Minimal acute toxicity from proton beam therapy for major salivary gland cancer.

Introduction: Proton beam therapy (PBT) reduces normal organ dose compared to intensity-modulated radiation therapy (IMRT) for patients with major salivary gland tumors. It is not known whether this dosimetric advantage is clinically meaningful for reducing acute toxicity.Methods: We evaluated treatment parameters and acute toxicity outcomes of patients with major salivary gland cancers enrolled on the Proton Collaborative Group REG001-09 trial (NCT01255748).Results: One-hundred and five patients with a median age of 61 years were included. The majority had parotid (N = 90) versus submandibular gland (N = 15) tumors. The patients were treated across seven institutions in the United States between 2010 and 2017, most commonly in the postoperative setting (70.5%) although a minority were treated definitively (29.5%). Median PBT dose was 66.5 GyE in 33 fractions; only one patient was prescribed less than 50 GyE. Chemotherapy was given concurrently to 20%. Median follow-up was 14.3 months. Acute grade 2 or higher toxicity included nausea (1.5%), dysgeusia (4.8%), xerostomia (7.6%), mucositis (10.5%) and dysphagia (10.5%).Conclusions: PBT should be strongly considered when ipsilateral radiation therapy is indicated for major salivary gland cancer based on a considerably lower incidence of acute grade 2 or higher toxicity in this analysis compared to historical IMRT outcomes.

Minimal toxicity after proton beam therapy for prostate and pelvic nodal irradiation: results from the proton collaborative group REG001-09 trial.

BACKGROUND: Proton beam therapy (PBT) reduces normal organ dose compared to intensity modulated radiation therapy (IMXT) for prostate cancer patients who receive pelvic radiation therapy. It is not known whether this dosimetric advantage results in less gastrointestinal (GI) and genitourinary (GU) toxicity than would be expected from IMXT. MATERIAL AND METHODS: We evaluated treatment parameters and toxicity outcomes for non-metastatic prostate cancer patients who received pelvic radiation therapy and enrolled on the PCG REG001-09 trial. Patients who received X-ray therapy and/or brachytherapy were excluded. Of 3210 total enrolled prostate cancer patients, 85 received prostate and pelvic radiation therapy exclusively with PBT. Most had clinically and radiographically negative lymph nodes although 6 had pelvic nodal disease and one also had para-aortic involvement. Pelvic radiation therapy was delivered using either 2 fields (opposed laterals) or 3 fields (opposed laterals and a posterior beam). Median pelvic dose was 46.9 GyE (range 39.7-56) in 25 fractions (range 24-30). Median boost dose to the prostate +/- seminal vesicles was 30 GyE (range 20-41.4) in 16 fractions (range 10-24). RESULTS: Median follow-up was 14.5 months (range 2.8-49.2). Acute grade 1, 2, and 3 GI toxicity rates were 16.4, 2.4, 0%, respectively. Acute grade 1, 2, and 3 GU toxicity rates were 60, 34.1, 0%, respectively. CONCLUSIONS: Prostate cancer patients who receive pelvic radiation therapy using PBT experience significantly less acute GI toxicity than is expected using IMXT. Further investigation is warranted to confirm whether this favorable acute GI toxicity profile is related to small bowel sparing from PBT.

Establishing quality indicators for neck dissection: Correlating the number of lymph nodes with oncologic outcomes (NRG Oncology RTOG 9501 and RTOG 0234).

BACKGROUND: Prospective quality metrics for neck dissection have not been established for patients with head and neck squamous cell carcinoma. The purpose of this study was to investigate the association between lymph node counts from neck dissection, local-regional recurrence, and overall survival. METHODS: The number of lymph nodes counted from neck dissection in patients treated in 2 NRG Oncology trials (Radiation Therapy Oncology Group [RTOG] 9501 and RTOG 0234) was evaluated for its prognostic impact on overall survival with a multivariate Cox model adjusted for demographic, tumor, and lymph node data and stratified by the postoperative treatment group. RESULTS: Five hundred seventy-two patients were analyzed at a median follow-up of 8 years. Ninety-eight percent of the patients were pathologically N+. The median numbers of lymph nodes recorded on the left and right sides were 24 and 25, respectively. The identification of fewer than 18 nodes was associated with worse overall survival in comparison with 18 or more nodes (hazard ratio [HR], 1.38; 95% confidence interval [CI], 1.09-1.74; P = .007). The difference appeared to be driven by local-regional failure (HR, 1.46; 95% CI, 1.02-2.08; P = .04) but not by distant metastases (HR, 1.08; 95% CI, 0.77-1.53; P = .65). When the analysis was limited to NRG Oncology RTOG 0234 patients, adding the p16 status to the model did not affect the HR for dissected nodes, and the effect of nodes did not differ with the p16 status. CONCLUSIONS: The removal and identification of 18 or more lymph nodes was associated with improved overall survival and lower rates of local-regional failure, and this should be further evaluated as a measure of quality in neck dissections for mucosal squamous cell carcinoma. Cancer 2016;122:3464-71. © 2016 American Cancer Society.

Low contralateral failure rate with unilateral proton beam radiotherapy for oropharyngeal squamous cell carcinoma: A multi-institutional prospective study from the proton collaborative group.

INTRODUCTION: Unilateral radiation therapy is appropriate for select patients with oropharyngeal squamous cell carcinoma (OPSCC). The use of proton beam therapy (PBT) in the unilateral setting decreases the dose to the contralateral neck and organs at risk. This study aims to evaluate contralateral recurrences in patients who received ipsilateral PBT. METHODS: We evaluated the Proton Collaborative Group database for patients treated with PBT for head and neck squamous cell carcinoma between the years 2015-2020 at 12 institutions. Dosimetric analysis was performed in five cases. RESULTS: Our analysis included 41 patients that received ipsilateral PBT with a mean follow-up of 14.7 months. 37% patients (n = 15) were treated for recurrent disease, and 63% (n = 26) were treated for de novo disease. Oropharyngeal sites included tonsillar fossa (n = 30) and base of tongue (n = 11). The median dose and BED delivered were 69.96 CGE and 84 Gy, respectively. Eight (20%) patients experienced at least one grade 3 dysphagia (n = 4) or esophagitis (n = 4) toxicity. No grade ≥ 4 toxicities were reported. There was one (2.4%) failure in the contralateral neck. The 1-year locoregional control was 88.9% and the freedom from distant metastasis was 95.5% (n = 2). The dosimetric analysis demonstrated similar ipsilateral level II cervical nodal region doses, whereas contralateral doses were higher with photon plans, mean: 15.5 Gy and 0.7CGE, D5%: 25.1 Gy and 6.6CGE. CONCLUSIONS: Our series is the first to report outcomes for patients with OPSCC receiving unilateral PBT. The contralateral neck failure rate was excellent and comparable to failure rates with photon irradiation.

Neutron radiotherapy for adenoid cystic carcinoma of the lacrimal gland.

PURPOSE: Lacrimal gland adenoid cystic carcinomas are rare, aggressive orbital tumors that share histopathologic similarities with salivary gland malignancies. Neutron radiotherapy may be useful for treatment due to its high biological effectiveness for salivary malignancies. METHODS: The authors retrospectively reviewed the outcomes for 11 lacrimal gland adenoid cystic carcinoma patients treated with neutrons from 1988 to 2011. Most had undergone surgery prior to radiation therapy. However, gross residual disease was present in 8 patients. The most common American Joint Committee on Cancer stage was T4cN0M0. Four patients with skull base involvement received a radiosurgery boost and 1 received a proton therapy boost. RESULTS: Median follow up was 6.2 years. Median overall survival was 11.1 years and median disease-free survival was 6.3 years. Five-year local control was estimated by the Kaplan-Meier method as 80%. Three patients had a local recurrence; 4 developed distant metastases. Six patients died. Seven patients had intact vision in the affected eye before neutron radiation. Two required enucleation for a painful dry eye. Of the 5 who avoided an enucleation, 3 had either severe visual impairment (20/400) or only light perception and 2 were without known vision compromise or complications at the time of their death. One patient developed asymptomatic frontal lobe radionecrosis after 2 courses of radiation therapy. CONCLUSIONS: Neutron radiation therapy achieved excellent 5-year local control in this series of high-risk patients, with most cases having gross residual disease. Late recurrences and distant metastases remain a challenge. Meaningful ipsilateral vision preservation was not possible in most cases in the long term, although only 2 patients required an enucleation for treatment effects.

Effects of tissue heterogeneity and comparisons of collapsed cone and Monte Carlo fast neutron patient dosimetry using the University of Washington clinical neutron therapy system (CNTS).

Fast neutron therapy is a high linear energy transfer (LET) radiation treatment modality offering advantages over low LET radiations. Multileaf collimator technology reduces normal-tissue dose (toxicity) and makes neutron therapy more comparable to MV x-ray treatments. Published clinical-trial and other experiences with fast neutron therapy are reported. Early comparative studies failed to consider differences in target-dose spatial conformality between x-ray and neutron treatments, which is especially important for organs-at-risk close to tumor targets. Treatments planning systems (TPS) for high-energy neutrons lag behind TPS tools for MV x-rays, creating challenges for comparative studies of clinical outcomes. A previously published Monte Carlo model of the University of Washington (UW) Clinical Neutron Therapy System (CNTS) is refined and integrated with the RayStation TPS as an external dose planning/verification tool. The collapsed cone (CC) dose calculations in the TPS are based on measured dose profiles and output factors in water, with the absolute dose determined using a tissue-equivalent ionization chamber. For comparison, independent (external) Monte Carlo simulation computes dose on a voxel-by-voxel basis using an atlas that maps Hounsfield Unit (HU) numbers to elemental composition and density. Although the CC algorithm in the TPS accurately computes neutron dose to water compared to Monte Carlo calculations, calculated dose to water differs from bone or tissue depending largely on hydrogen content. Therefore, the elemental composition of tissue and bone, rather than the material or electron density, affects fast neutron dose. While the CC algorithm suffices for reproducible patient dosimetry in fast neutron therapy, adopting methods that consider tissue heterogeneity would enhance patient-specific neutron dose accuracy relative to national standards for other types of ionizing radiation. Corrections for tissue composition have a significant impact on absolute dose and the relative biological effectiveness (RBE) of neutron treatments compared to other radiation types (MV x-rays, protons, and carbon ions).

Peripheral lymphocytes and lactate dehydrogenase correlate with response and survival in head and neck cancers treated with immune checkpoint inhibitors.

BACKGROUND: Little is known regarding associations between peripheral blood biomarkers (PBBMs) and survival, response, and toxicity in recurrent/metastatic head and neck squamous cell carcinomas (R/M HNSCC) treated with immune checkpoint inhibitors (ICIs). METHODS: In this single-institution retrospective cohort study, a dataset of patients with R/M HNSCC treated with ICIs between 08/2012-03/2021 was established, including demographic and clinicopathologic characteristics. Pretreatment PBBMs were collected and evaluated for associations with grade ≥3 adverse events (G ≥ 3AE) by CTCAEv5, objective response (ORR) by RECIST 1.1, overall survival (OS), and progression-free survival (PFS). Multivariable models for each outcome were created using elastic net variable selection. RESULTS: Our study included 186 patients, with 51 (27%) demonstrating complete or partial response to immunotherapy. Multivariable models adjusted for ECOG performance status (PS), p16, and smoking demonstrated that pretreatment higher LDH and absolute neutrophils, as well as lower percent lymphocytes correlated with worse OS and PFS. Higher LDH and lower % lymphocytes also correlated with worse ORR. CONCLUSIONS: In the largest study to date examining PBBMs in ICI-treated R/M HNSCCs, our variable selection method revealed PBBMs prognostic for survival and response to immunotherapy. These biomarkers warrant further investigation in a prospective study along with validation with CPS biomarker.

Neutrophil to lymphocyte ratio and peripheral blood biomarkers correlate with survival outcomes but not response among head and neck and salivary cancer treated with pembrolizumab and vorinostat.

BACKGROUND: Associations between peripheral blood biomarkers and oncologic outcomes were explored in recurrent/metastatic (R/M) head and neck squamous cell carcinoma (HN) and salivary gland cancer (SGC) treated with pembrolizumab and vorinostat on a phase II trial (NCT02538510). EXPERIMENTAL DESIGN: Twenty-five HN and 25 SGCs were treated with pembrolizumab and vorinostat. Baseline peripheral blood was available in 21 HN and 20 SGCs and evaluated for associations with grade ≥3 adverse events (G ≥ 3AE) by CTCAEv4, objective response rate (ORR), overall survival (OS), and progression-free survival (PFS). RESULTS: Higher pretreatment neutrophil-to-lymphocyte ratio (NLR) and neutrophils, as well as lower pretreatment lymphocytes and T helper cells correlated with worse OS and PFS. Higher NLR further predicted increased rates of G ≥ 3AEs. No correlations with ORR were observed. CONCLUSIONS: In a prospectively evaluated cohort of HN and SGCs treated with pembrolizumab and vorinostat, we observed novel associations between peripheral blood biomarkers and oncologic outcomes and toxicities.

Radiation therapy for low- and high-risk perineural invasion in head and neck cutaneous squamous cell carcinoma: Clinical outcomes and patterns of failure.

BACKGROUND: Perineural invasion (PNI) in head and neck squamous cell carcinoma (HNSCC) portends poor prognosis. Extent of treatment of nerve pathways with varying degrees of PNI and patterns of failure following elective neural radiotherapy (RT) remain unclear. METHODS: Retrospective review of HNSCC patients with high-risk (clinical/gross, large-nerve, extensive) or low-risk (microscopic/focal) PNI who underwent curative-intent treatment from 2010 to 2021. RESULTS: Forty-four patients (mean follow-up 22 months; 59% high-risk, 41% low-risk PNI) were included. Recurrence following definitive treatment occurred in 31% high-risk and 17% low-risk PNI patients. Among high-risk patients, 69% underwent surgery with post-operative RT and 46% underwent elective neural RT. Local control (83% low-risk vs. 75% high-risk), disease-free, and overall survival did not differ between groups. CONCLUSIONS: High local control rates were achieved in high-risk PNI patients treated with adjuvant or primary RT, including treatment of both involved and uninvolved, communicating cranial nerves, with few failures in electively treated regions.

Performance status (PS) as a predictor of poor response to immune checkpoint inhibitors (ICI) in recurrent/metastatic head and neck cancer (RMHNSCC) patients.

BACKGROUND: Anti-PD1 checkpoint inhibitors (ICI) represent an established standard-of-care for patients with recurrent/metastatic head and neck squamous cell carcinoma (RMHNSCC). Landmark studies excluded patients with ECOG performance status (PS) ≥2; the benefit of ICI in this population is therefore unknown. METHODS: We retrospectively reviewed RMHNSCC patients who received 1+ dose of ICI at our institution between 2013 and 2019. Demographic and clinical data were obtained; the latter included objective response (ORR), toxicity, and any unplanned hospitalization (UH). Associations were explored using uni- and multivariate analysis. Overall survival (OS) was estimated using a Cox proportional hazards model; ORR, toxicity, and UH were evaluated with logistic regression. RESULTS: Of the 152 patients, 29 (19%) had an ECOG PS ≥2. Sixty-six (44%) experienced toxicity; 54 (36%) had a UH. A multivariate model for OS containing PS, smoking status, and HPV status demonstrated a strong association between ECOG ≥2 and shorter OS (p < 0.001; HR = 3.30, CI = 2.01-5.41). An association between OS and former (vs. never) smoking was also seen (p < 0.001; HR = 2.17, CI = 1.41-3.35); current smoking did not reach statistical significance. On univariate analysis, poor PS was associated with inferior ORR (p = 0.03; OR = 0.25, CI = 0.06-0.77) and increased UH (p = 0.04; OR = 2.43, CI = 1.05-5.71). There was no significant association between toxicity and any patient characteristic. CONCLUSIONS: We observed inferior OS, ORR, and rates of UH among ICI-treated RMHNSCC patients with ECOG 2/3. Our findings help frame discussion of therapeutic options in this poor-risk population.

High End-of-Life Health Care Utilization in a Contemporary Cohort of Head and Neck Cancer Patients Treated with Immune Checkpoint Inhibitors.

Background/Objective: End-of-life health care utilization (EOLHCU) is largely uncharacterized among patients with recurrent/metastatic head and neck squamous cell carcinomas (RMHNSCC), particularly now that immune checkpoint inhibitors (ICI) have been introduced to the treatment landscape. We examined this in a single-institution, retrospective study. Design/Settings: We utilized a database of deceased, ICI-treated RMHNSCC patients to obtain demographic and EOLHCU data, the latter of which included advanced care plan documentation (ACPD) and systemic therapy or emergency room (ER)/hospital/intensive care unit (ICU) admission within 30 days of death (DOD). This was compared with a cohort of deceased thoracic malignancy (TM) patients in an exploratory analysis. Multivariate analysis was performed to examine for association between patient factors (such as age, Eastern Cooperative Oncology Group (ECOG) performance status, or smoking status) and overall survival (OS); associations between the said patient factors and EOLHCU were also evaluated. This study was conducted at an academic, tertiary center in the United States. Results: The RMHNSCC patients (n = 74) were more likely to have ACPD (p < 0.01), an emergency department visit (p < 0.01), and/or hospital admission (p < 0.01) within 30 DOD relative to the TM group. There was no difference in ICU admissions, ICU deaths, or systemic therapy at end of life (EOL). The OS declined in association with ECOG performance status (PS) and smoking. No association was observed between patient factors and any EOLHCU metric. Conclusions: At our center, patients with ICI-treated RMHNSCC have higher rates of both ACPD and EOLHCU, suggesting high symptom burden and representing opportunities for further study into supportive care augmentation.

Intensity-Modulated Proton Therapy for Nasopharynx Cancer: 2-year Outcomes from a Single Institution.

PURPOSE: Advances in radiotherapy have improved tumor control and reduced toxicity in the management of nasopharyngeal carcinoma (NPC). Local failure remains a problem for some patients with advanced primary tumors, and toxicities are significant given the large treatment volume and tumor proximity to critical structures, even with modern photon-based radiotherapy. Proton therapy has unique dosimetric advantages, and recent technological advances now allow delivery of intensity-modulated proton therapy (IMPT), which can potentially improve the therapeutic ratio in NPC. We report our 2-year clinical outcomes with IMPT for NPC. MATERIALS AND METHODS: We retrospectively reviewed treatment records of patients with NPC treated with IMPT at our center. Demographics, dosimetry, tumor response, local regional control (LRC), distant metastasis, overall survival, and acute and late toxicity outcomes were reviewed. Analyses were performed with descriptive statistics and Kaplan-Meier method. Toxicity was graded per Common Terminology Criteria for Adverse Events (version 4.0). RESULTS: Twenty-six patients were treated from 2015 to 2020. Median age was 48 years (range, 19-73 years), 62% (n = 16) had T3-T4 disease, 92% (n = 24) were node positive, 92% (n = 24) had stage III-IV disease, and 69% (n = 18) had positive results for Epstein-Barr virus. Dose-painted pencil-beam IMPT was used. Most patients (85%; 22 of 26) were treated with 70 Gy(RBE) in 33 fractions once daily; 4 (15%) underwent hyperfractionated accelerated treatment twice daily. All received concurrent cisplatin chemotherapy; 7 (27%) also received induction chemotherapy. All patients (100%) completed the planned radiotherapy, and no acute or late grade 4 or 5 toxicities were observed. At median follow-up of 25 months (range, 4-60), there were 2 local regional failures (8%) and 3 distant metastases (12%). The Kaplan-Meier 2-year LRC, freedom from distant metastasis, and overall survival were 92%, 87%, and 85% respectively. CONCLUSION: IMPT is feasible in locally advanced NPC with early outcomes demonstrating excellent LRC and favorable toxicity profile. Our data add to the growing body of evidence supporting the clinical use of IMPT for NPC.

Comparisons of 3-Dimensional Conformal and Intensity-Modulated Neutron Therapy for Head and Neck Cancers.

PURPOSE: Neutron therapy is a high linear energy transfer modality that is useful for the treatment of radioresistant head and neck (H&N) cancers. It has been limited to 3-dimensioanal conformal-based fast-neutron therapy (3DCNT), but recent technical advances have enabled the clinical implementation of intensity-modulated neutron therapy (IMNT). This study evaluated the comparative dosimetry of IMNT and 3DCNT plans for the treatment of H&N cancers. MATERIALS AND METHODS: Seven H&N IMNT plans were retrospectively created for patients previously treated with 3DCNT at the University of Washington (Seattle). A custom RayStation model with neutron-specific scattering kernels was used for inverse planning. Organ-at-risk (OAR) objectives from the original 3DCNT plan were initially used and were then systematically reduced to investigate the feasibility of improving a therapeutic ratio, defined as the ratio of the mean tumor to OAR dose. The IMNT and 3DCNT plan quality was evaluated using the therapeutic ratio, isodose contours, and dose volume histograms. RESULTS: When compared with the 3DCNT plans, IMNT reduces the OAR dose for the equivalent tumor coverage. Moreover, IMNT is most advantageous for OARs in close spatial proximity to the target. For the 7 patients with H&N cancers examined, the therapeutic ratio for IMNT increased by an average of 56% when compared with the 3DCNT. The maximum OAR dose was reduced by an average of 20.5% and 20.7% for the spinal cord and temporal lobe, respectively. The mean dose to the larynx decreased by an average of 80%. CONCLUSION: The IMNT significantly decreases the OAR doses compared with 3DCNT and provides comparable tumor coverage. Improvements in the therapeutic ratio with IMNT are especially significant for dose-limiting OARs near tumor targets. Moreover, IMNT provides superior sparing of healthy tissues and creates significant new opportunities to improve the care of patients with H&N cancers treated with neutron therapy.

Neutron Therapy for High-Grade Salivary Carcinomas in the Adjuvant and Primary Treatment Setting.

OBJECTIVES/HYPOTHESIS: Our primary objective was to compare differences in survival of patients with high-grade salivary gland carcinomas (SGCs) receiving adjuvant neutron versus photon radiotherapy using a hospital-based national cohort and restricted mean survival time (RMST) analysis. Our secondary objective was to compare survival of similar patients treated with primary neutron versus photon radiation. STUDY DESIGN: Multicenter, retrospective population-based study of patients within the National Cancer Database from 2004 to 2014. METHODS: One thousand eight hundred forty-four patients were selected on diagnosis of high-grade parotid and submandibular malignancies. One thousand seven hundred seventy-seven patients receiving photon and 67 patients receiving neutron therapy were identified who met inclusion criteria. Patients were then categorized as having primary surgery with adjuvant radiation or primary radiation without prior surgery. Bivariate analysis was performed to assess for differences between groups, and RMST analysis was performed at 1-, 2-, and 5-year timepoints with controlling for available covariate data. RESULTS: There was no significant difference in RMST for patients receiving neutrons over photons at 1, 2, and 5 years in the adjuvant setting. Among patients undergoing primary radiotherapy, there was a difference in RMST of 2.29 months at 1 year and 5.05 months at 2 years for neutrons over photons, though this benefit was not observed at 5 years post-therapy. CONCLUSIONS: For patients with high grade SGCs undergoing adjuvant photon versus neutron radiotherapy, there was no difference in RMST. There was observed to be a significant difference in RMST at 1 and 2 years among patients undergoing primary neutron therapy of up to 5 months. Given the benefit observed with primary neutron therapy, it should be considered in both the primary and adjuvant treatment setting. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:541-547, 2021.

Proton Therapy for Locally Advanced Oropharyngeal Cancer: Initial Clinical Experience at the University of Washington.

PURPOSE: Proton therapy can potentially improve the therapeutic ratio over conventional radiation therapy for oropharyngeal squamous cell cancer (OPSCC) by decreasing acute and late toxicity. We report our early clinical experience with intensity-modulated proton therapy (IMPT). MATERIALS AND METHODS: We retrospectively reviewed patients with OPSCC treated with IMPT at our center. Endpoints include local regional control (LRC), progression-free survival (PFS), overall survival (OS), tumor response, and toxicity outcomes. Toxicity was graded as per the Common Terminology Criteria for Adverse Events v4.03. Descriptive statistics and Kaplan-Meier method were used. RESULTS: We treated 46 patients from March 2015 to August 2017. Median age was 58 years, 93.5% were male, 67% were nonsmokers, 98% had stage III-IVB disease per the 7th edition of the AJCC [American Joint Committee on Cancer] Cancer Staging Manual, and 89% were p16 positive. Twenty-eight patients received definitive IMPT to total dose of 70 to 74.4 Gy(RBE), and 18 patients received postoperative IMPT to 60 to 66 Gy(RBE) following transoral robotic surgery (TORS). Sixty-four percent of patients received concurrent systemic therapy. There were no treatment interruptions or observed acute grade 4 or 5 toxicities. Eighteen patients had percutaneous endoscopic gastrostomy (PEG) tube placement; the majority (14) were placed prophylactically. The most common grade 3 acute toxicities were dermatitis (76%) and mucositis (72%). The most common late toxicity was grade 2 xerostomia (30%). At a median follow-up time of 19.2 months (interquartile range [IQR], 11.2-28.4), primary complete response was 100% and nodal complete response was 92%. One patient required a salvage neck dissection owing to an incomplete response at 4 months. There were no recorded local regional or marginal recurrences, PFS was 93.5%, and OS was 95.7%. CONCLUSION: Our early results for IMPT in OPSCC are promising with no local regional or marginal recurrences and a favorable toxicity profile. Our data add to a body of evidence that supports the clinical use of IMPT. Randomized comparative trials are encouraged.

Scattering kernels for fast neutron therapy treatment planning.

The University of Washington (UW) Clinical Neutron Therapy System (CNTS) has been used to treat over 3300 patients. Treatment planning for these patients is currently performed using an MV x-ray model in Pinnacle® adapted to fit measurements of fast neutron output factors, wedge factors, depth-dose and lateral profiles. While this model has provided an adequate representation of the CNTS for 3D conformal treatment planning, later versions of Pinnacle did not allow for isocentric gantry rotation machines with a source-to-axis distance of 150 cm. This restriction limited the neutron model to version 9.0 while the photon and electron treatment planning at the UW had moved on to newer versions. Also, intensity modulated neutron therapy (IMNT) is underdevelopment at the UW, and the Pinnacle neutron model developed cannot be used for inverse treatment planning. We have used the MCNP6 Monte Carlo code system to develop Collapsed Cone (CC) and Singular Value Decomposition (SVD) neutron scattering kernels suitable for integration into the RayStation treatment planning system. Kernels were generated for monoenergetic neutrons with energies ranging from 1 keV to 51 MeV, i.e. the energy range most relevant to the CNTS. Percent depth dose (PDD) profiles computed in RayStation for the CC and SVD kernels are in excellent agreement with each other for depths beyond the beam's dose build-up region (depths greater than about 1.7 cm) for open 2.8 × 2.8 cm2, 10.3 × 10.3 cm2, and 28.8 × 32.8 cm2 fields. Lateral profiles at several depths, as well as the PDD, calculated using the CC kernels in RayStation for the full CNTS energy spectrum pass a 3%/3 mm gamma test for field sizes of 2.8 × 2.8 cm2, 10.0 × 10.3 cm2, and 28.8 × 32.8 cm2.

Rectal Hydrogel Spacer Improves Late Gastrointestinal Toxicity Compared to Rectal Balloon Immobilization After Proton Beam Radiation Therapy for Localized Prostate Cancer: A Retrospective Observational Study.

PURPOSE: Our purpose was to compare dosimetric parameters and late gastrointestinal outcomes between patients treated with proton beam therapy (PBT) for localized prostate cancer with rectal balloon immobilization versus a hydrogel rectal spacer. METHODS AND MATERIALS: Patients with localized, clinical stage T1-4 prostate adenocarcinoma were treated at a single institution using conventionally fractionated, dose-escalated PBT from 2013 to 2018. Patient-reported gastrointestinal toxicity was prospectively collected, and the incidence of rectal bleeding was retrospectively reviewed from patient records. RESULTS: One hundred ninety-two patients were treated with rectal balloon immobilization, and 75 were treated with a rectal spacer. Rectal hydrogel spacer significantly improved rectal dosimetry while maintaining excellent target coverage. The 2-year actuarial rate of grade 2+ late rectal bleeding was 19% and 3% in the rectal balloon and hydrogel spacer groups, respectively (P = .003). In univariable analysis, the probability of grade 2+ rectal bleeding was significantly correlated with increasing rectal dose. In multivariable analysis, only receipt of spacer hydrogel (hazard ratio, 0.145; P = .010) and anticoagulation use (hazard ratio, 5.019; P < .001) were significantly associated with grade 2+ bleeding. At 2-year follow-up, patient-reported Expanded Prostate Cancer Index Composite bowel quality of life composite scores were less diminished in the hydrogel spacer group (absolute mean difference, 5.5; P = .030). CONCLUSIONS: Use of rectal hydrogel spacer for prostate PBT is associated with a significantly lower incidence of clinically relevant, late rectal bleeding and lower decrement in long-term, patient-reported bowel quality of life compared with rectal balloon immobilization. Our results suggest that hydrogel spacer may improve rectal sparing compared with rectal balloon immobilization during PBT for prostate cancer.

Role of particle radiotherapy in the management of head and neck cancer.

PURPOSE OF REVIEW: Modern imaging techniques and powerful computers allow a radiation oncologist to design treatments delivering higher doses of radiation than previously possible. Dose distributions imposed by the physics of 'standard' photon and electron beams limit further dose escalation. Hadron radiotherapy offers advantages in either dose distribution and/or improved radiobiology that may significantly improve the treatment of certain head and neck malignancies. RECENT FINDINGS: Clinical studies support the effectiveness of fast-neutron radiotherapy in the treatment of major and minor salivary gland tumors. Data show highly favorable outcomes with proton radiotherapy for skull-base malignancies and tumors near highly critical normal tissues compared with that expected with standard radiotherapy. Heavy-ion radiotherapy clinical studies are mainly being conducted with fully stripped carbon ions, and limited data seem to indicate a possible improvement over proton radiotherapy for the same subset of radioresistant tumors where neutrons show a benefit over photons. SUMMARY: Fast-neutron radiotherapy has different radiobiological properties compared with standard radiotherapy but similar depth dose distributions. Its role in the treatment of head and neck cancer is currently limited to salivary gland malignancies and certain radioresistant tumors such as sarcomas. Protons have the same radiobiological properties as standard radiotherapy beams but more optimal depth dose distributions, making it particularly advantageous when treating tumors adjacent to highly critical structures. Heavy ions combine the radiobiological properties of fast neutrons with the physical dose distributions of protons, and preliminary data indicate their utility for radioresistant tumors adjacent to highly critical structures.

The efficacy of neutron radiation therapy in treating salivary gland malignancies.

OBJECTIVES: Radiation therapy is commonly used to treat head and neck malignancies. While there is abundant research regarding photon radiation therapy, literature on neutron radiotherapy (NRT) and oral complications is limited. This study aims to determine: (1) the 6-year and 10-year locoregional control and survival rates, (2) factors associated with locoregional control and survival and (3) the frequency of oral complications in patients undergoing NRT for salivary gland malignancies. MATERIALS AND METHODS: This is a retrospective cohort study. The sample was composed of patients with salivary gland malignancies treated with NRT between 1997 and 2010. Data were extracted from patient charts, telephone surveys, and social security records. Multivariate competing risk and Cox regression models were used to assess predictors of locoregional control and survival. RESULTS: The sample was composed of 545 subjects with a mean age of 54.2 years (±16). The predominant tumor and location were adenoid cystic carcinoma (47%) and the parotid (56%). Multivariate analysis indicated that positive surgical margins, biopsied/inoperable malignancies, neck involvement, and lymphovascular invasion were prognostic risk factors associated with decreased survival. The 6- and 10-year locoregional control rates were 84% and 79%. The 6- and 10-year survival rates were 72% and 62%. Osteoradionecrosis developed in 3.4% of subjects. CONCLUSIONS: The 6- and 10-year locoregional control and survival rates compare favorably to rates reported for conventional photon radiation. Osteoradionecrosis rates were comparable to that of photon radiation treatment (2-7%). Given the potential benefits of NRT, healthcare professionals should be educated regarding its indications and oral complications.