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Purpose: Noncoplanar plans (NCPs) are commonly used for proton treatment of bilateral head and neck (HN) malignancies. NCP requires additional verification setup imaging between beams to correct residual errors of robotic couch motion, which increases imaging dose and total treatment time. This study compared the quality and robustness of NCPs with those of coplanar plans (CPs). Methods and Materials: Under an IRB‐approved study, CPs were created retrospectively for 10 bilateral HN patients previously treated with NCPs maintaining identical beam geometry of the original plan but excluding couch rotations. Plan robustness to the inter‐fractional variation (IV) of both plans was evaluated through the Dose Volume Histograms (DVH) of weekly quality assurance CT (QACT) sets (39 total). In addition, delivery efficiency for both plans was compared using total treatment time (TTT) and beam‐on time (BOT). Results: No significant differences in plan quality were observed in terms of clinical target volume (CTV) coverage (D95) or organ‐at‐risk (OAR) doses (p > 0.4 for all CTVs and OARs). No significant advantage of NCPs in the robustness to IV was found over CP, either. Changes in D95 of QA plans showed a linear correlation (slope = 1.006, R2 > 0.99) between NCP and CP for three CTV data points (CTV1, CTV2, and CTV3) in each QA plan (117 data points for 39 QA plans). NCPs showed significantly higher beam delivery time than CPs for TTT (539 ± 50 vs. 897 ± 142 s; p < 0.001); however, no significant differences were observed for BOT. Conclusion: NCPs are not more robust to IV than CPs when treating bilateral HN tumors with pencil‐beam scanning proton beams. CPs showed plan quality and robustness similar to NCPs while reduced treatment time (∼6 min). This suggests that CPs may be a more efficient planning technique for bilateral HN cancer proton therapy. [ABSTRACT FROM AUTHOR]

Most patients with p16-positive oropharynx cancer (p16+OPC) receive elective nodal radiation therapy that improves regional control but increases acute and long-term toxicity. We evaluated the efficacy and toxicity profile of a reduced contralateral elective nodal volume in patients with p16+OPC receiving definitive or adjuvant radiation therapy. Patients with newly diagnosed p16+OPC without contralateral nodal involvement treated with primary proton or photon-based (chemo)radiation therapy or adjuvant (chemo)radiation therapy following transoral robotic surgery (TORS) were eligible for enrollment. The reduced contralateral nodal volume included high-risk regions of levels II and III1. The primary endpoint was elective out-of-field contralateral nodal failure. Dosimetric studies comparing standard versus reduced elective nodal volumes were analyzed with the t-test. Acute toxicity was collected using CTCAE v4.0. Fifty-two patients were enrolled of which 36 (69.2%) received definitive (chemo)radiation therapy. Sixteen (30.8%) patients underwent adjuvant radiation therapy following TORS of which 5 (31.2%) received concurrent chemotherapy. Proton therapy was used in 38 (73.1%) of patients. There were no elective nodal failures at a median follow up of 15 months (range 1-24 months). For the first 20 patients enrolled, dosimetric comparison of the reduced contralateral elective nodal volume to a consensus elective nodal volume demonstrated a decrease in mean dose (14.1 Gy to 18.5 Gy [p<0.05]) and V30 Gy (11.6% to 21.3% [p<0.01]) of the contralateral parotid gland. Significant differences were independent of radiation modality or technology. Acute grade 3 toxicity was observed in 13 (25%) patients including 6 (11.5%) who received a gastrostomy tube during treatment. There were no grade 4-5 acute toxicities, and no patients with 6 months of follow up retained gastrostomy tube. Precise delivery of radiation therapy to high-risk areas for contralateral nodal disease results in excellent regional control regardless of treatment approach. Dose to contralateral organs at risk and toxicity profile were favorable. Longer follow-up is needed to further support this de-intensification strategy. [ABSTRACT FROM AUTHOR]

Purpose: Pencil-beam scanning proton therapy has been considered as a potential modality for the 3D form of spatially-fractionated-radiation-therapy called lattice therapy. However, few practical solutions have been introduced in the clinic. Existing limitations include degradation in plan quality and robustness when using single-field versus multifield lattice plans, respectively. We propose a practical and robust proton lattice (RPL) planning method using multifield and evaluate its dosimetric characteristics compared to clinically acceptable photon lattice plans., Methods: Seven cases previously treated with photon lattice therapy were used to evaluate a novel RPL planning technique using two-orthogonal beams: a primary beam (PB) and a robust complementary beam (RCB) that deliver 67% and 33%, respectively, of the prescribed dose to vertices inside the gross-target-volume (GTV). Only RCB is robustly optimized for setup and range uncertainties. The number and volume of vertices, peak-to-valley dose ratios (PVDRs), and volume of low dose to GTV of proton and photon plans were compared. The RPL technique was then used in treatment of two patients and their dosimetric parameters are reported., Results: The RPL strategy was able to achieve the clinical planning goals. Compared to previously-treated photon plans, the average number of vertices increased by 30%, average vertex volume by 49% (18.2±25.9cc vs. 12.2±14.5cc, P=0.21), and higher PVDR (10.5±4.8 vs. 2.5±0.9, P<0.005) was achieved. In addition, RPL plans show more conformal dose with less low-dose to GTV (V30%: 60.9±7.2% vs. 81.6±13.9% and V10%: 88.3±4.5% vs. 98.6±3.6% [P<0.01]). The RPL plan for two treated patients showed PVDRs of 4.61 and 14.85 with vertices-to-GTV ratios of 1.52% and 1.30%, respectively., Conclusion: A novel RPL planning strategy using a pair of orthogonal beams was developed and successfully translated to the clinic. The proposed method can generate better quality plans, a higher number of vertices, and higher PVDRs than currently used photon lattice plans., (Copyright © 2024. Published by Elsevier Inc.)

Introduction: Due to the radiation-sparing effects on salivary gland acini, changes in the composition of the oral microbiome may be a driver for improved outcomes in patients receiving proton radiation, with potentially worse outcomes in patients exposed to photon radiation therapy. To date, a head-to-head comparison of oral microbiome changes at a metagenomic level with longitudinal sampling has yet to be performed in these patient cohorts., Methods and Materials: To comparatively analyze oral microbiome shifts during head and neck radiation therapy, a prospective pilot cohort study was performed at the Maryland Proton Treatment Center and the University of Maryland Marlene and Stewart Greenebaum Comprehensive Cancer Center. A longitudinal metagenomic comparative analysis of oral microbiome shifts was performed at three time points (pre-radiation, during radiation, and immediately post-radiation). Head and neck cancer patients receiving proton radiation ( n = 4) were compared to photon radiation ( n = 4). Additional control groups included healthy age- and sex-matched controls ( n = 5), head and neck cancer patients who never received radiation therapy ( n = 8), and patients with oral inflammatory disease ( n = 3)., Results: Photon therapy patients presented with lower microbial alpha diversity at all timepoints, and there was a trend towards reduced species richness as compared with proton therapy. Healthy controls and proton patients exhibited overall higher and similar diversity. A more dysbiotic state was observed in patients receiving photon therapy as compared to proton therapy, in which oral microbial homeostasis was maintained. Mucositis was observed in 3/4 photon patients and was not observed in any proton patients during radiation therapy. The bacterial de novo pyrimidine biosynthesis pathway and the nitrate reduction V pathway were comparatively higher following photon exposure. These functional changes in bacterial metabolism may suggest that photon exposure produces a more permissive environment for the proliferation of pathogenic bacteria., Conclusion: Oral microbiome dysbiosis in patients receiving photon radiation may be associated with increased mucositis occurrence. Proton radiation therapy for head and neck cancer demonstrates a safer side effect profile in terms of oral complications, oral microbiome dysbiosis, and functional metabolic status., Competing Interests: The author(s) declare(s) that there is no conflict of interest., (Copyright: © 2024 Meiller T, et al.)