PBM were contoured on baseline PET-CT and using deformable registration mapped onto mid-treatment PET-CT. Volumes were cropped to exclude definitive bone, voxel SUV extracted and the change between scans calculated. Change was compared using Mann-Whitney U testing.

RESULTS

Active and inactive PBM were shown to respond differentially to concurrent chemoradiotherapy. The median absolute response of active PBM for all patients was -0.25 g/ml, whereas the median inactive PBM response was -0.02 g/ml. Significantly, the inactive PBM median absolute response was shown to be near zero with a relatively unskewed distribution (0.12).

CONCLUSIONS

These results would support the definition of active PBM as FDG uptake greater than the mean of the whole structure as being representative of underlying cell physiology. This work would support the development of atlas-based approaches published in the literature to contour active PBM based on the current definition as being suitable.

Active bone marrow segmentation based on computed tomography imaging in anal cancer patients: A machine-learning-based proof of concept

PURPOSE

Different methods are available to identify haematopoietically active bone marrow (ActBM). However, their use can be challenging for radiotherapy routine treatments, since they require specific equipment and dedicated time. A machine learning (ML) approach, based on radiomic features as inputs to three different classifiers, was applied to computed tomography (CT) images to identify haematopoietically active bone marrow in anal cancer patients.

METHODS

A total of 40 patients was assigned to the construction set (training set + test set). Fluorine-18-Fluorodeoxyglucose Positron Emission Tomography (18FDG-PET) images were used to detect the active part of the pelvic bone marrow (ActPBM) and stored as ground-truth for three subregions: iliac, lower pelvis and lumbosacral bone marrow (ActIBM, ActLPBM, ActLSBM). Three parameters were used for the correspondence analyses between 18FDG-PET and ML classifiers: DICE index, Precision and Recall.

RESULTS

For the 40-patient cohort, median values [min; max] of the Dice index were 0.69 [0.20; 0.84], 0.76 [0.25; 0.89], and 0.36 [0.15; 0.67] for ActIBM, ActLSBM, and ActLPBM, respectively. The Precision/Recall (P/R) ratio median value for the ActLPBM structure was 0.59 [0.20; 1.84] (over segmentation), while for the other two subregions the P/R ratio median has values of 1.249 [0.43; 4.15] for ActIBM and 1.093 [0.24; 1.91] for ActLSBM (under segmentation).

CONCLUSION

A satisfactory degree of overlap compared to 18FDG-PET was found for 2 out of the 3 subregions within pelvic bones. Further optimization and generalization of the process is required before clinical implementation.

Pelvic bones ADC could help to predict severe hematologic toxicity in patients undergoing concurrent chemoradiotherapy for cervical cancer

BACKGROUND

Hematologic toxicity (HT) during concurrent chemoradiotherapy (CCRT) for cervical cancer can lead to treatment breaks and compromise efficacy.

PURPOSE

To evaluate the association between severe hematologic toxicity (HT) and clinical factors and pelvic apparent diffusion coefficient (ADC) during CCRT of cervical cancer patients.

METHODS

Data from 120 patients with cervical cancer who were treated with CCRT from January 2016 and December 2018 were retrospectively analyzed. The clinical data (age, menopausal status, clinical stage, body mass index, chemotherapy regimen and chemotherapy cycle) of the patients were collected, and the cohort were divided into two groups based on the HT grade: HT3+ group (HT grade ≥ 3; 66 patients) and HT3- group (HT grade<3; 54 patients). All patients performed MRI before CCRT, and pelvic (ilium, pubis, ischium) ADC value was measured on ADC map. The correlation between severe HT and clinical parameters and pelvic ADC value were analyzed by univariate analysis, and the diagnostic performance was further assessed by receiver operating characteristic (ROC) analysis.

RESULTS

In univariate analysis, the menopausal status (p = 0.012) and chemotherapy regimen (p = 0.011) were significantly correlated with severe HT in overall patients, and menopausal patients or patients receiving paclitaxel plus cisplatin (TP) regimen were more likely to develop severe HT. HT3+ group showed a significantly lower pelvic ADC value than HT3- group. The ADC value cut-offs derived from our study for predicting severe HT was 0.317 × 10^-3 mm²/s in overall patients. Neither clinical parameters or pelvic ADCs were associated with severe HT in menopausal patients when analyzed separately (p > 0.05).

CONCLUSIONS

Severe HT was significantly associated with menopausal status and chemotherapy regimen in patients with cervical cancer treated with CCRT, and HT3+ group showed a lower pelvic ADC value.

PET Imaging for Gynecologic Malignancies

This review article summarizes the clinical applications of established and emerging PET tracers in the evaluation of the 5 most common gynecologic malignancies: endometrial, ovarian, cervical, vaginal, and vulvar cancers. Emphasis is given to 2-deoxy-2-[¹⁸F]fluoro-d-glucose as the most widely used and studied tracer, with additional clinical tracers also explored. The common imaging protocols are discussed, including standard dose ranges and uptake times, established roles, as well as the challenges and future directions of these imaging techniques. The key points are emphasized with images from selected cases.

Which Bone Marrow Sparing Strategy and Radiotherapy Technology Is Most Beneficial in Bone Marrow-Sparing Intensity Modulated Radiation Therapy for Patients With Cervical Cancer?

Background

To evaluate the dosimetric parameters of different bone marrow sparing strategies and radiotherapy technologies and determine the optimal strategy to reduce hematologic toxicity associated with concurrent chemoradiation (cCRT) for cervical cancer.

Methods

A total of 15 patients with Federation International of Gynecology and Obsterics (FIGO) Stage IIB cervical cancer treated with cCRT were re-planned for bone marrow (BM)-sparing plans. First, we determined the optimal BM sparing strategy for intensity modulated radiotherapy (IMRT), including a BMS-IMRT plan that used total BM sparing (IMRT-BM) as the dose-volume constraint, and another plan used os coxae (OC) and lumbosacral spine (LS) sparing (IMRT-LS+OC) to compare the plan without BM-sparing (IMRT-N). Then, we determined the optimal technology for the BMS-IMRT, including fixed-field IMRT (FF-IMRT), volumetric-modulated arc therapy (VMAT), and helical tomotherapy (HT). The conformity and homogeneity of PTV, exposure volume of OARs, and efficiency of radiation delivery were analyzed.

Results

Compared with the IMRT-N group, the average volume of BM that received ≥10, ≥20, ≥30, and ≥40 Gy decreased significantly in both two BM-sparing groups, especially in the IMRT-LS+OC group, meanwhile, two BMS-IMRT plans exhibited the similar effect on PTV coverage and other organs at risk (OARs) sparing. Among three common IMRT techniques in clinic, HT was significantly less effective than VMAT and FF-IMRT in the aspect of BM-Sparing. Additionally, VMAT exhibited more efficient radiation delivery.

Conclusion

We recommend the use of VMAT with OC and LS as separate dose-volume constraints in cervical cancer patients aiming at reducing hematologic toxicity associated with cCRT, especially in developing countries.

Comparison of Hematologic Toxicity and Bone Marrow Compensatory Response in Head and Neck vs. Cervical Cancer Patients Undergoing Chemoradiotherapy

Background: Hematologic toxicity is a critical problem limiting treatment delivery in cancer patients undergoing concurrent chemoradiotherapy. However, the extent to which anatomic variations in radiation dose limit chemotherapy delivery is poorly understood. A unique natural experiment arises in patients with head and neck and cervical cancer, who frequently undergo identical chemotherapy but receive radiation to different regions of the body. Comparing these cohorts can help elucidate to what extent hematologic toxicity is attributable to marrow radiation as opposed to chemotherapy.

Methods: In this longitudinal cohort study, we compared hematologic toxicity and bone marrow compensatory response in 148 patients (90 cervix, 58 head/neck) undergoing chemoradiotherapy with concurrent weekly cisplatin 40 mg/m². We used linear mixed effect models to compare baseline and time-varying peripheral cell counts and hemoglobin levels between cohorts. To assess bone marrow compensatory response, we measured the change in metabolically active bone marrow (ABM) volume on ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography.

Results: We observed greater reductions in log-transformed lymphocyte, platelet, and absolute neutrophil counts (ANC) for cervix compared to head/neck cancer patients (fixed effects for time-cohort interaction [95% CI]: lymphocytes, −0.06 [−0.09, −0.031]; platelets,−0.028 [-0.051, −0.0047]; ANC, −0.043 [−0.075, −0.011]). Mean ANC nadirs were also lower for cervical vs. head/neck cancer cohorts (2.20 vs. 2.85 × 10³ per μL, p < 0.01). Both cohorts exhibited reductions in ABM volume within the radiation field, and increases in ABM volume in out-of-field areas, indicating varying compensatory response to radiation injury.

Conclusions: Cervical cancer patients had faster decreases in ANC, lymphocyte, and platelet counts, and lower ANC nadirs, indicating a significant effect of pelvic irradiation on acute peripheral blood cell counts. Both cohorts exhibited a compensatory response with increased out-of-field bone marrow activity.

Dose-volume parameters of MRI-based active bone marrow predict hematologic toxicity of chemoradiotherapy for rectal cancer

Purpose

Magnetic resonance imaging (MRI) is routinely used for locoregional staging of rectal cancer and offers promise for the prediction of hematologic toxicity. The present study compares the clinical utility of MRI-based active bone marrow (BMact) delineation with that of CT-based bone marrow total (BMtot) delineation for predicting hematologic toxicity.

Methods

A prospective cohort study was performed. Eligible patients had stage II/III rectal cancer and qualified for preoperative chemoradiotherapy. The BMact areas on T1-weighted MRI were contoured. The impact of the dose–volume parameters of BMact/BMtot and clinical data on hematologic toxicity were assessed. Basic endpoints were the occurrence of grade 3/4 hematologic toxicity and peripheral blood parameters reaching a nadir. Linear regression models were generated for the nadirs and receiver operating characteristic (ROC) curves for the occurrence of grade 3/4 hematologic toxicity.

Results

Thirty-five patients were enrolled. Women presented higher dose–volume parameters of BMact, BMtot, and lymphocyte nadir (ALCnadir%) than men. Models for the prediction of ALCnadir% (V5-V20BMtot, V5-V30BMact) and platelet nadir (PLTnadir%; V5-V10BMtot, V5-V20BMact) were statistically significant. In the ROC curves, a baseline lymphocyte level of 1.81 × 10³/ml was adopted as the cutoff for predicting grade 3/4 lymphopenia, with specificity of 77.8% and sensitivity of 73.1%. The multivariate linear regression model for ALCnadir% had R² = 0.53, p = 0.038. In the tenth step of selection, V5BMact (p = 0.002) and gender (p = 0.019) remained. The multivariate linear regression model for PLTnadir% had R² = 0.20, p = 0.34. In the sixth step of selection, V15BMact remained (p = 0.026).

Conclusion

The dose–volume parameters of BMact serve as better predictors of ALCnadir% and PLTnadir% than BMtot.

A Multi-atlas Approach for Active Bone Marrow Sparing Radiation Therapy: Implementation in the NRG-GY006 Trial

PURPOSE

Sparing active bone marrow (ABM) can reduce acute hematologic toxicity in patients undergoing chemoradiotherapy for cervical cancer, but ABM segmentation based on positron emission tomography/computed tomography (PET/CT) is costly. We sought to develop an atlas-based ABM segmentation method for implementation in a prospective clinical trial.

METHODS AND MATERIALS

A multiatlas was built on a training set of 144 patients and validated in 32 patients from the NRG-GY006 clinical trial. ABM for individual patients was defined as the subvolume of pelvic bone greater than the individual mean standardized uptake value on registered ¹⁸F-fluorodeoxyglucose PET/CT images. Atlas-based and custom ABM segmentations were compared using the Dice similarity coefficient and mean distance to agreement and used to generate ABM-sparing intensity modulated radiation therapy plans. Dose-volume metrics and normal tissue complication probabilities of the two approaches were compared using linear regression.

RESULTS

Atlas-based ABM volumes (mean [standard deviation], 548.4 [88.3] cm³) were slightly larger than custom ABM volumes (535.1 [93.2] cm³), with a Dice similarity coefficient of 0.73. Total pelvic bone marrow V₂₀ and D_mean were systematically higher and custom ABM V₁₀ was systematically lower with custom-based plans (slope: 1.021 [95% confidence interval (CI), 1.005-1.037], 1.014 [95% CI, 1.006-1.022], and 0.98 [95% CI, 0.97-0.99], respectively). We found no significant differences between atlas-based and custom-based plans in bowel, rectum, bladder, femoral heads, or target dose-volume metrics.

CONCLUSIONS

Atlas-based ABM segmentation can reduce pelvic bone marrow dose while achieving comparable target and other normal tissue dosimetry. This approach may allow ABM sparing in settings where PET/CT is unavailable.

The Role of Positron Emission Tomography Imaging in Radiotherapy Target Delineation

Positron emission tomography (PET) is an advanced functional imaging modality in oncology care for the diagnosis, staging, prognostication, and surveillance of numerous malignancies. PET can also offer considerable advantages for target volume delineation as part of radiation treatment planning. In this review, data and clinical practice from 6 general oncology disease sites are assessed to descriptively evaluate the role of PET in target volume delineation. Also highlighted are several specific and practical utilities for PET imaging in radiation treatment planning. Publication of several ongoing prospective trials in the future may further expand the utility of PET for target delineation and patient care.

Response of FDG avid pelvic bone marrow to concurrent chemoradiation for anal cancer

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Chemoradiation suppression of active bone marrow shown in on-treatment FDG-PET.

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No suppression shown in un-irradiation bone marrow.

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Volumes of active bone marrow receiving 20 Gy are associated with blood count nadirs.

Background and purpose

To determine if suppression of active bone marrow, as defined on FDG PETCT, is seen in on-treatment imaging of anal cancer patients receiving concurrent chemoradiation.

Methods and materials

Scans from 26 patients participating in the ART trial (full title: Anal squamous cell carcinoma: Investigation of functional imaging during chemoRadioTherapy), a single center observational study with FDG PETCT prior to radiotherapy and at fraction 8–10 of concurrent chemoradiation were analysed. Active bone marrow was contoured in both the pelvis and un-irradiated thoracic spine. SUV and volume of active bone marrow after 8–10 fractions of treatment were compared to baseline. Dose metrics to pelvic active bone marrow were extracted and compared to reduction in SUV/active bone marrow volume and to blood count nadir using linear regression.

Results

Suppression of active bone marrow is seen in the pelvis by a reduction in mean SUV and volume of active bone marrow after 8–10 fractions of treatment. Suppression is not seen in un-irradiated thoracic spine. Dose metrics were associated with reduced SUV and reduced volume of active bone marrow. Volume of active bone marrow receiving <20 Gy was associated with WCC/ANC nadir. 20 Gy was identified as the most likely clinically meaningful dose threshold for toxicity. Volume of active bone marrow receiving <20 Gy correlated to WCC and ANC with an increase of 100 cc being associated with an increase of 0.4 and 0.3 respectively.

Conclusion

The effect of concurrent chemoradiation in suppression of active bone marrow is seen in on-treatment FDG PETCT scans. Chemotherapy appears well tolerated after 2 weeks of treatment.

Incorporating 18FDG-PET-defined pelvic active bone marrow in the automatic treatment planning process of anal cancer patients undergoing chemo-radiation

BACKGROUND

To investigate whether the incorporation of ¹⁸FDG-PET into the automatic treatment planning process may be able to decrease the dose to active bone marrow (BM) for locally advanced anal cancer patients undergoing concurrent chemo-radiation (CHT-RT).

METHODS

Ten patients with locally advanced anal cancer were selected. Bone marrow within the pelvis was outlined as the whole outer contour of pelvic bones or employing ¹⁸FDG-PET to identify active BM within osseous structures. Four treatment planning solutions were employed with different automatic optimization approaches toward bone marrow. Plan A used iliac crests for optimization as per RTOG 05-29 trial; plan B accounted for all pelvic BM as outlined by the outer surface of external osseous structures; plan C took into account both active and inactive BM as defined using ¹⁸FDG-PET; plan D accounted only for the active BM subregions outlined with ¹⁸FDG-PET. Dose received by active bone marrow within the pelvic (^ACTPBM) and in different subregions such as lumbar-sacral (^ACTLSBM), iliac (^ACTIBM) and lower pelvis (^ACTLPBM) bone marrow was analyzed.

RESULTS

A significant difference was found for ^ACTPBM in terms of D_mean (p = 0.014) V₂₀ (p = 0.015), V₂₅ (p = 0.030), V₃₀ (p = 0.020), V₃₅ (p = 0.010) between Plan A and other plans. With respect to specific subsites, a significant difference was found for ^ACTLSBM in terms of V₃₀ (p = 0.020)), V₃₅ (p = 0.010), V₄₀ (p = 0.050) between Plan A and other solutions. No significant difference was found with respect to the investigated parameters between Plan B,C and D. No significant dosimetric differences were found for ^ACTLSPBM and ^ACTIBM and inactive BM subregions within the pelvis between any plan solution.

CONCLUSIONS

Accounting for pelvic BM as a whole compared to iliac crests is able to decrease the dose to active bone marrow during the planning process of anal cancer patients treated with intensity-modulated radiotherapy. The same degree of reduction may be achieved optimizing on bone marrow either defined using the outer bone contour or through ¹⁸FDG-PET imaging. The subset of patients with a benefit in terms of dose reduction to active BM through the inclusion of ¹⁸FDG-PET in the planning process needs further investigation.

Evaluation of Functional Marrow Irradiation Based on Skeletal Marrow Composition Obtained Using Dual-Energy Computed Tomography

PURPOSE

To develop an imaging method to characterize and map marrow composition in the entire skeletal system, and to simulate differential targeted marrow irradiation based on marrow composition.

METHODS AND MATERIALS

Whole-body dual energy computed tomography (DECT) images of cadavers and leukemia patients were acquired, segmented to separate bone marrow components, namely, bone, red marrow (RM), and yellow marrow (YM). DECT-derived marrow fat fraction was validated using histology of lumbar vertebrae obtained from cadavers. The fractions of RM (RMF = RM/total marrow) and YMF were calculated in each skeletal region to assess the correlation of marrow composition with sites and ages. Treatment planning was simulated to target irradiation differentially at a higher dose (18 Gy) to either RM or YM and a lower dose (12 Gy) to the rest of the skeleton.

RESULTS

A significant correlation between fat fractions obtained from DECT and cadaver histology samples was observed (r=0.861, P<.0001, Pearson). The RMF decreased in the head, neck, and chest was significantly inversely correlated with age but did not show any significant age-related changes in the abdomen and pelvis regions. Conformity of radiation to targets (RM, YM) was significantly dependent on skeletal sites. The radiation exposure was significantly reduced (P<.05, t test) to organs at risk (OARs) in RM and YM irradiation compared with standard total marrow irradiation (TMI).

CONCLUSIONS

Whole-body DECT offers a new imaging technique to visualize and measure skeletal-wide marrow composition. The DECT-based treatment planning offers volumetric and site-specific precise radiation dosimetry of RM and YM, which varies with aging. Our proposed method could be used as a functional compartment of TMI for further targeted radiation to specific bone marrow environment, dose escalation, reduction of doses to OARs, or a combination of these factors.