An automatic method for accurate volume delineation of heterogeneous tumors in PET

PURPOSE

Accurate volumetric tumor delineation is of increasing importance in radiation treatment planning. Many tumors exhibit only moderate tracer uptake heterogeneity and delineation methods using an adaptive threshold lead to robust results. These methods use a tumor reference value R (e.g., ROI maximum) and the tumor background Bg to compute the volume reproducing threshold. This threshold corresponds to an isocontour which defines the tumor boundary. However, the boundaries of strongly heterogeneous tumors can not be described by an isocontour anymore and therefore conventional threshold methods are not suitable for accurate delineation. The aim of this work is the development and validation of a delineation method for heterogeneous tumors.

METHODS

The new method (voxel-specific threshold method, VTM) can be considered as an extension of an adaptive threshold method (lesion-specific threshold method, LTM), where instead of a lesion-specific threshold for the whole ROI, a voxel-specific threshold is computed by determining for each voxel Bg and R in the close vicinity of the voxel. The absolute threshold for the considered voxel is then given by Tabs=T×(R-Bg)+Bg, where T=0.39 was determined with phantom measurements.

VALIDATION

30 clinical datasets from patients with non-small-cell lung cancer were used to generate 30 realistic anthropomorphic software phantoms of tumors with different heterogeneities and well-known volumes and boundaries. Volume delineation was performed with VTM and LTM and compared with the known lesion volumes and boundaries.

RESULTS

In contrast to LTM, VTM was able to reproduce the true tumor boundaries accurately, independent of the heterogeneity. The deviation of the determined volume from the true volume was (0.8±4.2)% for VTM and (11.0±16.4)% for LTM.

CONCLUSIONS

In anthropomorphic software phantoms, the new method leads to promising results and to a clear improvement of volume delineation in comparison to conventional background-corrected thresholding. In the next step, the suitability for clinical routine will be further investigated.

Evaluation of PET quantification accuracy in vivo. Comparison of measured FDG concentration in the bladder with urine samples

Quantitative positron emission tomography (PET) requires accurate scanner calibration, which is commonly performed using phantoms. It is not clear to what extent this procedure ensures quantitatively correct results in vivo, since certain conditions differ between phantom and patient scans.

AIM

We, therefore, have evaluated the actual quantification accuracy in vivo of PET under clinical routine conditions.

PATIENTS, METHODS

We determined the activity concentration in the bladder in patients undergoing routine [18F]FDG whole body investigations with three different PET scanners (Siemens ECAT EXACT HR+ PET: n = 21; Siemens Biograph 16 PET/CT: n = 16; Philips Gemini-TF PET/CT: n = 19). Urine samples were collected immediately after scan. Activity concentration in the samples was determined in well counters cross-calibrated against the respective scanner. The PET (bladder) to well counter (urine sample) activity concentration ratio was determined.

RESULTS

Activity concentration in the bladder (PET) was systematically lower than in the urine samples (well counter). The patient-averaged PET to well counter ratios for the investigated scanners are (mean ± SEM): 0.881 ± 0.015 (ECAT HR+), 0.898 ± 0.024 (Biograph 16), 0.932 ± 0.024 (Gemini-TF). These values correspond to underestimates by PET of 11.9%, 10.2%, and 6.8%, respectively.

CONCLUSIONS

The investigated PET systems consistently underestimate activity concentration in the bladder. The comparison of urine samples with PET scans of the bladder is a straightforward means for in vivo evaluation of the expectable quantification accuracy. The method might be interesting for multi-center trials, for additional quality assurance in PET and for investigation of PET/MR systems for which clear proof of sufficient quantitative accuracy in vivo is still missing.

Potential of a Cetuximab-based radioimmunotherapy combined with external irradiation manifests in a 3-D cell assay

Targeting epidermal growth factor receptor (EGFR)-overexpressing tumors with radiolabeled anti-EGFR antibodies is a promising strategy for combination with external radiotherapy. In this study, we evaluated the potential of external plus internal irradiation by [(90) Y]Y-CHX-A″-DTPA-C225 (Y-90-C225) in a 3-D environment using FaDu and SAS head and neck squamous cell carcinoma (HNSCC) spheroid models and clinically relevant endpoints such as spheroid control probability (SCP) and spheroid control dose 50% (SCD50 , external irradiation dose inducing 50% loss of spheroid regrowth). Spheroids were cultured using a standardized platform. Therapy response after treatment with C225, CHX-A"-DTPA-C225 (DTPA-C225), [(90) Y]Y-CHX-A"-DTPA (Y-90-DTPA) and Y-90-C225 alone or in combination with X-ray was evaluated by long-term monitoring (60 days) of spheroid integrity and volume growth. Penetration kinetics into spheroids and EGFR binding capacities on spheroid cells were identical for unconjugated C225 and Y-90-C225. Spheroid-associated radioactivity upon exposure to the antibody-free control conjugate Y-90-DTPA was negligible. Determination of the SCD50 demonstrated higher intrinsic radiosensitivity of FaDu as compared with SAS spheroids. Treatment with unconjugated C225 alone did not affect spheroid growth and cell viability. Also, C225 treatment after external irradiation showed no additive effect. However, the combination of external irradiation with Y-90-C225 (1 µg/ml, 24 hr) resulted in a considerable benefit as reflected by a pronounced reduction of the SCD50 from 16 Gy to 9 Gy for SAS spheroids and a complete loss of regrowth for FaDu spheroids due to the pronounced accumulation of internal dose caused by the continuous exposure to cell-bound radionuclide upon Y-90-C225-EGFR interaction.

Automatic volume delineation in oncological PET. Evaluation of a dedicated software tool and comparison with manual delineation in clinical data sets

AIM

Evaluation of a dedicated software tool for automatic delineation of 3D regions of interest in oncological PET.

PATIENTS, METHODS

The applied procedure encompasses segmentation of user-specified subvolumes within the tomographic data set into separate 3D ROIs, automatic background determination, and local adaptive thresholding of the background corrected data. Background correction and adaptive thresholding are combined in an iterative algorithm. Nine experienced observers used this algorithm for automatic delineation of a total of 37 ROIs in 14 patients. Additionally, the observers delineated the same ROIs also manually (using a freely chosen threshold for each ROI) and the results of automatic and manual ROI delineation were compared.

RESULTS

For the investigated 37 ROIs the manual delineation shows a strong interobserver variability of (26.8±6.3)% (range: 15% to 45%) while the corresponding value for automatic delineation is (1.1±1.0)% (range: <0.1% to 3.6%). The fractional deviation of the automatic volumes from the observer-averaged manual ones is (3.7±12.7)%.

CONCLUSION

The evaluated software provides results in very good agreement with observer-averaged manual evaluations, facilitates and accelerates the volumetric evaluation, eliminates the problem of interobserver variability and appears to be a useful tool for volumetric evaluation of oncological PET in clinical routine.

Two or four hour [¹⁸F]FMISO-PET in HNSCC. When is the contrast best?

[¹⁸F]Fluoromisonidazole positron emission tomography (FMISO-PET) is a non invasive imaging technique that can assist detecting intra tumour regions of hypoxia. FMISO-PET evinces comparatively low signal-to-noise-ratio (SNR) and may be acquired dynamically or after different uptake times post injection (p.i.). The aim of this study was to identify, if static images acquired two hours (MISO2) or four hours (MISO4) p.i. reveal higher contrast.

PATIENTS, METHODS

As part of a prospective trial, 23 patients with cancers of the head and neck underwent [¹⁸F]fluorodeoxyglucose (FDG) PET before and during curative radiochemotherapy. Additionally, FMISO-PET studies 2 h and 4 h p.i. were done before treatment and after a mean dose of 11Gy, 23 Gy and 57 Gy during RCT. After coregistration, a dedicated software was used to define the gross tumour volume (GTV) by FDG PET for the primary tumour. This volume was overlaid to the FMISO images and hypoxia within the GTV was determined. The contrast between hypoxia determined by MISO2 and by MISO4 was investigated and analysed with the Wilcoxon-matched-pairs test.

RESULTS

Mean SUVmax in tumours of all examinations was 2.2 (stdev: 0.4, min: 1.3, max: 3.4) after 2 h and 2.4 (stdev: 0.7, min: 1.1, max: 4.4) after 4 h. In the neck musculature the mean SUVmax was 1.5 at both time points and the mean SUVmean decreased from 1.2 after 2 h to 1.1 after 4 h, respectively. These effects resulted in significantly rising contrast ratios from MISO2 to MISO4. The differently defined contrasts revealed significantly higher values for examinations 4 h p.i. (p < 0.002).

CONCLUSION

Data acquisition of [¹⁸F]FMISO should be done 4 h p.i. to gather the optimal contrast, preferably allowing further analysis, e. g. hypoxic sub volume definition for therapy planning.

NOA-08 randomized phase III trial of 1-week-on/1-week-off temozolomide versus involved-field radiotherapy in elderly (older than age 65) patients with newly diagnosed anaplastic astrocytoma or glioblastoma (Methusalem)

LBA2001

Background: The median survival time for elderly patients (pts) with malignant gliomas is in the range of a few months. Radiotherapy (RT) is the standard treatment and superior to best supportive care both with respect to progression-free and overall survival. The benefit derived from surgery and RT is modest, and both treatments are less well tolerated in elderly pts than in the young. The availability of a potentially effective pharmacological agent, temozolomide (TMZ), for malignant glioma, which exhibits a favorable safety profile, necessitated a reconsideration of the widespread therapeutic nihilism with malignant glioma in the elderly.

Methods: The NOA-08 trial of the Neurooncology Working Group (NOA) of the German Cancer Society compared standard postsurgical involved-field RT to a dose of 54-60 Gy, in pts with anaplastic astrocytoma or glioblastoma > 65 ys with a Karnofsky performance score ≥ 60, to TMZ in an one week on/one week off schedule at 100 mg/m2 with dose modification in 25 mg steps in both directions. The primary endpoint was the median survival time (OS) during the follow-up in the 12 months after date of operation. The trial sought to demonstrate the non-inferiority of TMZ compared with RT. Regarding a maximal difference of 25% between both treatment arms in OS as being equivalent, 2 x 206 pts were randomized between May 15, 2005 and Nov 2, 2009 in 22 German and one Suisse sites to provide 80% power to achieve significance at a one-sided level of 0.05. Thirty-nine patients were excluded from the intention-to-treat (ITT) population because no therapy was applied (n=22) or withdrawal of informed consent (n=17).

Results: All histological diagnoses were centrally confirmed. Pts characteristics were balanced between arms in the ITT population (n=373) except for more resections and more anaplastic astrocytomas in the RT arm. The non-inferiority of TMZ was not shown. In contrast, pts in the TMZ arm had an increased risk of death (HR=1.24 [95% CI: 0.94-1.63]) compared to pts in the RT arm. The rate of adverse and serious adverse events was higher in the TMZ arm.

Conclusions: This trial fails to show the non-inferiority of dose-intensified TMZ alone compared with RT alone in the primary treatment of older pts with malignant glioma. Unlike anaplastic glioma in the younger patient population, RT cannot be safely deferred in the treatment of elderly patients with anaplastic astrocytoma or glioblastoma. Whether RT plus TMZ is superior to RT alone, is addressed in the ongoing companion trial conducted by NCIC, EORTC and TROG.

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