A Pilot Study of Simulation-Free Hippocampal-Avoidance Whole Brain Radiotherapy Using Diagnostic MR-Based and Online Adaptive Planning

PURPOSE/OBJECTIVE(S)

We aimed to demonstrate the clinical feasibility and safety of a simulation-free hippocampal avoidance whole brain radiotherapy (HA-WBRT) workflow in a Phase I clinical trial (NCT05096286). Feasibility was defined as successful completion of the simulation-free HA-WBRT workflow through treatment delivery in at last 70% of treated patients.

MATERIALS/METHODS

Ten candidates for HA-WBRT were enrolled for treatment on a ring gantry CT-guided Linac with online adaptive capabilities. Structures were contoured on the diagnostic brain MRI, which was then registered to a separate head computed tomography (CT) of similar head shape, obtained from an atlas-based database. A HA-WBRT "pre-plan" was generated using the atlas-based CT (AB-CT) and the NRG-CC001 constraints. At first fraction, the AB-CT was used as the primary dataset and deformed to the patient's cone-beam CT (CBCT) for dose calculation. The brain, ventricles, and brainstem contours were matched through rigid translation and rotation to the corresponding anatomy on the CBCT to aid in alignment, given the differences in rotational head positioning from diagnostic MRI to CBCT setup. Lastly, the lens, optic nerves, and brain contours were manually edited based on CBCT visualization. Plans were then optimized, and the adaptive plan was chosen for treatment if the plan met all objectives. Workflow tasks were timed. In addition, conventional plans using patients' sim CTs were created for each patient for the purpose of prospective dosimetric comparison. The dosimetric parameters were compared for each patient between the delivered sim-free plan and the conventional sim CT plan using the sign test via statistical software, with p<.05 indicating significance.

RESULTS

Median time from approved sim order to first fraction was 4 days (range: 2-7); median time in room (door-to-door) was 49 minutes (range: 35-70). All patients successfully completed all ten fractions and 90% of the simulation-free radiation plans met all NRG-CC001 constraints. For one patient, the sim-free plan at fraction one failed the planning target volume (PTV) coverage objective (coverage of 89%); this was deemed acceptable for delivery by the treating radiation oncologist. An offline replan was then performed to meet NRG-CC001 constraints and used for the subsequent nine fractions. There was no clinically meaningful difference in dosimetric constraints between the sim-free plan (calculated on AB-CT) and conventional CT sim plan. Statistically, the sim-free plans provided improved PTV coverage to higher doses compared to the conventional plans (Table). At a median follow-up of 43 days (range: 9 -280), the intracranial progression-free survival rate was 90%.

CONCLUSION

Simulation-free HA-WBRT is feasible, results in plans that are dosimetrically comparable to conventional CT sim workflows and succeeds in decreasing time to initiation of HA-WBRT by at least 50%. Further studies with a larger cohort are warranted to optimize the workflow.

ARTIA-Bladder: Daily Online Adaptive Short-Course Radiation Therapy (RT) and Concurrent Chemotherapy for Muscle-Invasive Bladder Cancer (MIBC): A Prospective Trial of an Individualized Approach for Reducing Bowel and Bladder Toxicity

PURPOSE/OBJECTIVE(S)

Concurrent chemo-radiotherapy is commonly prescribed for muscle-invasive bladder cancer (MIBC). Post hoc analysis of two large, randomized trials found that hypofractionation improves loco-regional control (LRC) vs. standard fractionation in this population. A challenge in traditional image-guided radiotherapy of the bladder is that daily changes in bladder position and size requires large margins to ensure target coverage. This makes it difficult to spare uninvolved bladder from high-dose treatment, increases the risk of bowel toxicity, and results in historical rates of acute G3+ toxicity exceeding 20-30%. Daily online adaptive RT (ART) may enable reduced, personalized margins that maintain target coverage while reducing dose to OARs. This prospective clinical trial will test whether: 1) participants undergoing ART for MIBC have a lower rate of acute G3+ GI/GU toxicity compared with the 31% historical control rate (Stage III BC2001 trial), and 2) 2-year LRC with ART will be non-inferior to historical controls (75%).

MATERIALS/METHODS

This multi-national trial will enroll 165 adult subjects with stage cT2-T4aN0M0 urothelial MIBC. Subjects will have undergone an attempt at maximal transurethral resection of bladder tumor. Patients with clinically involved nodes or G2+ GI or G3+ GU symptoms/conditions at baseline are ineligible. Concurrent with chemotherapy, participants will receive (at the discretion of the investigator) either 55 Gy in 20 fx to whole-bladder or 46 Gy in 20 fx to whole-bladder plus simultaneous in-field boost of 55 Gy in 20 fx to tumor bed. A personalized ITV will be derived for each subject based on bladder expansion, as assessed on two CT simulations separated by 30 min. Daily ART will be attempted for all subjects. The primary endpoint is acute G3+ GI/GU toxicity. Secondary endpoints are LRC; quality of life (EORTC QLQ-BLM30, EPIC 26 bowel and urinary); global function (EQ-5D-5L ); 2-year disease-free, bladder intact event-free, and overall survival; 2-year bladder cancer-specific mortality; NTCP model of acute GI toxicity for hypofractionated bladder RT; workflow feasibility of ART; improved target coverage ± reduced dose to critical OARs vs. non-ART dosimetry; acute G3+ GI/GU toxicity rate in subjects with ≥75% of their treatments as ART; and acute G3+ GI/GU toxicity in the cohort treated with partial bladder boost. Exploratory translational and correlative endpoints will also be examined.

RESULTS

This trial opened to enrollment on Feb 2, 2023; the study duration is expected to be 4-5 years.

CONCLUSION

This prospective clinical trial will provide robust clinical data to inform healthcare providers' decisions on the use of daily online ART and hypofractionation as a bladder preservation strategy for this population.

The Impact of Intra-Fraction Bowel Motion on Luminal Gastrointestinal Organ at Risk Dosimetry When Using Stereotactic Adaptive Radiotherapy for Abdominal Malignancies

PURPOSE/OBJECTIVE(S)

Daily online adaptive radiotherapy (ART) provides inter-fraction motion management of the luminal gastrointestinal (GI) structures when delivering abdominal SBRT. One potential drawback of ART is the time-consuming process, and intra-fraction GI changes from completion of the ART process to the end of treatment delivery have not been thoroughly evaluated. We explored intra-fraction bowel motion for patients receiving abdominal stereotactic adaptive radiotherapy (sART) MATERIALS/METHODS: Six patients with abdominal malignancies treated with CT-guided sART on a prospective feasibility trial had additional CBCT's acquired post-treatment (pTx-CBCT). All patients were prescribed to 50 Gy/5 fractions (fx), and the constraint for all GI OARs was V33≤0.5 cc. Time from initial CBCT (I-CBCT) used for adaptive planning to pTx-CBCT was collected. The luminal GI OAR (stomach (S), duodenum (D), small bowel (SB), and large bowel (LB)) were retrospectively contoured on pTx-CBCT. The OAR doses were compared between the I-CBCT and pTx-CBCT. The adaptive plan (PA) and initial plan (PI) doses were overlayed on the pTx-CBCT contours. The PA pTx-CBCT OAR doses were then compared to the PI pTx-CBCT OAR doses. A Boolean OAR structure of all GI OARs was evaluated to remove potential differences in structure definitions between providers. The T-test was used to compare differences in instances of D0.5cc ≥ 33 and 50 Gy. Patient charts were reviewed for grades (G) ≥ 3 toxicity.

RESULTS

Thirty fractions (fx) of sART were delivered and pTx-CBCT were acquired in 26 fx. Mean time from I-CBCT to pTx-CBCT acquisition was 66 min (38-98 min). On average at 0.5 cc the PA overdosed the S by 1.74 Gy based on pTx-CBCT anatomy compared to 2.35 Gy by the PI, the D by 0.47 Gy (PA) vs .84 Gy (PI), the SB by 1.14 Gy (PA) vs 1.43 Gy (PI), and the LB by 0.13 Gy (PA) vs 0.60 Gy (PI). The dose to the Boolean OAR structure was on average 2.51 Gy/fx higher than expected when overlaying the PA on the pTx-CBCT compared to 3.38 Gy/fx higher when overlaying the PI on the pTx-CBCT. There was no significant difference in the instance of the PA exceeding D0.5 cc ≥33 Gy vs the PI (p = 0.083), but the PA significantly reduced the instances of D0.5cc≥50 Gy (p = 0.001) compared to the PI. No patient experienced G≥3 toxicity at a median follow-up of 8 months (3-12).

CONCLUSION

These data demonstrate sART led to a significant decrease in dose to GI OARs, particularly for prescription dose or greater, even after accounting for intra-fractional bowel motion. While both the PI and the PA violated the V33 luminal GI OAR constraint in approximately ½ of pTx-CBCTs, the fraction of OARs receiving at least 50 Gy was significantly higher when overlaying the PI compared to the PA. While no G3 toxicities were reported in this small cohort, further studies are needed to characterize if the increased dose to GI OARs over the expected dose is clinically significant.

Hydrazinonaphthalene and azonaphthalene thrombopoietin mimics are nonpeptidyl promoters of megakaryocytopoiesis

High-throughput screening for the induction of a luciferase reporter gene in a thrombopoietin (TPO)-responsive cell line resulted in the identification of 4-diazo-3-hydroxy-1-naphthalenesulfonic acids as TPO mimics. Modification of the core structure and adjustment of unwanted functionality resulted in the development of (5-oxo-1,5-dihydropyrazol-4-ylidene)hydrazines which exhibited efficacies equivalent to those of TPO in several cell-based assays designed to measure thrombopoietic activity. Furthermore, these compounds elicited biochemical responses in TPO-receptor-expressing cells similar to those in TPO itself, including kinase activation and protein phosphorylation. Potencies for the best compounds were high for such low molecular weight compounds (MW < 500) with EC(50) values in the region of 1-20 nM.

Studies on the total synthesis of disorazole C1. An advanced macrocycle intermediate

Synthesis of protected tetradehydro-(6,6'-S)-(14,14'-S)-(16,16'-R)-disorazole (3), a potential precursor to the natural product disorazole C1 (1), is described. Key features of this work include (a) an unprecedented sequential 1,5 O --> O silyl rearrangement/Horner-Wadsworth-Emmons reaction used to construct 18, (b) a highly convergent Sonogashira reaction between the dienyl iodide 7 and the alkyne 8 to assemble the dienyne monomeric fragment 5, and (c) the selective cyclization of 5 to give either the cyclic monomer 23 or the dimer 3.