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Hodgson D.C.,University of Toronto | Charpentier A.-M.,University of Toronto | Cigsar C.,A+ Network | Atenafu E.G.,A+ Network | And 5 more authors.
International Journal of Radiation Oncology Biology Physics | Year: 2013

Purpose: Stereotactic radiosurgery (SRS) for brain metastases is a relatively well-studied technology with established guidelines regarding patient selection, although its implementation is technically complex. We evaluated the extent to which local availability of SRS affected the treatment of patients with brain metastases. Methods and Materials: We identified 3030 patients who received whole-brain radiation therapy (WBRT) for brain metastases in 1 of 7 cancer centers in Ontario. Clinical data were abstracted for a random sample of 973 patients. Logistic regression analyses were performed to identify factors associated with the use of SRS as a boost within 4 months following WBRT or at any time following WBRT. Results: Of 898 patients eligible for analysis, SRS was provided to 70 (7.8%) patients at some time during the course of their disease and to 34 (3.8%) patients as a boost following WBRT. In multivariable analyses, factors significantly associated with the use of SRS boost following WBRT were fewer brain metastases (odds ratio [OR] = 6.50), controlled extracranial disease (OR = 3.49), age (OR = 0.97 per year of advancing age), and the presence of an on-site SRS program at the hospital where WBRT was given (OR = 12.34; all P values were <.05). Similarly, availability of on-site SRS was the factor most predictive of the use of SRS at any time following WBRT (OR = 5.98). Among patients with 1-3 brain metastases, good/fair performance status, and no evidence of active extracranial disease, SRS was provided to 40.3% of patients who received WBRT in a hospital that had an on-site SRS program vs 3.0% of patients who received WBRT at a hospital without SRS (P<.01). Conclusions: The availability of on-site SRS is the factor most strongly associated with the provision of this treatment to patients with brain metastases and appears to be more influential than accepted clinical eligibility factors. © 2013 Elsevier Inc. All rights reserved.


Abbas A.S.,Stronach Regional Cancer Center
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2013

Recently, volumetric-modulated arc therapy (VMAT) has demonstrated the ability to deliver radiation dose precisely and accurately with a shorter delivery time compared to conventional intensity-modulated fixed-field treatment (IMRT). We applied the hypothesis of VMAT technique for the treatment of thoracic esophageal carcinoma to determine superior or equivalent conformal dose coverage for a large thoracic esophageal planning target volume (PTV) with superior or equivalent sparing of organs-at-risk (OARs) doses, and reduce delivery time and monitor units (MUs), in comparison with conventional fixed-field IMRT plans. We also analyzed and compared some other important metrics of treatment planning and treatment delivery for both IMRT and VMAT techniques. These metrics include: 1) the integral dose and the volume receiving intermediate dose levels between IMRT and VMATI plans; 2) the use of 4D CT to determine the internal motion margin; and 3) evaluating the dosimetry of every plan through patient-specific QA. These factors may impact the overall treatment plan quality and outcomes from the individual planning technique used. In this study, we also examined the significance of using two arcs vs. a single-arc VMAT technique for PTV coverage, OARs doses, monitor units and delivery time. Thirteen patients, stage T2-T3 N0-N1 (TNM AJCC 7th edn.), PTV volume median 395 cc (range 281-601 cc), median age 69 years (range 53 to 85), were treated from July 2010 to June 2011 with a four-field (n = 4) or five-field (n = 9) step-and-shoot IMRT technique using a 6 MV beam to a prescribed dose of 50 Gy in 20 to 25 F. These patients were retrospectively replanned using single arc (VMATI, 91 control points) and two arcs (VMATII, 182 control points). All treatment plans of the 13 study cases were evaluated using various dose-volume metrics. These included PTV D99, PTV D95, PTV V9547.5Gy(95%), PTV mean dose, Dmax, PTV dose conformity (Van't Riet conformation number (CN)), mean lung dose, lung V20 and V5, liver V30, and Dmax to the spinal canal prv3mm. Also examined were the total plan monitor units (MUs) and the beam delivery time. Equivalent target coverage was observed with both VMAT single and two-arc plans. The comparison of VMATI with fixed-field IMRT demonstrated equivalent target coverage; statistically no significant difference were found in PTV D99 (p = 0.47), PTV mean (p = 0.12), PTV D95 and PTV V9547.5Gy (95%) (p = 0.38). However, Dmax in VMATI plans was significantly lower compared to IMRT (p = 0.02). The Van't Riet dose conformation number (CN) was also statistically in favor of VMATI plans (p = 0.04). VMATI achieved lower lung V20 (p = 0.05), whereas lung V5 (p = 0.35) and mean lung dose (p = 0.62) were not significantly different. The other OARs, including spinal canal, liver, heart, and kidneys showed no statistically significant differences between the two techniques. Treatment time delivery for VMATI plans was reduced by up to 55% (p = 5.8E-10) and MUs reduced by up to 16% (p = 0.001). Integral dose was not statistically different between the two planning techniques (p = 0.99). There were no statistically significant differences found in dose distribution of the two VMAT techniques (VMATI vs. VMATII) Dose statistics for both VMAT techniques were: PTV D99 (p = 0.76), PTV D95 (p = 0.95), mean PTV dose (p = 0.78), conformation number (CN) (p = 0.26), and MUs (p = 0.1). However, the treatment delivery time for VMATII increased significantly by two-fold (p = 3.0E-11) compared to VMATI. VMAT-based treatment planning is safe and deliverable for patients with thoracic esophageal cancer with similar planning goals, when compared to standard IMRT. The key benefit for VMATI was the reduction in treatment delivery time and MUs, and improvement in dose conformality. In our study, we found no significant difference in VMATII over single-arc VMATI for PTV coverage or OARs doses. However, we observed significant increase in delivery time for VMATII compared to VMATI.


Kim S.M.,University of Toronto | Haider M.A.,Sunnybrook Health science Center | Haider M.A.,University of Toronto | Jaffray D.A.,University of Toronto | And 2 more authors.
Medical Physics | Year: 2016

Purpose: A previously proposed method to reduce radiation dose to patient in dynamic contrast-enhanced (DCE) CT is enhanced by principal component analysis (PCA) filtering which improves the signal-to-noise ratio (SNR) of time-concentration curves in the DCE-CT study. The efficacy of the combined method to maintain the accuracy of kinetic parameter estimates at low temporal resolution is investigated with pixel-by-pixel kinetic analysis of DCE-CT data. Methods: The method is based on DCE-CT scanning performed with low temporal resolution to reduce the radiation dose to the patient. The arterial input function (AIF) with high temporal resolution can be generated with a coarsely sampled AIF through a previously published method of AIF estimation. To increase the SNR of time-concentration curves (tissue curves), first, a region-of-interest is segmented into squares composed of 3 × 3 pixels in size. Subsequently, the PCA filtering combined with a fraction of residual information criterion is applied to all the segmented squares for further improvement of their SNRs. The proposed method was applied to each DCE-CT data set of a cohort of 14 patients at varying levels of down-sampling. The kinetic analyses using the modified Tofts' model and singular value decomposition method, then, were carried out for each of the down-sampling schemes between the intervals from 2 to 15 s. The results were compared with analyses done with the measured data in high temporal resolution (i.e., original scanning frequency) as the reference. Results: The patients' AIFs were estimated to high accuracy based on the 11 orthonormal bases of arterial impulse responses established in the previous paper. In addition, noise in the images was effectively reduced by using five principal components of the tissue curves for filtering. Kinetic analyses using the proposed method showed superior results compared to those with down-sampling alone; they were able to maintain the accuracy in the quantitative histogram parameters of volume transfer constant [standard deviation (SD), 98th percentile, and range], rate constant (SD), blood volume fraction (mean, SD, 98th percentile, and range), and blood flow (mean, SD, median, 98th percentile, and range) for sampling intervals between 10 and 15 s. Conclusions: The proposed method of PCA filtering combined with the AIF estimation technique allows low frequency scanning for DCE-CT study to reduce patient radiation dose. The results indicate that the method is useful in pixel-by-pixel kinetic analysis of DCE-CT data for patients with cervical cancer. © 2016 American Association of Physicists in Medicine.


Fenkell L.,Aarhus University Hospital | Fenkell L.,Stronach Regional Cancer Center | Assenholt M.,Aarhus University Hospital | Nielsen S.K.,Aarhus University Hospital | And 4 more authors.
International Journal of Radiation Oncology Biology Physics | Year: 2011

Purpose: Midline-blocked boost (MBB) fields are frequently used in the treatment of locally advanced cervical cancer. The purpose of this study was to evaluate the dose contribution from MBBs to tumor and organs at risk. Methods and Materials: Six patients with locally advanced cervical cancer (IIB-IIIB) treated with definitive chemoradiotherapy and magnetic resonance imaging (MRI)-guided brachytherapy were analyzed. A three-phase plan was modeled: 45 Gy (1.8 Gy per fraction) four-field box, 9 Gy (1.8 Gy per fraction) MBB (midline-shielded anteroposterior/posteroanterior fields), and intracavitary MRI-guided brachytherapy boost of 28 Gy (7 Gy per fraction). Midline shields 3, 4, and 5 cm wide were simulated for each patient. Brachytherapy and MBB plans were volumetrically summed. The rectum, sigmoid, and bladder minimum dose in the most exposed 2 cm3 of an organ at risk (D2 cc) and high-risk clinical target volume (HR-CTV) and intermediate-risk clinical target volume (IR-CTV) D90 and D100 were evaluated. The intended HR-CTV D90 was 85 Gy or greater, and the intended IR-CTV D90 was greater than 60 Gy. Results: After a 4-cm MBB, HR-CTV D90 remained lower than 85 Gy in all cases (mean, 74 Gy; range, 64-82 Gy). High-risk clinical target volume (85 Gy) coverage increased slightly from 73% (range, 64-82%) to 78% (range, 69-88%). Mean IR-CTV D90 increased from 56 Gy (range, 53-64 Gy) to 62 Gy (range, 59-67 Gy). Intermediate-risk clinical target volume 60-Gy dose coverage increased from 81% (range, 72-96%) to 96% (range, 90-100%). The mean volume irradiated to 85 Gy increased by 14 cm3 (range, 10-22 cm3), whereas the volume irradiated to 60 Gy increased from 276 cm3 (range, 185-417 cm 3) to 592 cm3 (range, 385-807 cm3). Bladder, rectum, or sigmoid D2 cc increased by more than 50% of the boost dose in 4 of 6 patients. Conclusions: Midline-blocked boosts contribute substantial dose to rectum, sigmoid, and bladder D2 cc. HR-CTV dose and 85-Gy coverage remain compromised in large tumors despite MBB. IR-CTV 60-Gy coverage improved at the expense of a considerable increase in volume of normal tissue irradiated to 60 Gy. © 2011 Elsevier Inc.


Abbas A.S.,Stronach Regional Cancer Center | Moseley D.,Stronach Regional Cancer Center | Moseley D.,Princess Margaret Cancer Center | Moseley D.,University of Toronto | And 6 more authors.
Journal of Applied Clinical Medical Physics | Year: 2013

Recently, volumetric-modulated arc therapy (VMAT) has demonstrated the ability to deliver radiation dose precisely and accurately with a shorter delivery time compared to conventional intensity-modulated fixed-field treatment (IMRT). We applied the hypothesis of VMAT technique for the treatment of thoracic esophageal carcinoma to determine superior or equivalent conformal dose coverage for a large thoracic esophageal planning target volume (PTV) with superior or equivalent sparing of organs-at-risk (OARs) doses, and reduce delivery time and monitor units (MUs), in comparison with conventional fixed-field IMRT plans. We also analyzed and compared some other important metrics of treatment planning and treatment delivery for both IMRT and VMAT techniques. These metrics include: 1) the integral dose and the volume receiving intermediate dose levels between IMRT and VMATI plans; 2) the use of 4D CT to determine the internal motion margin; and 3) evaluating the dosimetry of every plan through patient-specific QA. These factors may impact the overall treatment plan quality and outcomes from the individual planning technique used. In this study, we also examined the significance of using two arcs vs. a single-arc VMAT technique for PTV coverage, OARs doses, monitor units and delivery time. Thirteen patients, stage T2-T3 N0-N1 (TNM AJCC 7th edn.), PTV volume median 395 cc (range 281-601 cc), median age 69 years (range 53 to 85), were treated from July 2010 to June 2011 with a four-field (n = 4) or five-field (n = 9) step-and-shoot IMRT technique using a 6 MV beam to a prescribed dose of 50 Gy in 20 to 25 F. These patients were retrospectively replanned using single arc (VMATI, 91 control points) and two arcs (VMATII, 182 control points). All treatment plans of the 13 study cases were evaluated using various dose-volume metrics. These included PTV D99, PTV D95, PTV V9547.5Gy(95%), PTV mean dose, Dmax, PTV dose conformity (Van't Riet conformation number (CN)), mean lung dose, lung V20 and V5, liver V30, and Dmax to the spinal canal prv3mm. Also examined were the total plan monitor units (MUs) and the beam delivery time. Equivalent target coverage was observed with both VMAT single and two-arc plans. The comparison of VMATI with fixed-field IMRT demonstrated equivalent target coverage; statistically no significant difference were found in PTV D99 (p = 0.47), PTV mean (p = 0.12), PTV D95 and PTV V9547.5Gy(95%) (p = 0.38). However, Dmax in VMATI plans was significantly lower compared to IMRT (p = 0.02). The Van't Riet dose conformation number (CN) was also statistically in favor of VMATI plans (p = 0.04). VMATI achieved lower lung V20 (p = 0.05), whereas lung V5 (p = 0.35) and mean lung dose (p = 0.62) were not significantly different. The other OARs, including spinal canal, liver, heart, and kidneys showed no statistically significant differences between the two techniques. Treatment time delivery for VMATI plans was reduced by up to 55% (p = 5.8E-10) and MUs reduced by up to 16% (p = 0.001). Integral dose was not statistically different between the two planning techniques (p = 0.99). There were no statistically significant differences found in dose distribution of the two VMAT techniques (VMATI vs. VMATII) Dose statistics for both VMAT techniques were: PTV D99 (p = 0.76), PTV D95 (p = 0.95), mean PTV dose (p = 0.78), conformation number (CN) (p = 0.26), and MUs (p = 0.1). However, the treatment delivery time for VMATII increased significantly by two-fold (p = 3.0E-11) compared to VMATI. VMAT-based treatment planning is safe and deliverable for patients with thoracic esophageal cancer with similar planning goals, when compared to standard IMRT. The key benefit for VMATI was the reduction in treatment delivery time and MUs, and improvement in dose conformality. In our study, we found no significant difference in VMATII over single-arc VMATI for PTV coverage or OARs doses. However, we observed significant increase in delivery time for VMATII compared to VMATI.

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