Search

While dose escalation of radiotherapy (DERT) has failed to improve overall survival (OS) or progression-free survival (PFS) for glioblastoma in previous studies, a recent phase II clinical trial utilizing 18F-DOPA-PET-directed DERT demonstrated improved PFS in MGMT-unmethylated patients and OS in MGMT-methylated patients compared to historical controls. This planned secondary analysis sought to determine 1) how 18F-DOPA-PET changes RT volumes beyond standard MRI-planning, 2) which patients benefit most and least from this protocol, 3) which are mostly likely to experience clinically significant radionecrosis after DERT, and 4) patterns of failure after DERT. For 69 evaluable patients, median MRI-defined, PET-defined, and combined low-dose gross tumor volumes (GTV51) were 54 cc (range 9-248), 23 cc (0.4-179), and 62 cc (10-260), respectively. Median MRI-defined, PET-defined, and combined high-dose GTVs (GTV76) were 32 cc (range 4-136), 6 cc (0.1-138), and 34 cc (4-162), respectively. 18F-DOPA-PET resulted in a median volumetric expansion of 13% (0-243%) and 5% (0-217%) from MRI-defined low-dose and high-dose GTV’s, respectively. Central failures ( >95% of recurrence tumor volume) occurred within the 76 Gy, 60 Gy, and 51 Gy isodose lines in 32 (46%), 60 (87%), and 64 (93%) patients, respectively. Recursive partitioning analysis stratified patients by OS and PFS. Patients with 18F-DOPA-PET-defined GTV76 > 7.8cc, MRI-defined GTV76 > 42.7cc, and MGMT promotor-unmethylated tumors had the shortest OS, while patients with smaller PET and MRI-defined tumors had the longest OS (median 10.4 vs. 64.6 months, p< 0.001). Similarly, PFS was worst in patients with 18F-DOPA-PET-defined GTV76 > 2.17 cc who had biopsy only (median PFS 3.2 months, p< 0.001). Patients with 18F-DOPA-PET-defined GTV51 > 50 cc had the highest risk of grade 3+ radionecrosis (p< 0.001). In conclusion, larger 18F-DOPA-PET and MRI-defined tumor volumes were associated with worse outcomes, and 18F-DOPA-PET-directed DERT appears to reduce risk of central recurrence in high-dose volumes.

Purpose: A breast specific radiosurgery device (BSRD) has recently been FDA cleared for treatment of accelerated partial breast irradiation. Using this device requires a vacuum assisted immobilization system to treat patients in the prone position. Alternatively, APBI delivery using intensity modulated proton therapy (IMPT) treats patients in the supine position at University of Maryland. This study aimed to compare dose distribution to targets and organs at risk (OARS), using BSRD plans versus IMPT plans for APBI. We hypothesized that despite the physical characteristics of IMPT the BSRD plans would be superior in conformality. Methods:An IRB approved retrospective review was performed for 13 patients who previously received a lumpectomy boost using the BSRD in prone position followed by whole breast irradiation in the supine position. APBI plans were created using dose a fractionation of 30Gy in 5 fractions. Previously contoured LPC volumes with a 1cm CTV expansion were created (modified at anatomic boundaries and within 5 mm of skin) followed by a 3 mm PTV expansion for BSRD plans, our standard for all BSRD plans, or CTV with beam specific PTV for IMPT plans. A single physicist created plans for BSRD with a different physicist for IMPT. Physicists were blinded to the results of the comparative plans. Plans were compared with respect to heart max, heart mean, ipsilateral lung V5, V20, normal breast D5, D20, D50 and D80, skin max, CTV coverage, conformality index (CI) and homogeneity index (HI). Paired t-test was used for statistical analysis. Results:Six out of thirteen patients had left sided breast cancer. The CTV volumes were comparable, with no difference in coverage of 95% of the CTV receiving the prescription dose (98% vs 97%). BSRD plans had superior CI (0.82 vs 0.63, p Citation Format: Santanu Samanta, Elizabeth Nichols, Mark Zakhary, Mariana Guerrero, Baoshe Zhang, Ariel Pollock, Naru Lamichhane, Stewart Becker. Comparison between a breast specific radiosurgery device and intensity modulated proton therapy for accelerated partial breast irradiation [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS15-14.

BACKGROUND: 18F-DOPA-PET thresholds reliably delineate areas of high-grade astrocytoma not otherwise recognized with standard MRI and may more accurately identify regions of aggressive, high-density disease. Herein we report the preliminary safety and feasibility data from an ongoing phase II study (MC1374; R01CA178200) evaluating 18F-DOPA-PET guided-dose-escalated radiotherapy for glioblastoma. METHODS: Newly diagnosed glioblastoma patients without contra-indications to 18F-DOPA-PET are eligible for study enrollment. Target volumes include: CTV51Gy=T1-gadolinium contrast-enhancing (T1-CE) disease, T2 FLAIR signal abnormality, and low-grade 18F-DOPA-PET uptake, +1cm; CTV60Gy=T1-CE and high-grade 18F-DOPA-PET uptake, +1cm; and CTV76Gy=T1-CE and high-grade 18F-DOPA-PET disease without expansion all given in 30 fractions simultaneously. Patients are followed with 18F-DOPA-PET in addition to standard clinical follow-up. Safety stopping rule specifies that after 10 or more patients have been enrolled, if more than 10% experience any of the following adverse events considered to be at least possibly related to treatment, enrollment will be suspended: Grade 3 or 4 irreversible CNS toxicity, Grade 4 non-hematologic, non-CNS toxicity, any Grade 5 toxicity. Futility analysis (and primary study aim) is powered to consider a success to be an MGMT-unmethylated patient who is without progression within 6 months from the time of craniotomy. If 16 or more successes are observed in the first 25 evaluable patients study will continue. RESULTS: 77 patients have been accrued since December 2013 with 68 evaluable for toxicity. Grade 3 CNS necrosis was noted in 3 (4.4%) patients; 2 additional patients developed symptoms that resolved in the subsequent cycle so did not count towards stopping rule. Other grade 3+ toxicities include: 1 patient with pre-existing vision dysfunction had Grade 4 optic nerve dysfunction; 2 Grade 4 hematologic events and 1 Grade 5 event(sepsis) due to temozolamide-induced cytopenias. CONCLUSION: 18F-DOPA-PET -guided dose escalation appears reasonably safe and tolerable in patients with high-grade glioma.

BACKGROUND: Multiple studies have demonstrated that amino acid PET tracers identify aggressive disease beyond what is contrast enhancing on T1-weighted conventional MR (T1CE). In this study, we explored discrepancies between 18F-DOPA PET and conventional MR for defining target volumes in newly diagnosed glioblastoma (GBM) radiotherapy patients. METHODS: In an ongoing NCI-funded trial (NCT:R01CA178200), 18F-DOPA PET was acquired prior to chemoradiation for newly diagnosed GBM patients and incorporated prospectively into the target volumes, modifying low and high dose target volumes, and guiding dose escalation to the most aggressive disease. Based on the results of our pilot biopsy-validation study, two 18F-DOPA PET volumes were defined, one with a T/N threshold >2.0 (PET_high) depicting the most aggressive disease and another with a T/N threshold default of ≥1.5 (PET_low) with modifications if needed by a Nuclear Medicine physician. Both PET volumes were compared with the T1CE+cavity MR volumes for 30 MGMT unmethylated newly diagnosed GBM patients. RESULTS: The PET_low volume extended beyond T2-FLAIR signal abnormality for all patients, and extended beyond standard CTV expansion in 60% of patients. Sixty-seven per cent of patients had at least 20% of the PET_high uptake outside the T1CE volume, and would not have been covered by standard CTV expansion in 8% of patients. The average (range) Dice Similarity Coefficient comparing T1CE with PET_high was 0.3(0.0–0.7). The average (range) Haursdorff maximum distance (cm) between PET uptake and T1CE was found to be 2.4(0.9–7.1). CONCLUSIONS: 18F-DOPA-PET identified regions of biologically active disease outside the T1CE in 67% of patients with significant discordance in volumes. Evaluation of the impact prospective 18F-DOPA PET guidance for dose escalated radiation therapy is under investigation in the ongoing trial.