Adam Bayliss headshot

Adam Bayliss, PhD

Associate Professor (CHS)

Department of Human Oncology

I am an associate professor in the Department of Human Oncology, where I apply my skills as a physicist and research scientist to the study of physics in medicine and daily clinical practice. I assess the available literature, test and safely implement new modalities and provide quality assurance of existing techniques and equipment. I have experience researching small field dosimetry, novel treatment planning techniques on volumetric arc therapy (VMAT) and Tomotherapy machines and CT/MRI-based brachytherapy planning. Currently, I oversee quality improvement of dosimetric planning techniques for the UW Hospitals and Clinics dosimetry group and streamlining of planning workflows.

Education

Resident, University of Wisconsin–Madison, Medical Physics (2012)

PhD, University of Wisconsin–Madison, Physics (2006)

MS, University of Wisconsin–Madison, Medical Physics (2010)

BA, University of Montana–Missoula, Physics (1999)

Academic Appointments

Associate Professor (CHS), Human Oncology (2021)

Assistant Professor (CHS), Human Oncology (2012)


Dr. Adam Bayliss tests and safely implements new modalities and provides quality assurance of existing techniques and equipment. He has experience researching small field dosimetry, novel treatment planning techniques on volumetric arc therapy (VMAT) and Tomotherapy machines and CT/MRI-based brachytherapy planning.

  • Pulsed reduced-dose rate re-irradiation for patients with recurrent grade 2 gliomas Neuro-oncology advances
    Harari CM, Burr AR, Morris BA, Tomé WA, Bayliss A, Bhatia A, Grogan PT, Robins HI, Howard SP
    2024 May 10;6(1):vdae073. doi: 10.1093/noajnl/vdae073. eCollection 2024 Jan-Dec.
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      BACKGROUND: Patients with grade 2 glioma exhibit highly variable survival. Re-irradiation for recurrent disease has limited mature clinical data. We report treatment results of pulsed reduced-dose rate (PRDR) radiation for patients with recurrent grade 2 glioma.

      METHODS: A retrospective analysis of 58 patients treated with PRDR from 2000 to 2021 was performed. Radiation was delivered in 0.2 Gy pulses every 3 minutes encompassing tumor plus margin. Survival outcomes and prognostic factors on outcome were Kaplan-Meier and Cox regression analyses.

      RESULTS: The median survival from the date of initial surgery was 8.6 years (95% CI: 5.5-11.8 years). 69% of patients showed malignant transformation to grade 3 (38%) or grade 4 (31%) glioma. Overall survival following PRDR was 12.6 months (95% CI: 8.3-17.0 months) and progression-free survival was 6.2 months (95% CI: 3.8-8.6 months). Overall response rate based on post-PRDR MRI was 36%. In patients who maintained grade 2 histology at recurrence, overall survival from PRDR was 22.0 months with 5 patients remaining disease-free, the longest at 8.2 and 11.4 years. PRDR was generally well tolerated.

      CONCLUSIONS: To the best of our knowledge, this is the largest reported series of patients with recurrent grade 2 gliomas treated with PRDR radiation for disease recurrence. We demonstrate promising survival and acceptable toxicity profiles following re-irradiation. In the cohort of patients who maintain grade 2 disease, prolonged survival (>5 years) is observed in selected patients. For the entire cohort, 1p19q codeletion, KPS, and longer time from initial diagnosis to PRDR were associated with improved survival.

      PMID:38845694 | PMC:PMC11154132 | DOI:10.1093/noajnl/vdae073


      View details for PubMedID 38845694
  • A Phase 2 Randomized Clinical Trial Evaluating 4-Dimensional Computed Tomography Ventilation-Based Functional Lung Avoidance Radiation Therapy for Non-Small Cell Lung Cancer International journal of radiation oncology, biology, physics
    Baschnagel AM, Flakus MJ, Wallat EM, Wuschner AE, Chappell RJ, Bayliss RA, Kimple RJ, Christensen GE, Reinhardt JM, Bassetti MF, Bayouth JE
    2024 Feb 20:S0360-3016(24)00327-4. doi: 10.1016/j.ijrobp.2024.02.019. Online ahead of print.
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      PURPOSE: To determine whether 4-dimensional computed tomography (4DCT) ventilation-based functional lung avoidance radiation therapy preserves pulmonary function compared with standard radiation therapy for non-small cell lung cancer (NSCLC).

      METHODS AND MATERIALS: This single center, randomized, phase 2 trial enrolled patients with NSCLC receiving curative intent radiation therapy with either stereotactic body radiation therapy or conventionally fractionated radiation therapy between 2016 and 2022. Patients were randomized 1:1 to standard of care radiation therapy or functional lung avoidance radiation therapy. The primary endpoint was the change in Jacobian-based ventilation as measured on 4DCT from baseline to 3 months postradiation. Secondary endpoints included changes in volume of high- and low-ventilating lung, pulmonary toxicity, and changes in pulmonary function tests (PFTs).

      RESULTS: A total of 122 patients were randomized and 116 were available for analysis. Median follow up was 29.9 months. Functional avoidance plans significantly (P < .05) reduced dose to high-functioning lung without compromising target coverage or organs at risk constraints. When analyzing all patients, there was no difference in the amount of lung showing a reduction in ventilation from baseline to 3 months between the 2 arms (1.91% vs 1.87%; P = .90). Overall grade ≥2 and grade ≥3 pulmonary toxicities for all patients were 24.1% and 8.6%, respectively. There was no significant difference in pulmonary toxicity or changes in PFTs between the 2 study arms. In the conventionally fractionated cohort, there was a lower rate of grade ≥2 pneumonitis (8.2% vs 32.3%; P = .049) and less of a decline in change in forced expiratory volume in 1 second (-3 vs -5; P = .042) and forced vital capacity (1.5 vs -6; P = .005) at 3 months, favoring the functional avoidance arm.

      CONCLUSIONS: There was no difference in posttreatment ventilation as measured by 4DCT between the arms. In the cohort of patients treated with conventionally fractionated radiation therapy with functional lung avoidance, there was reduced pulmonary toxicity, and less decline in PFTs suggesting a clinical benefit in patients with locally advanced NSCLC.

      PMID:38387810 | DOI:10.1016/j.ijrobp.2024.02.019


      View details for PubMedID 38387810
  • Dose-rate dependence and IMRT QA suitability of EBT3 radiochromic films for pulse reduced dose-rate radiotherapy (PRDR) dosimetry Journal of applied clinical medical physics
    Khan AU, Radtke J, Hammer C, Malyshev J, Morris B, Glide-Hurst C, DeWerd L, Culberson W, Bayliss A
    2024 Jan;25(1):e14229. doi: 10.1002/acm2.14229. Epub 2023 Nov 30.
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      BACKGROUND: Pulsed reduced dose rate (PRDR) is an emerging radiotherapy technique for recurrent diseases. It is pertinent that the linac beam characteristics are evaluated for PRDR dose rates and a suitable dosimeter is employed for IMRT QA.

      PURPOSE: This study sought to investigate the pulse characteristics of a 6 MV photon beam during PRDR irradiations on a commercial linac. The feasibility of using EBT3 radiochromic film for use in IMRT QA was also investigated by comparing its response to a commercial diode array phantom.

      METHODS: A plastic scintillator detector was employed to measure the photon pulse characteristics across nominal repetition rates (NRRs) in the 5-600 MU/min range. Film was irradiated with dose rates in the 0.033-4 Gy/min range to study the dose rate dependence. Five clinical PRDR treatment plans were selected for IMRT QA with the Delta4 phantom and EBT3 film sheets. The planned and measured dose were compared using gamma analysis with a criterion of 3%/3 mm. EBT3 film QA was performed using a cumulative technique and a weighting factor technique.

      RESULTS: Negligible differences were observed in the pulse width and height data between the investigated NRRs. The pulse width was measured to be 3.15 ± 0.01 μ s $\mu s$ and the PRF was calculated to be 3-357 Hz for the 5-600 MU/min NRRs. The EBT3 film was found to be dose rate independent within 3%. The gamma pass rates (GPRs) were above 99% and 90% for the Delta4 phantom and the EBT3 film using the cumulative QA method, respectively. GPRs as low as 80% were noted for the weighting factor EBT3 QA method.

      CONCLUSIONS: Altering the NRRs changes the mean dose rate while the instantaneous dose rate remains constant. The EBT3 film was found to be suitable for PRDR dosimetry and IMRT QA with minimal dose rate dependence.

      PMID:38032123 | PMC:PMC10795427 | DOI:10.1002/acm2.14229


      View details for PubMedID 38032123
  • Using <sup>18</sup>F-DCFPyL Prostate-Specific Membrane Antigen-Directed Positron Emission Tomography/Magnetic Resonance Imaging to Define Intraprostatic Boosts for Prostate Stereotactic Body Radiation Therapy Advances in radiation oncology
    Floberg JM, Wells SA, Ojala D, Bayliss RA, Hill PM, Morris BA, Morris ZS, Ritter M, Cho SY
    2023 Apr 9;8(5):101241. doi: 10.1016/j.adro.2023.101241. eCollection 2023 Sep-Oct.
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      PURPOSE: The recently reported FLAME trial demonstrated a biochemical disease-free survival benefit to using a focal intraprostatic boost to multiparametric magnetic resonance imaging (mpMRI)-identified lesions in men with localized prostate cancer treated with definitive radiation therapy. Prostate-specific membrane antigen (PSMA)-directed positron emission tomography (PET) may identify additional areas of disease. In this work, we investigated using both PSMA PET and mpMRI in planning focal intraprostatic boosts using stereotactic body radiation therapy (SBRT).

      METHODS AND MATERIALS: We evaluated a cohort of patients (n = 13) with localized prostate cancer who were imaged with 2-(3-(1-carboxy-5-[(6-[18F]fluoro-pyridine-2-carbonyl)-amino]-pentyl)-ureido)-pentanedioic acid (18F-DCFPyL) PET/MRI on a prospective imaging trial before undergoing definitive therapy. The number of lesions concordant (overlapping) and discordant (no overlap) on PET and MRI was assessed. Overlap between concordant lesions was evaluated using the Dice and Jaccard similarity coefficients. Prostate SBRT plans were created fusing the PET/MRI imaging to computed tomography scans acquired the same day. Plans were created using only MRI-identified lesions, only PET-identified lesions, and the combined PET/MRI lesions. Coverage of the intraprostatic lesions and doses to the rectum and urethra were assessed for each of these plans.

      RESULTS: The majority of lesions (21/39, 53.8%) were discordant between MRI and PET, with more lesions seen by PET alone (12) than MRI alone (9). Of lesions that were concordant between PET and MRI, there were still areas that did not overlap between scans (average Dice coefficient, 0.34). Prostate SBRT planning using all lesions to define a focal intraprostatic boost provided the best coverage of all lesions without compromising constraints on the rectum and urethra.

      CONCLUSIONS: Using both mpMRI and PSMA-directed PET may better identify all areas of gross disease within the prostate. Using both imaging modalities could improve the planning of focal intraprostatic boosts.

      PMID:37250282 | PMC:PMC10209128 | DOI:10.1016/j.adro.2023.101241


      View details for PubMedID 37250282
  • Pulsed Reduced Dose Rate for Reirradiation of Recurrent Breast Cancer Practical radiation oncology
    Burr AR, Robins HI, Bayliss RA, Howard SP
    2020 Mar-Apr;10(2):e61-e70. doi: 10.1016/j.prro.2019.09.004. Epub 2019 Sep 14.
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      PURPOSE: Locoregionally recurrent breast cancer within a previously irradiated field requires weighing the benefits of reirradiation against the increased rates of toxicity. Here we evaluate the outcomes of patients treated with pulsed reduced dose rate (PRDR) radiation therapy with concurrent low-dose capecitabine as a method to increase the therapeutic ratio of re-treatment.

      METHODS AND MATERIALS: Patients treated from November 2000 to June 1, 2018 with PRDR radiation therapy at University of Wisconsin were identified. Patients were re-treated to a median dose of 54 Gy (range, 37.5-66 Gy) using PRDR radiation therapy, delivering radiation at an apparent dose rate of 6.67 cGy/min to allow for increased sublethal damage repair of normal tissues. The median cumulative dose was 109.8 Gy. Twenty-two patients were treated with concurrent capecitabine, most frequently at 500 mg twice per day. The Kaplan-Meier method was used for survival analysis, and Cox regression analysis was used for univariate and multivariate analysis.

      RESULTS: Forty-three patients were identified who underwent reirradiation for locoregionally recurrent invasive breast cancer, with a median follow-up of 20.5 months. Twenty-four patients had gross disease. Nineteen patients had simultaneous metastatic disease. The complete response rate was 83.3% in treated patients with gross disease. Locoregional recurrence-free survival was 81.3% and 73.8% for all patients at 1 and 2 years, respectively. Overall survival for patients with localized disease was 95.7% at 1 year and 91.1% at 2 years. The rate of acute grade 3 radiation dermatitis was 25.6% with no other acute grade 3 toxicities. Grade 3 late toxicity occurred in 18.6% of patients.

      CONCLUSIONS: PRDR radiation therapy with capecitabine was a well-tolerated and effective method for treating patients with recurrent breast cancer. Prospective studies are necessary to compare side effects and efficacy with conventional dose rate reirradiation and to evaluate the potential role for capecitabine in the recurrent setting.

      PMID:31526900 | DOI:10.1016/j.prro.2019.09.004


      View details for PubMedID 31526900
  • Large volume re-irradiation for recurrent meningioma with pulsed reduced dose rate radiotherapy Journal of neuro-oncology
    Witt JS, Musunuru HB, Bayliss RA, Howard SP
    2019 Jan;141(1):103-109. doi: 10.1007/s11060-018-03011-z. Epub 2018 Nov 3.
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      PURPOSE: Meningiomas comprise up to 30% of primary brain tumors. The majority of meningioma patients enjoy high rates of control after conventional therapies. However, patients with recurrent disease previously treated with radiotherapy have few options for salvage treatment, and systemic interventions have proven largely ineffective. The aim of this study was to determine whether pulsed reduced dose rate radiotherapy (PRDR) was well tolerated in a small cohort of patients with recurrent meningioma.

      METHODS: We retrospectively identified eight patients with recurrent intracranial meningioma treated with PRDR from April 2013 to August of 2017 at a single institution. All patients had radiographic and/or pathologic evidence of progression prior to treatment and had previously completed conventional radiotherapy. Acute and late toxicities were graded based on CTCAE 4.0.

      RESULTS: Of eight patients, six had histologically confirmed atypical meningiomas upon recurrence. All patients were re-treated with IMRT at an apparent dose rate of 0.0667 Gy/min. Median time between radiation courses was 7.7 years. Median PRDR dose was 54 Gy in 27 fractions to a median volume of 261.6 cm3. Two patients (25%) had in field failure with a median follow up of 23.3 months. PFS at 6 months was 100%. All but one (87.5%) patient was still alive at last follow up. No patient experienced grade ≥ 2 acute or late toxicities.

      CONCLUSIONS: PRDR re-irradiation was well tolerated and appeared effective for a small cohort of patients with recurrent meningioma previously treated with radiotherapy. A phase II trial to assess this prospectively is in development.

      PMID:30392090 | DOI:10.1007/s11060-018-03011-z


      View details for PubMedID 30392090
  • Radiation treatment planning and delivery strategies for a pregnant brain tumor patient Journal of applied clinical medical physics
    Labby ZE, Barraclough B, Bayliss RA, Besemer AE, Dunkerley AP, Howard SP
    2018 Sep;19(5):368-374. doi: 10.1002/acm2.12262. Epub 2018 Jul 30.
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      The management of a pregnant patient in radiation oncology is an infrequent event requiring careful consideration by both the physician and physicist. The aim of this manuscript was to highlight treatment planning techniques and detail measurements of fetal dose for a pregnant patient recently requiring treatment for a brain cancer. A 27-year-old woman was treated during gestational weeks 19-25 for a resected grade 3 astrocytoma to 50.4 Gy in 28 fractions, followed by an additional 9 Gy boost in five fractions. Four potential plans were developed for the patient: a 6 MV 3D-conformal treatment plan with enhanced dynamic wedges, a 6 MV step-and-shoot (SnS) intensity-modulated radiation therapy (IMRT) plan, an unflattened 6 MV SnS IMRT plan, and an Accuray TomoTherapy HDA helical IMRT treatment plan. All treatment plans used strategies to reduce peripheral dose. Fetal dose was estimated for each treatment plan using available literature references, and measurements were made using thermoluminescent dosimeters (TLDs) and an ionization chamber with an anthropomorphic phantom. TLD measurements from a full-course radiation delivery ranged from 1.0 to 1.6 cGy for the 3D-conformal treatment plan, from 1.0 to 1.5 cGy for the 6 MV SnS IMRT plan, from 0.6 to 1.0 cGy for the unflattened 6 MV SnS IMRT plan, and from 1.9 to 2.6 cGy for the TomoTherapy treatment plan. The unflattened 6 MV SnS IMRT treatment plan was selected for treatment for this particular patient, though the fetal doses from all treatment plans were deemed acceptable. The cumulative dose to the patient's unshielded fetus is estimated to be 1.0 cGy at most. The planning technique and distance between the treatment target and fetus both contributed to this relatively low fetal dose. Relevant treatment planning strategies and treatment delivery considerations are discussed to aid radiation oncologists and medical physicists in the management of pregnant patients.

      PMID:30062720 | PMC:PMC6123144 | DOI:10.1002/acm2.12262


      View details for PubMedID 30062720
  • Dosimetric Comparison of Real-Time MRI-Guided Tri-Cobalt-60 Versus Linear Accelerator-Based Stereotactic Body Radiation Therapy Lung Cancer Plans Technology in cancer research & treatment
    Wojcieszynski AP, Hill PM, Rosenberg SA, Hullett CR, Labby ZE, Paliwal B, Geurts MW, Bayliss RA, Bayouth JE, Harari PM, Bassetti MF, Baschnagel AM
    2017 Jun;16(3):366-372. doi: 10.1177/1533034617691407. Epub 2017 Feb 7.
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      PURPOSE: Magnetic resonance imaging-guided radiation therapy has entered clinical practice at several major treatment centers. Treatment of early-stage non-small cell lung cancer with stereotactic body radiation therapy is one potential application of this modality, as some form of respiratory motion management is important to address. We hypothesize that magnetic resonance imaging-guided tri-cobalt-60 radiation therapy can be used to generate clinically acceptable stereotactic body radiation therapy treatment plans. Here, we report on a dosimetric comparison between magnetic resonance imaging-guided radiation therapy plans and internal target volume-based plans utilizing volumetric-modulated arc therapy.

      MATERIALS AND METHODS: Ten patients with early-stage non-small cell lung cancer who underwent radiation therapy planning and treatment were studied. Following 4-dimensional computed tomography, patient images were used to generate clinically deliverable plans. For volumetric-modulated arc therapy plans, the planning tumor volume was defined as an internal target volume + 0.5 cm. For magnetic resonance imaging-guided plans, a single mid-inspiratory cycle was used to define a gross tumor volume, then expanded 0.3 cm to the planning tumor volume. Treatment plan parameters were compared.

      RESULTS: Planning tumor volumes trended larger for volumetric-modulated arc therapy-based plans, with a mean planning tumor volume of 47.4 mL versus 24.8 mL for magnetic resonance imaging-guided plans ( P = .08). Clinically acceptable plans were achievable via both methods, with bilateral lung V20, 3.9% versus 4.8% ( P = .62). The volume of chest wall receiving greater than 30 Gy was also similar, 22.1 versus 19.8 mL ( P = .78), as were all other parameters commonly used for lung stereotactic body radiation therapy. The ratio of the 50% isodose volume to planning tumor volume was lower in volumetric-modulated arc therapy plans, 4.19 versus 10.0 ( P < .001). Heterogeneity index was comparable between plans, 1.25 versus 1.25 ( P = .98).

      CONCLUSION: Magnetic resonance imaging-guided tri-cobalt-60 radiation therapy is capable of delivering lung high-quality stereotactic body radiation therapy plans that are clinically acceptable as compared to volumetric-modulated arc therapy-based plans. Real-time magnetic resonance imaging provides the unique capacity to directly observe tumor motion during treatment for purposes of motion management.

      PMID:28168936 | PMC:PMC5616053 | DOI:10.1177/1533034617691407


      View details for PubMedID 28168936
  • Gadoxetate for direct tumor therapy and tracking with real-time MRI-guided stereotactic body radiation therapy of the liver Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
    Wojcieszynski AP, Rosenberg SA, Brower JV, Hullett CR, Geurts MW, Labby ZE, Hill PM, Bayliss RA, Paliwal B, Bayouth JE, Harari PM, Bassetti MF
    2016 Feb;118(2):416-8. doi: 10.1016/j.radonc.2015.10.024. Epub 2015 Nov 25.
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      SBRT is increasingly utilized in liver tumor treatment. MRI-guided RT allows for real-time MRI tracking during therapy. Liver tumors are often poorly visualized and most contrast agents are transient. Gadoxetate may allow for sustained tumor visualization. Here, we report on the first use of gadoxetate during real-time MRI-guided SBRT.

      PMID:26627702 | DOI:10.1016/j.radonc.2015.10.024


      View details for PubMedID 26627702
  • Impact of Node Negative Target Volume Delineation on Contralateral Parotid Gland Dose Sparing Using IMRT in Head and Neck Cancer Technology in cancer research & treatment
    Magnuson WJ, Urban E, Bayliss RA, Harari PM
    2015 Jun;14(3):315-9. doi: 10.1177/1533034614547456. Epub 2014 Sep 10.
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      There is considerable practice variation in treatment of the node negative (N0) contralateral neck in patients with head and neck cancer. In this study, we examined the impact of N0 neck target delineation volume on radiation dose to the contralateral parotid gland. Following institutional review board approval, 12 patients with head and neck cancer were studied. All had indications for treatment of the N0 neck, such as midline base of tongue or soft palate extension or advanced ipsilateral nodal disease. The N0 neck volumes were created using the Radiation Therapy Oncology Group head and neck contouring atlas. The physician-drawn N0 neck clinical target volume (CTV) was expanded by 25% to 200% to generate volume variation, followed by a 3-mm planning target volume (PTV) expansion. Surrounding organs at risk were contoured and complete intensity-modulated radiation therapy plans were generated for each N0 volume expansion. The median N0 target volume drawn by the radiation oncologist measured 93 cm(3) (range 71-145). Volumetric expansion of the N0 CTV by 25% to 200% increased the resultant mean dose to the contralateral parotid gland by 1.4 to 8.5 Gray (Gy). For example, a 4.1-mm increase in the N0 neck CTV translated to a 2.0-Gy dose increase to the parotid, 7.4 mm to a 4.5 Gy dose increase, and 12.5 mm to an 8.5 Gy dose increase, respectively. The treatment volume designated for the N0 neck has profound impact on resultant dose to the contralateral parotid gland. Variations of up to 15 mm are routine across physicians in target contouring, reflecting individual preference and training expertise. Depending on the availability of immobilization and image guidance techniques, experts commonly recommend 3 to 10 mm margin expansions to generate the PTV. Careful attention to the original volume of the N0 neck CTV, as well as expansion margins, is important in achieving effective contralateral gland sparing to reduce the resultant xerostomia and dysguesia that may ensue after radiotherapy.

      PMID:25782188 | DOI:10.1177/1533034614547456


      View details for PubMedID 25782188
  • Selective omission of level V nodal coverage for patients with oropharyngeal cancer: Clinical validation of intensity-modulated radiotherapy experience and dosimetric significance Head & neck
    Mohindra P, Urban E, Pagan JD, Geye HM, Patel VB, Bayliss AA, Bender ET, Harari PM
    2016 Apr;38(4):499-505. doi: 10.1002/hed.23924. Epub 2015 Jun 16.
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      BACKGROUND: We sought to validate the consensus recommendation and assess dosimetric significance of selective omission of nodal level V from intensity-modulated radiotherapy (IMRT) clinical target volume (CTV) for oropharyngeal cancer.

      METHODS: IMRT plans and clinical outcomes for 112 patients with oropharyngeal cancer (nodal classification N0-N2b) were analyzed for coverage of ipsilateral and contralateral nodal level V. Additionally, new IMRT plans were generated in 6 randomly selected patients to assess its dosimetric impact.

      RESULTS: With median follow-up of 3.4 years, there were no failures identified in nodal level V with or without nodal level V omission. Upon dosimetric evaluation, significant reduction in integral dose, V10 Gy , V20 Gy , V30 Gy , V40 Gy , and V50 Gy was observed by excluding unilateral and bilateral level V from the CTV.

      CONCLUSION: We clinically validate the consensus recommendation for selective omission of level V nodal coverage in IMRT planning of patients with oropharyngeal cancer and demonstrate significant dosimetric advantages.

      PMID:25445257 | DOI:10.1002/hed.23924


      View details for PubMedID 25445257
  • Improvements in dose calculation accuracy for small off-axis targets in high dose per fraction tomotherapy Medical physics
    Hardcastle N, Bayliss A, Wong HD, Rosenfeld AB, Tomé WA
    2012 Aug;39(8):4788-94. doi: 10.1118/1.4736811.
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      PURPOSE: A recent field safety notice from TomoTherapy detailed the underdosing of small, off-axis targets when receiving high doses per fraction. This is due to angular undersampling in the dose calculation gantry angles. This study evaluates a correction method to reduce the underdosing, to be implemented in the current version (v4.1) of the TomoTherapy treatment planning software.

      METHODS: The correction method, termed "Super Sampling" involved the tripling of the number of gantry angles from which the dose is calculated during optimization and dose calculation. Radiochromic film was used to measure the dose to small targets at various off-axis distances receiving a minimum of 21 Gy in one fraction. Measurements were also performed for single small targets at the center of the Lucy phantom, using radiochromic film and the dose magnifying glass (DMG).

      RESULTS: Without super sampling, the peak dose deficit increased from 0% to 18% for a 10 mm target and 0% to 30% for a 5 mm target as off-axis target distances increased from 0 to 16.5 cm. When super sampling was turned on, the dose deficit trend was removed and all peak doses were within 5% of the planned dose. For measurements in the Lucy phantom at 9.7 cm off-axis, the positional and dose magnitude accuracy using super sampling was verified using radiochromic film and the DMG.

      CONCLUSIONS: A correction method implemented in the TomoTherapy treatment planning system which triples the angular sampling of the gantry angles used during optimization and dose calculation removes the underdosing for targets as small as 5 mm diameter, up to 16.5 cm off-axis receiving up to 21 Gy.

      PMID:22894403 | DOI:10.1118/1.4736811


      View details for PubMedID 22894403
  • High dose per fraction dosimetry of small fields with gafchromic EBT2 film Medical physics
    Hardcastle N, Basavatia A, Bayliss A, Tomé WA
    2011 Jul;38(7):4081-5. doi: 10.1118/1.3597834.
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      PURPOSE: Small field dosimetry is prone to uncertainties due to the lack of electronic equilibrium and the use of the correct detector size relative to the field size measured. It also exhibits higher sensitivity to setup errors as well as large variation in output with field size and shape. Radiochromic film is an attractive method for reference dosimetry in small fields due to its ability to provide 2D dose measurements while having minimal impact on the dose distribution. Gafchromic EBT2 has a dose range of up to 40 Gy; therefore, it could potentially be useful for high dose reference dosimetry with high spatial resolution. This is a requirement in stereotactic radiosurgery deliveries, which deliver high doses per fraction to small targets.

      METHODS: Targets of 4 mm and 12 mm diameters were treated to a minimum peripheral dose of 21 Gy prescribed to 80% of the maximum dose in one fraction. Target doses were measured with EBT2 film (both targets) and an ion chamber (12 mm target only). Measured doses were compared with planned dose distributions using profiles through the target and minimum peripheral dose coverage.

      RESULTS: The measured target doses and isodose coverage agreed with the planned dose within +/-1 standard deviation of three measurements, which were 2.13% and 2.5% for the 4 mm and 12 mm targets, respectively.

      CONCLUSIONS: EBT2 film is a feasible dosimeter for high dose per fraction reference 2D dosimetry.

      PMID:21859007 | DOI:10.1118/1.3597834


      View details for PubMedID 21859007

Contact Information

Adam Bayliss, PhD

600 Highland Avenue Madison,
K4/b100
Madison, WI 53792