Durable Local Control Research Articles

Stereotactic radiosurgery for patients with spinal metastases from prostate cancer.

Spinal metastases may result in intractable pain, neurological deficit, and vertebral body collapse. There are only a few studies describing outcomes following spine stereotactic radiosurgery (SRS) specifically for prostate cancer metastases. A prospectively collected database of patients with prostate cancer spinal metastases treated at the University of Pittsburgh Medical Center from 2003 to 2023 was analyzed. The primary outcome was local control (LC). Secondary outcomes were overall survival (OS), pain resolution, and adverse radiation effects (AREs). Thirty-seven patients and 51 lesions were identified. Fifteen lesions (29%) were previously resected and 34 lesions (67%) were previously irradiated. The median tumor volume was 37.0cc (range: 2.9-263.3). A majority of lesions (71%) were treated in a single fraction (median 20Gy, range: 14-22.5); multi-fractionated treatment consisted of 21-30Gy in 2-5 fractions. Median follow-up was 12 months (range: 1-146). The 6-month, 1-year, and 2-year LC rates were 97%, 91%, and 91%, respectively. No tested prognostic factors were associated with LC, including hormone sensitivity. The 6-month, 1-year, and 2-year OS rates were 71%, 56%, and 32%; age > 70 years (p = 0.048) and tumor volume > 30cc (p = 0.03) were associated with inferior rates of OS. Complete or partial pain response was observed in 58% of patients. There were 8 instances (16%) of AREs, 2 of which were vertebral compression fractures (4%). Radiosurgery as a primary or adjuvant treatment modality for prostate cancer spinal metastases confers durable LC and moderate pain relief with minimal toxicity. Further studies are warranted to optimize management in this patient population.

Durable local control with hypofractionated radiation therapy for unresectable or metastatic melanoma

Background and purposeAs patients with advanced melanoma live longer in the context of systemic therapy advancements, better strategies for durable control of bulky tumors are needed. In this study, we evaluated if dose-escalated hypofractionated radiation therapy (HFRT) can provide durable local control and improve tumor-associated symptoms in patients with unresectable or bulky metastatic melanoma for whom stereotactic ablative radiotherapy (RT) approaches are not feasible due to tumor size or location. Materials and methodsWe retrospectively reviewed 49 patients with unresectable or bulky metastatic melanoma who were treated to a total of 53 tumor targets with 12–17 fractions HFRT at our institution between 2015–2022. Clinical scenarios included: unresectable, locoregional only disease (26 %); oligometastatic disease (<3 total sites, 17 %); oligoprogressive disease (<3 sites progressing, 17 %); and aggressive palliation (>5 known sites of disease or with at least 3 sites progressing, 40 %). ResultsOf the 53 HFRT targets, 91 % (n = 48) had radiographic evidence of response as defined by either stabilization (6 %, n = 3), decreased size (74 %, n = 39), or decreased FDG avidity (11 %, n = 6). Of the 43 symptomatic patients, 98 % (n = 42) had symptomatic improvement. One −year local control was 79 %, with 2-year progression-free and overall survival of 33 % and 39 % respectively. The most common acute toxicities were radiation dermatitis (16 %, n = 8) or a pain flare (14 %, n = 7). Late toxicities were uncommon and typically grade 1. ConclusionHFRT provides favorable local control and symptomatic relief with limited toxicity in tumors not amenable to surgical resection or stereotactic ablative RT.

Stereotactic Ablative Radiation Therapy (SABR) for Adolescent and Young Adult Malignancies.

There are limited studies examining local control (LC) and overall survival (OS) following stereotactic ablative radiation therapy (SABR) for adolescent and young adult (AYA) populations/histologies with local recurrences or metastatic disease. The RSSearch® Patient Registry, an international SABR registry, was evaluated for AYA patients treated with SABR. AYA patients with adult histologies/primaries were excluded. Kaplan-Meier analyses were employed to characterize LC and OS following SABR. Potential prognostic factors were assessed with log-rank tests for initial univariate analysis (UVA). For multivariate analyses (MVA), a Cox proportional hazards multivariate model was utilized. A total of 19 AYA patients with 39 lesions treated with SABR were identified and included in the analysis. Four lesions (10.3%) were treated with SABR for primary tumor recurrence and 35 lesions were treated for metastatic disease. The median patient age was 34 years (range: 16-39 years). Common lesion locations included lung (11 lesions; 28.2%), non-spinal bone (nine lesions; 23.1%), and spine (six lesions; 15.4%). The median biological effective dose (BED10) was 61.5 Gy (range: 26.4-180). One-year LC and OS following SABR were 77.7% (95% CI: 58.5-88.7) and 72.7% (95% CI: 46.3-87.6), respectively. On UVA, BED10 ≥ 60 Gy was associated with superior one-year LC (94.4% vs. 47.6%; p<0.0001) as were sarcoma primaries (two-year LC: 92.3% vs. 42.2%;p = 0.0002). Central nervous system (CNS) primaries had significantly poorer one-year LC (20% vs 87.5%; p<0.0001) as well as spinal metastases (33.3% vs. 87.0%; p<0.0001). On MVA, BED10 < 60 Gy was associated with inferior LC (hazard ratio (HR) = 5.51;p = 0.01) with sarcoma primaries associated with superior LC (HR = 0.04;p = 0.008). SABR with BED10 ≥ 60 Gy resulted in durable LC for AYA patients, particularly those with sarcoma primaries, though poor outcomes were noted in metastatic CNS malignancies.

Radiation Therapy Dose Response in Bulky Relapsed/Refractory Large B-Cell Lymphoma

PurposeTo assess whether a radiotherapy (RT) dose affects response in bulky tumors in relapsed/refractory (r/r) diffuse large B-cell lymphoma (DLBCL). MethodsData from r/r DLBCL patients treated with salvage- or palliative-intent RT (2008-2020) at a single institution were examined. Index lesion size ≥7.5 cm was defined as bulky. Equivalent doses in 2 Gray (Gy) fractions (EQD2) were calculated to compare doses between conventional and hypofractionated (HF, ≥2.5 Gy/fraction) schemes. Objective response rates (ORR) were compared using non-parametric Mann-Whitney U test or Kruskal-Wallis tests with Dunn's multiple comparison corrections. Freedom from local progression (FFLP) was assessed using Kaplan-Meier and Cox proportional hazard regression analyzes. Results183 courses of 151 unique patients were included (salvage: 37%, palliative: 63%). Non-bulky and bulky tumors were irradiated in 109 (60%) and 74 (40%) courses, respectively. Median EQD2 was 33 Gy (IQR=23-39 Gy) with HF in 84 (46%) cases. Of those with post-RT imaging (80%), the ORR was 59% with a trend towards worsened ORR in bulky tumors (50% vs. 65%, p=0.077). For bulky tumors, RT regimens with EQD2s >30 Gy were associated with better ORR (≤30 Gy vs. >30 Gy: 27% vs. 64%, p=0.0073), whereas a lower EQD2 cut-off was sufficient for non-bulky tumors (≤20 Gy vs. >20 Gy: 38% vs. 75%, p=0.0011). On multivariable regression, bulky tumor size was associated with worsened FFLP (HR=2.07, 95% CI=1.16-3.68, p=0.014), while high EQD2s >30 Gy were associated with better FFLP (HR=0.48, 95% CI=0.25-0.93, p=0.031). Bulky tumors treated with EQD2s ≤30 Gy had the lowest median FFLP (4.0 months), while EQD2s >30 Gy had an unreached median FFLP (p=0.0047). ConclusionsBulky r/r DLBCL tumors were associated with less favorable tumor control outcomes in the salvage and palliative settings. RT regimens with higher EQD2s (>30 Gy) should be considered if durable local control of bulky tumors is desired.

Re-irradiation practice and ESTRO/EORTC consensus recommendations: 2023 ASTRO education panel.

Indications for re-irradiation are increasing both for palliation and potentially curative attempts to achieve durable local control. This has been in part driven by the technological advances in the last decade including image-guided brachytherapy, volumetric-modulated arc therapy and stereotactic body radiotherapy. These enable high dose focal irradiation to be delivered to a limited target volume with minimal normal tissue re-irradiation. The European Society for Radiotherapy and Oncology (ESTRO) and the European Organisation for Research and Treatment of Cancer (EORTC) have collaboratively developed a comprehensive consensus on re-irradiation practices, aiming to standardise definitions, reporting, and clinical decision-making processes. The document introduces a universally applicable definition for re-irradiation, categorised into two primary types based on the presence of geometric overlap of irradiated volumes and concerns for cumulative dose toxicity. It also identifies "repeat organ irradiation" and "repeat irradiation" for cases without such overlap, emphasising the need to consider toxicity risks associated with cumulative doses. Additionally, the document presents detailed reporting guidelines for re-irradiation studies, specifying essential patient and tumour characteristics, treatment planning and delivery details, and follow-up protocols. These guidelines are designed to improve the quality and reproducibility of clinical research, thus fostering a more robust evidence base for future re-irradiation practices. The consensus underscores the necessity of interdisciplinary collaboration and shared decision-making, highlighting performance status, patient survival estimates, and response to initial radiotherapy as critical factors in determining eligibility for re-irradiation. It advocates for a patient-centric approach, with transparent communication about treatment intent and potential risks. Radiobiological considerations, including the application of the linear-quadratic model, are recommended for assessing cumulative doses and guiding re-irradiation strategies. By providing these comprehensive recommendations, the ESTRO-EORTC consensus aims to enhance the safety, efficacy, and quality of life for patients undergoing re-irradiation, while paving the way for future research and refinement of treatment protocols in the field of oncology.

A preliminary study on the timing of radiotherapy for chemoimmunotherapy in oligometastatic non-small-cell lung cancer with negative driver genes.

e20084 Background: Local radiotherapy (LRT) is reported to provide durable local and distant disease control for oligometastatic non-small cell lung cancer (NSCLC) in accumulating evidence, but research on the optimal initial time point remains scarce. We conducted a study to preliminarily evaluate the timing of radiotherapy for chemoimmunotherapy in Oligometastatic Non-small-cell lung cancer with negative driver genes. Methods: 50 patients diagnosed with Oligometastatic Non-small-cell lung cancer with negative driver genes who were treated with chemoimmunotherapy and radiotherapy were retrospectively recruited between January 2018 and October 2023. They were divided into two groups: one early to initiate radiotherapy group (≤2 cycles of immunotherapy, EAR group) and one deferred radiotherapy group (&gt;2 cycles of immunotherapy, DEF group). The clinical efficacy and adverse reactions were compared between the two groups. Progression-free survival (PFS) and overall survival (OS) were evaluated by Kaplan-Meier curves, the Cox proportional hazard model was used to find out predictors of PFS and OS. Results: The tumor control rates had no significance was observed when comparing these two groups (50.0% and 26.9%, respectively, p = 0.093). The PFS in the RAE group was significantly higher than that in the DEF group (median PFS: 12.2 months vs 5.3 months, P&lt;0.05). The OS in two groups were no significance (median OS: 20.5months vs 23.1months, P&gt;0.05). The results of the Cox multivariate regression analysis revealed that the number of metastatic lesions and organs were independent prognostic factors for PFS. The number of metastatic lesions and organs, maintain therapy were independent predictors associated with OS. All patients well tolerated the treatments. Conclusions: Early initiation of local radiotherapy resulted in better PFS and no significant increase in adverse reactions was observed.

Success of Ultra-low Dose Radiation Therapy for Primary Cutaneous B-cell Lymphoma.

Primary cutaneous B-cell lymphoma (PCBCL) is a relatively rare disease, associated with 5-year overall survival of nearly 95% when treated with external beam radiation therapy (EBRT) alone. However, standard EBRT doses yield acute skin toxicity in more than 70% of patients and grade 3 to 4 acute skin toxicity in nearly 10% of patients. Consequently, the PCBCL treatment paradigm is shifting towards lower EBRT doses. This study evaluates our early experience with ultra-low dose EBRT (total dose of 4 Gy in 2 fractions) for PCBCL. Four biopsy-confirmed PCBCL lesions (1 anterior thigh and 3 chest) in 2 male patients were treated with 2 Gy×2 fraction EBRT using electrons through a clinical setup. The anterior thigh lesion was treated using a clamshell to protect the scrotum from scatter dose. Treatment was achieved using 9 MeV electrons to the 85% isodose line using no bolus, with follow-up every 4 months and potential retreatment if no visible response at 8 to 9 months. All lesions demonstrated a response to EBRT by 4 months, visibly manifesting as flattening with changes in pigmentation. At the last follow-up (20, 20, 16.5, and 4 mo, respectively), all lesions had flattened with no evidence of local recurrence and no skin toxicity. Treatment of PCBCL with ultra-low dose EBRT to 4 Gy total dose in 2 fractions provides durable local control with zero skin toxicity. These results are encouraging for both the success of treatment and the potential to use similarly low doses for retreatment should patients exhibit local recurrence.

Radiation enhancement using focussed ultrasound-stimulated microbubbles for breast cancer: A Phase 1 clinical trial.

Preclinical studies have demonstrated that tumour cell death can be enhanced 10- to 40-fold when radiotherapy is combined with focussed ultrasound-stimulated microbubble (FUS-MB) treatment. The acoustic exposure of microbubbles (intravascular gas microspheres) within the target volume causes bubble cavitation, which induces perturbation of tumour vasculature and activates endothelial cell apoptotic pathways responsible for the ablative effect of stereotactic body radiotherapy. Subsequent irradiation of a microbubble-sensitised tumour causes rapid increased tumour death. The study here presents the mature safety and efficacy outcomes of magnetic resonance (MR)-guided FUS-MB (MRgFUS-MB) treatment, a radioenhancement therapy for breast cancer. This prospective, single-center, single-arm Phase 1 clinical trial included patients with stages I-IV breast cancer with in situ tumours for whom breast or chest wall radiotherapy was deemed adequate by a multidisciplinary team (clinicaltrials.gov identifier: NCT04431674). Patients were excluded if they had contraindications for contrast-enhanced MR or microbubble administration. Patients underwent 2 to 3 MRgFUS-MB treatments throughout radiotherapy. An MR-coupled focussed ultrasound device operating at 800 kHz and 570 kPa peak negative pressure was used to sonicate intravenously administrated microbubbles within the MR-guided target volume. The primary outcome was acute toxicity per Common Terminology Criteria for Adverse Events (CTCAE) v5.0. Secondary outcomes were tumour response at 3 months and local control (LC). A total of 21 female patients presenting with 23 primary breast tumours were enrolled and allocated to intervention between August/2020 and November/2022. Three patients subsequently withdrew consent and, therefore, 18 patients with 20 tumours were included in the safety and LC analyses. Two patients died due to progressive metastatic disease before 3 months following treatment completion and were excluded from the tumour response analysis. The prescribed radiation doses were 20 Gy/5 fractions (40%, n = 8/20), 30 to 35 Gy/5 fractions (35%, n = 7/20), 30 to 40 Gy/10 fractions (15%, n = 3/20), and 66 Gy/33 fractions (10%, n = 2/20). The median follow-up was 9 months (range, 0.3 to 29). Radiation dermatitis was the most common acute toxicity (Grade 1 in 16/20, Grade 2 in 1/20, and Grade 3 in 2/20). One patient developed grade 1 allergic reaction possibly related to microbubbles administration. At 3 months, 18 tumours were evaluated for response: 9 exhibited complete response (50%, n = 9/18), 6 partial response (33%, n = 6/18), 2 stable disease (11%, n = 2/18), and 1 progressive disease (6%, n = 1/18). Further follow-up of responses indicated that the 6-, 12-, and 24-month LC rates were 94% (95% confidence interval [CI] [84%, 100%]), 88% (95% CI [75%, 100%]), and 76% (95% CI [54%, 100%]), respectively. The study's limitations include variable tumour sizes and dose fractionation regimens and the anticipated small sample size typical for a Phase 1 clinical trial. MRgFUS-MB is an innovative radioenhancement therapy associated with a safe profile, potentially promising responses, and durable LC. These results warrant validation in Phase 2 clinical trials. clinicaltrials.gov, identifier NCT04431674.

Abstract CT080: A phase I study of CPI-613 (devimistat) in combination with chemoradiation in patients with pancreatic ductal adenocarcinoma

Abstract Background: Local tumor progression is a cause of significant mortality and morbidity in patients (pts) with inoperable pancreatic ductal adenocarcinoma (PDAC). Effective approaches to achieve durable local control are urgently needed. Metabolic reprogramming and enhanced mitochondrial function are known contributors to chemo- and radio-resistance in PDAC. CPI-613, a lipoic acid analog that selectively inhibits components of the Krebs cycle in tumors, showed promising preclinical synergy in combination with gemcitabine and radiation (gem-RT). We initiated a phase I study (NCT05325281) to determine the maximum tolerated dose (MTD) of CPI-613 when used with gem-RT. Here, we present the results from the first cohort of this study. Methods: Adult pts with inoperable PDAC that, by institutional multidisciplinary review, were considered to benefit from definitive local control of the primary tumor were eligible for the study. CPI-613 was administered once weekly by intravenous infusion over ~ 2 hours at a starting dose of 500 mg/m2 and dose-escalated using a Bayesian optimal interval design. Gemcitabine was given once weekly at 400 mg/m2 and RT at 45-54 Gray (Gy) in 25-30 fractions. Results: By Jan 7, 2024, six pts were enrolled, and five completed the treatment and dose-limiting toxicity (DLT) period. Table 1 describes the characteristics of these five pts. As CPI-613 was not associated with any additional toxicities, specifically cytopenia(s), after the first two pts, the study protocol was amended to allow CPI-613 to be administered on weeks gemcitabine was held for cytopenia(s). The study, therefore, enrolled five pts in the first cohort. All pts received ≥ 16 weeks of systemic chemotherapy with at least stable disease per imaging prior to enrollment. None of the pts experienced DLTs. All treatment-related toxicities were expected from gem-RT, unrelated to CPI-613, and manageable. The trial is currently enrolling pts in the second cohort (CPI-613 dose of 1000 mg/m2). Conclusions: CPI-613 combined with gem-RT was safe and well tolerated at a dose of 500 mg/m2. Recruitment to the study is ongoing to determine the MTD of CPI-613 in combination with gem-RT. Table 1. Characteristic of Patients Sex Race Age ECOG Stage Prior chemotherapy Chemotherapy duration (weeks) M W 67 1 LA FFX 16 M W 64 1 LA GnP 35 M W 73 1 BR* GnP 16 M B 71 1 LA GnP 27 M W 80 1 Oligometastatic** GnP 18 * Medically inoperable ** Two lung metastases treated with stereotactic body radiation therapy (SBRT); BR: Borderline resectable; B: Black; FFX: FOLFIRINOX; GnP: Gemcitabine/Nab-paclitaxel; LA: Locally advanced. M: Male; W: White Citation Format: Mandana Kamgar, Husain Yar Khan, Amro Aboukameel, Sahar F. Bannoura, Brian Y. Chung, Aniko Szabo, Yiwei Li, Mohammed Najeeb Al Hallak, Philip A. Philip, Ben George, Kathleen K. Christians, Douglas B. Evans, Susan Tsai, Beth Erickson, John M. Goldberg, Asfar S. Azmi, William A. Hall. A phase I study of CPI-613 (devimistat) in combination with chemoradiation in patients with pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT080.

Applications of Yttrium-90 (90Y) in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the most common primary liver cancer, affecting millions of people worldwide. Due to the lack of systemic radiation therapy in hepatocellular carcinoma, researchers have been investigating the use of yttrium-90 (90Y) radioembolization for local-regional tumor control since the 1960s. With the development of glass and resin 90Y microspheres and the durable local control, good long-term efficacy, and equivalent tumor responsiveness and tolerability of 90Y-selective internal irradiation compared with alternative therapies such as transarterial chemoembolization (TACE) and sorafenib, 90Y radioembolization has gradually been applied in the treatment of hepatocellular carcinoma of all stages. In this article, we summarize the latest progress of 90Y in the treatment of hepatocellular carcinoma in terms of its principle, advantages, indications, contraindications, efficacy and adverse effects.

Neoadjuvant SBRT plus regional nodal irradiation with concurrent capecitabine for patients with resectable pancreatic cancer: Survival analysis of prospective phase 1 trial.

652 Background: Radiation may have a role in management of patients with early-stage pancreatic cancer. However, the role of regional nodal irradiation (RNI) is not well defined despite the high frequency of occult nodal disease. The goal of this trial was to evaluate the safety and feasibility of stereotactic body radiation therapy (SBRT) to primary disease with RNI, combined with capecitabine as a neoadjuvant approach for patients with resectable pancreatic cancer. Updated survival analysis will be presented here. Methods: This is a prospective, single institution, phase IA/B dose-escalation trial that enrolled patients with biopsy-proven, resectable, pancreatic adenocarcinoma between 2014 – 2019 (NCT1918644). Patients were enrolled into one of the 3 cohorts with escalating dose levels. Neoadjuvant SBRT to the primary tumor was delivered in 5 fractions of 5, 6, or 7 Gy with concomitant capecitabine. All patients received RNI 5 Gy x 5 fractions. Our initial report found no dose-limiting toxicities (Witt et al IJROBP 2020). Clinicopathologic features were summarized using descriptive statistics. Kaplan-Meier curves were employed for survival analysis. Results: Seventeen patients were enrolled on the protocol with sixteen evaluable (94.1%). Thirteen (76.5%) patients proceeded to surgery. Median follow up was 31.1 months (2.0 – 73.2). Among the evaluable patients, 63% were male, median age at diagnosis was 73 years (63 – 84), pre-treatment CA 19-9 149.5 U/mL (2.0 – 19358.0). The majority of patients had cT2-3 (94%) and cN0 (87.5%) disease. In patients who underwent resection, median time from radiation to surgery was 19.7 days (14.8 – 42.4), with median of 18 lymph nodes removed (11 – 27). Pathologically involved nodes were present in 69.2% of patients with a median of 2 nodes (1 – 10). Five patients (31.3%) received neoadjuvant chemotherapy, and ten (62.5%) received adjuvant chemotherapy. At the time of data cutoff, median overall survival was 31.1 months (2.3 – 73.6), and median locoregional control and distant metastasis free survivals were 32.8 months (4.0 – 59.5) and 15.3 months (0.4 – 73.6), respectively. No further radiation related toxicities were noted since the prior report. Conclusions: Neoadjuvant chemoradiation with SBRT and capecitabine to primary disease with RNI is feasible and provided a promising signal of durable local control in our study, despite high rates of pathological nodal involvement. Further investigation of this strategy is warranted in a larger cohort of patients. Clinical trial information: NCT1918644 .

Palliative Radiotherapy for Symptomatic Primary Tumors in Patients With Locally Advanced Breast Cancer.

Breast cancer remains a significant health concern for women, with a significant number of women facing unresectable, symptomatic, and advanced disease that severely affects their quality of life. Palliative radiotherapy (RT) is a well-established modality for managing such cases and alleviating symptoms. Recent advancements in systemic therapies and the resulting increase in long-term survival rates have not only heightened the need for retreatment in certain patients, but have also emphasized the importance of achieving durable local control. Additionally, inconsistencies in RT referral timing and variations in disease severity and extent contribute to diverse RT objectives and expected outcomes. The optimal dose fractionation for RT remains underexplored. Furthermore, a deeper understanding of breast radiobiology, along with the introduction of ultra- and moderately hypofractionated regimens and the widespread adoption of conformal techniques such as intensity-modulated RT, has diversified the approaches in RT dose and target volume. This review aimed to provides a comprehensive summary of the current evidence on the efficacy, outcomes, and toxicity profiles of palliative RT for symptomatic breast cancer. It highlights the need for more optimized regimens and further research to address the evolving treatment landscape and differing expectations of patients and physicians regarding RT.

Improved local control following dose-escalated stereotactic ablative radiation therapy (SABR) for metastatic sarcomas: An international multi-institutional experience

BackgroundWe aimed to characterize local control (LC) and overall survival (OS) following stereotactic ablative radiation therapy (SABR) for extracranial sarcoma metastases. MethodsA prospectively-maintained institutional registry was queried for patients with metastases from sarcoma primaries managed with SABR. Kaplan-Meier analysis was utilized for univariate analyses to assess potential prognostic factors regarding LC and OS. A Cox proportional hazards multivariate (MVA) model was employed to further assess initially identified independent variables. ResultsA total of 94 patients with 118 lesions with LC information were identified. Common metastatic sites treated were lung (77), non-spinal bone (15), and spine (10). The median biologically effective dose (BED4) was 175 Gy4 (range56.3 Gy4–360 Gy4) with a median dose/fractionation schedule of 50 Gy/5 fractions. One- and 2-year OS rates were 81.3 % (95 % CI: 71.2–88.1 %6) and 50.5 % (95 % CI: 38.6–61.3 %, respectively. On Cox MVA, advanced age and non-lung metastases were associated with inferior OS (p < 0.03) with patients with 0–2 of these risk factors having estimated 2-year OS of 65.1 %, 38.9 %, and N/A, respectively. One- and 2-year LC rates were 85.3 % (95 % CI: 77.7–90.9 %) and 78.2 % (95 % CI: 67.9–85.6 %), respectively. On MVA, only BED4 < 175 Gy was associated with inferior LC (hazard ratio (HR) = 3.33; p = 0.01). Ten of 118 treated lesions had treatment-related toxicities (all Grade 1–2). ConclusionAge and lung vs. non-lung metastases were prognostic of OS and should be considered in patient selection for SABR. Dose escalation when feasible with BED4 ≥ 175 Gy is recommended given durable LC achieved without a subsequent increase in toxicity.

SURG-31. DEFINING THE NEW POSSIBILITIES FOR CESIUM BRACHYTHERAPY IN PATIENTS WITH PERIVENTRICULAR GBM

Abstract INTRODUCTION Re-irradiation of patients with external beam radiotherapy (EBRT) for recurrent glioblastoma (GBM) continues to present a therapeutic dilemma due to a high risk of radiation induced necrosis (RN). In contrast, brachytherapy represents a safer, more conformal radiation option aimed at optimizing local control while minimizing the risk of brain tissue damage. Immediate intra-operative implantation with brachytherapy prevents tumor repopulation and offers patients two procedures in one setting. However, due to the risk of seed migration, surgical resection and brachytherapy in periventricular regions was deemed unachievable. In heavily pretreated periventricular GBM, where further EBRT is complicated by RN, a barrier between the ventricular lining and tumor cavity is needed to prevent seed migration. We present two patients where such a barrier allowed successful implantation of brachytherapy to improve disease control. METHODS Two patients, previously treated with surgery and EBRT, presented with recurrent GBM abutting the ventricles. Following GTR of the tumors, a barrier was created by patching the ventricle with Gelfoam to prevent seed migration. Intraoperative brachytherapy implantation of suture stranded Cs-131 seeds (Isoray) for patient 1 and collagen embedded Cs-131 (GammaTile) for patient 2 was performed. A total of 20 Cs-131 seeds on strings threaded through Surgicel, and 6 GammaTiles (24 Cs-131 seeds), were used implanted in patients 1 and 2, respectively. Surgicel covered the implanted seeds and the resection cavity filled with Adherus. RESULTS Post-operative CT scan demonstrated all 20 Cs-131 seeds and 24 Cs-131 seeds in the surgical cavities of patients 1 and 2, respectively, and had serial post operative imaging with MRI scans showing Cs-131 seeds layering surgical cavity, as late as 6 months in total follow up. To date, both patients have had durable local control and no seed migration.

RADT-13. A BIOLOGIC EQUIVALENT DOSE COMPARISON BETWEEN RADIOSURGERY AND COLLAGEN TILE BRACHYTHERAPY FOR POST-OPERATIVE TREATMENT OF A BRAIN METASTASIS RESECTION CAVITY

Abstract INTRODUCTION Recurrence of a previously irradiated brain metastasis represents a challenging clinical scenario. Repeat radiosurgery results in sub-optimal local control (LC). Two independently published prospective cohort studies demonstrated durable LC in this setting with collagen tile brachytherapy (CTBT), a novel Cesium-131 carrier. Here we compare biologically equivalent dosimetric parameters of CTBT to radiosurgery to understand dose metrics that may underlie durable LC from CTBT. METHODS A patient was selected from the multi-institutional prospective CTBT registry (NCT04427384) with a brain metastasis resection cavity near brainstem. Planning was performed for radiosurgery (30Gy in 5 fractions, BED of 48Gy) and CTBT (Cs-131, activity of 3.5U). To directly compare dosimetric parameters between radiosurgery and CTBT, biologic equivalent doses (BED) were calculated for brainstem(α/β of 3, BED3) and oncologically at-risk tissue(α/β of 10, BED10). TG101 brainstem dose-constraints were referenced, and respective BED were calculated. RESULTS The resection cavity was 4mm away from brainstem and contained 7 CTBT tiles (28 Cs131 seeds). Gradient index (GI) (24Gy BED10 volume/48Gy BED10 volume) was 3.8 for radiosurgery and 2.2 for CTBT. Conformality index (CI) (48Gy BED10 volume/CTV volume) was 1.2 for radiosurgery and 2.6 for CTBT. BED10 to 90% of the cavity wall (2mm rim around the resection cavity) was 49.6Gy for radiosurgery and 92.6Gy for CTBT. BED3 dose limit goals (max dose 31Gy in 5 fractions, BED3 95.1Gy and threshold dose 23Gy in 5 fractions, BED3 of 58.3Gy to 0.5cc) were met for both radiosurgery and CTBT. CONCLUSION BED comparisons demonstrate that CTBT leads to higher CI, lower GI, and higher dose to the cavity wall than radiosurgery while meeting BED3 dose limit goals to an adjacent organ at risk. These dose characteristics might underlie durable LC seen in the recurrent brain metastasis setting, though larger scale analyses are being performed with with clinical outcomes on NCT04427384.

Toll-Like Receptor 4 Agonist Injection With Concurrent Radiotherapy in Patients With Metastatic Soft Tissue Sarcoma

Metastatic soft tissue sarcomas (STSs) have limited systemic therapy options, and immunomodulation has not yet meaningfully improved outcomes. Intratumoral (IT) injection of the toll-like receptor 4 (TLR4) agonist glycopyranosyl lipid A in stable-emulsion formulation (GLA-SE) has been studied as immunotherapy in other contexts. To evaluate the safety, efficacy, and immunomodulatory effects of IT GLA-SE with concurrent radiotherapy in patients with metastatic STS with injectable lesions. This phase 1 nonrandomized controlled trial of patients with STS was performed at a single academic sarcoma specialty center from November 17, 2014, to March 16, 2016. Data analysis was performed from August 2016 to September 2022. Two doses of IT GLA-SE (5 μg and 10 μg for 8 weekly doses) were tested for safety in combination with concurrent radiotherapy of the injected lesion. Primary end points were safety and tolerability. Secondary and exploratory end points included local response rates as well as measurement of antitumor immunity with immunohistochemistry and T-cell receptor (TCR) sequencing of tumor-infiltrating and circulating lymphocytes. Twelve patients (median [range] age, 65 [34-78] years; 8 [67%] female) were treated across the 2 dose cohorts. Intratumoral GLA-SE was well tolerated, with only 1 patient (8%) experiencing a grade 2 adverse event. All patients achieved local control of the injected lesion after 8 doses, with 1 patient having complete regression (mean regression, -25%; range, -100% to 4%). In patients with durable local response, there were detectable increases in tumor-infiltrating lymphocytes. In 1 patient (target lesion -39% at 259 days of follow-up), TCR sequencing revealed expansion of preexisting and de novo clonotypes, with convergence of numerous rearrangements coding for the same binding sequence (suggestive of clonal convergence to antitumor targets). Single-cell sequencing identified these same expanded TCR clones in peripheral blood after treatment; these T cells had markedly enhanced Tbet expression, suggesting TH1 phenotype. In this nonrandomized controlled trial, IT GLA-SE with concurrent radiotherapy was well tolerated and provided more durable local control than radiotherapy alone. Patients with durable local response demonstrated enhanced IT T-cell clonal expansion, with matched expansion of these clonotypes in the circulation. Additional studies evaluating synergism of IT GLA-SE and radiotherapy with systemic immune modulation are warranted. ClinicalTrials.gov Identifier: NCT02180698.

Delivery of re-irradiation and complex palliative radiotherapy using proton therapy in pediatric cancer patients.

The intent of this study is to characterize indications for pediatric palliative-intent proton radiation therapy (PIPRT). We retrospectively reviewed patients 21years and younger who received PIPRT. We defined PIPRT as radiotherapy (RT) aimed to improve cancer-related symptoms/provide durable local control in the non-curative setting. Mixed proton/photon plans were included. Adjacent re-irradiation (reRT) was defined as a reRT volume within the incidental dose cloud of a prior RT target, whereas direct reRT was defined as in-field overlap with prior RT target. Acute toxicity during RT until first inspection visit was graded according to the Common Terminology Criteria for Adverse Events. The Kaplan-Meier method, measured from last PIPRT fraction, was used to assess progression-free survival (PFS) and overall survival (OS). Eighteen patients underwent PIPRT between 2014 and 2020. Median age at treatment start was 10years [2-21]. Median follow-up was 8.2months [0-48]. Treatment sites included: brain/spine [10], abdomen/pelvis [3], thorax [3], and head/neck [2]. Indications for palliation included: durable tumor control [18], neurologic symptoms [4], pain [3], airway compromise [2], and great vessel compression [1]. Indications for protons included: reRT [15] (three adjacent, 12 direct), craniospinal irradiation [4], reduction of dose to normal tissues [3]. Sixteen experienced grade (G) 1-2 toxicity; two G3. There were no reports of radionecrosis. Median PFS was 5.3months [95% confidence interval (CI): 2.7-16.3]. Median OS was 8.3months [95% CI: 5.5-26.3]. The most common indication for PIPRT was reRT to provide durable tumor control. PIPRT appears to be safe, with no cases of high-grade toxicity.

Treatment of ambulatory patients with metastatic epidural spinal cord compression: a systematic review and meta-analysis.

Approximately 10% of patients with spinal metastases develop metastatic epidural spinal cord compression (MESCC), which left undiagnosed and untreated can lead to the loss of ambulation. Timely diagnosis and efficient multidisciplinary treatment are critically important to optimize neurological outcomes. This meta-analysis aimed to determine the most efficient treatment for ambulatory patients with MESCC. The authors conducted a systematic review and meta-analysis of the treatment of mobile patients with MESCC in terms of outcomes described as local control (LC), ambulatory function, quality of life (QOL), morbidity, and overall survival (OS). Overall, 54 papers (4101 patients) were included. A trend toward improved LC with stereotactic body radiotherapy (SBRT) compared with conventional external beam radiotherapy (cEBRT) was demonstrated: random effects modeling 1-year LC rate 86% (95% CI 84%-88%) versus 81% (95% CI 74%-86%) (p > 0.05), respectively, and common effects modeling 1-year LC rate 85% (95% CI 82%-87%) versus 76% (95% CI 74%-78%) (p < 0.05). Surgery followed by adjuvant radiotherapy, either cEBRT or SBRT, showed no significant benefit in either LC (OR 0.88, 95% CI 0.65-1.19) or ambulatory function (OR 1.51, 95% CI 0.83-2.74) compared with radiotherapy without surgery. There was a significant benefit of surgery compared with cEBRT regarding QOL, and furthermore SBRT alone provided long-term improvement in QOL. The type of treatment was not a significant predictor of OS, but fully ambulatory status was significantly associated with improved OS (HR 0.46-0.52, relative risk 1.79-2.3). Radiation-induced myelopathy is a rare complication of SBRT (2 patients [0.1%] in the included papers). The morbidity rate associated with surgery was relatively high, with a 10% wound complication rate and 1.6% hardware-failure rate. SBRT is an extremely promising treatment modality being integrated into treatment algorithms and provides durable LC. In mobile patients with MESCC, surgery does not improve LC, survival, or ambulatory function; nonetheless, there is a significant benefit of surgery in terms of QOL. In patients with MESCC without neurological deficit, the role of surgery is still debatable as studies demonstrate good LC for patients who undergo SBRT without preceding surgery. However, surgery can provide safe margins for the administration of the ablative dose of SBRT to the entire tumor volume within the constraints of spinal cord tolerance. Further randomized controlled trials are needed on the benefit of surgery before SBRT in mobile patients with MESCC. With the excellent results of separation surgery and SBRT, the role of highly invasive vertebrectomy is diminishing given the complication rate and morbidity of these procedures.

Long-Term Safety and Efficacy of SAbR for Metastatic RCC.

Metastasis-directed stereotactic ablative radiation (SAbR) in metastatic renal cell carcinoma (mRCC) has been shown to prolong time to systemic therapy start/change. However, there is a paucity of data on the durability of local control by SAbR and long-term side effects, limiting its investigation in prospective trials. Here we report the long-term local control rates of SAbR for mRCC, focusing on factors that lead to local failure where dose escalation may be beneficial. We retrospectively reviewed 354 metastatic RCC patients who received SAbR to 902 lesions between 2005 and September 2021. Acute and late adverse events and their Common Terminal Criteria for Adverse Events (CTCAE) v. 5.0 grades were collected. RECIST v. 1.1 was used to evaluate treatment response. LC was estimated using the cumulative incidence function, with death as a competing risk. Local control (LC) was calculated using the Kaplan-Meier method. Lesions were followed for a median of 16 months; 136 lesions had >36 months of follow-up. The most common radiation prescription was 36 Gy in 3 fractions, and the median biological effective dose was 72 Gy10. 3-year local control was 80% (95% CI 75, 83). 3-year LC differed according to lesion location, ranging from 65% (95% CI 52, 75) in the spine to 93% (95% CI 80, 98) in the lungs. Radiation-induced adverse events were experienced by 101 patients: 79 had an acute (≤90 days of SAbR) grade 1-2 toxicity; 20 had an acute grade 3-4 toxicity; 59 had a late grade 1-2 toxicity; 15 had a late grade 3-4 toxicity. The most common acute grade 1-2 toxicity was pain (n = 32), followed by nausea (n = 22) and fatigue (n = 16). There were 7 occurrences of acute grade 3-4 pain, 4 of nausea, and 2 fractures. The most common late grade 1-2 toxicity was fracture (n = 16), followed by pain (n = 15) and pneumonitis (n = 12). Hyperglycemia was the only late grade 3-4 toxicity that occurred more than once (n = 2). SAbR offers durable LC of mRCC lesions with an acceptable toxicity profile. LC was affected by treated lesion location, with bone (including long bones and ribs) and spine locations experiencing less durable LC, corresponding to locations that received lower-BED treatments.

Local Control after Low-Dose Radiation for Two Rare Forms of Indolent Non-Hodgkin Lymphoma.

Small lymphocytic lymphoma (SLL) and lymphoplasmacytic lymphoma (LPL) are two rare subsets of indolent non-Hodgkin lymphoma (NHL). National guidelines recommend 24-30 Gy for localized SLL. However, based on data for follicular and marginal zone lymphoma, lower dose RT (4 Gy) has been increasingly utilized. We reviewed our experience with SLL and LPL and hypothesized that low dose RT would provide excellent local control. We retrospectively reviewed patients at three tertiary cancer centers who had been treated with RT for SLL or LPL. Response to RT was classified using the World Health Organization response criteria and by examining available PET and CT imaging. Radiographic response was assessed at first imaging follow-up and clinical response was recorded if no imaging was performed. Time to best response was noted, and Kaplan Meier estimates and cumulative incidence tests were performed to determine progression-free survival (PFS) and local progression (LP), respectively. From 2014-2022, 16 patients with 18 sites of SLL (n = 13) or LPL (n = 5) were treated with RT and available to review. Five sites of SLL represented diffuse large B-cell lymphoma transformation and were excluded from analysis. In total, eight sites of SLL (seven patients) and five sites of LPL (five patients) were treated with doses ranging from 4 to 30 Gy in 2 to 12 fractions (median 20 Gy). Four sites of disease received 4 Gy in 2 fractions, one of which (SLL) progressed approximately four months after RT. This site was successfully salvaged with 24 Gy in 12 fractions. There were no other LP. Toxicity overall was low: one patient experienced grade 2 mucositis after 25 Gy in 10 fractions to the maxillary sinus and palate and the remainder of patients experienced grade 1 or no toxicity. Of 10 symptomatic sites, seven (5/7 SLL and 2/3 LPL) attained at least partial relief after RT. A complete response (CR) was achieved in 14% of SLL disease sites and 60% of LPL sites. Partial response was achieved in 57% of SLL and 40% of LPL sites, and 29% of SLL sites were deemed to be stable. One patient with SLL died after their first RT treatment, but this was unrelated to RT. The median time to best response was 284 days (IQR 189-292 days) for SLL and 131 days (IQR 106-166 days) for LPL. 4 Gy in 2 fractions did not result in any CR, yet one patient from the LPL group exhibited a striking CR after 8 Gy in 2 fractions. PFS at one year was 51% for SLL and 100% for LPL - cumulative incidence of LP at two years was 15% and 0% respectively. In this cohort of patients with two types of indolent NHL, one patient progressed locally after 4 Gy, while none progressed after higher doses. LPL sites achieved more complete responses than SLL sites, and RT was tolerated extremely well. These results indicate that similar to other indolent lymphomas, clinical judgment should be used when deciding between 4 Gy or higher doses of RT. For SLL in particular, higher doses of RT are more likely to provide durable local control and CR.