A Pilot Study of Simulation-Free Hippocampal-Avoidance Whole Brain Radiation Therapy Using Diagnostic MRI-Based and Online Adaptive Planning

PURPOSE

We aimed to demonstrate the clinical feasibility and safety of simulation-free hippocampal avoidance whole brain radiation therapy (HA-WBRT) in a pilot study (National Clinical Trial 05096286).

METHODS AND MATERIALS

Ten HA-WBRT candidates were enrolled for treatment on a commercially available computed tomography (CT)-guided linear accelerator with online adaptive capabilities. Planning structures were contoured on patient-specific diagnostic magnetic resonance imaging (MRI), which were registered to a CT of similar head shape, obtained from an atlas-based database (AB-CT). These patient-specific diagnostic MRI and AB-CT data sets were used for preplan calculation, using NRG-CC001 constraints. At first fraction, AB-CTs were used as primary data sets and deformed to patient-specific cone beam CTs (CBCT) to give patient-matched density information. Brain, ventricle, and brain stem contours were matched through rigid translation and rotation to the corresponding anatomy on CBCT. Lens, optic nerve, and brain contours were manually edited based on CBCT visualization. Preplans were then reoptimized through online adaptation to create final, simulation-free plans, which were used if they met all objectives. Workflow tasks were timed. In addition, patients underwent CT-simulation to create immobilization devices and for prospective dosimetric comparison of simulation-free and simulation-based plans.

RESULTS

Median time from MRI importation to completion of "preplan" was 1 weekday (range, 1-4). Median on-table workflow duration was 41 minutes (range, 34-70). NRG-CC001 constraints were achieved by 90% of the simulation-free plans. One patient's simulation-free plan failed a planning target volume coverage objective (89% instead of 90% coverage); this was deemed acceptable for first-fraction delivery, with an offline replan used for subsequent fractions. Both simulation-free and simulation CT-based plans otherwise met constraints, without clinically meaningful differences.

CONCLUSIONS

Simulation-free HA-WBRT using online adaptive radiation therapy is feasible, safe, and results in dosimetrically comparable treatment plans to simulation CT-based workflows while providing convenience and time savings for patients.

Stereotactic MR-guided on-table adaptive radiation therapy (SMART) for borderline resectable and locally advanced pancreatic cancer: A multi-center, open-label phase 2 study

BACKGROUND AND PURPOSE

Radiation dose escalation may improve local control (LC) and overall survival (OS) in select pancreatic ductal adenocarcinoma (PDAC) patients. We prospectively evaluated the safety and efficacy of ablative stereotactic magnetic resonance (MR)-guided adaptive radiation therapy (SMART) for borderline resectable (BRPC) and locally advanced pancreas cancer (LAPC). The primary endpoint of acute grade ≥ 3 gastrointestinal (GI) toxicity definitely related to SMART was previously published with median follow-up (FU) 8.8 months from SMART. We now present more mature outcomes including OS and late toxicity.

MATERIALS AND METHODS

This prospective, multi-center, single-arm open-label phase 2 trial (NCT03621644) enrolled 136 patients (LAPC 56.6 %; BRPC 43.4 %) after ≥ 3 months of any chemotherapy without distant progression and CA19-9 ≤ 500 U/mL. SMART was delivered on a 0.35 T MR-guided system prescribed to 50 Gy in 5 fractions (biologically effective dose10 [BED10] = 100 Gy). Elective coverage was optional. Surgery and chemotherapy were permitted after SMART.

RESULTS

Mean age was 65.7 years (range, 36-85), induction FOLFIRINOX was common (81.7 %), most received elective coverage (57.4 %), and 34.6 % had surgery after SMART. Median FU was 22.9 months from diagnosis and 14.2 months from SMART, respectively. 2-year OS from diagnosis and SMART were 53.6 % and 40.5 %, respectively. Late grade ≥ 3 toxicity definitely, probably, or possibly attributed to SMART were observed in 0 %, 4.6 %, and 11.5 % patients, respectively.

CONCLUSIONS

Long-term outcomes from the phase 2 SMART trial demonstrate encouraging OS and limited severe toxicity. Additional prospective evaluation of this novel strategy is warranted.

The Use of MR-Guided Radiation Therapy for Liver Cancer

The role of radiotherapy in the management of primary and metastatic liver malignancies has expanded in recent years due to advances such as IGRT and SBRT. MRI-guided radiotherapy (MRgRT) has arisen as an excellent option for the management of hepatocellular carcinoma, cholangiocarcinoma, and liver metastases due to the ability to combine improved hepatic imaging with conformal treatment planning paradigms like adaptive radiotherapy and advanced motion management techniques. Herein we review the data for MRgRT for liver malignancies, as well as describe workflow and technical considerations for the 2 commercially available MRgRT delivery platforms.

A Multi-Institutional Phase 2 Trial of Ablative 5-Fraction Stereotactic Magnetic Resonance-Guided On-Table Adaptive Radiation Therapy for Borderline Resectable and Locally Advanced Pancreatic Cancer

PURPOSE

Magnetic resonance (MR) image guidance may facilitate safe ultrahypofractionated radiation dose escalation for inoperable pancreatic ductal adenocarcinoma. We conducted a prospective study evaluating the safety of 5-fraction Stereotactic MR-guided on-table Adaptive Radiation Therapy (SMART) for locally advanced (LAPC) and borderline resectable pancreatic cancer (BRPC).

METHODS AND MATERIALS

Patients with LAPC or BRPC were eligible for this multi-institutional, single-arm, phase 2 trial after ≥3 months of systemic therapy without evidence of distant progression. Fifty gray in 5 fractions was prescribed on a 0.35T MR-guided radiation delivery system. The primary endpoint was acute grade ≥3 gastrointestinal (GI) toxicity definitely attributed to SMART.

RESULTS

One hundred thirty-six patients (LAPC 56.6%, BRPC 43.4%) were enrolled between January 2019 and January 2022. Mean age was 65.7 (36-85) years. Head of pancreas lesions were most common (66.9%). Induction chemotherapy mostly consisted of (modified)FOLFIRINOX (65.4%) or gemcitabine/nab-paclitaxel (16.9%). Mean CA19-9 after induction chemotherapy and before SMART was 71.7 U/mL (0-468). On-table adaptive replanning was performed for 93.1% of all delivered fractions. Median follow-up from diagnosis and SMART was 16.4 and 8.8 months, respectively. The incidence of acute grade ≥3 GI toxicity possibly or probably attributed to SMART was 8.8%, including 2 postoperative deaths that were possibly related to SMART in patients who had surgery. There was no acute grade ≥3 GI toxicity definitely related to SMART. One-year overall survival from SMART was 65.0%.

CONCLUSIONS

The primary endpoint of this study was met with no acute grade ≥3 GI toxicity definitely attributed to ablative 5-fraction SMART. Although it is unclear whether SMART contributed to postoperative toxicity, we recommend caution when pursuing surgery, especially with vascular resection after SMART. Additional follow-up is ongoing to evaluate late toxicity, quality of life, and long-term efficacy.

Bridging the Gap of Radiotherapy Treatment Planning Quality between High-Income, and Low- and Middle-Income Countries Using Knowledge-Based Planning

PURPOSE/OBJECTIVE(S)

Radiotherapy departments in low- and middle-income countries (LMICs) like Guatemala have recently introduced intensity-modulated radiotherapy (IMRT). IMRT has become the standard of care in high-income countries (HIC) due to reduced toxicity and improved outcomes in some cancers. The purpose of this work is to show the feasibility of adapting knowledge-based (KB) models established in a HIC to a LMIC lacking experience in IMRT to improve plan quality and planning efficiency.

MATERIALS/METHODS

A Halcyon Linac was installed at our clinic in Guatemala in 2019 and has been used to treat approximately 90 patients daily with IMRT. A model developed on a cohort of head and neck cancer patients at a US academic radiotherapy center were applied at our center to create 20head and neck VMAT plans with different prescriptions, including simultaneous-integrated and sequential boosts.

RESULTS

The plans created using the KB models achieved similar coverage of the planning target volume for each plan KB plans showed better 1) Parotid sparing with a mean dose reduction between 5%-25% and spinal cord maximum dose reduction between 3%-15%. The time efficiency to create VMAT plans using KB model versus manual planning improved four-fold, on average one hour versus more than 4 hours, respectively.

CONCLUSION

Despite different prescriptions, guidelines and demographics of cancer patients between two institutions in a HIC and LMIC, this work demonstrates that KB planning can be used to generate better and more consistent VMAT plans versus manually created plans. In addition, KB planning has the potential to greatly increase planning efficiency higher efficiency and help address the shortage of medical physicists and dosimetrists in LMICs.

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.

Standardizing LT Chest Wall Radiotherapy Treatment Planning in a Low- or Middle- Income Country Radiotherapy Clinic Using Knowledge Based Planning

PURPOSE/OBJECTIVE(S)

Radiotherapy departments in low- or middle-income countries (LMICs) tend to lag behind introducing emerging technologies like intensity-modulated radiotherapy (IMRT). IMRT has become the standard of care in high-income countries (HIC) due to reduced toxicity and improved outcomes in a wide variety of cancers. The purpose of this work is showing the results of left Chest-Wall knowledge-based planning (KBP) standardization and implementation in a LMIC setting.

MATERIALS/METHODS

A Halcyon Linac was installed at our clinic in Guatemala in 2019 and currently used to treat ∼90 IMRT patients daily. The standardization of IMRT procedures has been difficult for complex sites like chest-wall. The steps for standardization included: AAPM TG-263 nomenclature implementation, and planning workflows within the TPS, creation of optimization structures, and plan quality evaluation following RTOG1005 protocol hypofractionation arm. 25 plans were created manually achieving all RTOG1005 protocol constraints. The statistics were analyzed trough the model analytics tool provided by KPB manufacturer.

RESULTS

The results show that more plans are needed to improve the KBP model. This initial model was used to create a standardized clinical protocol in the TPS in order to continue adding plans to the KBP model database. This approach ensures that we obtain consistent plan quality and standardize our planning. The manual planning objectives achieved: CONCLUSION: The experience using the TPS to standardize our treatment planning process achieved good consistency in our planning objectives. This approach will help create KBP models according to our own clinic-specific requirements. Future work will be made to compare our LMIC KBP models with those made at a HIC academic radiotherapy center.

In silico trial of simulation-free hippocampal-avoidance whole brain adaptive radiotherapy

Background and Purpose

Hippocampal-avoidance whole brain radiotherapy (HA-WBRT) can be a time-consuming process compared to conventional whole brain techniques, thus potentially limiting widespread utilization. Therefore, we evaluated the in silico clinical feasibility, via dose-volume metrics and timing, by leveraging a computed tomography (CT)-based commercial adaptive radiotherapy (ART) platform and workflow in order to create and deliver patient-specific, simulation-free HA-WBRT.

Materials and methods

Ten patients previously treated for central nervous system cancers with cone-beam computed tomography (CBCT) imaging were included in this study. The CBCT was the adaptive image-of-the-day to simulate first fraction on-board imaging. Initial contours defined on the MRI were rigidly matched to the CBCT. Online ART was used to create treatment plans at first fraction. Dose-volume metrics of these simulation-free plans were compared to standard-workflow HA-WBRT plans on each patient CT simulation dataset. Timing data for the adaptive planning sessions were recorded.

Results

For all ten patients, simulation-free HA-WBRT plans were successfully created utilizing the online ART workflow and met all constraints. The median hippocampi D100% was 7.8 Gy (6.6-8.8 Gy) in the adaptive plan vs 8.1 Gy (7.7-8.4 Gy) in the standard workflow plan. All plans required adaptation at first fraction due to both a failing hippocampal constraint (6/10 adaptive fractions) and sub-optimal target coverage (6/10 adaptive fractions). Median time for the adaptive session was 45.2 min (34.0-53.8 min).

Conclusions

Simulation-free HA-WBRT, with commercially available systems, was clinically feasible via plan-quality metrics and timing, in silico.

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.

Patient Selection is Critical When Evaluating Candidates for 5-Fraction Stereotactic MRI-Guided Adaptive Radiotherapy (SMART) for Locally Advanced Pancreatic Cancer

PURPOSE/OBJECTIVE(S)

Stereotactic magnetic resonance image-guided adaptive radiotherapy (SMART) allows for the safe delivery of biologically effective doses (BED10 ∼ 100 Gy) to patients with pancreatic cancer who otherwise have limited therapeutic avenues. In this study, we analyze long-term outcomes in the largest cohort of patients with borderline-resectable (BR), locally advanced (LA), or medically inoperable (MI) pancreatic cancer treated with a 5-fraction SMART technique.

MATERIALS/METHODS

A single institution analysis of patients with BR, LA, or MI pancreatic cancer treated with SMART between 2015 and 2021 was performed. Patients with locally recurrent disease, non-adenocarcinoma histology, de-novo metastatic disease, or who did not receive induction chemotherapy were excluded. Baseline and treatment characteristics were collected. Local control (LC), progression free survival (PFS), and overall survival (OS) were calculated using the Kaplan-Meier method, and factors associated with outcomes were evaluated using Cox regression analyses. Oncologic outcomes measured from time of initial diagnosis; local control defined as freedom from local progression.

RESULTS

A total of 129 patients were reviewed. Median age at diagnosis was 67 years. The majority were male (60%) and White (84%). 23% of patients had an ECOG 2. Most patients had LA disease (66%), followed by BR (20%) and MI (14%). Median follow up was 17.0 months (6-61 months). Median LC was not reached, and LC was 81%, 54%, and 48% at 1, 2, and 3-years, respectively. Median PFS was 12.9 months [95% confidence interval 11.8-14.71] with 1, 2, and 3-year PFS of 60%, 20%, and 7%, respectively. Median OS was 17.7 months [15.7-19.7] with 1, 2, and 3-year OS of 78%, 28%, 11%, respectively. On univariate analysis, increased duration of induction chemotherapy had a statistically significant impact on PFS and OS. Those receiving equal to or greater than 4 months of induction chemotherapy had a median OS of 19.2 months [17.2-21.2] as compared to 13.6 [11.9-15.3] for those with less than 4 months.

CONCLUSION

In this patient population which included a large portion of patients with ECOG of 2 or greater and those deemed MI, a 5-fraction SMART regimen yielded durable long-term LC. The impact of increasing duration of induction chemotherapy underlies the importance of patient selection and improved understanding of tumor-specific biology when selecting patient's with locally advanced pancreatic cancer for aggressive local therapy.

Initial clinical experience building a dual CT- and MR-guided adaptive radiotherapy program

Introduction

Our institution was the first in the world to clinically implement MR-guided adaptive radiotherapy (MRgART) in 2014. In 2021, we installed a CT-guided adaptive radiotherapy (CTgART) unit, becoming one of the first clinics in the world to build a dual-modality ART clinic. Herein we review factors that lead to the development of a high-volume dual-modality ART program and treatment census over an initial, one-year period.

Materials and Methods

The clinical adaptive service at our institution is enabled with both MRgART (MRIdian, ViewRay, Inc, Mountain View, CA) and CTgART (ETHOS, Varian Medical Systems, Palo Alto, CA) platforms. We analyzed patient and treatment information including disease sites treated, radiation dose and fractionation, and treatment times for patients on these two platforms. Additionally, we reviewed our institutional workflow for creating, verifying, and implementing a new adaptive workflow on either platform.

Results

From October 2021 to September 2022, 256 patients were treated with adaptive intent at our institution, 186 with MRgART and 70 with CTgART. The majority (106/186) of patients treated with MRgART had pancreatic cancer, and the most common sites treated with CTgART were pelvis (23/70) and abdomen (20/70). 93.0% of treatments on the MRgART platform were stereotactic body radiotherapy (SBRT), whereas only 72.9% of treatments on the CTgART platform were SBRT. Abdominal gated cases were allotted a longer time on the CTgART platform compared to the MRgART platform, whereas pelvic cases were allotted a shorter time on the CTgART platform when compared to the MRgART platform. Our adaptive implementation technique has led to six open clinical trials using MRgART and seven using CTgART.

Conclusions

We demonstrate the successful development of a dual platform ART program in our clinic. Ongoing efforts are needed to continue the development and integration of ART across platforms and disease sites to maximize access and evidence for this technique worldwide.

Clinical outcomes of patients with unresectable primary liver cancer treated with MR-guided stereotactic body radiation Therapy: A Six-Year experience

Purpose

Magnetic resonance-guided stereotactic body radiation therapy (MRgSBRT) with optional online adaptation has shown promise in delivering ablative doses to unresectable primary liver cancer. However, there remain limited data on the indications for online adaptation as well as dosimetric and longer-term clinical outcomes following MRgSBRT.

Methods and Materials

Patients with unresectable hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), and combined biphenotypic hepatocellular-cholangiocarcinoma (cHCC-CCA) who completed MRgSBRT to 50 Gy in 5 fractions between June of 2015 and December of 2021 were analyzed. The necessity of adaptive techniques was evaluated. The cumulative incidence of local progression was evaluated and survival and competing risk analyses were performed.

Results

Ninety-nine analyzable patients completed MRgSBRT during the study period and 54 % had planning target volumes (PTVs) within 1 cm of the duodenum, small bowel, or stomach at the time of simulation. Online adaptive RT was used in 53 % of patients to correct organ-at-risk constraint violation and/or to improve target coverage. In patients who underwent adaptive RT planning, online replanning resulted in superior target coverage when compared to projected, non-adaptive plans (median coverage ≥ 95 % at 47.5 Gy: 91 % [IQR: 82-96] before adaptation vs 95 % [IQR: 87-99] after adaptation, p < 0.01). The median follow-up for surviving patients was 34.2 months for patients with HCC and 10.1 months for patients with CCA/cHCC-CCA. For all patients, the 2-year cumulative incidence of local progression was 9.8 % (95 % CI: 1.5-18 %) for patients with HCC and 9.0 % (95 % CI: 0.1-18) for patients with CCA/cHCC-CCA. Grade 3 through 5 acute and late clinical gastrointestinal toxicities were observed in < 10 % of the patients.

Conclusions

MRgSBRT, with the option for online adaptive planning when merited, allows delivery of ablative doses to primary liver tumors with excellent local control with acceptable toxicities. Additional studies evaluating the efficacy and safety of MRgSBRT in the treatment of primary liver cancer are warranted.

Circumferential Resection Margin as Predictor of Nonclinical Complete Response in Nonoperative Management of Rectal Cancer

BACKGROUND

Short-course radiation therapy and consolidation chemotherapy with nonoperative intent has emerged as a novel treatment paradigm for patients with rectal cancer, but there are no data on the predictors of clinical complete response.

OBJECTIVE

Evaluate the predictors of clinical complete response and survival.

DESIGN

Retrospective cohort.

SETTINGS

National Cancer Institute-designated cancer center.

PATIENTS

Patients with stage I to III rectal adenocarcinoma treated between January 2018 and May 2019 (n = 86).

INTERVENTIONS

Short-course radiation therapy followed by consolidation chemotherapy.

MAIN OUTCOME MEASURES

Logistic regression was performed to assess for predictors of clinical complete response. The end points included local regrowth-free survival, regional control, distant metastasis-free survival, and overall survival.

RESULTS

A positive (+) circumferential resection margin by MRI at diagnosis was a significant predictor of nonclinical complete response (OR: 4.1, p = 0.009) when adjusting for CEA level and primary tumor size. Compared to patients with a negative (-) pathologic circumferential resection margin, patients with a positive (+) pathologic circumferential resection margin had inferior local regrowth-free survival (29% vs 87%, p < 0.001), regional control (57% vs 94%, p < 0.001), distant metastasis-free survival (43% vs 95%, p < 0.001), and overall survival (86% vs 95%, p < 0.001) at 2 years. However, the (+) and (-) circumferential resection margin by MRI subgroups in patients who had a clinical complete response both had similar regional control, distant metastasis-free survival, and overall survival of more than 90% at 2 years.

LIMITATIONS

Retrospective design, modest sample size, short follow-up, and the heterogeneity of treatments.

CONCLUSIONS

Circumferential resection margin involvement by MRI at diagnosis is a strong predictor of nonclinical complete response. However, patients who achieve a clinical complete response after short-course radiation therapy and consolidation chemotherapy with nonoperative intent have excellent clinical outcomes regardless of the initial circumferential resection margin status. See Video Abstract at http://links.lww.com/DCR/C190 .

EL MARGEN DE RESECCIN CIRCUNFERENCIAL COMO PREDICTOR NO CLNICO DE RESPUESTA COMPLETA EN EL MANEJO CONSERVADOR DEL CNCER DE RECTO

ANTECEDENTES:La radioterapia de corta duración y la quimioterapia de consolidación en el manejo conservador, han surgido como un nuevo paradigma de tratamiento, para los pacientes con cáncer de recto, lastimosamente no hay datos definitivos sobre los predictores de una respuesta clínica completa.OBJETIVO:Evaluar los predictores de respuesta clínica completa y de la sobrevida.DISEÑO:Estudio retrospectivo de cohortes.AJUSTES:Centro oncológico designado por el NCI.PACIENTES:Adenocarcinomas de recto estadio I-III tratados entre 01/2018 y 05/2019 (n = 86).INTERVENCIONES:Radioterapia de corta duración seguida de quimioterapia de consolidación.PRINCIPALES MEDIDAS DE RESULTADO:Se realizó una regresión logística para evaluar los predictores de respuesta clínica completa. Los criterios de valoración incluyeron la sobrevida libre de recidiva local, el control regional, la sobrevida libre de metástasis a distancia y la sobrevida general.RESULTADOS:Un margen de resección circunferencial positivo (+) evaluado por imagenes de resonancia magnética nuclear en el momento del diagnóstico fue un predictor no clínico muy significativo de respuesta completa (razón de probabilidades/ OR: 4,1, p = 0,009) al ajustar el nivel de antígeno carcinoembrionario y el tamaño del tumor primario. Comparando con los pacientes que presetaban un margen de resección circunferencial patológico negativo (-), los pacientes con un margen de resección circunferencial patológico positivo (+) tuvieron una sobrevida libre de recidiva local (29% frente a 87%, p < 0,001), un control regional (57% frente a 94%, p < 0,001), una sobrevida libre de metástasis a distancia (43% frente a 95%, p < 0,001) y una sobrevida global (86% frente a 95%, p < 0,001) inferior en 2 años de seguimiento. Sin embargo, los subgrupos de margen de resección circunferencial (+) y (-) evaluados por imágenes de resonancia magnética nuclear en pacientes que tuvieron una respuesta clínica completa tuvieron un control regional similar, una sobrevida libre de metástasis a distancia y una sobrevida general >90% en 2 años de seguimiento.LIMITACIONES:Diseño retrospectivo, tamaño modesto de la muestra, seguimiento corto y heterogeneidad de tratamientos.CONCLUSIONES:La afectación del margen de resección circunferencial evaluado por resonancia magnética nuclear al momento del diagnóstico es un fuerte factor predictivo no clínico de respuesta completa. Sin embargo, los pacientes que logran una respuesta clínica completa después de un curso corto de radioterapia y quimioterapia de consolidación como manejo conservador tienen excelentes resultados clínicos independientemente del estado del margen de resección circunferencial inicial. Consulte Video Resumen en http://links.lww.com/DCR/C190 . (Traducción-Dr. Xavier Delgadillo ).

Knowledge-based adaptive planning quality assurance using dosimetric indicators for stereotactic adaptive radiotherapy for pancreatic cancer

INTRODUCTION

We aimed to develop knowledge-based tools for robust adaptive radiotherapy (ART) planning to determine on-table adaptive DVH metric variations or planning process errors for stereotactic pancreatic ART. We developed volume-based dosimetric identifiers to identify deviations of ART plans from simulation plans.

MATERIALS AND METHODS

Two patient cohorts who were treated on MR-Linac for pancreas cancer were included in this retrospective study; a training cohort and a validation cohort. All patients received 50 Gy in 5 fractions. PTV-OPT was generated by subtracting the critical organs plus a 5 mm-margin from PTV. Several metrics that potentially can identify failure-modes were calculated including PTV & PTV_OPT V95% and PTV & PTV_OPT D95%/D5%. The difference between each DVH metric in each adaptive plan with the DVH metric in simulation plan was calculated. The 95% confidence interval (CI) of the variations in each DVH metric was calculated for the patient training cohort. Variations in DVH metrics that exceeded the 95% CI for all fractions in training and validation cohort were flagged for retrospective investigation for root-cause analysis to determine their predictive power for identifying failure-modes.

RESULTS

The CIs for the PTV & PTV_OPT V95% and PTV & PTV_OPT D95%/D5% were ± 13%, ± 5%, ± 0.1, ± 0.03, respectively. We estimated the positive predictive value and negative predictive value of our method to be 77% and 89%, respectively, for the training cohort, and 80% for both in the validation cohort.

DISCUSSION

We developed dosimetric indicators for ART planning QA to identify population-based deviations or planning errors during online adaptive process for stereotactic pancreatic ART. This technology may be useful as an ART clinical trial QA tool and improve overall ART quality at an institution.

Ablative radiotherapy for colorectal liver metastases and intrahepatic cholangiocarcinoma

The role of radiation therapy in the management of liver cancers, both primary and metastatic, has changed drastically over the past several decades. Although conventional radiation was limited by technology, the advent of advanced image-guided radiotherapy and the rise in evidence for and popularity of stereotactic body radiotherapy have expanded the indications for radiation in these two distinct disease types. Magnetic resonance imaging-guided radiation therapy, daily online adaptive radiotherapy, and proton radiotherapy are some of many modern radiotherapy techniques that allow for increasingly efficacious treatment of intrahepatic disease while simultaneously allowing for increased normal tissue sparing, including sparing of the normal liver and the radiosensitive luminal gastrointestinal tract. Modern radiation therapy should be considered along with approaches such as surgical resection and radiofrequency ablation for the management of liver cancers of diverse histologies. Herein we describe the use of modern radiotherapy in two example settings, colorectal liver metastases and intrahepatic cholangiocarcinoma, and how external beam radiotherapy provides options within multidisciplinary discussions to elect optimal patient-specific treatments.

Patient specific contouring region of interest for abdominal stereotactic adaptive radiotherapy

Contouring during adaptive radiotherapy (ART) can be a time-consuming process. This study describes the generation of patient specific contouring regions of interest (CRoI) for evaluating the high dose fall-off in stereotactic abdominal ART. An empirical equation was derived to determine the radius of a cylindrical patient specific CRoIs. These CRoIs were applied to 60 patients and their adaptive fractions (301 unique treatment plans). Out of the 301 unique treatment plans, 284 (94%) treatment plans contained the high dose fall-off within the CRoI. There was an expected predicted average timesaving of 2.9-min-per case. Patient specific CRoIs improves the efficiency of ART.

First treatments for Lattice stereotactic body radiation therapy using magnetic resonance image guided radiation therapy

Two abdominal patients were treated with Lattice stereotactic body radiation therapy (SBRT) using magnetic resonance guided radiation therapy (MRgRT). This is one of the first reported treatments of Lattice SBRT with the use of MRgRT. A description of the treatment approach and planning considerations were incorporated into this report. MRgRT Lattice SBRT delivered similar planning quality metrics to established dosimetric parameters for Lattice SBRT. Increased signal intensity were seen in the MRI treatments for one of the patients during the course of treatment.

Prospective imaging comparison of anatomic delineation with rapid kV cone beam CT on a novel ring gantry radiotherapy device

INTRODUCTION

A kV imager coupled to a novel, ring-gantry radiotherapy system offers improved on-board kV-cone-beam computed tomography (CBCT) acquisition time (17-40 seconds) and image quality, which may improve CT radiotherapy image-guidance and enable online adaptive radiotherapy. We evaluated whether inter-observer contour variability over various anatomic structures was non-inferior using a novel ring gantry kV-CBCT (RG-CBCT) imager as compared to diagnostic-quality simulation CT (simCT).

MATERIALS/METHODS

Seven patients undergoing radiotherapy were imaged with the RG-CBCT system at breath hold (BH) and/or free breathing (FB) for various disease sites on a prospective imaging study. Anatomy was independently contoured by seven radiation oncologists on: 1. SimCT 2. Standard C-arm kV-CBCT (CA-CBCT), and 3. Novel RG-CBCT at FB and BH. Inter-observer contour variability was evaluated by computing simultaneous truth and performance level estimation (STAPLE) consensus contours, then computing average symmetric surface distance (ASSD) and Dice similarity coefficient (DSC) between individual raters and consensus contours for comparison across image types.

RESULTS

Across 7 patients, 18 organs-at-risk (OARs) were evaluated on 27 image sets. Both BH and FB RG-CBCT were non-inferior to simCT for inter-observer delineation variability across all OARs and patients by ASSD analysis (p < 0.001), whereas CA-CBCT was not (p = 0.923). RG-CBCT (FB and BH) also remained non-inferior for abdomen and breast subsites compared to simCT on ASSD analysis (p < 0.025). On DSC comparison, neither RG-CBCT nor CA-CBCT were non-inferior to simCT for all sites (p > 0.025).

CONCLUSIONS

Inter-observer ability to delineate OARs using novel RG-CBCT images was non-inferior to simCT by the ASSD criterion but not DSC criterion.

MR-Guided Radiation Therapy With Concurrent Gemcitabine/Nab-Paclitaxel Chemotherapy in Inoperable Pancreatic Cancer: A TITE-CRM Phase I Trial

PURPOSE

Ablative radiation therapy for borderline resectable or locally advanced pancreatic ductal adenocarcinoma (BR/LA-PDAC) may limit concurrent chemotherapy dosing and usually is only safely deliverable to tumors distant from gastrointestinal organs. Magnetic resonance guided radiation therapy may safely permit radiation and chemotherapy dose escalation.

METHODS AND MATERIALS

We conducted a single-arm phase I study to determine the maximum tolerated dose of ablative hypofractionated radiation with full-dose gemcitabine/nab-paclitaxel in patients with BR/LA-PDAC. Patients were treated with gemcitabine/nab-paclitaxel (1000/125 mg/m2) x 1c then concurrent gemcitabine/nab-paclitaxel and radiation. Gemcitabine/nab-paclitaxel and radiation doses were escalated per time-to-event continual reassessment method from 40 to 45 Gy 25 fxs with chemotherapy (600-800/75 mg/m2) to 60 to 67.5 Gy/15 fractions and concurrent gemcitabine/nab-paclitaxel (1000/100 mg/m2). The primary endpoint was maximum tolerated dose of radiation as defined by 60-day dose limiting toxicity (DLT). DLT was treatment-related G5, G4 hematologic, or G3 gastrointestinal requiring hospitalization >3 days. Secondary endpoints included resection rates, local progression free survival (LPFS), distant metastasis free survival (DMFS), and overall survival (OS).

RESULTS

Thirty patients enrolled (March 2015-February 2019), with 26 evaluable patients (2 progressed before radiation, 1 was determined ineligible for radiation during planning, 1 withdrew consent). One DLT was observed. The DLT rate was 14.1% (3.3%-24.9%) with a maximum tolerated dose of gemcitabine/nab-paclitaxel (1000/100 mg/m2) and 67.5 Gy/15 fractions. At a median follow-up of 40.6 months for living patients the median OS was 14.5 months (95% confidence interval [CI], 10.9-28.2 months). The median OS for patients with Eastern Collaborative Oncology Group 0 and carbohydrate antigen 19-9 <90 were 34.1 (95% CI, 13.6-54.1) and 43.0 (95% CI, 8.0-not reached) months, respectively. Two-year LPFS and DMFS were 85% (95% CI, 63%-94%) and 57% (95% CI, 34%-73%), respectively.

CONCLUSIONS

Full-dose gemcitabine/nab-paclitaxel with ablative magnetic resonance guided radiation therapy dosing is safe in patients with BR/LA-PDAC, with promising LPFS and DMFS.

A pilot study of same-day MRI-only simulation and treatment with MR-guided adaptive palliative radiotherapy (MAP-RT)

We conducted a prospective pilot study evaluating the feasibility of same day MRI-only simulation and treatment with MRI-guided adaptive palliative radiotherapy (MAP-RT) for urgent palliative indications (NCT#03824366). All (16/16) patients were able to complete 99% of their first on-table attempted fractions, and no grades 3-5 toxicities occurred.

FDG-PET/MRI for Nonoperative Management of Rectal Cancer: A Prospective Pilot Study

Nonoperative management (NOM) is increasingly utilized for rectal cancer patients with a clinical complete response (cCR) following total neoadjuvant therapy (TNT). The objective of this pilot study was to determine whether FDG-PET/MRI alters clinical response assessments among stage I-III rectal cancer patients undergoing TNT followed by NOM, relative to MRI alone. This prospective study included 14 subjects with new rectal cancer diagnoses. Imaging consisted of FDG-PET/MRI for initial staging, post-TNT restaging, and surveillance during NOM. Two independent readers assessed treatment response on MRI followed by FDG-PET/MRI. Inter-reader differences were resolved by consensus review. The reference standard for post-TNT restaging consisted of surgical pathology or clinical follow-up. 7/14 subjects completed post-TNT restaging FDG-PET/MRIs. 5/7 subjects had evidence of residual disease and underwent total mesorectal excision; 2/7 subjects had initial cCR with no evidence of disease after 12 months of NOM. FDG-PET/MRI assessments of cCR status at post-TNT restaging had an accuracy of 100%, compared with 71% for MRI alone, as FDG-PET detected residual tumor in 2 more subjects. Inter-reader agreement for cCR status on FDG-PET/MRI was moderate (kappa, 0.56). FDG-PET provided added value in 82% (9/11) of restaging/surveillance scans. Our preliminary data indicate that FDG-PET/MRI can detect more residual disease after TNT than MRI alone, with the FDG-PET component providing added value in most restaging/surveillance scans.

The first reported case of a patient with pancreatic cancer treated with cone beam computed tomography-guided stereotactic adaptive radiotherapy (CT-STAR)

BACKGROUND

Online adaptive stereotactic radiotherapy allows for improved target and organ at risk (OAR) delineation and inter-fraction motion management via daily adaptive planning. The use of adaptive SBRT for the treatment of pancreatic cancer (performed until now using only MRI or CT on rails-guided adaptive radiotherapy), has yielded promising outcomes. Herein we describe the first reported case of cone beam CT-guided stereotactic adaptive radiotherapy (CT-STAR) for the treatment of pancreatic cancer.

CASE PRESENTATION

A 61-year-old female with metastatic pancreatic cancer presented for durable palliation of a symptomatic primary pancreatic mass. She was prescribed 35 Gy/5 fractions utilizing CT-STAR. The patient was simulated utilizing an end-exhale CT with intravenous and oral bowel contrast. Both initial as well as daily adapted plans were created adhering to a strict isotoxicity approach in which coverage was sacrificed to meet critical luminal gastrointestinal OAR hard constraints. Kilovoltage cone beam CTs were acquired on each day of treatment and the radiation oncologist edited OAR contours to reflect the patient's anatomy-of-the-day. The initial and adapted plan were compared using dose volume histogram objectives, and the superior plan was delivered. Use of the initial treatment plan would have resulted in nine critical OAR hard constraint violations. The adapted plans achieved hard constraints in all five fractions for all four critical luminal gastrointestinal structures.

CONCLUSIONS

We report the successful treatment of a patient with pancreatic cancer treated with CT-STAR. Prior to this treatment, the delivery of ablative adaptive radiotherapy for pancreatic cancer was limited to clinics with MR-guided and CT-on-rails adaptive SBRT technology and workflows. CT-STAR is a promising modality with which to deliver stereotactic adaptive radiotherapy for pancreatic cancer.

Simulated computed tomography-guided stereotactic adaptive radiotherapy (CT-STAR) for the treatment of locally advanced pancreatic cancer

BACKGROUND AND PURPOSE

We conducted a prospective, in silico imaging clinical trial to evaluate the feasibility and potential dosimetric benefits of computed tomography-guided stereotactic adaptive radiotherapy (CT-STAR) for the treatment of locally advanced pancreatic cancer (LAPC).

MATERIALS AND METHODS

Eight patients with LAPC received five additional CBCTs on the ETHOS system before or after their standard of care radiotherapy treatment. Initial plans were created based on their initial simulation anatomy (P_I) and emulated adaptive plans were created based on their anatomy-of-the-day (P_A). The prescription was 50 Gy/5 fractions. Plans were created under a strict isotoxicity approach, in which organ-at-risk (OAR) constraints were prioritized over planning target volume coverage. The P_I was evaluated on the patient's anatomy-of-the-day, compared to the daily P_A, and the superior plan was selected. Feasibility was defined as successful completion of the workflow in compliance with strict OAR constraints in ≥80% of fractions.

RESULTS

CT-STAR was feasible in silico for LAPC and improved OAR and/or target dosimetry in 100% of fractions. Use of the P_I based on the patient's anatomy-of-the-day would have yielded a total of 94 OAR constraint violations and ≥1 hard constraint violation in 40/40 fractions. In contrast, 39/40 P_A met all OAR constraints. In one fraction, the P_A minimally exceeded the large bowel constraint, although dosimetrically improved compared to the P_I. Total workflow time per fraction was 36.28 minutes (27.57-55.86).

CONCLUSION

CT-STAR for the treatment of LAPC cancer proved feasible and was dosimetrically superior to non-adapted CT-stereotactic body radiotherapy.

Clinical Outcomes of Patients With Unresectable Primary Liver Cancer Treated With Yttrium-90 Radioembolization With an Escalated Dose

Purpose

Yttrium-90 (90Y) radioembolization with an escalated dose has been shown to improve clinical outcomes compared with standard dose radioembolization, but there are few data on the local control of primary liver tumors. We reported the clinical outcomes of patients with unresectable primary liver tumors treated with 90Y radioembolization with an escalated dose.

Methods and Materials

Clinical data of patients with unresectable hepatocellular carcinoma (HCC), cholangiocarcinoma (CC), and biphenotypic tumors (cHCC-CC) treated with radioembolization with an escalated dose (≥150 Gy) between 2013 and 2020 with >3 months follow-up were retrospectively reviewed. The primary endpoint was freedom from local progression. Clinical response was defined by Modified Response Evaluation Criteria in Solid Tumours and toxic effects were assessed using Common Terminology Criteria for Adverse Events version 5.0.

Results

Fifty-three patients with HCC and 15 patients with CC/cHCC-CC were analyzed. The median dose delivered was 205 Gy (interquartile range, 183-253 Gy) and 198 Gy (interquartile range, 154-234 Gy) for patients with HCC and CC/cHCC-CC, respectively. The 1-year freedom from local progression rate was 54% (95% confidence interval [CI], 38%-78%) for patients with HCC and 66% (95% CI, 42%-100%) for patients with CC/cHCC-CC. For patients with HCC, United Network for Organ Sharing nodal stage 1 (P = .01), nonsolitary tumors (P = .02), pretreatment α-fetoprotein of >7.7 ng/mL (P = .006), and ≤268 Gy dose delivered (P = .003) were predictors for local progression on multivariate Cox analysis. No patients with HCC who received a dose >268 Gy had a local tumor progression. The 1-year overall survival for patients with HCC was 74% (95% CI, 61%-89%). After radioembolization, 5 (7%) patients had grade 3 ascites, and 4 (6%) patients had grade 3/4 hyperbilirubinemia.

Conclusions

Treatment of unresectable primary liver tumors with 90Y radioembolization with an escalated dose was safe and well tolerated. Delivery of >268 Gy may improve local tumor control of HCC. Determination of the maximum tolerated dose needs to be performed in the context of future prospective dose-escalation trials to further evaluate the safety and efficacy of such an approach.

In Silico Trial of Computed Tomography-Guided Stereotactic Adaptive Radiotherapy (CT-STAR) for the Treatment of Abdominal Oligometastases

PURPOSE

We conducted a prospective, in silico clinical imaging study (NCTXXXX) to evaluate the feasibility of cone-beam computed tomography-guided stereotactic adaptive radiotherapy (CT-STAR) for the treatment of abdominal oligometastases. We hypothesized that CT-STAR produces improved dosimetry compared to non-adapted CT-stereotactic body radiotherapy (SBRT).

METHODS/MATERIALS

Eight patients receiving SBRT for abdominal oligometastatic disease received five additional kV cone beam CTs (CBCTs) on the ETHOS system. These additional CBCTs were used for imaging during an emulator treatment session. Initial plans were created based on their simulation (P_I) and emulated adaptive plans (P_A) were based on anatomy-of-the-day. The prescription was 50 Gy/5 fractions. Organ-at-risk (OAR) constraints were prioritized over planning target volume coverage under a strict isotoxicity approach. The P_I was applied to the patient's anatomy-of-the-day and compared to the re-optimized P_A using dose volume histogram metrics, with selection of the superior plan. Feasibility was defined as completion of the adaptive workflow and compliance with strict OAR constraints in ≥80% of fractions. Fractions were performed under time pressures by a physician and physicist to mimic the adaptive process.

RESULTS

CT-STAR was feasible, with successful workflow completion in 38/40 (95%) fractions. P_I application to daily anatomy created OAR constraint violations in 30/40 (75%) fractions. There were 8 stomach, 18 duodenum, 16 small bowel, and 11 large bowel P_I OAR constraint violations. In contrast, OAR violations occurred in 2/40 (5%) P_A (both small bowel violations, both improved from the P_I). CT-STAR also improved GTV V100 and D95 coverage in 25/40 (63%) and 20/40 (50%) fractions, respectively. 0/40 (0%) fractions were deemed non-feasible due to poor image quality and/or inability to delineate structures. Adaptation time per fraction was a median of 22.59 minutes (10.97-47.23).

CONCLUSIONS

CT-STAR resolved OAR hard constraint violations and/or improved target coverage in silico when compared to non-adapted CT-guided SBRT for the ablation of abdominal oligometastatic disease. While limitations of this study include its small sample size and in silico design, the consistently high quality CBCT images captured and comparable timing metrics to prior adaptive studies suggest that CT- STAR is a viable treatment paradigm for the ablation of abdominal oligometastatic disease. Clinical trials are in development to further evaluate CT-STAR in the clinic.

Breast cancer in young women in Guatemala: A retrospective comparative cohort study

e13523

Background: In Guatemala, breast cancer is the most common malignancy among women, the socioeconomic variability among the population directly affects the access to screening and treatment, and little is known about the behavior of the disease among younger women, reason why the aim of our study is to describe the clinico-pathological characteristics in this population. Methods: Retrospective study performed of patients with a confirmed biopsy of breast cancer that were treated at Liga Nacional Contra el Cáncer - INCAN in Guatemala, the largest cancer center in the country. From medical records, we obtained: clinico-pathological and treatment (surgery, radiotherapy, endocrine therapy) data and compared results between ≤40 years and >40 years old women. Results: The study identified 1,347 patients, 190 (16.42%) ≤40 years old women and 1,157 (83.57%) >40 years old. The mean age at diagnosis among patients was 36 vs. 56 years old, respectively (p<0.01). According to our findings, even though most patients came from the region I of the country that is the capital city, there was a higher percentage of patients from the West regions (VI, VII) that belonged to the younger group 22.22% vs 10.58%. Furthermore, 74.4% of ≤40 years old patients were staged as locally advanced or metastatic vs >40 year old patients (48.04%), and 65.34% of ≤40 years old were found to have triple negative and Her2 enriched subtypes vs 46.13% in >40 years old (p<0.01). Conclusions: Young breast cancer patients in Guatemala are characterized by being diagnosed at locally advanced and advanced stages of the disease with more biologically aggressive subtypes such as triple negative and her2 enriched. [Table: see text]

Techno-Economic Feasibility Analysis of a Fully Mobile Radiation Oncology System Using Monte Carlo Simulation

Disparities in radiation oncology (RO) can be attributed to geographic location, socioeconomic status, race, sex, and other societal factors. One potential solution is to implement a fully mobile (FM) RO system to bring radiotherapy to rural areas and reduce barriers to access. We use Monte Carlo simulation to quantify techno-economic feasibility with uncertainty, using two rural Missouri scenarios.

Cost-effectiveness of Total Neoadjuvant Therapy With Short-Course Radiotherapy for Resectable Locally Advanced Rectal Cancer

IMPORTANCE

Short-course radiotherapy and total neoadjuvant therapy (SCRT-TNT) followed by total mesorectal excision (TME) has emerged as a new treatment paradigm for patients with locally advanced rectal adenocarcinoma. However, the economic implication of this treatment strategy has not been compared with that of conventional long-course chemoradiotherapy (LCCRT) followed by TME with adjuvant chemotherapy.

OBJECTIVE

To perform a cost-effectiveness analysis of SCRT-TNT vs LCCRT in conjunction with TME for patients with locally advanced rectal cancer.

DESIGN, SETTING, AND PARTICIPANTS

A decision analytical model with a 5-year time horizon was constructed for patients with biopsy-proven, newly diagnosed, primary locally advanced rectal adenocarcinoma treated with SCRT-TNT or LCCRT. Markov modeling was used to model disease progression and patient survival after treatment in 3-month cycles. Data on probabilities and utilities were extracted from the literature. Costs were evaluated from the Medicare payer's perspective in 2020 US dollars. Sensitivity analyses were performed for key variables. Data were collected from October 3, 2020, to January 20, 2021, and analyzed from November 15, 2020, to April 25, 2021.

EXPOSURES

Two treatment strategies, SCRT-TNT vs LCCRT with adjuvant chemotherapy, were compared.

MAIN OUTCOMES AND MEASURES

Cost-effectiveness was evaluated using the incremental cost-effectiveness ratio and net monetary benefits. Effectiveness was defined as quality-adjusted life-years (QALYs). Both costs and QALYs were discounted at 3% annually. Willingness-to-pay threshold was set at $50 000/QALY.

RESULTS

During the 5-year horizon, the total cost was $41 355 and QALYs were 2.21 for SCRT-TNT; for LCCRT, the total cost was $54 827 and QALYs were 2.12, resulting in a negative incremental cost-effectiveness ratio (-$141 256.77). The net monetary benefit was $69 300 for SCRT-TNT and $51 060 for LCCRT. Sensitivity analyses using willingness to pay at $100 000/QALY and $150 000/QALY demonstrated the same conclusion.

CONCLUSIONS AND RELEVANCE

These findings suggest that SCRT-TNT followed by TME incurs lower cost and improved QALYs compared with conventional LCCRT followed by TME and adjuvant chemotherapy. These data offer further rationale to support SCRT-TNT as a novel cost-saving treatment paradigm in the management of locally advanced rectal cancer.

Long-Term Outcomes of NRG Oncology/RTOG 0529: A Phase 2 Evaluation of Dose-Painted Intensity Modulated Radiation Therapy in Combination With 5-Fluorouracil and Mitomycin-C for the Reduction of Acute Morbidity in Anal Canal Cancer

PURPOSE

A multi-institutional phase 2 trial assessed long-term outcomes of dose-painted intensity modulated radiation therapy (IMRT) with 5-fluorouracil (5FU) and mitomycin-C (MMC) for anal canal cancer.

METHODS AND MATERIALS

T2-4N0-3M0 anal cancers received 5FU (1000 mg/m²/d, 96-hour infusion) and MMC (10 mg/m² bolus) on days 1 and 29 of dose-painted IMRT prescribed as follows: T2N0 = 42 Gy elective nodal and 50.4 Gy anal tumor planning target volumes, 28 fractions; T3-4N0-3 = 45Gy elective nodal, 50.4 Gy ≤3 cm and 54 Gy >3cm metastatic nodal and 54 Gy anal tumor planning target volumes, 30 fractions. Local-regional failures, distant metastases, and colostomy failures were assessed using the cumulative incidence method, and disease-free survival, overall survival, and colostomy-free survival were assessed using the Kaplan-Meier method. Late effects were scored using National Cancer Institute-Common Terminology Criteria for Adverse Events v3.

RESULTS

Of 52 patients, 54% were stage II, 25% were stage IIIA, and 21% were stage IIIB. Median follow-up was 7.9 years (min-max, 0.02-9.2 years). Local-regional failure, colostomy failures, distant metastases, overall survival, disease-free survival, and colostomy-free survival at 5 years are 16% (95% confidence interval [CI], 7%-27%), 10% (95% CI, 4%-20%), 16% (95% CI, 7%-27%), 76% (95% CI, 61%-86%), 70% (95% CI, 56%-81%), and 74% (95% CI, 59%-84%); and at 8 years they are 16% (95% CI, 7%-27%), 12% (95% CI, 5%-23%), 22% (95% CI, 12%-34%), 68% (95% CI, 53%-79%), 62% (95% CI, 47%-74%) and 66% (95% CI, 51%-77%), respectively. Eight patients experienced local-regional failure, with 5 patients having persistent disease at 12 weeks. No isolated nodal failures occurred in the microscopic elective nodal volumes. Six patients required colostomy-5 for local-regional salvage and 1 for a temporary ostomy for anorectal dysfunction. Rates of late adverse events included: 28 patients (55%) with grade 2, 8 patients (16%) with grade 3, 0 patients with grade 4, and 2 patients (4%) with grade 5 events (sinus bradycardia and myelodysplasia, possibly owing to chemotherapy). Only 11 patients reported grade 1 to 3 sexual dysfunction.

CONCLUSIONS

Dose-painted IMRT with 5FU/MMC for the treatment of anal canal cancer yields comparable long-term efficacy as conventional radiation cohorts. Enhanced normal tissue protection lowered rates of grade 3 and higher late effects without compromising pelvic tumor control.

Clinical Complete Response in Patients With Rectal Adenocarcinoma Treated With Short-Course Radiation Therapy and Nonoperative Management

PURPOSE

This study aimed to determine the clinical efficacy and safety of nonoperative management (NOM) for patients with rectal cancer with a clinical complete response (cCR) after short-course radiation therapy and consolidation chemotherapy.

METHODS AND MATERIALS

Patients with stage I-III rectal adenocarcinoma underwent short-course radiation therapy followed by consolidation chemotherapy between January 2018 and May 2019 (n = 90). Clinical response was assessed by digital rectal examination, pelvic magnetic resonance imaging, and endoscopy. Of the patients with an evaluable initial response, those with a cCR (n = 43) underwent NOM, and those with a non-cCR (n = 43) underwent surgery. The clinical endpoints included local regrowth-free survival, regional control, distant metastasis-free survival, disease-free survival, and overall survival.

RESULTS

Compared with patients with an initial cCR, patients with initial non-cCR had more advanced T and N stage (P = .05), larger primary tumors (P = .002), and more circumferential resection margin involvement on diagnostic magnetic resonance imaging (P < .001). With a median follow-up of 30.1 months, the persistent cCR rate was 79% (30 of 38 patients) in the NOM cohort. The 2-year local regrowth-free survival was 81% (95% confidence interval [CI], 70%-94%) in the initial cCR group, and all patients with local regrowth were successfully salvaged. Compared with those with a non-cCR, patients with a cCR had improved 2-year regional control (98% [95% CI, 93%-100%] vs 85% [95% CI, 74%-97%], P = .02), distant metastasis-free survival (100% [95% CI, 100%-100%] vs 80% [95% CI, 69%-94%], P < .01), disease-free survival (98% [95% CI, 93%-100%] vs 71% [95% CI, 59%-87%], P < .01), and overall survival (100% [95% CI, 100%-100%] vs 88% [95% CI, 79%-98%], P = .02). No late grade 3+ gastrointestinal or genitourinary toxicities were observed in the patients who underwent continued NOM.

CONCLUSIONS

Short-course radiation therapy followed by consolidation chemotherapy may be a feasible organ preservation strategy in rectal cancer. Additional prospective studies are necessary to evaluate the safety and efficacy of this approach.

Implementing stereotactic accelerated partial breast irradiation using magnetic resonance guided radiation therapy

INTRODUCTION

Accelerated partial breast irradiation (APBI) seeks to reduce irradiated volumes and radiation exposure for patients while maintaining acceptable clinical outcomes. Magnetic resonance image-guided radiotherapy (MRgRT) provides excellent soft-tissue contrast for treatment localization, which can reduce setup uncertainty, thus reducing margins in the external beam setting. Additionally, stereotactic body radiotherapy (SBRT)-style regimens with high gradients can also be executed. This MR-guided stereotactic APBI (MRgS-APBI) approach can be utilized for a lower number of fractions and spare a greater volume of healthy tissues compared to conventional 3D external beam APBI.

METHODS

Our MRgS-APBI program was developed for two prospective non-randomized phase I/II clinical trials (20Gyx1 and 8.5Gyx3). Both breast SBRT treatment planning and MRgRT delivery techniques were described in this study. Simulation included both CT and MRI with specialized immobilization to accommodate MR-guided setup and cine-MRI treatment gating. Dosimetry data from 48 single-fraction and 19 three-fraction patients were collected and evaluated. This included planning objectives and SBRT-specific indices. During treatment, setup errors were calculated to evaluate setup reproducibility and duty cycle was calculated using cine-MRI data during gated delivery.

RESULTS

In both the single- and three- fraction trials combined, 88.5% of the possible dosimetric objectives across all patients were met during planning. The majority of the planning objectives were easily achievable indicating the potential for stricter objectives for subsequent S-APBI treatments. The average magnitude of setup uncertainties was 1.0 cm ± 0.6 cm across all treatments. In the three-fraction trial, the average beam-on duty-cycle for the MRI-gated delivery was 83.0 ± 13.0%. There were no technical MRgS-APBI related issues that resulted in discontinuation of treatment across all patients.

CONCLUSION

SBRT-style dosimetry and delivery for APBI is feasible using MR-guidance. The program development and dosimetric outcomes reported here can serve as a guide for other institutions considering the clinical implementation of MR-guided stereotactic APBI.

Phase I Trial of Stereotactic MRI-Guided Online Adaptive Radiation Therapy (SMART) for the Treatment of Oligometastatic Ovarian Cancer

PURPOSE

Stereotactic body radiation therapy is increasingly used to treat a variety of oligometastatic histologies, but few data exist for ovarian cancer. Ablative stereotactic body radiation therapy dosing is challenging in sites like the abdomen, pelvis, and central thorax due to proximity and motion of organs at risk. A novel radiation delivery method, stereotactic magnetic-resonance-guided online-adaptive radiation therapy (SMART), may improve the therapeutic index of stereotactic body radiation therapy through enhanced soft-tissue visualization, real-time nonionizing imaging, and ability to adapt to the anatomy-of-the-day, with the goal of producing systemic-therapy-free intervals. This phase I trial assessed feasibility, safety, and dosimetric advantage of SMART to treat ovarian oligometastases.

METHODS AND MATERIALS

Ten patients with recurrent oligometastatic ovarian cancer underwent SMART for oligometastasis ablation. Initial plans prescribed 35 Gy/5 fractions with goal 95% planning target volume coverage by 95% of prescription, with dose escalation permitted, subject to strict organ-at-risk dose constraints. Daily adaptive planning was used to protect organs-at-risk and/or increase target dose. Feasibility (successful delivery of >80% of fractions in the first on-table attempt) and safety of this approach was evaluated, in addition to efficacy, survival metrics, quality-of-life, prospective timing and dosimetric outcomes.

RESULTS

Ten women with seventeen ovarian oligometastases were treated with SMART, and 100% of treatment fractions were successfully delivered. Online adaptive plans were selected at time of treatment for 58% of fractions, due to initial plan violation of organs-at-risk constraints (84% of adapted fractions) or observed opportunity for planning target volume dose escalation (16% of adapted fractions), with a median on-table time of 64 minutes. A single Grade ≥3 acute (within 6 months of SMART) treatment-related toxicity (duodenal ulcer) was observed. Local control at 3 months was 94%; median progression-free survival was 10.9 months. Median Kaplan-Meier estimated systemic-therapy-free survival after radiation completion was 11.5 months, with concomitant quality-of-life improvements.

CONCLUSIONS

SMART is feasible and safe for high-dose radiation therapy ablation of ovarian oligometastases of the abdomen, pelvis, and central thorax with minimal toxicity, high rates of local control, and prolonged systemic-therapy-free survival translating into improved quality-of-life.

Nonoperative Rectal Cancer Management With Short-Course Radiation Followed by Chemotherapy: A Nonrandomized Control Trial

PURPOSE

Short-course radiation therapy (SCRT) and nonoperative management are emerging paradigms for rectal cancer treatment. This clinical trial is the first to evaluate SCRT followed by chemotherapy as a nonoperative treatment modality.

METHODS

Patients with nonmetastatic rectal adenocarcinoma were treated on the single-arm, Nonoperative Radiation Management of Adenocarcinoma of the Lower Rectum study of SCRT followed by chemotherapy. Patients received 25 Gy in 5 fractions to the pelvis followed by FOLFOX ×8 or CAPOX ×5 cycles. Patients with clinical complete response (cCR) underwent nonoperative surveillance. The primary end point was cCR at 1 year. Secondary end points included safety profile and anorectal function.

RESULTS

From June 2016 to March 2019, 19 patients were treated (21% stage I, 32% stage II, and 47% stage III disease). At a median follow-up of 27.7 months for living patients, the 1-year cCR rate was 68%. Eighteen of 19 patients are alive without evidence of disease. Patients with cCR versus without had improved 2-year disease-free survival (93% vs 67%; P = .006), distant metastasis-free survival (100% vs 67%; P = .03), and overall survival (100% vs 67%; P = .03). Involved versus uninvolved circumferential resection margin on magnetic resonance imaging was associated with less initial cCR (40% vs 93%; P = .04). Anorectal function by Functional Assessment of Cancer Therapy-Colorectal cancer score at 1 year was not different than baseline. There were no severe late effects.

CONCLUSIONS

Treatment with SCRT and chemotherapy resulted in high cCR rate, intact anorectal function, and no severe late effects. NCT02641691.

Sensible Introduction of MR-Guided Radiotherapy: A Warm Plea for the RCT

Magnetic resonance guided radiotherapy (MRgRT) is the newest face of technology within a field long-characterized by continual technologic advance. MRgRT may offer improvement in the therapeutic index of radiation by offering novel planning types, like online adaptation, and improved image guidance, but there is a paucity of randomized data or ongoing randomized controlled trials (RCTs) to demonstrate clinical gains. Strong clinical evidence is needed to confirm the theoretical advantages of MRgRT and for the rapid dissemination of (and reimbursement for) appropriate use. Although some future evidence for MRgRT may come from large registries and non-randomized studies, RCTs should make up the core of this future data, and should be undertaken with thoughtful preconception, endpoints that incorporate patient-reported outcomes, and warm collaboration across existing MRgRT platforms. The advance and future success of MRgRT hinges on collaborative pursuit of the RCT.

ctDNA MRD Detection and Personalized Oncogenomic Analysis in Oligometastatic Colorectal Cancer From Plasma and Urine

We hypothesized that circulating tumor DNA (ctDNA) molecular residual disease (MRD) analysis without prior mutational knowledge could be performed after neoadjuvant chemotherapy to assess oligometastatic colorectal cancer (CRC) treated surgically with curative intent. We also investigated urine as an alternative analyte for ctDNA MRD detection in this nongenitourinary setting.

PATIENTS AND METHODS

We applied AVENIO targeted next-generation sequencing to plasma, tumor, and urine samples acquired on the day of curative-intent surgery from 24 prospectively enrolled patients with oligometastatic CRC. Age-related clonal hematopoiesis was accounted for by removing variants also present in white blood cells. Plasma and urine ctDNA MRD were correlated with tumor cells detected in the surgical specimen, and adjuvant treatment strategies were proposed based on ctDNA-inferred tumor mutational burden (iTMB) and targetable alterations.

RESULTS

Seventy-one percent of patients were treated with neoadjuvant chemotherapy. Tumor-naive plasma ctDNA analysis detected MRD at a median level of 0.62% with 95% sensitivity and 100% specificity, and 94% and 77% sensitivity when only considering patients treated with neoadjuvant chemotherapy and putative driver mutations, respectively. In urine, ctDNA MRD detection specificity remained high at 100%, but sensitivity decreased to 64% with median levels being 11-fold lower than in plasma (P < .0001). Personalized ctDNA MRD oncogenomic analysis revealed 81% of patients might have been candidates for adjuvant immunotherapy based on high iTMB or targeted therapy based on actionable PIK3CA mutations.

CONCLUSION

Tumor-naive plasma ctDNA analysis can sensitively and specifically detect MRD in patients with oligometastatic CRC after neoadjuvant chemotherapy. Urine-based ctDNA MRD detection is also feasible; however, it is less sensitive than plasma because of significantly lower levels. Oligometastatic patients with detectable MRD may benefit from additional personalized treatment based on ctDNA-derived oncogenomic profiling.

Evaluation of the Metastatic Spine Disease Multidisciplinary Working Group Algorithms as Part of a Multidisciplinary Spine Tumor Conference

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

The Metastatic Spine Disease Multidisciplinary Working Group Algorithms are evidence and expert opinion-based strategies for utilizing radiation therapy, interventional radiology procedures, and surgery to treat 5 types of spine metastases: asymptomatic spinal metastases, uncomplicated spinal metastases, stable vertebral compression fractures (VCF), unstable VCF, and metastatic epidural spinal cord compression (MESCC). Evaluation of this set of algorithms in a clinical setting is lacking. The authors aimed to identify rate of treatment adherence to the Working Group Algorithms and, subsequently, update these algorithms based on actual patient management decisions made at a single-institution, multidisciplinary, spine tumor conference.

METHODS

Patients with metastatic spine disease from primary non-hematologic malignancies discussed at an institutional spine tumor conference from 2013 to 2016 were evaluated. Rates of Working Group Algorithms adherence were calculated for each type of metastasis. Based on the reasons for algorithm nonadherence, and patient outcomes in such cases, updated Working Group Algorithms recommendations were proposed.

RESULTS

In total, 154 eligible patients with 171 spine metastases were evaluated. Rates of algorithm adherence were as follows: asymptomatic (67%), uncomplicated (73%), stable VCF (20%), unstable VCF (32%), and MESCC (41%). The most common deviation from the Working Group Algorithms was surgery for MESCC despite poor prognostic factors, but this treatment strategy was supported based on median survival surpassing 6 months in these patients.

CONCLUSIONS

Adherence to the Working Group Algorithm was lowest for MESCC and VCF patients, but many nonadherent treatments were supported by patient survival outcomes. We proposed updates to the Working Group Algorithm based on these findings.

Implementing a Novel Remote Physician Treatment Coverage Practice for Adaptive Radiation Therapy During the Coronavirus Pandemic

PURPOSE

The 2019 coronavirus disease pandemic has placed an increased importance on physical distancing to minimize the risk of transmission in radiation oncology departments. The pandemic has also increased the use of hypofractionated treatment schedules where magnetic resonance-guided online adaptive radiation therapy (ART) can aid in dose escalation. This specialized technique requires increased staffing in close proximity, and thus the need for novel coverage practices to increase physical distancing while still providing specialty care.

METHODS AND MATERIALS

A remote-physician ART coverage practice was developed and described using commercially available software products. Our remote-physician coverage practice provided control to the physician to contour and review of the images and plans. The time from completion of image registration to the beginning of treatment was recorded for 20 fractions before remote-physician ART coverage and 14 fractions after implementation of remote-physician ART coverage. Visual quality was calculated using cross-correlation between the treatment delivery and remote-physician computer screens.

RESULTS

For the 14 fractions after implementation, the average time from image registration to the beginning of treatment was 24.9 ± 6.1 minutes. In comparison, the 20 fractions analyzed without remote coverage had an average time of 29.2 ± 9.8 minutes. The correlation between the console and remote-physician screens was R = .95.

CONCLUSIONS

Our novel remote-physician ART coverage practice is secure, interactive, timely, and of high visual quality. When using remote physicians for ART, our department was able to increase physical distancing to lower the risk of virus transmission while providing specialty care to patients in need.

Implementation of a Novel Remote Physician Stereotactic Body Radiation Therapy Coverage Process during the Coronavirus Pandemic

PURPOSE

During the coronavirus 2019 disease (COVID-19) pandemic, alternative methods of care are needed to reduce the relative risk of transmission in departments. Also needed is the ability to provide vital radiation oncological care if radiation oncologists (RO) are reallocated to other departments. We implemented a novel remote RO stereotactic body radiation therapy (SBRT) coverage practice, requiring it to be reliable, of high audio and visual quality, timely, and the same level of specialty care as our current in-person treatment coverage practice.

METHODS AND MATERIALS

All observed failure modes were recorded during implementation over the first 15 sequential fractions. The time from cone beam computed tomography to treatment was calculated before and after implementation to determine timeliness of remote coverage. Image quality metrics were calculated between the imaging console screen and the RO's shared screen. Comfort levels with audio and visual communication as well as overall comfort in comparison to in-person RO coverage was evaluated using Likert scale surveys after treatment.

RESULTS

Remote RO SBRT coverage was successfully implemented in 14 of 15 fractions with 3 observed process failures that were all corrected before treatment. Average times of pretreatment coverage before and after implementation were 8.74 and 8.51 minutes, respectively. The cross correlation between the imaging console screen and RO's shared screen was r = 0.96 and lag was 0.05 seconds. The average value for all survey questions was more than 4.5, approaching in-person RO coverage comfort levels.

CONCLUSION

Our novel method of remote RO SBRT coverage permits reduced personnel and patient interactions surrounding radiation therapy procedures. This may help to reduce transmission of COVID-19 in our department and provides a means for SBRT coverage if ROs are reallocated to other areas of the hospital for COVID-19 support.

Eliminating Postoperative Radiation to the Pathologically Node-Negative Neck: Long-Term Results of a Prospective Phase II Study

PURPOSE

The volume treated with postoperative radiation therapy (PORT) is a mediator of toxicity, and reduced volumes result in improved quality of life (QOL). In this phase II trial, treatment volumes were reduced by omitting PORT to the pathologically negative (PN0) neck in patients with primary head and neck squamous cell carcinoma.

METHODS

Patients with head and neck squamous cell carcinoma who underwent surgical resection and neck dissection with a PN0 neck and high-risk features mandating PORT to the primary and/or involved neck were eligible. The primary end point was greater than 90% disease control in the unirradiated neck. QOL was evaluated using the MD Anderson Dysphagia Inventory and the University of Michigan patient-reported xerostomia questionnaire.

RESULTS

Seventy-three patients were enrolled, and 72 were evaluable. Median age was 56 years (range, 31 to 81 years); 58 patients were male, and 47 (65%) had a smoking history. Sites included oral cavity (n = 14), oropharynx (n = 37), hypopharynx (n = 4), larynx (n = 16), and unknown primary tumor (n = 1). According to the American Joint Committee on Cancer Staging Manual (7^th edition), 67 patients (93%) had stage III/IV disease, and 71% of tumors involved or crossed midline. No patient had contralateral neck PORT. In 17 patients (24%), only the primary site was treated. At a median follow-up of 53 months, two patients experienced treatment failure of the PN0 unirradiated neck; they also experienced treatment failure locally. Unirradiated neck control was 97% (95% CI, 93.4% to 100.0%). Five-year rates of local control, regional control, progression-free survival, and overall survival were 84%, 93%, 60%, and 64%, respectively. QOL measures were not significantly different from baseline at 12 and 24 months post-PORT (P > .05).

CONCLUSION

Eliminating PORT to the PN0 neck resulted in excellent control rates in the unirradiated neck without long-term adverse effects on global QOL.

Practical Clinical Workflows for Online and Offline Adaptive Radiation Therapy

Adaptive radiotherapy emerged over 20 years ago and is now an established clinical practice in a number of organ sites. No one solution for adaptive therapy exists. Rather, adaptive radiotherapy is a process which combines multiple tools for imaging, assessment of need for adaptation, treatment planning, and quality assurance of this process. Workflow is therefore a critical aspect to ensure safe, effective, and efficient implementation of adaptive radiotherapy. In this work, we discuss the tools for online and offline adaptive radiotherapy and introduce workflow concepts for these types of adaptive radiotherapy. Common themes and differences between the workflows are introduced and controversies and areas of active research are discussed.

Characterization of a prototype rapid kilovoltage x-ray image guidance system designed for a ring shape radiation therapy unit

PURPOSE

This study aims to characterize the performance of a prototype rapid kilovoltage (kV) x-ray image guidance system onboard the newly released Halcyon 2.0 linear accelerator (Varian Medical Systems, Palo Alto, CA) by use of conventional and innovatively designed testing procedures.

METHODS

Basic imaging system performance tests and radiation dose measurements were performed for all eleven kV-cone beam computed tomography (CBCT) imaging protocols available on a preclinical Halcyon 2.0 LINAC. Both conventional CBCT reconstruction using the Feldkamp-Davis-Kress (FDK) algorithm and a novel, advanced iterative reconstruction (iCBCT) available on this platform were evaluated. Standard image quality metrics, including slice thickness accuracy, high-contrast resolution, low-contrast resolution, regional uniformity and noise, and CT Hounsfield unit (HU) number accuracy and linearity were evaluated using a manufacturer-supplied QUART phantom (GmbH, Zorneding, Germany) and an independent image quality phantom (Catphan 500, The Phantom Laboratory, New York, NY). Due to the simplified design of the QUART phantom, we developed surrogate and clinically feasible strategies for measuring slice thickness and high- and low-contrast resolution. Imaging dose delivered by these eleven protocols was measured using a computed tomography dose index phantom and pencil chamber with commonly accepted methods and procedures. A subset of measurements were repeated on a conventional C-arm LINAC (TrueBeam and Trilogy, Varian Medical System) for comparison. Clinical patient images of pelvic and abdominal regions are also presented for qualitative assessment as part of a feasibility study for clinical implementation.

RESULTS

Image acquisition time was 17-42 s on the Halcyon system compared with 60 s on the C-arm LINAC systems. The kV imager projection offset, imaging and treatment isocenter coincidence and the couch three-dimensional match movement all achieved less than1 mm mechanical accuracy. All major image quality metrics were within either the national guideline or vendor-recommended tolerances. The designed surrogate approach with the QUART phantom showed a range of 0.24-0.35 cycles/mm for spatial resolution, a contrast-to-noise ratio (CNR) of 2-20 for FDK reconstruction and a tolerance of 0.5 mm for slice thickness. Other metrics derived from the Catphan images obtained on the Halcyon and C-arm LINACs showed comparable values for the FDK reconstruction. The iterative reconstruction tended to reduce noise, as evidenced by a higher CNR ratio. The fast scan pelvis protocols for Halcyon resulted in 50% lower dose compared to the standard scans, and the thorax fast protocol similarly delivered 10% lower dose than the standard thoracic scan. Preliminary patient images indicated that rapid kV CBCT with breath-hold is feasible, with improved imaging quality compared to free-breathing scans.

CONCLUSION

Independent and comprehensive characterization of the kV imaging guidance system on the Halcyon 2.0 system demonstrated acceptable image quality for clinical use. The imaging unit onboard the Halcyon meets vendor specifications and satisfies requirements for routine clinical use. The fast kV imaging system enables the potential for volumetric CBCT acquisition during a single breath-hold and the iterative reconstruction tends to reduce the noise therefore has the potential to improve the CNR for normal size patient.

Feasibility and safety assessment of magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU)-mediated mild hyperthermia in pelvic targets evaluated using an in vivo porcine model

Purpose: To evaluate the feasibility and assess safety parameters of magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU)-mediated hyperthermia (HT; heating to 40-45 °C) in various pelvic targets in a porcine model in vivo.Methods: Thirteen HT treatments were performed in six pigs with a commercial MRgHIFU system (Sonalleve V2, Profound Medical Inc., Mississauga, Canada) to muscle adjacent to the ventral/dorsal bladder wall and uterus to administer 42 °C (±1°) for 30 min (±5%) using an 18-mm target diameter and 100 W power. Feasibility was assessed using accuracy, uniformity, and MR-thermometry performance-based metrics. Safety parameters were assessed for tissues in the targets and beam-path by contrast-enhanced MRI, gross-pathology and histopathology.Results: Across all HT sessions, the mean difference between average temperature (Tavg) and the target temperature within the target region-of-interest (tROI, the cross-section of the heated volume at focal depth) was 0.51 ± 0.33 °C. Within the tROI, the temperature standard deviation averaged 1.55 ± 0.31 °C, the average 30-min Tavg variation was 0.80 ± 0.17 °C, and the maximum difference between Tavg and the 10th- or 90th-percentile temperature averaged 2.01 ± 0.44 °C. The average time to reach ≥41 °C and cool to ≤40 °C within the tROI at the beginning and end of treatment was 47.25 ± 27.47 s and 66.37 ± 62.68 s, respectively. Compared to unheated controls, no abnormally-perfused tissue or permanent damage was evident in the MR images, gross pathology or histological analysis.Conclusions: MRgHIFU-mediated HT is feasible and safety assessment is satisfactory for treating an array of clinically-mimicking pelvic geometries in a porcine model in vivo, implying the technique may have utility in treating pelvic targets in human patients.

Long-term outcomes of follicular variant vs classic papillary thyroid carcinoma

The majority of papillary thyroid carcinoma (PTC) cases comprise classic papillary (C-PTC) and follicular variant (FV-PTC) histologic sub-types. Historically, clinical equivalency was assumed, but recent data suggest C-PTC may have poorer outcomes. However, large single-institution series with long-term outcomes of C-PTC and FV-PTC, using modern pathologic criteria for FV-PTC, are needed. Our objective was to compare prevalence and impact of clinicopathologic factors, including BRAF mutation status, on long-term outcomes of C-PTC and FV-PTC. We hypothesized that patients with C-PTC would have higher risk disease features and worse survival outcomes. This retrospective study included 1293 patients treated at a single, US academic institution between 1943 and 2009 with mean follow-up of 8.6 years. All patients underwent either partial or total thyroidectomy and had invasive C-PTC or FV-PTC per modern pathology criteria. Primary study measurements included differences in recurrence-free survival (RFS), disease-specific survival (DSS) and associations with clinicopathologic factors including the BRAF mutation. Compared to FV-PTC, C-PTC was associated with multiple features of high-risk disease (P < 0.05) and significantly reduced RFS and DSS. Survival differences were consistent across univariate, multivariate and Kaplan-Meier analyses. BRAF mutations were more common in C-PTC (P = 0.002). However, on Kaplan-Meier analysis, mutational status did not significantly impact RFS or DSS for patients with either histologic sub-type. C-PTC therefore indicates higher-risk disease and predicts for significantly poorer long-term outcomes when compared to FV-PTC. The nature of this difference in outcome is not explained by traditional histopathologic findings or by the BRAF mutation.

Magnetic Resonance Image-Guided Radiotherapy (MRIgRT): A 4.5-Year Clinical Experience

AIMS

Magnetic resonance image-guided radiotherapy (MRIgRT) has been clinically implemented since 2014. This technology offers improved soft-tissue visualisation, daily imaging, and intra-fraction real-time imaging without added radiation exposure, and the opportunity for adaptive radiotherapy (ART) to adjust for anatomical changes. Here we share the longest single-institution experience with MRIgRT, focusing on trends and changes in use over the past 4.5 years.

MATERIALS AND METHODS

We analysed clinical information, including patient demographics, treatment dates, disease sites, dose/fractionation, and clinical trial enrolment for all patients treated at our institution using MRIgRT on a commercially available, integrated 0.35 T MRI, tri-cobalt-60 device from 2014 to 2018. For each patient, factors including disease site, clinical rationale for MRIgRT use, use of ART, and proportion of fractions adapted were summated and compared between individual years of use (2014-2018) to identify shifts in institutional practice patterns.

RESULTS

Six hundred and forty-two patients were treated with 666 unique treatment courses using MRIgRT at our institution between 2014 and 2018. Breast cancer was the most common disease, with use of cine MRI gating being a particularly important indication, followed by abdominal sites, where the need for cine gating and use of ART drove MRIgRT use. One hundred and ninety patients were treated using ART in 1550 fractions, 67.6% (1050) of which were adapted. ART was primarily used in cancers of the abdomen. Over time, breast and gastrointestinal cancers became increasingly dominant for MRIgRT use, hypofractionated treatment courses became more popular, and gastrointestinal cancers became the principal focus of ART.

DISCUSSION

MRIgRT is widely applicable within the field of radiation oncology and new clinical uses continue to emerge. At our institution to date, applications such as ART for gastrointestinal cancers and accelerated partial breast irradiation (APBI) for breast cancer have become dominant indications, although this is likely to continue to evolve.