Comparative effectiveness of frame-based and mask-based Gamma Knife stereotactic radiosurgery in brain metastases: A 509 patient meta-analysis.

PURPOSE: Stereotactic Radiosurgery (SRS) is the primary treatment for patients with limited numbers of small brain metastases. Head fixation is usually performed with framed-based (FB) fixation; however, mask-based (MB) fixation has emerged as a less invasive alternative. A comparative meta-analysis between both approaches has not been performed. METHODS: Databases were searched until August 28th, 2023, to identify studies comparing MB and FB SRS in the treatment of brain metastases. Our outcomes of interest included local tumor control (LTC), radiation necrosis (RN), mortality, and treatment time (TT). Mean difference (MD), risk ratio (RR), and hazard ratio (HR) were used for statistical comparisons. RESULTS: From 295 articles initially identified, six studies (1 clinical trial) involving 509 patients were included. LTC revealed comparable RR at 6-months (RR = 0.95[95%CI = 0.89-1.01], p = 0.12) and a marginal benefit in FB SRS at 1-year (RR = 0.87[95%CI = 0.78-0.96], p = 0.005). However, in oligometastases exclusively treated with single-fraction SRS, LTC was similar among groups (RR = 0.92 [95%CI = 0.89-1.0], p = 0.30). Similarly, in patients with oligometastases treated with single-fraction SRS, RN (HR = 1.69; 95%CI = 0.72-3.97, p = 0.22), TT (MD = -29.64; 95%CI = -80.38-21.10, p = 0.25), and mortality were similar among groups (RR = 0.62; 95%CI = 0.22-1.76, p = 0.37). CONCLUSION: Our findings suggest that FB and MB SRS, particularly oligometastases treated with single-fraction, are comparable in terms of LTC, RN, TT, and mortality. Further research is essential to draw definitive conclusions.

Pleomorphic Xanthoastrocytoma: Multi-Institutional Evaluation of Stereotactic Radiosurgery.

BACKGROUND AND OBJECTIVES: Pleomorphic xanthoastrocytoma (PXA) is a rare low-grade glial tumor primarily affecting young individuals. Surgery is the primary treatment option; however, managing residual/recurrent tumors remains uncertain. This international multi-institutional study retrospectively assessed the use of stereotactic radiosurgery (SRS) for PXA. METHODS: A total of 36 PXA patients (53 tumors) treated at 11 institutions between 1996 and 2023 were analyzed. Data included demographics, clinical variables, SRS parameters, tumor control, and clinical outcomes. Kaplan-Meier estimates summarized the local control (LC), progression-free survival, and overall survival (OS). Secondary end points addressed adverse radiation effects and the risk of malignant transformation. Cox regression analysis was used. RESULTS: A total of 38 tumors were grade 2, and 15 tumors were grade 3. Nine patients underwent initial gross total resection, and 10 received adjuvant therapy. The main reason for SRS was residual tumors (41.5%). The median follow-up was 34 months (range, 2-324 months). LC was achieved in 77.4% of tumors, with 6-month, 1-year, and 2-year LC estimates at 86.7%, 82.3%, and 77.8%, respectively. Younger age at SRS (hazard ratios [HR] 3.164), absence of peritumoral edema (HR 4.685), and higher marginal dose (HR 6.190) were significantly associated with better LC. OS estimates at 1, 2, and 5 years were 86%, 74%, and 49.3%, respectively, with a median OS of 44 months. Four patients died due to disease progression. Radiological adverse radiation effects included edema (n = 8) and hemorrhagic change (n = 1). One grade 3 PXA transformed into glioblastoma 13 months after SRS. CONCLUSION: SRS offers promising outcomes for PXA management, providing effective LC, reasonable progression-free survival, and minimal adverse events.

Metastatic Neoplasm Volume Kinetics Following 2-Stage Stereotactic Radiosurgery.

BACKGROUND: Multisession staged stereotactic radiosurgery (SRS) represents an alternative approach for management of large brain metastases (LBMs), with potential advantages over fractionated SRS. This study investigated clinical efficacy and safety of 2-stage stereotactic radiosurgery (2-SSRS) in patients with LBMs. METHODS: Patients with LBMs treated with 2-SSRS between 2014 and 2020 were evaluated. Demographic, clinical, and radiologic data were obtained. Volumetric measurements at first SRS session, second SRS session, and follow-up imaging studies were obtained. Characteristics that might predict response to 2-SSRS were evaluated through Fisher exact or Mann-Whitney U test. RESULTS: The study included 24 patients with 26 LBMs. Median (range) marginal doses for first and second SRS sessions were 15 Gy (14-18 Gy) and 15 Gy (12-16 Gy), respectively. Median (range) tumor volumes at first SRS session, second SRS session, and 3-month follow-up were 8.1 cm3 (1.5-28.5 cm3), 3.3 cm3 (0.8-26.1 cm3), and 2.2 cm3 (0.2-10.1 cm3), respectively. Of 26 lesions, 24 (92%) demonstrated early local control following the first SRS session, with 17 lesions (71%) demonstrating a decrease of ≥30% in T1 postcontrast MRI volume before the second SRS session and 3 lesions (12%) remaining stable. Eventually, 4 lesions showed disease progression after 2-SSRS. The median time to local progression was not reached; the median time to intracranial progression was 9.1 months. CONCLUSIONS: Our study supports the effectiveness and safety of 2-SSRS as a treatment modality for patients with LBMs, especially in poor surgical candidates. The local failure rate and low occurrence of adverse effects are comparable to other staged radiosurgery studies.

Impacts of genotypic variants on survival following reoperation for recurrent glioblastoma.

INTRODUCTION: Recurrent glioblastoma (rGBM) prognosis is dismal. In the absence of effective adjuvant treatments for rGBM, re-resections remain prominent in our arsenal. This study evaluates the impact of reoperation on post-progression survival (PPS) considering rGBM genetic makeup. METHODS: To assess the genetic heterogeneity and treatment-related changes (TRC) roles in re-operated or medically managed rGBMs, we compiled demographic, clinical, histopathological, and next-generation genetic sequencing (NGS) characteristics of these tumors from 01/2005 to 10/2019. Survival data and reoperation were analyzed using conventional and random survival forest analysis (RSF). RESULTS: Patients harboring CDKN2A/B loss (p = 0.017) and KDR mutations (p = 0.031) had notably shorter survival. Reoperation or bevacizumab were associated with longer PPS (11.2 vs. 7.4-months, p = 0.006; 13.1 vs 6.2, p < 0.001). Reoperated patients were younger, had better performance status and greater initial resection. In 136/273 (49%) rGBMs undergoing re-operation, CDKN2A/B loss (p = 0.03) and KDR mutations (p = 0.02) were associated with shorter survival. In IDH-WT rGBMs with NGS data (n = 166), reoperation resulted in 7.0-month longer survival (p = 0.004) than those managed medically. This reoperation benefit was independently identified by RSF analysis. Stratification analysis revealed that EGFR-mutant, CDKN2A/B-mutant, NF1-WT, and TP53-WT rGBM IDH-WT subgroups benefit most from reoperation (p = 0.03). Lastly, whether or not TRC was prominent at re-operation does not have any significant impact on PPS (10.5 vs. 11.5-months, p = 0.77). CONCLUSIONS: Maximal safe re-resection significantly lengthens PPS regardless of genetic makeup, but reoperations are especially beneficial for IDH-WT rGBMs with EGFR and CDKN2A/B mutations with TP53-WT, and NF1-WT. Histopathology at recurrence may be an imperfect gauge of disease severity at progression and the imaging progression may be more reflective of the prognosis.

NUT Carcinoma of the Submandibular Gland: A Case at This Uncommon Site with Review of the Literature.

Nuclear protein in testis (NUT) carcinoma is a rare, highly aggressive, undifferentiated carcinoma that harbors a characteristic rearrangement of the NUTM1 gene. The majority arise in adolescents and young adults especially from the midline structures of the thorax, head, and neck. Until the present, there have only been three reported cases of NUT carcinoma of the submandibular gland, two of which were reported in children and another one in an adult from Korea. Here, we report the first case of NUT carcinoma arising in the submandibular gland of an adult female in the United States, representing the fourth case worldwide. A fine needle aspiration and biopsy was performed, and the diagnosis was confirmed by NUT immunohistochemical staining and fusion of the BRD4 (19p13.12) and NUTM1 (15q14) gene loci by fluorescence in-situ hybridization on the resection specimen. Salivary gland is an unusual site for NUT carcinoma and is rarely described in submandibular gland. We reviewed the clinicopathologic features of this entity at this site along with role of NUTM1 gene rearrangements in NUT tumorigenesis.

Genomic alterations predictive of response to radiosurgery in recurrent IDH-WT glioblastoma.

INTRODUCTION: Despite aggressive treatment, glioblastoma invariably recurs. The optimal treatment for recurrent glioblastoma (rGBM) is not well defined. Stereotactic radiosurgery (SRS) for rGBM has demonstrated favorable outcomes for selected patients; however, its efficacy in molecular GBM subtypes is unknown. We sought to identify genetic alterations that predict response/outcomes from SRS in rGBM-IDH-wild-type (IDH-WT). METHODS: rGBM-IDH-WT patients undergoing SRS at first recurrence and tested by next-generation sequencing (NGS) were reviewed (2009-2018). Demographic, clinical, and molecular characteristics were evaluated. NGS interrogating 205-genes was performed. Primary outcome was survival from GK-SRS assessed by Kaplan-Meier method and multivariable Cox proportional-hazards. RESULTS: Sixty-three lesions (43-patients) were treated at 1st recurrence. Median age was 61-years. All patients were treated with resection and chemoradiotherapy. Median time from diagnosis to 1st recurrence was 8.7-months. Median cumulative volume was 2.895 cm3 and SRS median marginal dose was 18 Gy (median isodose-54%). Bevacizumab was administered in 81.4% patients. PFS from SRS was 12.9-months. Survival from SRS was 18.2-months. PTEN-mutant patients had a longer PFS (p = 0.049) and survival from SRS (p = 0.013) in multivariable analysis. Although no statistically significant PTEN-mutants patients had higher frequency of radiation necrosis (21.4% vs. 3.4%) and lower in-field recurrence (28.6% vs. 37.9%) compared to PTEN-WT patients. CONCLUSIONS: SRS is a safe and effective treatment option for selected rGBM-IDH-WT patients following first recurrence. rGBM-IDH-WT harboring PTEN-mutation have improved survival with salvage SRS compared to PTEN-WT patients. PTEN may be used as a molecular biomarker to identify a subset of rGBM patients who may benefit the most from SRS.

Role of Ethnicity and Geographic Location on Glioblastoma IDH1/IDH2 Mutations.

BACKGROUND: Previous studies have demonstrated possible differences in glioblastoma (GBM) survival attributable to ethnicity. The goal of this study was to quantify oncogenic differences and evaluate the overall survival (OS) and progression-free survival (PFS) differences in GBM patients across race/ethnicity using both population-based surveillance and institutional data sets from the United States (US) and Mexico. METHODS: Retrospective cohort study comprising the Texas Cancer Registry (TCR, n = 4134) and referral institutions located in US (n = 254) and Mexico (n = 47) were evaluated. Primary outcomes include OS and PFS. Oncogenic differences attributable to ethnicity were assessed. IDH1/IDH2 status was evaluated by sequencing in US and Mexico samples. Kaplan-Meier and Cox proportional hazards regression for survival analysis. RESULTS: A total of 4134 GBM patients were identified from the TCR data set, ethnicity comparison demonstrated that Hispanic patients were diagnosed at a significantly younger age compared to non-Hispanic white patients (NHW) (median: 58 vs. 62, P < 0.001) and had improved OS (hazard ratio: 0.82, P < 0.001). In the oncogenic analysis, we observed a significant enrichment of IDH1/IDH2 mutations in Mexican Hispanic patients compared to US Hispanic patients (29.8% vs. 7.9%, P = 0.012); IDH2 mutations drove this difference. Post-progression survival was significantly shorter in patients from Mexico than US (3.0 vs. 11.4 months; P < 0.001), while OS remained similar. CONCLUSIONS: IDH2 mutations are more prevalent in Mexican Hispanic individuals compared to US individuals and may be a crucial contributor to the previously reported survival benefit of Hispanic individuals in large population databases. These findings are critical for both screening of IDH2 mutations and targeted interventions in GBM.

Landscape of Genomic Alterations in IDH Wild-Type Glioblastoma Identifies PI3K as a Favorable Prognostic Factor.

PURPOSE: IDH wild-type (WT) glioblastoma (GBM) is an aggressive tumor with poor survival despite current therapies. The aim of this study was to characterize its genomic profile and determine whether a particular molecular signature is associated with improved survival outcomes. PATIENTS AND METHODS: Tumor samples from 232 patients with IDH-WT GBM were sequenced, and the landscape of genomic alterations was fully delineated. Genomics data from The Cancer Genome Atlas (TCGA) cohort were analyzed for confirmation. Association of alterations with survival was evaluated in both univariable and multivariable approaches. RESULTS: The genomic landscape of IDH-WT GBM revealed a high frequency of CDKN2A/B loss, TERT promoter mutations, PTEN loss, EGFR alteration, and TP53 mutations. Novel variants or gene mutations, such as ARID1B and MLL2, were identified. To better understand synergistic effects and facilitate decision making for precision medicine, we identified 11 pairs of gene alterations that tended to co-occur or were mutually exclusive, which were confirmed in the TCGA cohort. Survival analysis showed that genomic alterations in TP53 were associated with worse overall survival (OS). However, alterations in PI3K class I genes were associated with significantly better OS (univariable analysis: P = .002; multivariable analysis: hazard ratio [HR], 0.5785; P = .00162) and longer progression-free survival (univariable analysis: P = .0043; multivariable analysis: HR, 0.6228; P = .00913). CONCLUSION: Genomic alterations in PI3K class I are a favorable prognostic factor in IDH-WT GBM. This new prognostic biomarker may facilitate risk stratification of patients, assist in clinical trial enrollment, and provide potential therapeutic targets.

Impact of facility type and volume in low-grade glioma outcomes.

OBJECTIVE: The object of this study was to investigate the impact of facility type (academic center [AC] vs non-AC) and facility volume (high-volume facility [HVF] vs low-volume facility [LVF]) on low-grade glioma (LGG) outcomes. METHODS: This retrospective cohort study included 5539 LGG patients (2004-2014) from the National Cancer Database. Patients were categorized by facility type and volume (non-AC vs AC, HVF vs LVF). An HVF was defined as the top 1% of facilities according to the number of annual cases. Outcomes included overall survival, treatment receipt, and postoperative outcomes. Kaplan-Meier and Cox proportional-hazards models were applied. The Heller explained relative risk was computed to assess the relative importance of each survival predictor. RESULTS: Significant survival advantages were observed at HVFs (HR 0.67, 95% CI 0.55-0.82, p < 0.001) and ACs (HR 0.84, 95% CI 0.73-0.97, p = 0.015), both prior to and after adjusting for all covariates. Tumor resection was 41% and 26% more likely to be performed at HVFs vs LVFs and ACs vs non-ACs, respectively. Chemotherapy was 40% and 88% more frequently to be utilized at HVFs vs LVFs and ACs vs non-ACs, respectively. Prolonged length of stay (LOS) was decreased by 42% and 24% at HVFs and ACs, respectively. After tumor histology, tumor pattern, and codeletion of 1p19q, facility type and surgical procedure were the most important contributors to survival variance. The main findings remained consistent using propensity score matching and multiple imputation. CONCLUSIONS: This study provides evidence of survival benefits among LGG patients treated at HVFs and ACs. An increased likelihood of undergoing resections, receiving adjuvant therapies, having shorter LOSs, and the multidisciplinary environment typically found at ACs and HVFs are important contributors to the authors' finding.

Epstein-Barr Virus-Positive Large Cell Neuroendocrine Carcinoma of the Nasopharynx: Report of One Case and Review of the Literature.

Epstein-Barr Virus (EBV)-positive neuroendocrine carcinoma (NEC) of the nasopharynx is exceedingly rare, only two cases have been reported in the literature. While EBV infection is strongly associated with nasopharyngeal carcinoma, which is carcinoma with squamous differentiation, the link between EBV and NEC is not well known, and can be diagnostically challenging. In this study, we report the third case of EBV-positive large cell NEC of nasopharynx with neck lymph node metastasis. The patient was treated with combined radiation and chemotherapy and showed complete clinical and radiological response. Similar treatment response has been reported in another patient with high stage EBV-positive large cell NEC, suggesting that EBV status is an important prognostic factor. Recognition of this rare tumor is important for disease management and patient prognosis. We also review the literature about the clinical and pathologic presentation of neuroendocrine tumors of nasopharynx.

Planned Gamma Knife Boost After Chemoradiotherapy for Selected Sinonasal and Nasopharyngeal Cancers.

OBJECTIVE: To determine the feasibility of a Gamma Knife boost after intensity-modulated radiation therapy in combination with multimodal therapy in patients with nasopharyngeal carcinoma and sinonasal malignancies with skull base or cavernous sinus involvement. METHODS: Nine patients were treated with intensity-modulated radiation therapy followed by a Gamma Knife boost. In one case Gamma Knife was given as salvage treatment after resection. Five patients had sinonasal malignancies and 4 had nasopharyngeal carcinoma. The mean radiation therapy dose was 64.3 Gy (range, 54-70 Gy) at 2 Gy per fraction. The median interval from completion of radiation therapy to Gamma Knife boost was 2.2 months (range, 1-4 months). The most common indication for Gamma Knife boost was involvement of the cavernous sinus, which was identified in 7 patients. The median margin Gamma Knife dose delivered was 13 Gy (range, 12-20 Gy), with median prescription isodose of 50%. RESULTS: All patients tolerated the procedure well, with minimal toxicity. Local control rates were achieved in all patients and no acute grade 3-5 toxicity was observed. One patient experienced late grade 4 toxicity, which was potentially attributable to treatment. Distant failure occurred in 3 patients (1 patient with nasopharyngeal carcinoma and 2 patients with sinonasal malignancies). CONCLUSIONS: Planned Gamma Knife boost followed intensity-modulated radiation therapy is feasible, safe, and provides excellent local control in patients with sinonasal malignancies and nasopharyngeal carcinoma, particularly in cases with cavernous sinus involvement. Further follow-up will be necessary to determine the long-term effectiveness and complication profile.

Longitudinal monitoring of the head and neck lymphatics in response to surgery and radiation.

BACKGROUND: The lymphatic vasculature provides a route for cancer metastases, and its dysfunction after cancer treatment can result in lymphedema. However, changes in the lymphatics before, during, and after surgery and radiation remain unclear. METHODS: Near-infrared fluorescence lymphatic imaging was performed before and after lymph node dissection and fractionated radiotherapy to assess changes in external lymphatic function. RESULTS: Patients who underwent both lymph node dissection and radiotherapy developed lymphatic dermal backflow on treated sides ranging from days after the start of radiotherapy to weeks after its completion, whereas contralateral regions that were not associated with lymph node dissection but also treated with radiotherapy experienced no such changes in external lymphatic anatomies. CONCLUSION: The external lymphatics undergo transient changes during and weeks after lymph node dissection and radiotherapy. © 2017 Wiley Periodicals, Inc. Head Neck 39: 1177-1188, 2017.

Salvage intensity modulated radiotherapy using endorectal balloon after radical prostatectomy: clinical outcomes.

OBJECTIVES: To evaluate biochemical non-evidence of disease and adverse events of salvage intensity-modulated radiotherapy using an endorectal balloon for prostate cancer patients after radical prostatectomy. METHODS: Data of 107 patients (median age 65 years) with persistent (>0.1 ng/mL) or rising prostate-specific antigen after radical prostatectomy were retrospectively analyzed. The mean dose to clinical target volume was 70 Gy in 32 fractions (the equivalent dose in 2 Gy fraction is 73.2 Gy based on α:ß = 2). Biochemical non-evidence of disease and predictive factors were assessed. Genitourinary toxicity and gastrointestinal toxicity were also evaluated using the Radiation Therapy Oncology Group toxicity criteria. RESULTS: The median follow up was 37 months (range 6-126 months). A total of 48 patients developed biochemical recurrence. The 3- and 5-year biochemical non-evidence of disease rates of all patients were 52.6% and 48.8%, respectively. The Gleason score (≥4 + 3, ≤3 + 4) and pre-intensity-modulated radiotherapy prostate-specific antigen level (≥0.5 ng/mL, <0.5 ng/mL) were significant predictive factors for biochemical non-evidence of disease in univariate analysis. In multivariate analysis, only the Gleason score was detected as a significant variable. The highest late genitourinary toxicities were grade 2 in 13% and grade 3 in 6% of patients. The highest late gastrointestinal toxicities were grade 2 in 6% and grade 3 in 3% of patients. CONCLUSION: Despite a relatively high radiation dose, intensity-modulated radiotherapy with an endorectal balloon can be delivered with acceptable toxicity and efficacy for patients developing biochemical recurrence after radical prostatectomy.

A dose-response relationship for time to bone pain resolution after stereotactic body radiotherapy (SBRT) for renal cell carcinoma (RCC) bony metastases.

BACKGROUND: To investigate the utility of stereotactic body radiotherapy (SBRT) in the treatment of painful renal cell carcinoma (RCC) bone metastases, and for a possible dose effect on time to symptom relief. MATERIAL AND METHODS: Eighteen patients with 24 painful osseous lesions from metastatic RCC were treated with SBRT. The most common treatment regimens were 24 Gy in 3 fractions and 40 Gy in 5 fractions. The times from treatment to first reported pain relief and time to symptom recurrence were evaluated. Median follow-up was 38 weeks (1-156 weeks). RESULTS: Seventy-eight percent of all patients had pain relief. Patients treated with a BED > 85 Gy achieved faster and more durable pain relief compared to those treated with a BED < 85 Gy. There was decrease in time to pain relief after a change in treatment regimen to 8 Gy × 5 fractions (BED = 86). There was only one patient with grade 1 skin toxicity. No neurological or other toxicity was observed. CONCLUSIONS: SBRT can safely and effectively treat painful RCC bony metastases. There appears to be a relationship between radiation dose and time to stable pain relief.

Role of radiation therapy in the management of renal cell cancer.

Renal cell carcinoma (RCC) is traditionally considered to be radioresistant; therefore, conventional radiotherapy (RT) fraction sizes of 1.8 to 2 Gy are thought to have little role in the management of primary RCC, especially for curative disease. In the setting of metastatic RCC, conventionally fractionated RT has been an effective palliative treatment in 50% of patients. Recent technological advances in radiation oncology have led to the clinical implementation of image-guided radiotherapy, allowing biologically potent doses to the tumors intra- and extra-cranially. As predicted by radiobiologic modeling, favorable outcomes have been observed with highly hypofractionated schemes modeled after the experience with intracranial stereotactic radiosurgery (SRS) for RCC brain metastases with reported local control rates averaging 85%. At present, both primary and metastatic RCC tumors may be successfully treated using stereotactic approaches, which utilize steep dose gradients to maximally preserve function and avoid toxicity of adjacent organs including liver, uninvolved kidney, bowel, and spinal cord regions. Future endeavors will combine stereotactic body radiation therapy (SBRT) with novel targeted therapies, such as tyrosine kinase inhibitors and targeted rapamycin (mTOR) inhibitors, to maximize both local and systemic control.

Stereotactic body radiation therapy (SBRT) for genitourinary malignancies.

Stereotactic body radiation therapy (SBRT) is a novel treatment modality in radiation oncology that delivers a very high dose of radiation to the tumor target with high precision using single or a small number of fractions. SBRT is the result of technological advances in patient/tumor immobilization, image guidance, and treatment planning and delivery. This modality is safe and effective in both early stage primary cancer and oligometastases. Compared to the use of stereotactic radiosurgery for other tumor sites, SBRT is slow to be adopted in the management of genitourinary malignancies. There are now emerging data that show the safety and efficacy of this treatment modality in genitourinary (GU) malignancies especially in prostate cancer and renal cell carcinoma. Preclinical data, clinical experience, and challenges are reviewed and discussed.

The effect of dental artifacts, contrast media, and experience on interobserver contouring variations in head and neck anatomy.

OBJECTIVES: To investigate interobserver variability in the delineation of head-and-neck (H&N) anatomic structures on CT images, including the effects of image artifacts and observer experience. METHODS: Nine observers (7 radiation oncologists, 1 surgeon, and 1 physician assistant) with varying levels of H&N delineation experience independently contoured H&N gross tumor volumes and critical structures on radiation therapy treatment planning CT images alongside reference diagnostic CT images for 4 patients with oropharynx cancer. Image artifacts from dental fillings partially obstructed 3 images. Differences in the structure volumes, center-of-volume positions, and boundary positions (1 SD) were measured. In-house software created three-dimensional overlap distributions, including all observers. The effects of dental artifacts and observer experience on contouring precision were investigated, and the need for contrast media was assessed. RESULTS: In the absence of artifacts, all 9 participants achieved reasonable precision (1 SD < or =3 mm all boundaries). The structures obscured by dental image artifacts had larger variations when measured by the 3 metrics (1 SD = 8 mm cranial/caudal boundary). Experience improved the interobserver consistency of contouring for structures obscured by artifacts (1 SD = 2 mm cranial/caudal boundary). CONCLUSIONS: Interobserver contouring variability for anatomic H&N structures, specifically oropharyngeal gross tumor volumes and parotid glands, was acceptable in the absence of artifacts. Dental artifacts increased the contouring variability, but experienced participants achieved reasonable precision even with artifacts present. With a staging contrast CT image as a reference, delineation on a noncontrast treatment planning CT image can achieve acceptable precision.