Top Abstracts from ASTRO 2020

The American Society for Radiation Oncology’s (ASTRO) 2020 annual meeting presented the results of hundreds of important studies from the nation’s top cancer programs. The staff of Cleveland Clinic Cancer Center’s Department of Radiation Oncology has compiled the following list of ASTRO 2020 abstracts that our physicians consider to be the most intriguing, the most clinically relevant, or that have the greatest potential to change the practice of radiation oncology in the near future.

1. CCTG SC.24/TROG 17.06

This was a phase 2/3 study of stereotactic body radiotherapy (SBRT) 24 Gy/2 fx versus conventional palliative radiotherapy (CRT) 20 Gy/5 fx in 229 patients with previously untreated painful spine metastases, where up to three consecutive levels could be treated. Complete pain response improved from 14% to 35% with SBRT at three months (P < 0.001) and 16% to 32% at six months (P = 0.004). These results differ from RTOG 0631, which showed no benefit to SBRT (16 Gy/1 fx or 18 Gy/1 fx) versus CRT (8 Gy/1 fx) and may not have distinguished between pain at index site from SBRT site. This is the first phase 3 study that demonstrated superiority of SBRT 24 Gy/2 fx over CRT in treating painful spine metastases.

1. EMPIRE-1

This was a phase 3, prospective, randomized trial in which 157 prostate cancer patients with detectable PSA after prostatectomy were randomized to radiation based on conventional imaging (bone scan/CT/MRI) findings versus fluciclovine PET. With a median follow-up of 2.48 years, the three-year failure-free survival (FFS) was significantly higher (P = 0.003) for the PET arm (75.5%) than for the conventional imaging arm (63%). Toxicity was similar between arms. Variables significant on multivariate analysis included treatment arm, ECE, pelvic field and PSA. Inclusion of fluciclovine PET into RT decision making and planning significantly improved FFS.

1. ACNS0331

This was a planned molecular analysis of the phase 3 randomized trial ACNS0331, which enrolled average risk medulloblastoma (MB) patients ages 3 to 21 years of age who were randomized to whole posterior fossa boost (PFRT) or involved field volume boost (IFRT) after completing craniospinal irradiation (CSI). Patients age 3 to 7 years of age were additionally randomized to standard dose CSI (23.4 Gy, SD-CSI) or low dose CSI (18 Gy, LD-CSI). The initial reports of ACNS00331 were unchanged with IFRT noninferior to PFRT in all patients for five-year event-free survival (EFS) (82.5±2.7% and 80.5±2.7%, P = 0.44) and five-year overall survival (OS) (84.6±2.5% and 85.2±2.4%, P = 0.44), but LD-CSI was significantly worse than SD-CSI in younger children in regards to five-year EFS (71.4±4.4% and 82.9±3.7%) and five-year OS (77.5±4.0% and 85.6±3.5%, P = 0.049). EFS was significantly different by molecular subgroup (P < 0.001), with group 3 having the worst outcomes and WNT having the best outcomes.

1. HERO

This was a phase 3, prospective, randomized trial of 934 patients with hormone-sensitive prostate cancer (2 to 1 ratio) to oral relugolix 120 mg QD or leuprolide three-month depot injection. RT was allowed after two months of androgen deprivation therapy (ADT). Relugolix achieved more rapid castration, did not cause testosterone flare and achieved superior sustained castration over 48 weeks with fewer major adverse cardiovascular events compared with leuprolide. Relugolix has the potential to become a new standard of care for men with prostate cancer requiring ADT.

1. MDACC SRS vs WBRT for 4-15 Mets

This was a phase 3, prospective, randomized trial of 72 patients with four to 15 untreated nonmelanoma brain metastases using SRS (RTOG 9005 dosing) or whole body radiation therapy (WBRT) (30 Gy/10 fx). After a median follow-up of 6.6 months, SRS was associated with a significant improvement in the primary endpoint HVLT_R_TR measured at four months (z-score change from patient’s own baseline, +0.21 for SRS and -0.74 for WBRT; P = 0.04). OS did not differ between the groups (SRS 7.8 months vs WBRT 8.9 months; P = 0.59). These results strongly support the use of SRS in patients with four to 15 brain metastases to better preserve cognitive function and to minimize interruption of systemic therapy.

1. PARCER

This was a phase 3, prospective, randomized trial of 300 cervical cancer patients status post hysterectomy requiring adjuvant RT randomized to IG-IMRT or 3D-CRT, treating 50 Gy/25 fx with or without weekly cisplatin, followed by high dose rate (HDR) 6 Gy/2 fx. IG-IMRT had significantly lower V30 and V40 bowel bag doses (P < 0.0001). With a median follow-up of 49 months, four-year grade ≥ two late bowel toxicity in the IG-IMRT and 3D-CRT arms was 19.2% and 36.2% (HR = 0.53; 95% CI: 0.33-0.83; P = 0.005), respectively, and four-year grade ≥ 3 late bowel toxicity in the IG-IMRT and 3D-CRT arms was 2.0% and 8.7%, respectively (HR=0.23; 95% CI: 0.06-0.81; P < 0.01). DFS was the same between arms (73% vs. 68%, P = 0.30).

1. SAFFRON II/TROG 13.01

This was a phase 2, multicenter, prospective trial of 90 patients with one to three pulmonary oligometastases from any nonhematological malignancy randomized to SBRT with either 28 Gy/1 fx (arm 1) or 48 Gy/4 fx (arm 2). Both arms met the primary endpoint goal of < 5% G3+ toxicities within one year, 5% for arm 1 and 3% for arm 2. Comparable local control, OS and DFS at one-year was noted between arms. Single fraction lung SBRT is safe for treating up to three oligometastases.

1. FLAME

This was a phase 3, prospective, randomized trial of 571 patients with localized intermediate or high-risk prostate cancer treated to 77 Gy/35 fx +/- 95 Gy focal simultaneous integrated boost (SIB) to MRI-defined macroscopic tumor within the prostate. With a median follow-up of 71 months, the SIB arm had significantly improved five-year biochemical disease-free survival (bDFS) (86% vs 93%) without significant differences in late grade 3+ GI (1% in both arms) or genitourinary (4% vs 6%) toxicities. No difference was noted in quality of life outcomes. This is the first trial that demonstrates the value of focally boosting select patients with prostate cancer.

1. RTOG 0526

This was a phase 2, multicenter, single-arm trial of salvage low dose rate (LDR) brachytherapy for 92 men with local recurrence after external beam radiation therapy (EBRT) for initially low risk-intermediate risk prostate cancer. Median follow-up was 6.9 years, median EBRT dose was 74 Gy, and 16% had received ADT. Fourteen percent of LDR patients experienced late G3 GI/GU toxicity with no late > G4, comparable to ASCENDE-RT boost numbers. At 10 years, freedom from biochemical failure was 54%, local response was 5% and distant metastases (DM) was 19%. Salvage LDR brachytherapy is safe for treating local recurrence after conventionally-fractionated EBRT.

1. Multi-institutional analysis: impact of PMRT in women with T1-2N1M0 breast cancer

This was a retrospective review of 7096 patients from five North American institutions with pT1-2N1 disease status post mastectomy (no neoadjuvant therapy), 48% of whom received postmastectomy radiation therapy (PMRT) to determine the benefit. With a median follow-up of 9.6 years (survivors), patients who received PMRT had more adverse features. Patients who received PMRT had significant decrease in risk of LRR (HR 0.28), DM (HR 0.79), overall recurrence (HR 0.69) and breast cancer mortality (HR 0.81). In patients with T1-2N1 disease, PMRT significantly improved local and distant recurrence and breast cancer mortality.