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However, spectral imaging with PCDs such as material decomposition require highly quantitative raw data that accurately reflects X\u2010ray attenuation through the imaged object.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Purpose<\/jats:title>\n                    <jats:p>In CBCT, X\u2010ray scatter is the primary cause of degraded raw\u2010data fidelity. This study experimentally characterizes the effect of scatter on PCD counts and energy spectra and investigates a hardware\u2010driven approach to mitigate scatter contamination in photon counting CBCT (pcCBCT).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>A photon\u2010counting detector with a cadmium telluride (CdTe) sensor and two adjustable energy thresholds was integrated into a benchtop X\u2010ray imaging system mimicking the CBCT geometry of C\u2010arm linacs. Scatter contamination as a function of energy was characterized using phantoms of varying thicknesses and the beam\u2010stop method. Bias in the detected energy spectrum due to scatter, as well as the scatter\u2010to\u2010primary ratio (SPR) as a function of detected energy, were quantified. The effect of increased X\u2010ray fluence due to scatter on pulse pile up was measured under X\u2010ray fluence conditions relevant to image\u2010guided radiotherapy. To mitigate scatter, all experiments were repeated using a 2D antiscatter grid (ASG) prototype, which also served as a reference for quantifying scatter\u2010induced bias in contaminated raw data. The effect of scatter contamination on the energy\u2010specific CT number accuracy was evaluated in pcCBCT scans acquired with two energy bins.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Scatter bias increased counts by up to 96% in the 25\u201350\u00a0keV range in the normalized energy spectra. The mean energy of the spectrum shifted to lower energies by up to 8\u00a0keV as a result of scatter bias. Average scatter to primary ratio (SPR) was up to a factor of 5 higher at 35\u00a0keV than the SPR at 100\u00a0keV. SPR reached 4 in the 25\u221260\u00a0keV range. The incremental pulse pile up related count underestimation attributable to scatter\u2010induced fluence was\u00a0&lt;\u00a03%. The 2D ASG reduced SPR by 90%\u201394% across all energies and phantom configurations. The efficacy of 2D ASG in SPR reduction varied only 3% across 25\u2212120\u00a0keV range. Without scatter mitigation, mean CT\u2010number loss was 453 and 390 HU in the 25\u221260\u00a0keV and 60\u2212120\u00a0keV bins, respectively. The 2D ASG reduced CT number loss to 34 and 22 HU in the respective energy bins.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>Scatter fraction is substantially higher at lower energies and biases the energy spectrum toward lower energies under CBCT imaging scenarios relevant to radiotherapy. Consequently, CT number degradation is significantly greater at lower energies, which may challenge the quantitative utilization of low\u2010energy data in future pcCBCT systems and spectral imaging applications. The effect of scatter\u2010induced fluence increase on pulse pile up is deemed small. The 2D ASG effectively reduced scatter contamination across the entire energy spectrum and improved the fidelity of raw data for pcCBCT imaging.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1002\/mp.70389","type":"journal-article","created":{"date-parts":[[2026,3,16]],"date-time":"2026-03-16T03:08:11Z","timestamp":1773630491000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Experimental characterization and mitigation of scatter induced spectral contamination in photon counting CBCT for radiotherapy"],"prefix":"10.1002","volume":"53","author":[{"given":"Ryan","family":"Sabounchi","sequence":"first","affiliation":[{"name":"Department of Radiation Oncology University of Colorado School of Medicine  Aurora Colorado USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Uttam","family":"Pyakurel","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology University of Colorado School of Medicine  Aurora Colorado USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Abhinya","family":"Shukla","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology University of Colorado School of Medicine  Aurora Colorado USA"},{"name":"Department of Computer Science and Engineering University of Colorado Denver  Denver Colorado USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Farhang","family":"Bayat","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology University of Colorado School of Medicine  Aurora Colorado USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Cem","family":"Altunbas","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology University of Colorado School of Medicine  Aurora Colorado USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2026,3,15]]},"reference":[{"key":"e_1_2_8_2_1","doi-asserted-by":"publisher","DOI":"10.1002\/mp.14624"},{"key":"e_1_2_8_3_1","doi-asserted-by":"publisher","DOI":"10.1002\/mp.14121"},{"key":"e_1_2_8_4_1","doi-asserted-by":"publisher","DOI":"10.1148\/radiol.2015142631"},{"key":"e_1_2_8_5_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.crad.2017.04.002"},{"key":"e_1_2_8_6_1","doi-asserted-by":"publisher","DOI":"10.3390\/app14051724"},{"key":"e_1_2_8_7_1","doi-asserted-by":"publisher","DOI":"10.1007\/s00330\u2010006\u20100517\u20106"},{"key":"e_1_2_8_8_1","doi-asserted-by":"publisher","DOI":"10.1007\/s00330\u2010011\u20102062\u20101"},{"key":"e_1_2_8_9_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.radonc.2021.11.002"},{"key":"e_1_2_8_10_1","doi-asserted-by":"publisher","DOI":"10.1088\/0031\u20109155\/55\/5\/006"},{"key":"e_1_2_8_11_1","doi-asserted-by":"publisher","DOI":"10.1088\/1361\u20106560\/ab5c35"},{"key":"e_1_2_8_12_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.ijrobp.2014.03.004"},{"key":"e_1_2_8_13_1","doi-asserted-by":"publisher","DOI":"10.1002\/acm2.70083"},{"key":"e_1_2_8_14_1","doi-asserted-by":"publisher","DOI":"10.1002\/mp.14211"},{"key":"e_1_2_8_15_1","doi-asserted-by":"crossref","unstructured":"LuM WangA ShapiroE et\u00a0al.Dual energy imaging with a dual\u2010layer flat panel detector. 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