Magnetic resonance imaging organ at risk delineation for nasopharyngeal radiotherapy: Measuring the effectiveness of an educational intervention.

INTRODUCTION: Magnetic resonance imaging (MRI) demonstrates superior soft tissue contrast and is increasingly being used in radiotherapy planning. This study evaluated the impact of an education workshop in minimising inter-observer variation (IOV) for nasopharyngeal organs at risk (OAR) delineation on MRI. METHODS: Ten observers delineated 14 OARs on 4 retrospective nasopharyngeal MRI data sets. Standard contouring guidelines were provided pre-workshop. Following an education workshop on MRI OAR delineation, observers blinded to their original contours repeated the 14 OAR delineations. For comparison, reference volumes were delineated by two head and neck radiation oncologists. IOV was evaluated using dice similarity coefficient (DSC), Hausdorff distance (HD) and relative volume. Location of largest deviations was evaluated with centroid values. Observer confidence pre- and post-workshop was also recorded using a 6-point Likert scale. The workshop was deemed beneficial for an OAR if ≥50% of observers mean scores improved in any metric and ≥50% of observers' confidence improved. RESULTS: All OARs had ≥50% of observers improve in at least one metric. Base of tongue, larynx, spinal cord and right temporal lobe were the only OARs achieving a mean DSC score of ≥0.7. Base of tongue, left and right lacrimal glands, larynx, left optic nerve and right parotid gland all exhibited statistically significant HD improvements post-workshop (P < 0.05). Brainstem and left and right temporal lobes all had statistically significant relative volume improvements post-workshop (P < 0.05). Post-workshop observer confidence improvement was observed for all OARs (P < 0.001). CONCLUSIONS: The educational workshop reduced IOV and improved observers' confidence when delineating nasopharyngeal OARs on MRI.

Early outcomes of abbreviated multi-fractionated brachytherapy schedule for cervix cancer during COVID-19 pandemic.

PURPOSE: Brachytherapy (BT) for cervix cancer was listed as a level I priority and reduced number of implants and multiple fractions were recommended during COVID-19 pandemic. We present early clinical outcome of this approach. METHODS AND MATERIALS: Patients treated with (chemo)radiotherapy and BT with single implant and multiple fractions BT were included. Treatment protocol included 3-5 fractions of 5-8.5 Gy with an aim to achieve point A dose of 70 Gy EQD210Gy (or HRCTV dose of >80 Gy EQD210Gy) in those undergoing intracavitary (IC) and HRCTV dose >85 Gy EQD2 10Gy in patients undergoing Intracavitary-Interstitial (IC/IS) whereas maintaining bladder (B2cc), rectum (R2cc), sigmoid (S 2cc) doses of 90, 75, and 75 Gy EQD23Gy. Time to event analysis was used to report oncological endpoints. Toxicity was reported using crude proportions. RESULTS: From April 2020 to March, 2021, 64 patients with stage IB2-IV received single implant and multi-fraction BT after external radiation of 45 Gy/25 fractions/5 weeks. Only 76.7% (n = 49) received concurrent chemotherapy. Median overall treatment time (OTT) was 56 days (38-131 days). Overall, 62.5% (n = 40) patients received IC and 37.5% (n = 24) received IC+IS. The median HRCTV was 34.7 cc (IQR 25-41). Median (IQR) point A dose, HRCTV D90, B2cc, R2cc, and S2cc for those undergoing IC was 74 Gy (71-78), 80 Gy (73-84), 86 Gy (82-89), 70 Gy (65-74), 65 Gy (59-73) respectively. For the IC+IS cohort, HRCTV D90, B2cc, R2cc, and S2cc was 84 Gy (78-89 Gy), 89 Gy (86-92), 70 Gy (67-74), 68 Gy (59-76). At a median follow-up of 16 months (5-27) the 2-year local control, pelvic control, cause specific and overall survival was 88%, 85.3%, 92.2%, and 81.3% respectively. Late gastrointestinal and genitourinary grade ≥III toxicities were 14% and 1.5% each. CONCLUSIONS: Abbreviated BT outcomes are encouraging for oncological outcomes despite delays in overall treatment time and omission of chemotherapy. Further mature follow up is needed.

Comparing dosimetry of locally advanced cervical cancer patients treated with 3 versus 4 fractions of MRI-guided brachytherapy.

PURPOSE: To demonstrate the feasibility of treating cervical cancer patients with MRI-guided brachytherapy (MRgBT) using 24 Gy in 3 fractions (F) versus a standard, more resource-intensive regimen of 28 Gy in 4F, and its ability to meet EMBRACE II planning aims. METHODS AND MATERIALS: A retrospective review of 224 patients with FIGO Stage IB-IVA cervical cancer treated with 28 Gy/4F (n = 91) and 24 Gy/3F (n = 133) MRgBT between 2016-2021 was conducted. Multivariable linear regression models were fitted to compare dosimetric parameters between the two groups, adjusting for CTVHR and T stage. RESULTS: Most patients had squamous cell carcinoma, T2b disease, and were treated with intracavitary applicator plus interstitial needles (96%). The 28 Gy/4F group had higher CTVHR (median 28 vs. 26 cm3, p = 0.04), CTVIR D98% (mean 65.5 vs. 64.5 Gy, p = 0.03), rectum D2cm3 (mean 61.7 vs. 59.2 Gy, p = 0.04) and bladder D2cm3 (81.3 vs. 77.9 Gy, p = 0.03). There were no significant differences in the proportion of patients meeting the EMBRACE II OAR dose constraints and planning aims, except fewer patients treated with 28 Gy/4F met rectum D2cm3 < 65 Gy (73 vs. 85%, p = 0.027) and ICRU rectovaginal point < 65 Gy (65 vs. 84%, p = 0.005). CONCLUSIONS: Cervical cancer patients treated with 24 Gy/3F MRgBT had comparable target doses and lower OAR doses compared to those treated with 28 Gy/4F. A less-resource intense fractionation schedule of 24 Gy/3F is an alternative to 28 Gy/4F in cervix MRgBT.

Functional brain imaging interventions for radiation therapy planning in patients with glioblastoma: a systematic review.

RATIONALE: This systematic review aims to synthesise the outcomes of different strategies of incorporating functional biological markers in the radiation therapy plans of patients with glioblastoma to support clinicians and further research. METHODS: The systematic review protocol was registered on PROSPERO (CRD42021221021). A structured search for publications was performed following PRISMA guidelines. Quality assessment was performed using the Newcastle-Ottawa Scale. Study characteristics, intervention methodology and outcomes were extracted using Covidence. Data analysis focused on radiation therapy target volumes, toxicity, dose distributions, recurrence and survival mapped to functional image-guided radiotherapy interventions. RESULTS: There were 5733 citations screened, with 53 citations (n = 32 studies) meeting review criteria. Studies compared standard radiation therapy planning volumes with functional image-derived volumes (n = 20 studies), treated radiation therapy volumes with recurrences (n = 15 studies), the impact on current standard target delineations (n = 9 studies), treated functional volumes and survival (n = 8 studies), functionally guided dose escalation (n = 8 studies), radiomics (n = 4 studies) and optimal organ at risk sparing (n = 3 studies). The approaches to target outlining and dose escalation were heterogeneous. The analysis indicated an improvement in median overall survival of over two months compared with a historical control group. Simultaneous-integrated-boost dose escalation of 72-76 Gy in 30 fractions appeared to have an acceptable toxicity profile when delivered with inverse planning to a volume smaller than 100 cm[Formula: see text]. CONCLUSION: There was significant heterogeneity between the approaches taken by different study groups when implementing functional image-guided radiotherapy. It is recommended that functional imaging data be incorporated into the gross tumour volume with appropriate technology-specific margins used to create the clinical target volume when designing radiation therapy plans for patients with glioblastoma.

Medical dosimetry virtual clinical education: Mentors' perspectives.

The COVID-19 pandemic affected the United States in early 2020, and many universities began offering their curriculum remotely. The majority of medical dosimetry programs started to offer both didactic and clinical education in a virtual setting. With COVID-19 social distancing and patient protective measures, many clinical medical dosimetrists also began to work in a remote or hybrid setting. Medical dosimetry students interact and learn from their clinical mentors in this remote clinical environment. The purpose of this study was to investigate the perspective of medical dosimetry mentors concerning the effectiveness of virtual clinical education for medical dosimetry students as a result of COVID-19. The Medical Dosimetry Mentor Perspective on Virtual Clinical Education (MedDos_VCE) survey measured medical dosimetry mentors' perceptions of the students' virtual clinical experience during the COVID-19 pandemic. The subject of the study was medical dosimetry mentors who participated in a remote clinic due to the COVID-19 pandemic since March 2020. The MedDos_VCE questionnaire measured (1) the mentors' assessment of instructional quality in remote clinical education; (2) opportunities for and quality of interaction between students and medical dosimetry mentors; and (3) suggestions for success from medical dosimetry mentors for students and other mentors who are participating in virtual clinical education. The majority of the clinical mentors were satisfied with the quality of virtual clinical education and students' learning outcomes. They felt that students experienced a good mix of patients, problems, and clinical experience and engaged in the day-to-day activities of a medical dosimetrist. Challenges exist and mentors offered practical suggestions for success for students and mentors in the virtual clinical environment.

Perceptions of burnout in medical dosimetry within a postpandemic work environment.

According to the World Health Organization, burnout is described as having a negative attitude regarding one's work and being exhausted. Previous studies have shown that occupational burnout exists amongst medical dosimetrists, however, the incidence of medical dosimetrist burnout before and after a pandemic warrant continued research. Medical dosimetrists could be experiencing increased burnout in the workplace postpandemic due to staffing shortages and increased remote planning, which may reduce work performance. The researchers utilized a survey to answer research questions regarding whether staffing shortages or remote planning influenced perceived occupational burnout among medical dosimetrists in a post COVID-19 pandemic environment. The survey was intended to assess levels of emotional exhaustion (EE), depersonalization (DP) and personal accomplishment (PA). It was distributed electronically to 2591 certified medical dosimetrists in the United States through the American Association of Medical Dosimetrists (AAMD) membership database. A total of 160 responses were recorded, resulting in a response rate of 6% (160/2591). The results of this study indicated that increased staffing shortages have a direct relationship with increased burnout incidence. Increased remote work appears to be inversely related to the incidence of burnout among medical dosimetrists.

Low-dose radiotherapy to the lungs using an interventional radiology C-arm fluoroscope: Monte Carlo treatment planning and dose measurements in a postmortem subject.

Objective.The goal of this study was to use Monte Carlo (MC) simulations and measurements to investigate the dosimetric suitability of an interventional radiology (IR) c-arm fluoroscope to deliver low-dose radiotherapy to the lungs.Approach.A previously-validated MC model of an IR fluoroscope was used to calculate the dose distributions in a COVID-19-infected patient, 20 non-infected patients of varying sizes, and a postmortem subject. Dose distributions for PA, AP/PA, 3-field and 4-field treatments irradiating 95% of the lungs to a 0.5 Gy dose were calculated. An algorithm was created to calculate skin entrance dose as a function of patient thickness for treatment planning purposes. Treatments were experimentally validated in a postmortem subject by using implanted dosimeters to capture organ doses.Main results.Mean doses to the left/right lungs for the COVID-19 CT data were 1.2/1.3 Gy, 0.8/0.9 Gy, 0.8/0.8 Gy and 0.6/0.6 Gy for the PA, AP/PA, 3-field, and 4-field configurations, respectively. Skin dose toxicity was the highest probability for the PA and lowest for the 4-field configuration. Dose to the heart slightly exceeded the ICRP tolerance; all other organ doses were below published tolerances. The AP/PA configuration provided the best fit for entrance skin dose as a function of patient thickness (R2 = 0.8). The average dose difference between simulation and measurement in the postmortem subject was 5%.Significance.An IR fluoroscope should be capable of delivering low-dose radiotherapy to the lungs with tolerable collateral dose to nearby organs.

The dosimetric advantages of perirectal hydrogel spacer in men with localized prostate cancer undergoing stereotactic ablative radiotherapy (SABR).

To evaluate the dosimetric differences for patients receiving a perirectal hydrogel spacer (PR-HS) using SpaceOAR undergoing stereotactic ablative radiotherapy (SABR) for localized prostate cancer with the CyberKnife VSI system. Gold fiducial markers and a PR-HS was inserted in 22 consecutive patients with histologically confirmed localized prostate cancer. For planning comparison, dosimetry from the clinical plans was compared against replans based on a simulated rectum volume designed to recreate a clinically appropriate spacer-less anatomy for each patient. Both sets were planned to 36.25 Gy in 5 fractions using the treatment planning system associated with the CyberKnife VSI system. The aim was to ensure equivalent target coverage for both plans and to evaluate doses to the organs-at-risk (OARs): rectum, bladder and penile bulb. The median PR-HS implant volume was 11.2 cc (range 8.8 to 14.9 cc). The maximal median perirectal separation was 15.5 mm (10.5 to 20.7 mm). Statistically significant reductions were noted for the 3 OARs, with no statistically significant difference in planning target volumes or clinical target volume coverage. All rectal dose constraints were significantly improved in the PR-HS plans with a percentage dose difference of at least 24% (rectum V18.1Gy (%)) to 60.5% (rectum V36Gy (cc)). The bladder and penile bulb dose constraints parameters were also significantly improved: the bladder V37Gy was reduced by 17.1%, V18.1Gy was reduced by 4.2%; the penile bulb D50% was reduced by 7.7%. The use of PR-HS was able to significantly reduce planned dose to the rectum, bladder and penile bulb with SABR techniques associated with the CyberKnife VSI system.

Analyzing changes in radiotherapy treatment planning error reporting during the COVID-19 pandemic.

The 2019 coronavirus (COVID-19) pandemic has affected medical physics and radiation oncology departments and the delivery of radiation therapy. Among the changes implemented in response to the onset of the pandemic was a shift to remote treatment planning by health care institutions. The purpose of this study was to determine whether the overall frequency of errors changed after the implementation of remote radiation therapy treatment planning during the COVID-19 pandemic. Reported incidents were obtained from an incident reporting database operated by a multisite cancer care facility in the Northeast. Researchers compared the frequency of reported events in a period prior to the start of the pandemic (March 2019 to February 2020) with a period after the onset of the pandemic (March 2020 to February 2021). No significant increase in reported incidents was detected suggesting the efficiency and safety of remote radiotherapy treatment planning.

Improvement in bladder volume reproducibility using A-mode portable ultrasound bladder scanner in moderate-hypofractionated volumetric modulated arc therapy for prostate cancer patients.

PURPOSE: This study introduced an A-mode portable ultrasound bladder scanner, the Lilium® α-200 (here after Lilium; Lilium Otsuka, Kanagawa, Japan), for the treatment of prostate cancer patients with hypofractionated volumetric modulated arc therapy to improve the reproducibility of bladder volume (BV). MATERIALS AND METHODS: Thirty patients were advised to maintain full BV prior to computed tomography (CT) simulation and daily treatment. Among these, the BV of 15 patients was measured using Lilium until a BV of 80% in the simulation was achieved (with the Lilium group). Daily cone-beam CT (CBCT) was performed for treatment. The correlation between BV measured by CBCT and Lilium was assessed. The differences in the BV and dosimetric parameters of the bladder in the CBCT versus planning CT were compared between the groups with and without Lilium. RESULTS: There was a significantly strong relationship (r = 0.796, p < 0.05) between the BVs measured using CBCT and Lilium. The relative BV ratios to simulation CT < 0.5 and > 2 were observed in 10.3% and 12.7%, respectively, of treatment sessions without Lilium group, while these ratios were 1% and 2.8%, respectively, in the Lilium group. The mean absolute difference in the range of V30Gy to V40Gy without Lilium sessions was significantly larger (p < 0.05) than that in the Lilium group. CONCLUSION: The use of the A-mode portable ultrasound bladder scanner significantly improved the reproducibility of the BV, resulting in few variations in the dosimetric parameters for the bladder.

A retrospective analysis comparing set up errors from standard versus customised headrests for head and neck radiotherapy.

INTRODUCTION: In response to advice from The National Institute for Health and Care Excellence (1) to reduce hospital visits during COVID-19, standard headrests were introduced for head and neck radiotherapy within Northern Centre for Cancer Care (NCCC). The standard headrest requires one mould room appointment compared to 3 appointments with customised headrests. METHODS: Two groups of 10 patients treated between December 2019 and June 2020 were retrospectively analysed by 1 observer. Groups were stratified according to age, sex and tumour site. One group had customised headrest and the other had standard headrest. Five hundred and forty seven cone beam computed tomography images were reviewed. A 6 Degree of Freedom match was performed then chin, shoulder and spine position were assessed using dosimetrist drawn structures. Structures out of the tolerance were recorded. A chi-squared test was used for statistical analysis. RESULTS: The out of tolerance chin position count recorded was 21 for customised headrest and 36 for standard headrest, p-value 0.046. The shoulder position count was 13 for customised headrest and 77 for standard headrest p-value <0.001. The spine position count was 3 for CHR and 21 for standard headrest, p-value <0.001. This means the headrests compared are not equivalent in terms of set up reproducibility. Overall the standard headrest group had 10 set-up re-scans and no set up re-scans were recorded in the customised headrest group. CONCLUSION: Fewer hospital visits with SHR reduce patient exposure to COVID-19. However, CHR provided a more reliable level of immobilisation in this study. IMPLICATIONS FOR PRACTICE: The radiotherapy service will be reviewed in line with these findings.

Performance of a knowledge-based planning model for optimizing intensity-modulated radiotherapy plans for partial breast irradiation.

PURPOSE: To evaluate a knowledge-based (KB) planning model for RapidPlan, generated using a five-field intensity-modulated radiotherapy (IMRT) class solution beam strategy and rigorous dosimetric constraints for accelerated partial breast irradiation (APBI). MATERIALS AND METHODS: The RapidPlan model was configured using 64 APBI treatment plans and validated for 120 APBI patients who were not included in the training dataset. KB plan dosimetry was compared to clinical plan dosimetry, the clinical planning constraints, and the constraints used in phase III APBI trials. Dosimetric differences between clinical and KB plans were evaluated using paired two-tailed Wilcoxon signed-rank tests. RESULTS: KB planning was able to produce IMRT-based APBI plans in a single optimization without manual intervention that are comparable or better than the conventionally optimized, clinical plans. Comparing KB plans to clinical plans, differences in PTV, heart, contralateral breast, and ipsilateral lung dose-volume metrics were not clinically significant. The ipsilateral breast volume receiving at least 50% of the prescription dose was statistically and clinically significantly lower in the KB plans. CONCLUSION: KB planning for IMRT-based APBI provides equivalent or better dosimetry compared to conventional inverse planning. This model may be reliably applied in clinical practice and could be used to transfer planning expertise to ensure consistency in APBI plan quality.

Estimating cancer risks due to whole lungs low dose radiotherapy with different techniques for treating COVID-19 pneumonia.

BACKGROUND: Low dose radiotherapy (LDRT) of whole lungs with photon beams is a novel method for treating COVID-19 pneumonia. This study aimed to estimate cancer risks induced by lung LDRT for different radiotherapy delivery techniques. METHOD: Four different radiotherapy techniques, including 3D-conformal with anterior and posterior fields (3D-CRT AP-PA), 3D-conformal with 8 coplanar fields (3D-CRT 8 fields), eight fields intensity-modulated radiotherapy (IMRT), and volumetric modulated arc therapy using 2 full arcs (VMAT) were planned on the CT images of 32 COVID-19 patients with the prescribed dose of 1 Gy to the lungs. Organ average and maximum doses, and PTV dose distribution indexes were compared between different techniques. The radiation-induced cancer incidence and cancer-specific mortality, and cardiac heart disease risks were estimated for the assessed techniques. RESULTS: In IMRT and VMAT techniques, heart (mean and max), breast (mean, and max), and stomach (mean) doses and also maximum dose in the body were significantly lower than the 3D-CRT techniques. The calculated conformity indexes were similar in all the techniques. However, the homogeneity indexes were lower (i.e., better) in intensity-modulated techniques (P < 0.03) with no significant differences between IMRT and VMAT plans. Lung cancer incident risks for all the delivery techniques were similar (P > 0.4). Cancer incidence and mortality risks for organs located closer to lungs like breast and stomach were higher in 3D-CRT techniques than IMRT or VMAT techniques (excess solid tumor cancer incidence risks for a 30 years man: 1.94 ± 0.22% Vs. 1.68 ± 0.17%; and women: 6.66 ± 0.81% Vs. 4.60 ± 0.43%: cancer mortality risks for 30 years men: 1.63 ± 0.19% Vs. 1.45 ± 0.15%; and women: 3.63 ± 0.44% Vs. 2.94 ± 0.23%). CONCLUSION: All the radiotherapy techniques had low cancer risks. However, the overall estimated risks induced by IMRT and VMAT radiotherapy techniques were lower than the 3D-CRT techniques and can be used clinically in younger patients or patients having greater concerns about radiation induced cancers.

The Impact of COVID-19 on Medical Dosimetry Education: Students' Perception on the Effectiveness of Program's Immediate Response.

In early 2020, many medical dosimetry programs began to offer lectures and clinical rotations remotely in response to COVID-19. Faculty instituted an IRB-approved study to investigate the effectiveness of medical dosimetry educational programs' immediate response to COVID-19 and modifications to teaching practices during the pandemic. The Program Response to COVID-19 Effectiveness Questionnaire (PRCEQ) survey was developed to measure students' perceptions of their learning experience during COVID-19. The subject of the study was the medical dosimetry current and former student population who received modified education delivery during the COVID-19 pandemic. This study suggests that generally students are satisfied with the quality of their virtual didactic and clinical education as well as communication between faculty and students and students to students. Programs should develop strategies to engage students during the virtual classes to motivate them to learn; utilize a variety of formats for the evaluation of students' learning, incorporate activities to help students make connections with real-world clinical situations, and schedule clinical visits for students to learn tasks that require their physical presence in clinic.

A novel use for routine CBCT imaging during radiotherapy to detect COVID-19.

INTRODUCTION: Thoracic CT is a useful tool in the early diagnosis of patients with COVID-19. Typical appearances include patchy ground glass shadowing. Thoracic radiotherapy uses daily cone beam CT imaging (CBCT) to check for changes in patient positioning and anatomy prior to treatment through a qualitative assessment of lung appearance by radiographers. Observation of changes related to COVID-19 infection during this process may facilitate earlier testing improving patient management and staff protection. METHODS: A tool was developed to create overview reports for all CBCTs for each patient throughout their treatment. Reports contain coronal maximum intensity projection (MIP's) of all CBCTs and plots of lung density over time. A single therapeutic radiographer undertook a blinded off-line audit that reviewed 150 patient datasets for tool optimisation in which medical notes were compared to image findings. This cohort included 75 patients treated during the pandemic and 75 patients treated between 2014 and 2017. The process was repeated retrospectively on a subset of the 285 thoracic radiotherapy patients treated between January-June 2020 to assess the efficiency of the tool and process. RESULTS: Three patients in the n = 150 optimisation cohort had confirmed COVID-19 infections during their radiotherapy. Two of these were detected by the reported image assessment process. The third case was not detected on CBCT due to minimal density changes in the visible part of the lungs. Within the retrospective cohort four patients had confirmed COVID-19 based on RT-PCR tests, three of which were retrospectively detected by the reported process. CONCLUSION: The preliminary results indicate that the presence of COVID-19 can be detected on CBCT by therapeutic radiographers. IMPLICATIONS FOR PRACTICE: This process has now been extended to clinical service with daily assessments of all thoracic CBCTs. Changes noted are referred for oncologist review.

Uncertainty in the positioning of patients receiving treatment for brain metastases and wearing surgical mask underneath thermoplastic mask during COVID-19 crisis.

Thermoplastic masks, used along with surgical masks, enable immobilization methods to reduce the risk of infection in patients undergoing intracranial stereotactic radiosurgery and stereotactic radiotherapy (SRS/SRT) during the COVID-19 crisis. The purpose of this study was to investigate the feasibility of thermoplastic mask immobilization with a surgical mask using an ExacTrac system. Twelve patients each with brain metastases were immobilized using a thermoplastic mask and a surgical mask and only a thermoplastic mask. Two x-ray images were acquired to correct (XC) and verify (XV) the patient's position at a couch angle of 0°. Subsequently, the XC and XV images were acquired at each planned couch angle for non-coplanar beams. When the position errors were detected after couch rotation for non-coplanar beams, the errors were corrected at each planned couch angle until a clinically acceptable tolerance was attained. The position errors in the translational and rotational directions (vertical, lateral, longitudinal, pitch, roll, and yaw) were retrospectively investigated using data from the ExacTrac system database. A standard deviation of XC translational and rotational position errors with and without a surgical mask in the lateral (1.52 vs 2.07 mm), longitudinal (1.59 vs 1.87 mm), vertical (1.00 vs 1.73 mm), pitch (0.99 vs 0.79°), roll (1.24 vs 0.68°), and yaw (1.58 vs 0.90°) directions were observed at a couch angle of 0°. Most of patient positioning errors were less than 1.0 mm or 1.0° after the couch was rotated to the planned angle for non-coplanar beams. The overall absolute values of the translational and rotational XV position errors with and without the surgical mask were less than 0.5 mm and 0.5°, respectively. This study showed that a thermoplastic mask with a surgical mask is a feasible immobilization technique for brain SRS/SRT patients using the ExacTrac system.

Early-onset symptomatic radiation necrosis after stereotactic radiosurgery in the setting of COVID-19 infection.

In this brief report, we describe the case of a previously healthy 51-year gentleman who was treated with stereotactic radiosurgery to a dose of 12 Gy to a small right-sided vestibular schwannoma. MRI of the brain performed after treatment revealed stable treated disease but subsequently, the patient developed symptomatic COVID-19 based on PCR along with multiple cranial neurologic deficits, including right facial paralysis, hemifacial anesthesia, and anesthesia of the ipsilateral hard palate and tongue. MRI of the brain was repeated and demonstrated radiation necrosis in the adjacent brainstem for which he was treated with Pentoxifylline and Vitamin E, dexamethasone, and Bevacizumab with only partial improvement. The dose-volume metrics of the brainstem from his radiotherapy plan as well as the trajectory of his imaging findings do not match this clinical picture from radiotherapy alone. We review the basic pathogenesis of the inflammatory response to infection from the SARS-CoV-2 virus as well as the pathogenesis of radiation necrosis. Heightened awareness about potential risks with high-dose radiotherapy in patients with symptomatic COVID-19 should be considered.

Intra-fractional patient setup error during fractionated intracranial stereotactic irradiation treatment of patients wearing medical masks: comparison with and without bite block during COVID-19 pandemic.

The immobilization of patients with a bite block (BB) carries the risk of interpersonal infection, particularly in the context of pandemics such as COVID-19. Here, we compared the intra-fractional patient setup error (intra-SE) with and without a BB during fractionated intracranial stereotactic irradiation (STI). Fifteen patients with brain metastases were immobilized using a BB without a medical mask, while 15 patients were immobilized without using a BB and with a medical mask. The intra-SEs in six directions (anterior-posterior (AP), superior-inferior (SI), left-right (LR), pitch, roll, and yaw) were calculated by using cone-beam computed tomography images acquired before and after the treatments. We analyzed a total of 53 and 67 treatment sessions for the with- and without-BB groups, respectively. A comparable absolute mean translational and rotational intra-SE was observed (P > 0.05) in the AP (0.19 vs 0.23 mm with- and without-BB, respectively), SI (0.30 vs 0.29 mm), LR (0.20 vs 0.29 mm), pitch (0.18 vs 0.27°), roll (0.23 vs 0.23°) and yaw (0.27 vs 22°) directions. The resultant planning target volume (PTV) margin to compensate for intra-SE was <1 mm. No statistically significant correlation was observed between the intra-SE and treatment times. A PTV margin of <1 mm was achieved even when patients were immobilized without a BB during STI dose delivery.