[68Ga]-DOTATATE PET/MRI as an adjunct imaging modality for radiation treatment planning of meningiomas

Background

Meningiomas express high levels of somatostatin receptor 2 (SSTR2). SSTR2-targeted PET imaging with [⁶⁸Ga]-DOTATATE can aid with distinguishing residual meningioma from reactive changes in the postoperative setting. We present initial dosimetric analyses, acute events, and local control data utilizing [⁶⁸Ga]-DOTATATE PET/MRI-assisted target delineation for prospectively-treated intermediate-risk meningiomas.

Methods

Twenty-nine patients underwent DOTATATE PET/MRI meningioma evaluation in 2019. Eight patients with 9 postoperative meningiomas met RTOG 0539 intermediate-risk criteria (recurrent WHO grade I, 1/9; WHO grade II, 8/9). Target volumes were created using DOTATATE PET/MRI to determine residual disease and received a nominal dose of 35.0 Gy over 5 fractions. For comparison, cases were recontoured and planned with MRI alone per RTOG 0539 guidelines. Mean and maximum equivalent 2 Gy doses were generated for target volumes and organs at risk (OAR) within 1 cm of the PTV and compared using Wilcoxon matched pairs signed rank test.

Results

DOTATATE PET/MRI-guided planning significantly reduced mean PTV (11.12 cm³ compared to 71.39 cm³ based on MRI alone, P < .05) and mean and max dose to the whole brain, optic nerves, and scalp. PET/MRI plans resulted in at least 50% reduction of mean and max doses to the lens, eyes, chiasm, cochlea, brainstem, and hippocampi. One patient experienced focal alopecia. There were no local recurrences at 6 months.

Conclusion

Incorporating DOTATATE-PET/MRI for postoperative target delineation in patients with intermediate-risk intracranial meningiomas results in PTV reduction and decreased OAR dose. Our findings warrant larger studies evaluating DOTATATE-PET/MRI in the radiotherapeutic planning of postoperative meningiomas.

RTHP-40. EFFECT OF RIND-BASED DOSIMETRIC TECHNIQUES FOR SCALP DOSE REDUCTION IN BRAIN IRRADIATION

OBJECTIVE

Radiation-induced alopecia is an unwanted side effect causing permanent cosmetic distress if hair regrowth does not occur. Rind-based techniques can effectively control dosimetric spread. We evaluated this technique to reduce scalp dose and alopecia while maintaining tumor coverage.

METHODS

Ten consecutive brain tumor plans were retrospectively evaluated. All planning tumor volume (PTV) margins were ≤ 15.0mm from the skin surface. Departmental guidelines for fractionation were followed, with minimum 95% PTV coverage receiving 100% dose. Fractionation variation was accounted for with biologically effective dose calculation (alpha/beta=2). Rind structures encompassed 5mm depth from scalp surface; upper dose limits were customized to minimum values without PTV coverage compromise. Standard comparative plans using identical criteria, without rind structures, were calculated. Scalp dose evaluation was defined for tissue from skin to 5mm depth. Paired T-tests were used for comparative evaluation.

RESULTS

Median age: 58 (range 27–85); 70% female (n=7). Histologies included gliomas (n=7) and meningiomas (n=3). Median PTV distance to skin surface: 13.5mm (range 8.0–15.0). Median PTV minimum and mean dose for rind-based plans: 88.63% (range 73.14–95.2) and 104.39% (range 102.07–107.38) of prescription and 90.90% (range 68.64–98.21) and 103.02% (range 101.91–107.04) for standard plans, respectively. Statistically significant reduction in scalp maximum and mean dose of 19.65% (p=2.72E-06) and 0.48% (p=0.007), respectively, was seen with rind-based planning. Scalp volume receiving 1000cGy-equivalent increased 6.7cc using rind-based techniques, although insignificant (p=0.33). Volume receiving 1500cGy-equivalent was significantly reduced 3.88cc (p=0.03) using rind-based techniques. With median 28.5 day follow-up, of 5 patients treated using rind-based techniques, 40% (n=2) exhibited acute alopecia compared to 100% of those treated with standard plans.

CONCLUSION

Rind-based dosimetric techniques exhibit significant reduction of scalp dose in brain irradiation. 60% of patients treated using this technique experienced no alopecia, versus 0% receiving standard treatment. Further investigation is warranted to better evaluate correlation.

RADI-39. EFFECT OF RIND-BASED DOSIMETRIC TECHNIQUES FOR SCALP DOSE REDUCTION IN BRAIN IRRADIATION

OBJECTIVE: Radiation-induced alopecia is an unwanted side effect causing permanent cosmetic distress if hair regrowth does not occur. Rind-based techniques can effectively control dosimetric spread. We evaluated this technique to reduce scalp dose and alopecia while maintaining tumor coverage. METHODS: Ten consecutive brain tumor plans were retrospectively evaluated. All planning tumor volume (PTV) margins were ≤ 15.0mm from the skin surface. Departmental guidelines for fractionation were followed, with minimum 95% PTV coverage receiving 100% dose. Fractionation variation was accounted for with biologically effective dose calculation (alpha/beta=2). Rind structures encompassed 5mm depth from scalp surface; upper dose limits were customized to minimum values without PTV coverage compromise. Standard comparative plans using identical criteria, without rind structures, were calculated. Scalp dose evaluation was defined for tissue from skin to 5mm depth. Paired T-tests were used for comparative evaluation. RESULTS: Median age: 58 (range 27–85); 70% female (n=7). Histologies included gliomas (n=7) and meningiomas (n=3). Median PTV distance to skin surface: 13.5mm (range 8.0–15.0). Median PTV minimum and mean dose for rind-based plans: 88.63% (range 73.14–95.2) and 104.39% (range 102.07–107.38) of prescription and 90.90% (range 68.64–98.21) and 103.02% (range 101.91–107.04) for standard plans, respectively. Statistically significant reduction in scalp maximum and mean dose of 19.65% (p=2.72E^-06) and 0.48% (p=0.007), respectively, was seen with rind-based planning. Scalp volume receiving 1000cGy-equivalent increased 6.7cc using rind-based techniques, although insignificant (p=0.33). Volume receiving 1500cGy-equivalent was significantly reduced 3.88cc (p=0.03) using rind-based techniques. With median 28.5 day follow-up, of 5 patients treated using rind-based techniques, 40% (n=2) exhibited acute alopecia compared to 100% of those treated with standard plans. CONCLUSION: Rind-based dosimetric techniques exhibit significant reduction of scalp dose in brain irradiation. 60% of patients treated using this technique experienced no alopecia, versus 0% receiving standard treatment. Further investigation is warranted to better evaluate correlation.

RADI-26. DOSIMETRIC EVALUATION OF 6 MV VERSUS 10 MV PHOTONS FOR HIPPOCAMPAL AVOIDANCE WHOLE BRAIN RADIOTHERAPY

OBJECTIVE: Whole brain radiotherapy (WBRT) causes neurocognitive decline. Hippocampal avoidance WBRT (HA-WBRT) reduces hippocampal irradiation, potentially mitigating neurocognitive sequelae. We compared hippocampal and brain dosimetry with HA-WBRT with 6 megavoltage (MV) versus 10 MV photon energies. METHODS: Twenty consecutive patients treated with WBRT were retrospectively replanned with HA-WBRT techniques using 6 MV and 10 MV photons. Coplanar volumetric modulated arc therapy was employed, with a prescription dose of 3000 cGy in 10 fractions. Planning was done with Eclipse version 13.6 or 15.6. Nine patients were planned with 2.5 mm multileaf collimator leaves, with the remainder planned with 5 mm leaves. The hippocampi were contoured and a HA structure was generated using a uniform 5 mm expansion. A planning target volume (PTV) was defined as the brain parenchyma minus the HA structure. NRG-CC001 dose constraints were used. For each variable, descriptive statistics were calculated. Comparisons were made using two-tailed Wilcoxon signed rank tests or paired t-tests. RESULTS: The minimum hippocampal dose (D100%) was improved with 6 MV plans, 841 cGy compared to 914 cGy with 10 MV (p< 0.005). The maximum hippocampal dose (D0.03cc) was reduced with 6 MV planning, 1614 cGy versus 1676 cGy for 10 MV (p< 0.0001). With 6 MV photons, a greater number of plans met NRG-CC001 constraints without deviations. 6 MV photons improved PTV coverage by the 95% isodose line, 96.6% compared to 95.9% for 10 MV (p=0.021). 6 MV photon plans decreased the volume of PTV receiving ≥105% of the prescription, 84.2% versus 87.9% for 10 MV (p=0.006). The mean dose, hot spots, and cold spots did not differ by photon energy. PTV dose constraints were always met. CONCLUSION: 6 MV photon HA-WBRT plans are dosimetrically superior to 10 MV, reducing hippocampal radiation dose, without compromise in brain coverage and improved target dose homogeneity.

Characterization of Methicillin-resistant Staphylococcus aureus isolated from public surfaces on a university campus, student homes and local community

AIM

Isolation and characterization of methicillin-resistant Staphylococcus aureus (MRSA) from frequently touched nonhospital environmental surfaces at a large university, student homes and community sites.

METHODS AND RESULTS

Twenty-four isolates from 21 (4·1%, n = 509) surfaces were MRSA positive and included 14 (58%, n = 24) SCCmec type IV, two (8%, n = 24) type I, and eight (33%, n = 24) were not type I-IV (NT). Six different multilocus sequencing types were identified by PCR and sequencing. PCR assays identified one (4·2%, n = 24) Panton-Valentine leukocidin (PVL) positive, 22 (92%, n = 24) arginine catabolic mobile element (ACME) positive and 23 (96%, n = 24) multidrug-resistant (kanamycin, macrolide, tetracycline) MRSA isolates. Eleven (46%, n = 24) USA300 isolates were determined by pulsed-field gel electrophoresis.

CONCLUSION

The MRSA-positive environmental surfaces were identified in student homes (11·8%, n = 85), the community (2·3%, n = 130) and the university (2·7%, n = 294). USA300 strains were isolated from the university, student homes and community samples. This is the first report of the animal clone ST97 on urban environmental surfaces.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study highlights the distribution of USA300 on frequently touched surfaces. Whether contact with these MRSA contaminated environmental surfaces are associated with increased risk of transmission of MRSA to people needs further research.

Inducible gene expression in mammalian cells and transgenic mice

Advances in biomedicine have accentuated the need to develop methods to deliberately modulate gene activity. In addition to improved versions of the system based on components of the tetracycline resistance operon, several strategies have recently emerged to control gene function at the transcriptional level. Particularly promising are approaches based on non-mammalian steroid hormones, and on small molecules that bind immunophilins.

Ecdysone-inducible gene expression in mammalian cells and transgenic mice

During metamorphosis of Drosophila melanogaster, a cascade of morphological changes is triggered by the steroid hormone 20-OH ecdysone via the ecdysone receptor, a member of the nuclear receptor superfamily. In this report, we have transferred insect hormone responsiveness to mammalian cells by the stable expression of a modified ecdysone receptor that regulates an optimized ecdysone responsive promoter. Inductions reaching 4 orders of magnitude have been achieved upon treatment with hormone. Transgenic mice expressing the modified ecdysone receptor can activate an integrated ecdysone responsive promoter upon administration of hormone. A comparison of tetracycline-based and ecdysone-based inducible systems reveals the ecdysone regulatory system exhibits lower basal activity and higher inducibility. Since ecdysone administration has no apparent effect on mammals, its use for regulating genes should be excellent for transient inducible expression of any gene in transgenic mice and for gene therapy.