Bevacizumab and re-irradiation for recurrent high grade gliomas: does sequence matter?

PURPOSE/OBJECTIVES: We report the outcomes of the largest cohort to date of patients receiving both bevacizumab (BEV) and fractionated stereotactic radiotherapy (FSRT) for progressive or recurrent high grade glioma (HGG). Furthermore, the sequence of these two treatment regimens was analyzed to determine an optimal treatment paradigm for recurrent HGG. MATERIALS/METHODS: After Institutional Review Board approval, patients with pathologically confirmed WHO grade III anaplastic astrocytoma (AA) or IV glioblastoma multiforme (GBM) glioma who subsequently underwent re-irradiation at recurrence with FSRT were retrospectively reviewed. Patients from this group who had received BEV were also identified. Survival from initial diagnosis, as well as from recurrence and re-irradiation, were analyzed as study endpoints. Date of recurrence was defined as the date of radiographic evidence of progressive/recurrent disease. Kaplan-Meier curves were generated utilizing a log-rank test with a p-value ≤ 0.05 considered significant to compare treatment sequences in terms of survival outcomes. RESULTS: A total of 118 patients with recurrent/progressive HGG (GBM = 87, AA = 31) had received both BEV and FSRT. Patient characteristics were as follows: median KPS at recurrence was 80 (range 50-100); median age at recurrence was 57 years; median time to radiographic recurrence/progression was 10.8 months (mo) and 33.1% of patients had surgery for recurrence. The median time from the start of BEV to FSRT was 6.4 months and from FSRT to the start of BEV was 5.1 months. For the entire cohort, median overall survival (OS) was 26.7 months and median survival time (MST) from recurrence was 13.8 months (24.4 months and 11.9 months for GBM only). In patients that received BEV prior to FSRT (n = 50), median OS and MST from recurrence were 25.2 and 13.3 months respectively. In patients receiving FSRT first (n = 56), median OS and MST from recurrence were 28.8 months and 13.9 months, respectively. Sequencing of BEV and FSRT at recurrence was not significantly associated with OS (p = 0.08) or median survival from recurrence (p = 0.75). CONCLUSIONS: The combination of FSRT and BEV for recurrent/progressive HGG provides promising results in terms of overall survival and survival from recurrence. Combining these treatment modalities appears to improve upon the historic outcomes of either treatment alone. The outcomes data from this study support the ongoing RTOG trial exploring the combination of BEV and FSRT for recurrent HGG.

Dosing, administration, and safety of radium-223: How I do it.

Radium-223 dichloride is a first-in-class bone-directed radiopharmaceutical that has been shown to prolong survival in men with metastatic castrate resistant prostate cancer (mCRPC). Unlike other radiopharmaceuticals, radium-223 uniquely uses alpha-emission to deliver high intensity, short range cytoxic treatments resulting in minimal myelosuppression. Following the results of the ALSYMPCA trial, radium-223 (Xofigo) was FDA approved in the United States in May 2013 and approved by Health Canada in December 2013 for the treatment of mCRPC with symptomatic bone metastases and no visceral disease. This 'How I do it' article describes the background of radium 223 as well as the methods and techniques that our institution uses for safe and effective administration and notes the subtle differences when administering the drug in Canada.

Radioisotopes in management of metastatic prostate cancer.

INTRODUCTION: Metastatic prostate cancer continues to be a leading cause of morbidity and mortality in men with prostate cancer. Over the last decade, the treatment landscape for patients with castrate-resistant disease has drastically changed, with several novel agents demonstrating an improvement in overall survival in large, multi-institutional randomized trials. Traditional treatment with radioisotopes has largely been in the palliative setting. However, the first in class radiopharmaceutical radium-223 has emerged as the only bone-directed treatment option demonstrating an improvement in overall survival. METHODS: Medline publications from 1990 to 2016 were searched and reviewed to assess the use of currently approved radioisotopes in the management of prostate cancer including emerging data regarding integration with novel systemic therapies. New positron emission tomography-based radiotracers for advanced molecular imaging of prostate cancer were also queried. RESULTS: Radioisotopes play a crucial role in the diagnosis and treatment of prostate cancer in the definitive and metastatic setting. Molecular imaging of prostate cancer and theranostics are currently being investigated in the clinical arena. CONCLUSIONS: The use of modern radioisotopes in selected patients with mCRPC is associated with improvements in overall survival, pain control, and quality of life.

Modeling gamma knife radiosurgical toxicity for multiple brain metastases.

BACKGROUND AND PURPOSE: Radiation oncology protocols for single fraction radiosurgery recommend setting dosing criteria based on assumed risk of radionecrosis, which can be predicted by the 12 Gy normal brain volume (V12). In this study, we show that tumor surface area (SA) and a simple power-law model using only preplan variables can estimate and minimize radiosurgical toxicity. MATERIALS AND METHODS: A 245-patient cohort with 1217 brain metastases treated with single or distributed Gamma Knife sessions was reviewed retrospectively. Univariate and multivariable linear regression models and power-law models determined which modeling parameters best predicted V12. The V12 power-law model, represented by a product of normalized Rx dose Rxn, and tumor longest axial dimension LAD (V12 âˆ¼ Rxn1.5*LAD2), was independently validated using a secondary 63-patient cohort with 302 brain metastases. RESULTS: Surface area was the best univariate linear predictor of V12 (adjR2 = 0.770), followed by longest axial dimension (adjR2 = 0.755) and volume (adjR2 = 0.745). The power-law model accounted for 90% variance in V12 for 1217 metastatic lesions (adjR2 = 0.906) and 245 patients (adjR2 = 0.896). The average difference ΔV12 between predicted and measured V12s was (0.28 ± 0.55) cm3 per lesion and (1.0 ± 1.2) cm3 per patient. The power-law predictive capability was validated using a secondary 63-patient dataset (adjR2 = 0.867) with 302 brain metastases (adjR2 = 0.825). CONCLUSION: Surface area was the most accurate univariate predictor of V12 for metastatic lesions. We developed a preplan model for brain metastases that can help better estimate radionecrosis risk, determine prescription doses given a target V12, and provide safe dose escalation strategies without the use of any planning software.

Socioeconomic and demographic determinants of radiation treatment and outcomes in glioblastoma patients.

Introduction: Poor outcomes in glioblastoma patients, despite advancing treatment paradigms, indicate a need to determine non-physiologic prognostic indicators of patient outcome. The impact of specific socioeconomic and demographic patient factors on outcomes is unclear. We sought to identify socioeconomic and demographic patient characteristics associated with patient survival and tumor progression, and to characterize treatment options and healthcare utilization. Methods: A cohort of 169 patients with pathologically confirmed glioblastomas treated at our institution was retrospectively reviewed. Multivariable cox proportional hazards analysis for overall survival (OS) and cumulative incidence of progression was performed. Differences in treatment regimen, patient characteristics, and neuro-oncology office use between different age and depressive disorder history patient subgroups were calculated two-sample t-tests, Fisher's exact tests, or linear regression analysis. Results: The median age of all patients at the time of initiation of radiation therapy was 60.5 years. The median OS of the cohort was 13.1 months. Multivariable analysis identified age (Hazard Ratio 1.02, 95% CI 1.00-1.04) and total resection (Hazard Ratio 0.52, 95% CI 0.33-0.82) as significant predictors of OS. Increased number of radiation fractions (Hazard Ratio 0.90, 95% CI 0.82-0.98), depressive disorder history (Hazard Ratio 0.59, 95% CI 0.37-0.95), and total resection (Hazard Ratio 0.52, 95% CI 0.31-0.88) were associated with decreased incidence of progression. Notably, patients with depressive disorder history were observed to have more neuro-oncology physician office visits over time (median 12 vs. 16 visits, p = 0.0121). Patients older than 60 years and those with Medicare (vs. private) insurance were less likely to receive as many radiation fractions (p = 0.0014) or receive temozolomide concurrently with radiation (Odds Ratio 0.46, p = 0.0139). Conclusion: Older glioblastoma patients were less likely to receive as diverse of a treatment regimen as their younger counterparts, which may be partially driven by insurance type. Patients with depressive disorder history exhibited reduced incidence of progression, which may be due to more frequent health care contact during neuro-oncology physician office visits.

Neutrophilia and post-radiation thrombocytopenia predict for poor prognosis in radiation-treated glioma patients.

Introduction: Poor outcomes in glioma patients indicate a need to determine prognostic indicators of survival to better guide patient specific treatment options. While preoperative neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR) have been suggested as prognostic systemic inflammation markers, the impact of post-radiation changes in these cell types is unclear. We sought to identify which hematologic cell measurements before, during, or after radiation predicted for patient survival. Methods: A cohort of 182 patients with pathologically confirmed gliomas treated at our institution was retrospectively reviewed. Patient blood samples were collected within one month before, during, or within 3 months after radiation for quantification of hematologic cell counts, for which failure patterns were evaluated. Multivariable cox proportional hazards analysis for overall survival (OS) and progression-free survival (PFS) was performed to control for patient variables. Results: Multivariable analysis identified pre-radiation NLR > 4.0 (Hazard ratio = 1.847, p = 0.0039) and neutrophilia prior to (Hazard ratio = 1.706, p = 0.0185), during (Hazard ratio = 1.641, p = 0.0277), or after (Hazard ratio = 1.517, p = 0.0879) radiation as significant predictors of worse OS, with similar results for PFS. Post-radiation PLR > 200 (Hazard ratio = 0.587, p = 0.0062) and a percent increase in platelets after radiation (Hazard ratio = 0.387, p = 0.0077) were also associated with improved OS. Patients receiving more than 15 fractions of radiation exhibited greater post-radiation decreases in neutrophil and platelet counts than those receiving fewer. Patients receiving dexamethasone during radiation exhibited greater increases in neutrophil counts than those not receiving steroids. Lymphopenia, changes in lymphocyte counts, monocytosis, MLR, and changes in monocyte counts did not impact patient survival. Conclusion: Neutrophilia at any time interval surrounding radiotherapy, pre-radiation NLR, and post-radiation thrombocytopenia, but not lymphocytes or monocytes, are predictors of poor patient survival in glioma patients.

Impact of CDKN2A/B, MTAP, and TERT Genetic Alterations on Survival in IDH Wild Type Glioblastomas.

PURPOSE: Poor outcomes in IDH wild-type (IDHwt) glioblastomas indicate the need to determine which genetic alterations can indicate poor survival and guidance of patient specific treatment options. We sought to identify the genetic alterations in these patients that predict for survival when adjusting particularly for treatments and other genetic alterations. METHODS: A cohort of 167 patients with pathologically confirmed IDHwt glioblastomas treated at our institution was retrospectively reviewed. Next generation sequencing was performed for each patient to determine tumor genetic alterations. Multivariable cox proportional hazards analysis for overall survival (OS) was performed to control for patient variables. RESULTS: CDKN2A, CDKN2B, and MTAP deletion predict for worse OS independently of other genetic alterations and patient characteristics (hazard ratio [HR] 2.192, p = 0.0017). Patients with CDKN2A copy loss (HR 2.963, p = 0.0037) or TERT mutated (HR 2.815, p = 0.0008) glioblastomas exhibited significant associations between radiation dose and OS, while CDKN2A and TERT wild type patients did not. CDKN2A deleted patients with NF1 mutations had worse OS (HR 1.990, p = 0.0540), while CDKN2A wild type patients had improved OS (HR 0.229, p = 0.0723). Patients with TERT mutated glioblastomas who were treated with radiation doses < 45 Gy (HR 3.019, p = 0.0010) but not those treated with ≥ 45 Gy exhibited worse OS compared to those without TERT mutations. CONCLUSION: In IDHwt glioblastomas, CDKN2A, CDKN2B, and MTAP predict for poor prognosis. TERT and CDKN2A mutations are associated with worse survival only when treated with lower radiation doses, thus potentially providing a genetic marker that can inform clinicians on proper dose-fractionation schemes.

MicroRNA-21 is Required for Hematopoietic Cell Viability After Radiation Exposure.

PURPOSE: Radiation therapy is an essential intervention used in the treatment of more than half of cancer patients. With the increasing use of hypofractionated radiation regimens, concurrent use of radiation and chemotherapy, targeted agents and immunotherapy, the risk of radiation-induced toxicities is increased. However, much remains unknown about the molecular underpinnings responsible for radiation-induced toxicity. MicroRNA (miRNA) are small, non-coding RNA involved in post-transcriptional regulation of gene expression. miR-21 is an oncomiR that is dysregulated in a significant fraction of human malignancies, and its overexpression is linked to poor overall survival, chemoresistance, and radioresistance in several human cancers. However, the contribution of miR-21 in governing radiation sensitivity in normal, untransformed cells, and the impact of silencing this miRNA in normal tissues remains largely unexplored. MATERIALS AND METHODS: miR-21 levels were evaluated in tissues by qRT-PCR without and after total body irradiation (TBI). Mice lacking miR-21 were genetically engineered, subjected to TBI, and monitored for survival. Hematopoietic stem and progenitor cell (HSPC) numbers and function were assessed using flow cytometry, histology, complete blood cell counts, and bone marrow transplantation. RESULTS: miR-21 expression was increased in radiosensitive tissues, but not in radioinsensitive tissues following TBI in wild-type mice, suggesting it may have a critical function in the normal tissue response to irradiation. Compared to wild-type mice, mice lacking one or both alleles of miR-21 showed reduced numbers of HSPCs and increased sensitivity to an LD50/30 dose of TBI with evidence of bone marrow failure. Transplantation of wild-type bone marrow into irradiated miR-21-deficient mice rescued the mice from death. CONCLUSIONS: Our data identify miR-21 as a critical component of HSPC viability and essential for bone marrow recovery following irradiation. Further investigation is warranted to determine whether miR-21 can be used to stratify patients at risk for hematopoietic toxicity following irradiation.

Caloric restriction counteracts chemotherapy-induced inflammation and increases response to therapy in a triple negative breast cancer model.

Triple negative breast cancer (TNBC) is a heterogeneous disease that has no available targeted therapies. Previously, we have shown that caloric restriction (CR) can augment the effects of radiation therapy in a TNBC mouse model. To build upon this, we now present data regarding the combination of chemotherapy and CR in the same 4T1 model. Chemotherapy can induce inflammation that breeds resistance to therapy. We propose CR as a mechanism to decrease chemotherapy-induced inflammation and increase efficacy of therapy. 12-week old Balb/c mice were orthotopically injected with a syngeneic triple negative breast cancer cell line (4T1) and were treated in one of six cohorts: ad lib fed (AL), 30% reduction in calorie intake (CR), cisplatin or docetaxol alone or a combination CR+cisplatin/docetaxol. Mice in the cohorts receiving chemotherapy+CR had longer overall survival (12 ± 2 days) as compared to the AL group. These mice also demonstrated less lung metastases at the final time point of in vivo imaging. In addition, downregulation of the IGF-1R and IRS signaling pathways were noted most significantly in those mice receiving combination therapy. Lastly, serum from these mice demonstrated an increase in inflammatory cytokines TNF-α and IL-1ß in response to chemotherapy alone. This increase was dampened by the addition of CR. Taken together, these data suggest that while chemotherapy is effective in TNBC, it can cause inflammation, which can be a driver of resistance to therapy. This chemotherapy-induced inflammation can be reversed with the use of CR as a nontoxic adjunct to treatment.

The Influence of Health Insurance Policy on Radiation Oncology Physician SBRT/SABR Use Practices: A North American Survey.

PURPOSE: European data suggest that 8-fraction stereotactic body radiation therapy (SBRT) regimens may be similar in efficacy with less toxicity than ≤5-fraction SBRT for central lung lesions. However, under current Centers for Medicare and Medicaid Services guidelines, SBRT in the United States (US) is reimbursed for only ≤5 fractions, whereas there are no such restrictions for reimbursement in Canada. We hypothesize that US-specific SBRT reimbursement policies influence the use of ≥5-fraction SBRT in US academic centers in comparison with comparable Canadian centers. METHODS AND MATERIALS: A 15-question electronic survey was distributed to radiation oncologists at National Cancer Institute-designated cancer centers in the US and the 10 highest research-funded cancer centers in Canada. Fisher exact test or exact logistic regression if applicable was used, where P<.05 was considered statistically different from neutral. RESULTS: Of the 143 radiation oncologists from 60 US cancer centers and 6 Canadian cancer centers who completed the survey (17.6% response rate), 125 routinely prescribe SBRT. Fifty percent of US physicians versus 0% of Canadian physicians indicated that there are instances when they would like to prescribe >5-fraction SBRT but prescribe ≤5 fractions because of insurance reimbursement (P=.076 and P=.001, respectively). Seventy percent (P=.006) of US radiation oncologists versus 0% (P=.001) of Canadian radiation oncologists report that SBRT clinical investigation is constrained by the insurance reimbursement. The most common reported deterrent to prescribing >5-fraction SBRT in the US was insurance reimbursement (49.5%). CONCLUSIONS: US radiation oncologists are more likely than those in Canada to report that SBRT clinical investigation and >5-fraction SBRT use may be negatively influenced by health insurance reimbursement; this perception was not held by physicians in Canada. Health care environment may significantly affect radiation therapy decision making and practice patterns.

Hematologic Toxicity of Concurrent Administration of Radium-223 and Next-generation Antiandrogen Therapies.

PURPOSE/OBJECTIVES: Radium-223 is a first-in-class radiopharmaceutical recently approved for the treatment of castration-resistant prostate cancer in patients with symptomatic bone metastases. Initial studies investigating Radium-223 primarily used nonsteroidal first-generation antiandrogens. Since that time, newer antiandrogen therapies have demonstrated improved survival in patients with castration-resistant prostate cancer. It has been suggested that the rational combination of these newly approved agents with Radium-223 may lead to improved response rates and clinical outcomes. Currently, there is lack of information regarding the safety of concurrent administration of these agents with radiopharmaceuticals. Here, we report on hematologic toxicity findings from our institution in patients receiving concurrent Radium-223 and next-generation antiandrogen therapies with either enzalutamide or abiraterone. MATERIALS/METHODS: In a retrospective study, we analyzed patients who received Radium-223 as part of an early-access trial, and following FDA approval in May 2013, patients receiving Radium-223 as part of standard care. Radium-223 was given at standard dosing of 50 kBq/kg each month for 6 total cycles. Complete blood counts were performed before treatment monthly and following each injection. Blood counts from patients receiving Radium alone and concurrently with next-generation antiandrogens were compared. To date, 25 total patients were analyzed, with a median of 5 monthly doses received per patient. Fourteen patients received concurrent therapy during monthly Radium-223 with either enzalutamide (n=8) or abiraterone (n=6). RESULTS: Six patients expired due to disease progression. Two patients discontinued treatment due to grade 3 myelosuppression. For patients receiving either Radium alone and with concurrent next-generation antiandrogen therapy, there did not appear to be any statistically significant differences between initial and nadir blood counts. Mean change from initial neutrophil count to nadir was 1.9×10/L in patients receiving Radium alone, versus 2.3×10/L in patients receiving concurrent therapy (P=0.77). Mean change from initial hemoglobin value to nadir was 1.5 g/L in patients receiving Radium alone, versus 1.8 g/L in patients receiving concurrent therapy (P=0.31). Mean change from initial platelet count to nadir was 52.3×10 cells/L in patients receiving Radium alone versus 70.6×10 cells/L in patients receiving concurrent therapy (P=0.39). Individual blood counts for each measured laboratory are included in the supplemental data. PSA was stable or decreased in 22% of patients receiving Radium alone versus 35% of patients receiving combination treatment (P=0.24). CONCLUSIONS: Concurrent administration of Radium-223 and next-generation antiandrogen therapies appears to be well tolerated with similar toxicities to standard administration of Radium-223 alone. This particular cohort of patients represents a high-risk, heavily pretreated group of patients with advanced metastatic disease and significant marrow burden. Despite these risk factors, hematologic toxicity was modest and was in the range expected for this risk group based on previous trials. To date, this is the first study investigating the toxicity of combination treatment. Further studies investigating the safety and efficacy of combination treatments are warranted.

Emerging drugs to replace current leaders in first-line therapy for breast cancer.

Increasing knowledge of drug resistance and side effects of currently approved agents, and of the biology of breast cancer, has given way to new treatment options that improve on previously available agents, or medications that target specific kinases and proteins associated with an oncogenic phenotype. This paper discusses new agents, including improved formulations of paclitaxel and epothilones, and molecularly targeted agents such as bevacizumab, sunitinib malate, pertuzumab, lapatinib, the mTOR inhibitors and farnesyl transferase inhibitors. Although endocrine therapy is a targeted therapy, it is not covered in this paper. These agents have increased excitement in the treatment of breast cancer and stand on the forefront of a potential improvement in quality of life and treatment options for patients afflicted with this deadly disease.

Freedom from local and regional failure of contralateral neck with ipsilateral neck radiotherapy for node-positive tonsil cancer: updated results of an institutional clinical management approach.

PURPOSE: To update the outcomes of an institutional clinical management approach using ipsilateral neck radiotherapy in the treatment of node-positive squamous cell carcinoma of the tonsil with a well-lateralized primary lesion. METHODS AND MATERIALS: Between August 2003 and April 2014, 61 consecutive patients with ipsilateral node-positive squamous cell carcinoma of the tonsil without involvement of the base of the tongue or midline soft palate were treated at a community hospital-based cancer center with radiotherapy to the primary site and ipsilateral neck. Overall survival, disease-free survival and freedom from contralateral failure were calculated. RESULTS: Median follow up was 37.2months (range 4-121months). Freedom from contralateral nodal failure at 5years was 98% with one contralateral nodal failure noted. The patient underwent a salvage neck dissection and was treated with post-operative radiotherapy with no evidence of disease to date. 5-year overall survival (OS) was 92.4% and 5year disease-free survival (DFS) was 86.7%. CONCLUSIONS: This represents the single largest series reported from a community hospital-based cancer center in which lateralized tonsil cancers with N+ disease were treated with ipsilateral neck radiotherapy. In this carefully selected cohort of patients with well-lateralized tonsil cancers, the risk of contralateral nodal failure appears to be <5%, suggesting that prophylactic radiation of the contralateral neck may not be necessary. Future planned studies will focus on prospectively selecting subgroups of patients eligible for treatment de-intensification as survivorship issues in excellent prognosis HPV positive patients are increasingly becoming relevant.

microRNA alterations driving acute and late stages of radiation-induced fibrosis in a murine skin model.

PURPOSE: Although ionizing radiation is critical in treating cancer, radiation-induced fibrosis (RIF) can have a devastating impact on patients' quality of life. The molecular changes leading to radiation-induced fibrosis must be elucidated so that novel treatments can be designed. METHODS AND MATERIALS: To determine whether microRNAs (miRs) could be responsible for RIF, the fibrotic process was induced in the right hind legs of 9-week old CH3 mice by a single-fraction dose of irradiation to 35 Gy, and the left leg served as an unirradiated control. Fibrosis was quantified by measurements of leg length compared with control leg length. By 120 days after irradiation, the irradiated legs were 20% (P=.013) shorter on average than were the control legs. RESULTS: Tissue analysis was done on muscle, skin, and subcutaneous tissue from irradiated and control legs. Fibrosis was noted on both gross and histologic examination by use of a pentachrome stain. Microarrays were performed at various times after irradiation, including 7 days, 14 days, 50 days, 90 days, and 120 days after irradiation. miR-15a, miR-21, miR-30a, and miR-34a were the miRs with the most significant alteration by array with miR-34a, proving most significant on confirmation by reverse transcriptase polymerase chain reaction, c-Met, a known effector of fibrosis and downstream molecule of miR-34a, was evaluated by use of 2 cell lines: HCT116 and 1522. The cell lines were exposed to various stressors to induce miR changes, specifically ionizing radiation. Additionally, in vitro transfections with pre-miRs and anti-miRs confirmed the relationship of miR-34a and c-Met. CONCLUSIONS: Our data demonstrate an inverse relationship with miR-34a and c-Met; the upregulation of miR-34a in RIF causes inhibition of c-Met production. miRs may play a role in RIF; in particular, miR-34a should be investigated as a potential target to prevent or treat this devastating side effect of irradiation.

Comparison of intensity-modulated radiotherapy, adaptive radiotherapy, proton radiotherapy, and adaptive proton radiotherapy for treatment of locally advanced head and neck cancer.

BACKGROUND AND PURPOSE: Various radiotherapy planning methods for locally advanced squamous cell carcinoma of the head and neck (SCCHN) have been proposed to decrease normal tissue toxicity. We compare IMRT, adaptive IMRT, proton therapy (IMPT), and adaptive IMPT for SCCHN. MATERIALS AND METHODS: Initial and re-simulation CT images from 10 consecutive patients with SCCHN were used to quantify dosimetric differences between photon and proton therapy. Contouring was performed on both CTs, and plans (n=40 plans) and dose-volume histograms were generated. RESULTS: The mean GTV volume decreased 53.4% with re-simulation. All plans provided comparable PTV coverage. Compared with IMRT, adaptive IMRT significantly reduced the maximum dose to the mandible (p=0.020) and mean doses to the contralateral parotid gland (p=0.049) and larynx (p=0.049). Compared with IMRT and adaptive IMRT, IMPT significantly lowered the maximum doses to the spinal cord (p<0.002 for both) and brainstem (p<0.002 for both) and mean doses to the larynx (p<0.002 for both) and ipsilateral (p=0.004 IMRT, p=0.050 adaptive) and contralateral (p<0.002 IMRT, p=0.010 adaptive) parotid glands. Adaptive IMPT significantly reduced doses to all critical structures compared with IMRT and adaptive IMRT and several critical structures compared with non-adaptive IMPT. CONCLUSIONS: Although adaptive IMRT reduced dose to several normal structures compared with standard IMRT, non-adaptive proton therapy had a more favorable dosimetric profile than IMRT or adaptive IMRT and may obviate the need for adaptive planning. Protons allowed significant sparing of the spinal cord, parotid glands, larynx, and brainstem and should be considered for SCCHN to decrease normal tissue toxicity while still providing optimal tumor coverage.