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Alexei Trofimov - One of the best experts on this subject based on the ideXlab platform.

  • MO-A-213AB-09: Hypofractionated Proton Therapy of the Prostate: The Impact of the Uncertainties in Dose Delivery and Alpha/Beta Ratio on Tumor Dose Escalation.
    Medical physics, 2012
    Co-Authors: Yi Wang, Alexei Trofimov
    Abstract:

    Hypofractionation is expected to improve therapeutic Ratio for prostate radiotherapy, due to the relatively low alpha/beta Ratio of the prostate tumor (∼1.2 to 2.0 Gy). However, the gain in tumor equivalent dose in 2-Gy fractions (EQD2) is accompanied by the increased uncertainty in delivered dose due to inter-fractional variations. The purpose of this study is to evaluate how this trade-off is affected by the uncertainty of the tumor alpha/beta. We used serial CT images acquired from two prostate cancer patients. Target and normal organs were contoured on the simulation and daily images. A 3D conformal proton plan was designed based on standard fractionation (78 Gy in 39 fractions) and renormalized for hypofractionation (between 5 and 28 fractions). The fraction size of the hypofractionated protocols was adjusted so as to maintain the maximum rectal dose at 78 Gy-EQD2 (alpha/beta = 3 Gy). The fractional dose, calculated on each daily CT, was mapped to the simulation geometry via deformable registRation. The worst-case-scenario PTV dose for a hypofractionated protocol was estimated by summing the fractions (e.g., 28) with the lowest D97%. The target dose (e.g., D100%) was evaluated for alpha/beta of 1.2 to 2.0 Gy. The dose delivery uncertainty due to inter-fractional motion increased as the treatment became more hypofractionated. D100% was<78 Gy-EQD2 for protocols with 28, 26, 23 and 20 fractions when alpha/beta was >1.25, 1.46, 1.68 and 1.84 Gy, respectively. At alpha/beta of 2 Gy (1.2 Gy), D99% ranged from ∼79 (81) to 85 (98) Gy-EQD2 for treatments in 28 to 5 fractions. Below D97%, the target dose was predominantly determined by alpha/beta, and the motion impact was minimal. In prostate treatments, the impact of inter-fractional motion on tumor dose escalation is small for alpha/beta <2.0 Gy, and is of minimal concern to hypofractionated proton therapy. This study was supported by the Federal Share of program income earned by Massachusetts General Hospital on C06-CA059267, Proton Therapy Research and Treatment Center. © 2012 American Association of Physicists in Medicine.

  • MO-A-213AB-09: Hypofractionated Proton Therapy of the Prostate: The Impact of the Uncertainties in Dose Delivery and Alpha/Beta Ratio on Tumor Dose Escalation.
    Medical Physics, 2012
    Co-Authors: Yi Wang, Alexei Trofimov
    Abstract:

    Purpose: Hypofractionation is expected to improve therapeutic Ratio for prostate radiotherapy, due to the relatively low alpha/beta Ratio of the prostate tumor (∼1.2 to 2.0 Gy). However, the gain in tumor equivalent dose in 2‐Gy fractions (EQD2) is accompanied by the increased uncertainty in delivereddose due to inter‐fractional variations. The purpose of this study is to evaluate how this trade‐off is affected by the uncertainty of the tumor alpha/beta. Methods: We used serial CTimages acquired from two prostate cancer patients. Target and normal organs were contoured on the simulation and daily images. A 3D conformal proton plan was designed based on standard fractionation (78 Gy in 39 fractions) and renormalized for hypofractionation (between 5 and 28 fractions). The fraction size of the hypofractionated protocols was adjusted so as to maintain the maximum rectal dose at 78 Gy‐EQD2 (alpha/beta = 3 Gy). The fractional dose, calculated on each daily CT, was mapped to the simulation geometry via deformable registRation. The worst‐case‐scenario PTV dose for a hypofractionated protocol was estimated by summing the fractions (e.g., 28) with the lowest D97%. The target dose (e.g., D100%) was evaluated for alpha/beta of 1.2 to 2.0 Gy. Results: The dosedelivery uncertainty due to inter‐fractional motion increased as the treatment became more hypofractionated. D100% was 1.25, 1.46, 1.68 and 1.84 Gy, respectively. At alpha/beta of 2 Gy (1.2 Gy), D99% ranged from ∼79 (81) to 85 (98) Gy‐EQD2 for treatments in 28 to 5 fractions. Below D97%, the target dose was predominantly determined by alpha/beta, and the motion impact was minimal. Conclusions: In prostate treatments, the impact of inter‐fractional motion on tumordose escalation is small for alpha/beta

Yi Wang - One of the best experts on this subject based on the ideXlab platform.

  • MO-A-213AB-09: Hypofractionated Proton Therapy of the Prostate: The Impact of the Uncertainties in Dose Delivery and Alpha/Beta Ratio on Tumor Dose Escalation.
    Medical physics, 2012
    Co-Authors: Yi Wang, Alexei Trofimov
    Abstract:

    Hypofractionation is expected to improve therapeutic Ratio for prostate radiotherapy, due to the relatively low alpha/beta Ratio of the prostate tumor (∼1.2 to 2.0 Gy). However, the gain in tumor equivalent dose in 2-Gy fractions (EQD2) is accompanied by the increased uncertainty in delivered dose due to inter-fractional variations. The purpose of this study is to evaluate how this trade-off is affected by the uncertainty of the tumor alpha/beta. We used serial CT images acquired from two prostate cancer patients. Target and normal organs were contoured on the simulation and daily images. A 3D conformal proton plan was designed based on standard fractionation (78 Gy in 39 fractions) and renormalized for hypofractionation (between 5 and 28 fractions). The fraction size of the hypofractionated protocols was adjusted so as to maintain the maximum rectal dose at 78 Gy-EQD2 (alpha/beta = 3 Gy). The fractional dose, calculated on each daily CT, was mapped to the simulation geometry via deformable registRation. The worst-case-scenario PTV dose for a hypofractionated protocol was estimated by summing the fractions (e.g., 28) with the lowest D97%. The target dose (e.g., D100%) was evaluated for alpha/beta of 1.2 to 2.0 Gy. The dose delivery uncertainty due to inter-fractional motion increased as the treatment became more hypofractionated. D100% was<78 Gy-EQD2 for protocols with 28, 26, 23 and 20 fractions when alpha/beta was >1.25, 1.46, 1.68 and 1.84 Gy, respectively. At alpha/beta of 2 Gy (1.2 Gy), D99% ranged from ∼79 (81) to 85 (98) Gy-EQD2 for treatments in 28 to 5 fractions. Below D97%, the target dose was predominantly determined by alpha/beta, and the motion impact was minimal. In prostate treatments, the impact of inter-fractional motion on tumor dose escalation is small for alpha/beta <2.0 Gy, and is of minimal concern to hypofractionated proton therapy. This study was supported by the Federal Share of program income earned by Massachusetts General Hospital on C06-CA059267, Proton Therapy Research and Treatment Center. © 2012 American Association of Physicists in Medicine.

  • MO-A-213AB-09: Hypofractionated Proton Therapy of the Prostate: The Impact of the Uncertainties in Dose Delivery and Alpha/Beta Ratio on Tumor Dose Escalation.
    Medical Physics, 2012
    Co-Authors: Yi Wang, Alexei Trofimov
    Abstract:

    Purpose: Hypofractionation is expected to improve therapeutic Ratio for prostate radiotherapy, due to the relatively low alpha/beta Ratio of the prostate tumor (∼1.2 to 2.0 Gy). However, the gain in tumor equivalent dose in 2‐Gy fractions (EQD2) is accompanied by the increased uncertainty in delivereddose due to inter‐fractional variations. The purpose of this study is to evaluate how this trade‐off is affected by the uncertainty of the tumor alpha/beta. Methods: We used serial CTimages acquired from two prostate cancer patients. Target and normal organs were contoured on the simulation and daily images. A 3D conformal proton plan was designed based on standard fractionation (78 Gy in 39 fractions) and renormalized for hypofractionation (between 5 and 28 fractions). The fraction size of the hypofractionated protocols was adjusted so as to maintain the maximum rectal dose at 78 Gy‐EQD2 (alpha/beta = 3 Gy). The fractional dose, calculated on each daily CT, was mapped to the simulation geometry via deformable registRation. The worst‐case‐scenario PTV dose for a hypofractionated protocol was estimated by summing the fractions (e.g., 28) with the lowest D97%. The target dose (e.g., D100%) was evaluated for alpha/beta of 1.2 to 2.0 Gy. Results: The dosedelivery uncertainty due to inter‐fractional motion increased as the treatment became more hypofractionated. D100% was 1.25, 1.46, 1.68 and 1.84 Gy, respectively. At alpha/beta of 2 Gy (1.2 Gy), D99% ranged from ∼79 (81) to 85 (98) Gy‐EQD2 for treatments in 28 to 5 fractions. Below D97%, the target dose was predominantly determined by alpha/beta, and the motion impact was minimal. Conclusions: In prostate treatments, the impact of inter‐fractional motion on tumordose escalation is small for alpha/beta

Joost J. M. E. Nuyttens - One of the best experts on this subject based on the ideXlab platform.

  • predicting high grade esophagus toxicity after treating central lung tumors with stereotactic radiation therapy using a normal tissue complication probability model
    International Journal of Radiation Oncology Biology Physics, 2020
    Co-Authors: Marloes Duijm, Noelle C Van Der Voort Van Zyp, Esther Oomende Hoop, Mirjam E Mast, Paul Van De Vaart, Mischa S Hoogeman, Joost J. M. E. Nuyttens
    Abstract:

    PURPOSE: The treatment of central lung tumors with stereotactic body radiation therapy (SBRT) is challenged by the risk of excessive esophageal toxicity. To improve clinical decision making, we aimed to derive normal tissue complication probability (NTCP) models in a patient cohort with central lung tumors treated with SBRT and to evaluate the currently used esophagus dose constraints. METHODS AND MATERIALS: Patients with a central lung tumor who received SBRT (8 fractions of 7.5 Gy or 12 fractions of 5 Gy) were included. Doses were recalculated to an equivalent dose of 2 Gy with an alpha/beta-Ratio of 10 Gy for acute and 3 Gy for late toxicity (the cut-off was 3 months). The esophagus was manually delineated. NTCP modeling based on logistic regression was used to relate dose-volume histogram parameters (Dmax, D1cc, D2cc, D5cc) to acute and late toxicity. Parameters with a P < .05 were included in the model. Based on the NTCP models, we determined the probability of toxicity for the currently used dose constraints: D1cc toxicity occurred in 33 patients (18%). Late high-grade toxicity consisted of 2 possible treatment-related deaths (grade 5) and 2 patients with grade 3 toxicity. Acute toxicity consisted of only grade 1 (n = 19) and grade 2 toxicity (n = 10). All investigated dose-volume histogram parameters were significantly correlated to acute and late toxicity. The probability of late high-grade toxicity is 1.1% for 8 fractions and 1.4% for 12 fractions when applying the current dose constraints. CONCLUSIONS: High-grade esophageal toxicity occurred in 2.1% of the patients, including 2 possible treatment-related deaths. The currently used dose constraints correspond to a low risk of high-grade toxicity.

Lunde Liao - One of the best experts on this subject based on the ideXlab platform.

  • integrated treatment modality of cathodal transcranial direct current stimulation with peripheral sensory stimulation affords neuroprotection in a rat stroke model
    New Phytologist, 2017
    Co-Authors: Su Jing Chan, Aishwarya Bandla, Nicolas Kk King, You Yin Chen, Wai Hoe Ng, Lunde Liao, Peter T H Wong, Nitish V Thakor
    Abstract:

    Cathodal-transcranial direct current stimulation induces therapeutic effects in animal ischemia models by preventing the expansion of ischemic injury during the hyperacute phase of ischemia. However, its efficacy is limited by an accompanying decrease in cerebral blood flow. On the other hand, peripheral sensory stimulation can increase blood flow to specific brain areas resulting in rescue of neurovascular functions from ischemic damage. Therefore, the two modalities appear to complement each other to form an integrated treatment modality. Our results showed that hemodynamics was improved in a photothrombotic ischemia model, as cerebral blood volume and hemoglobin oxygen satuRation (SO2) recovered to 71% and 76% of the baseline values, respectively. Furthermore, neural activities, including somatosensory-evoked potentials (110% increase), the alpha-to-delta Ratio (27% increase), and the (delta+theta)/(alpha+beta) Ratio (27% decrease), were also restored. Infarct volume was reduced by 50% with a 2-fold preservation in the number of neurons and a 6-fold reduction in the number of active microglia in the infarct region compared with the untreated group. Grip strength was also better preserved (28% higher) compared with the untreated group. Overall, this nonpharmacological, nonintrusive approach could be prospectively developed into a clinical treatment modality.

M Dhanachai - One of the best experts on this subject based on the ideXlab platform.

  • SU‐FF‐T‐488: Estimation of Alpha/beta Ratio for Benign Tumor of the Brain From Clinical Data
    Medical Physics, 2009
    Co-Authors: Nauljun Stansook, V Boonkitticharoen, M Dhanachai
    Abstract:

    Purpose: To estimate a plausible α/β value for benign tumor of the brain from clinical data. Materials and Methods: Forty‐five articles published between 1997 and 2008 were selected for the analysis. These included publications on conventional external beam radiotherapy, fractionated stereotactic radiotherapy and stereotactic radiosurgery. Reports on combined radio‐chemotherapy were excluded. Three methods for α/β estimation were compared. These included two iso‐effect scheme matching, reciprocal iso‐effect dose plot and two‐step graphical matching. A 5‐year tumorcontrol rate (TCR) % was chosen as an end point for the analysis. The α/β values estimated by different methods were tested for their differences by t‐test. Results: The α/β values obtained from reciprocal iso‐effect dose plot, two iso‐effect scheme matching and two‐step graphical matching were 3.53 Gy (95% CI 2.08–4.98 Gy), 2.71 Gy (95% CI 2.67–2.75 Gy) and 2.67 Gy (95% CI 1.87–3.47 Gy), respectively. Statistical analysis showed no significant difference among α/β values obtained from these methods (p⩾ 0.14). Noteworthily, plausible estimate of α/β determined by the two iso‐effect scheme matching and two‐step graphical matching could be obtained only when the size of dose fraction differed by at least a factor of seven folds. Conclusion: The average α/β estimate (2.97 Gy, 95% CI 2.42–3.52) for benign braintumor obtained in this study was in remarkable agreement with the typical value of 2–3 Gy for the late responding tissue.