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Title: Poster — Thur Eve — 62: A Retrospective Assessment of the Prevalence and Dosimetric Effect of Lateral Electron Disequilibrium in a Population of Lung Cancer Patients Treated by Stereotactic Body Radiation Therapy

Abstract

Stereotactic Body Radiation Therapy (SBRT) is a treatment option for early stage non-small cell lung cancer (NSCLC). SBRT uses tightly conformed megavoltage (MV) x-ray beams to ablate the tumour. However, small MV x-ray fields may produce lateral electron disequilibrium (LED) within lung tissue, which can reduce the dose to tumour. The goal of this work is to estimate the prevalence of LED in NSCLC patients treated with SBRT, and determine dose effects for patients prone or averse to LED. Thirty NSCLC patients were randomly selected for analysis. 4-dimensional CT lung images were segmented into the right and left upper and lower lobes (RUL, RLL, LUL, LLL), and the right middle lobe. Dose calculations were performed using volume-modulated arc therapy in the Pinnacle{sup 3} TPS. Most tumours were located in the upper lobes (RUL 53%, LUL 27%) where density was significantly lower (RUL −808±46 HU vs. RLL −743±71 HU; LUL −808 ±56 HU vs. LLL −746±70 HU; p<0.001). In general, the prevalence of LED increased with higher beam energy. Using 6MV photons, patients with a RUL tumour experienced moderate (81 %), and mild (19%) levels of LED. At 18MV, LED became more prominent with severe (50%) and moderate (50%) LED exhibited.more » Dosimetrically, for patients prone to LED, poorer target coverage (i.e. increased R100 by 20%) and improved lung sparing (i.e. reduced V20 by −46%) was observed. The common location of lung cancers in the upper lobes, coupled with lower lung density, results in the potential occurrence of LED, which may underdose the tumour.« less

Authors:
;  [1]; ; ; ;  [1];  [2]
  1. London Regional Cancer Program (United Kingdom)
  2. (United Kingdom)
Publication Date:
OSTI Identifier:
22407682
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 8; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; LUNGS; NEOPLASMS; PATIENTS; RADIATION DOSES; RADIOTHERAPY; X RADIATION

Citation Formats

Disher, Brandon, Wade, Laura, Hajdok, George, Gaede, Stewart, Battista, Jerry J., Palma, David, and Department of Medical Biophysics, Department of Oncology, Western University, London, ON. Poster — Thur Eve — 62: A Retrospective Assessment of the Prevalence and Dosimetric Effect of Lateral Electron Disequilibrium in a Population of Lung Cancer Patients Treated by Stereotactic Body Radiation Therapy. United States: N. p., 2014. Web. doi:10.1118/1.4894922.
Disher, Brandon, Wade, Laura, Hajdok, George, Gaede, Stewart, Battista, Jerry J., Palma, David, & Department of Medical Biophysics, Department of Oncology, Western University, London, ON. Poster — Thur Eve — 62: A Retrospective Assessment of the Prevalence and Dosimetric Effect of Lateral Electron Disequilibrium in a Population of Lung Cancer Patients Treated by Stereotactic Body Radiation Therapy. United States. doi:10.1118/1.4894922.
Disher, Brandon, Wade, Laura, Hajdok, George, Gaede, Stewart, Battista, Jerry J., Palma, David, and Department of Medical Biophysics, Department of Oncology, Western University, London, ON. Fri . "Poster — Thur Eve — 62: A Retrospective Assessment of the Prevalence and Dosimetric Effect of Lateral Electron Disequilibrium in a Population of Lung Cancer Patients Treated by Stereotactic Body Radiation Therapy". United States. doi:10.1118/1.4894922.
@article{osti_22407682,
title = {Poster — Thur Eve — 62: A Retrospective Assessment of the Prevalence and Dosimetric Effect of Lateral Electron Disequilibrium in a Population of Lung Cancer Patients Treated by Stereotactic Body Radiation Therapy},
author = {Disher, Brandon and Wade, Laura and Hajdok, George and Gaede, Stewart and Battista, Jerry J. and Palma, David and Department of Medical Biophysics, Department of Oncology, Western University, London, ON},
abstractNote = {Stereotactic Body Radiation Therapy (SBRT) is a treatment option for early stage non-small cell lung cancer (NSCLC). SBRT uses tightly conformed megavoltage (MV) x-ray beams to ablate the tumour. However, small MV x-ray fields may produce lateral electron disequilibrium (LED) within lung tissue, which can reduce the dose to tumour. The goal of this work is to estimate the prevalence of LED in NSCLC patients treated with SBRT, and determine dose effects for patients prone or averse to LED. Thirty NSCLC patients were randomly selected for analysis. 4-dimensional CT lung images were segmented into the right and left upper and lower lobes (RUL, RLL, LUL, LLL), and the right middle lobe. Dose calculations were performed using volume-modulated arc therapy in the Pinnacle{sup 3} TPS. Most tumours were located in the upper lobes (RUL 53%, LUL 27%) where density was significantly lower (RUL −808±46 HU vs. RLL −743±71 HU; LUL −808 ±56 HU vs. LLL −746±70 HU; p<0.001). In general, the prevalence of LED increased with higher beam energy. Using 6MV photons, patients with a RUL tumour experienced moderate (81 %), and mild (19%) levels of LED. At 18MV, LED became more prominent with severe (50%) and moderate (50%) LED exhibited. Dosimetrically, for patients prone to LED, poorer target coverage (i.e. increased R100 by 20%) and improved lung sparing (i.e. reduced V20 by −46%) was observed. The common location of lung cancers in the upper lobes, coupled with lower lung density, results in the potential occurrence of LED, which may underdose the tumour.},
doi = {10.1118/1.4894922},
journal = {Medical Physics},
number = 8,
volume = 41,
place = {United States},
year = {Fri Aug 15 00:00:00 EDT 2014},
month = {Fri Aug 15 00:00:00 EDT 2014}
}
  • Stereotactic body radiation therapy (SBRT), due to its high precision for target localizing, has become widely used to treat tumours at various locations, including the lungs. Lung SBRT program was started at our institution a year ago. Eighteen patients with peripheral lesions up to 3 cm diameter have been treated with 48 Gy in 4 fractions. Based on four-dimensional computed tomography (4DCT) simulation, internal target volume (ITV) was delineated to encompass the respiratory motion of the lesion. A margin of 5 mm was then added to create the planning target volume (PTV) for setup uncertainties. There was no expansion frommore » gross tumour volume (GTV) to clinical target volume (CTV). Pinnacle 9.6 was used as the primary treatment planning system. Volumetric modulated arc therapy (VMAT) technique, with one or two coplanar arcs, generally worked well. For quality assurance (QA), each plan was exported to Eclipse 10 and dose calculation was repeated. Dose volume histograms (DVHs) of the targets and organs at risk (OARs) were then compared between the two treatment planning systems. Winston-Lutz tests were carried out as routine machine QA. Patient-specific QA included ArcCheck measurement with an insert, where an ionization chamber was placed at the centre to measure dose at the isocenter. For the first several patients, and subsequently for the plans with extremely strong modulation, Gafchromic film dosimetry was also employed. For each patient, a mock setup was scheduled prior to treatments. Daily pre- and post-CBCT were acquired for setup and assessment of intra-fractional motion, respectively.« less
  • Purpose: Quantification of volume changes on CBCT during SBRT for NSCLC may provide a useful radiological marker for radiation response and adaptive treatment planning, but the reproducibility of CBCT volume delineation is a concern. This study is to quantify inter-scan/inter-observer variability in tumor volume delineation on CBCT. Methods: Twenty earlystage (stage I and II) NSCLC patients were included in this analysis. All patients were treated with SBRT with a median dose of 54 Gy in 3 to 5 fractions. Two physicians independently manually contoured the primary gross tumor volume on CBCTs taken immediately before SBRT treatment (Pre) and after themore » same SBRT treatment (Post). Absolute volume differences (AVD) were calculated between the Pre and Post CBCTs for a given treatment to quantify inter-scan variability, and then between the two observers for a given CBCT to quantify inter-observer variability. AVD was also normalized with respect to average volume to obtain relative volume differences (RVD). Bland-Altman approach was used to evaluate variability. All statistics were calculated with SAS version 9.4. Results: The 95% limit of agreement (mean ± 2SD) on AVD and RVD measurements between Pre and Post scans were −0.32cc to 0.32cc and −0.5% to 0.5% versus −1.9 cc to 1.8 cc and −15.9% to 15.3% for the two observers respectively. The 95% limit of agreement of AVD and RVD between the two observers were −3.3 cc to 2.3 cc and −42.4% to 28.2% respectively. The greatest variability in inter-scan RVD was observed with very small tumors (< 5 cc). Conclusion: Inter-scan variability in RVD is greatest with small tumors. Inter-observer variability was larger than inter-scan variability. The 95% limit of agreement for inter-observer and inter-scan variability (∼15–30%) helps define a threshold for clinically meaningful change in tumor volume to assess SBRT response, with larger thresholds needed for very small tumors. Part of the work was funded by a Kaye award; Disclosure/Conflict of interest: Raymond H. Mak: Stock ownership: Celgene, Inc. Consulting: Boehringer-Ingelheim, Inc.« less
  • Purpose: To determine the effect of biologically effective dose (BED{sub 10}) and radiation treatment schedule on overall survival (OS) in patients with early-stage non-small cell lung cancer (NSCLC) undergoing stereotactic body radiation therapy (SBRT). Methods and Materials: Using data from 65 treatment centers in the United States, we retrospectively reviewed the records of T1-2 N0 NSCLC patients undergoing SBRT alone from 2006 to 2014. Biologically relevant covariates, including dose per fraction, number of fractions, and time between fractions, were used to quantify BED{sub 10} and radiation treatment schedule. The linear-quadratic equation was used to calculate BED{sub 10} and to generatemore » a dichotomous dose variable of <105 Gy versus ≥105 Gy BED{sub 10}. The primary outcome was OS. We used the Kaplan-Meier method, the log–rank test, and Cox proportional hazards regression with propensity score matching to determine whether prescription BED{sub 10} was associated with OS. Results: We identified 747 patients who met inclusion criteria. The median BED{sub 10} was 132 Gy, and 59 (7.7%) had consecutive-day fractions. Median follow-up was 41 months, and 452 patients (60.5%) had died by the conclusion of the study. The 581 patients receiving ≥105 Gy BED{sub 10} had a median survival of 28 months, whereas the 166 patients receiving <105 Gy BED{sub 10} had a median survival of 22 months (log–rank, P=.01). Radiation treatment schedule was not a significant predictor of OS on univariable analysis. After adjusting for T stage, sex, tumor histology, and Eastern Cooperative Oncology Group performance status, BED{sub 10} ≥105 Gy versus <105 Gy remained significantly associated with improved OS (hazard ratio 0.78, 95% confidence interval 0.62-0.98, P=.03). Propensity score matching on imbalanced variables within high- and low-dose cohorts confirmed a survival benefit with higher prescription dose. Conclusions: We found that dose escalation to 105 Gy BED{sub 10} and beyond may improve survival in NSCLC patients treated with SBRT.« less
  • Purpose: To report clinical and dosimetric factors predictive of radiation pneumonitis (RP) in patients receiving lung stereotactic body radiation therapy (SBRT) from a series of 240 patients. Methods and Materials: Of the 297 isocenters treating 263 patients, 240 patients (n=263 isocenters) had evaluable information regarding RP. Age, gender, current smoking status and pack-years, O{sub 2} use, Charlson Comorbidity Index, prior lung radiation therapy (yes/no), dose/fractionation, V{sub 5}, V{sub 13}, V{sub 20}, V{sub prescription}, mean lung dose, planning target volume (PTV), total lung volume, and PTV/lung volume ratio were recorded. Results: Twenty-nine patients (11.0%) developed symptomatic pneumonitis (26 grade 2, 3more » grade 3). The mean V{sub 20} was 6.5% (range, 0.4%-20.2%), and the average mean lung dose was 5.03 Gy (0.547-12.2 Gy). In univariable analysis female gender (P=.0257) and Charlson Comorbidity index (P=.0366) were significantly predictive of RP. Among dosimetric parameters, V{sub 5} (P=.0186), V{sub 13} (P=.0438), and V{sub prescription} (where dose = 60 Gy) (P=.0128) were significant. There was only a trend toward significance for V{sub 20} (P=.0610). Planning target volume/normal lung volume ratio was highly significant (P=.0024). In multivariable analysis the clinical factors of female gender, pack-years smoking, and larger gross internal tumor volume and PTV were predictive (P=.0094, .0312, .0364, and .052, respectively), but no dosimetric factors were significant. Conclusions: Rate of symptomatic RP was 11%. Our mean lung dose was <600 cGy in most cases and V20 <10%. In univariable analysis, dosimetric factors were predictive, while tumor size (or tumor/lung volume ratio) played a role in multivariable and univariable and analysis, respectively.« less
  • Purpose: To estimate the α/β ratio for which the dose-dependent lung perfusion reductions for stereotactic body radiation therapy (SBRT) and conventionally fractionated radiation therapy (CFRT) are biologically equivalent. Methods and Materials: The relations between local dose and perfusion reduction 4 months after treatment in lung cancer patients treated with SBRT and CFRT were scaled according to the linear-quadratic model using α/β ratios from 0 Gy to ∞ Gy. To test for which α/β ratio both treatments have equal biological effect, a 5-parameter logistic model was optimized for both dose–effect relationships simultaneously. Beside the α/β ratio, the other 4 parameters weremore » d{sub 50}, the steepness parameter k, and 2 parameters (M{sub SBRT} and M{sub CFRT}) representing the maximal perfusion reduction at high doses for SBRT and CFRT, respectively. Results: The optimal fitted model resulted in an α/β ratio of 1.3 Gy (0.5-2.1 Gy), M{sub SBRT} = 42.6% (40.4%-44.9%), M{sub CFRT} = 66.9% (61.6%-72.1%), d{sub 50} = 35.4 Gy (31.5-9.2 Gy), and k = 2.0 (1.7-2.3). Conclusions: An equal reduction of lung perfusion in lung cancer was observed in SBRT and CFRT if local doses were converted by the linear-quadratic model with an α/β ratio equal to 1.3 Gy (0.5-2.1 Gy)« less