Comparison of Gafchromic EBT2 and EBT3 for patient-specific quality assurance: Cranial stereotactic radiosurgery using volumetric modulated arc therapy with multiple noncoplanar arcs

Purpose: Patient-specific quality assurance in volumetric modulated arc therapy (VMAT) brain stereotactic radiosurgery raises specific issues on dosimetric procedures, mainly represented by the small radiation fields associated with the lack of lateral electronic equilibrium, the need of small detectors and the high dose delivered (up to 30 Gy). GafchromicTM EBT2 and EBT3 films may be considered the dosimeter of choice, and the authors here provide some additional data about uniformity correction for this new generation of radiochromic films. Methods: A new analysis method using blue channel for marker dye correction was proposed for uniformity correction both for EBT2 and EBT3 films. Symmetry, flatness, and field-width of a reference field were analyzed to provide an evaluation in a high-spatial resolution of the film uniformity for EBT3. Absolute doses were compared with thermoluminescent dosimeters (TLD) as baseline. VMAT plans with multiple noncoplanar arcs were generated with a treatment planning system on a selected pool of eleven patients with cranial lesions and then recalculated on a water-equivalent plastic phantom by Monte Carlo algorithm for patient-specific QA. 2D quantitative dose comparison parameters were calculated, for the computed and measured dose distributions, and tested for statistically significant differences. Results: Sensitometric curves showed a different behavior above dose of 5 Gy for EBT2 and EBT3 films; with the use of inhouse marker-dye correction method, the authors obtained values of 2.5% for flatness, 1.5% of symmetry, and a field width of 4.8 cm for a 5 × 5 cm2 reference field. Compared with TLD and selecting a 5% dose tolerance, the percentage of points with ICRU index below 1 was 100% for EBT2 and 83% for EBT3. Patients analysis revealed statistically significant differences (p < 0.05) between EBT2 and EBT3 in the percentage of points with gamma values <1 (p = 0.009 and p = 0.016); the percent difference as well as the mean difference between calculated and measured isodoses (20% and 80%) were found not to be significant (p = 0.074, p = 0.185, and p = 0.57). Conclusions: Excellent performances in terms of dose homogeneity were obtained using a new blue channel method for marker-dye correction on both EBT2 and EBT3 GafchromicTM films. In comparison with TLD, the passing rates for the EBT2 film were higher than for EBT3; a good agreement with estimated data by Monte Carlo algorithm was found for both films, with some statistically significant differences again in favor of EBT2. These results suggest that the use of GafchromicTM EBT2 and EBT3 films is appropriate for dose verification measurements in VMAT stereotactic radiosurgery; taking into account the uncertainty associated with Gafchromic film dosimetry, the use of adequate action levels is strongly advised, in particular, for EBT3

Dosimetric predictors of radiation-induced lung injury in stereotactic body radiation therapy

MATERIALS AND METHODS: The aim was to retrospectively investigate correlations between potential predictive parameters and the occurrence of radiation-induced lung injury in patients with primary or secondary lung tumours treated with stereotactic body radiation therapy (SBRT). Sixty patients (63 tumours) underwent SBRT, with a dose of 45 Gy in 3 fractions over 5 days or 26 Gy in single fraction. The following parameters were tested for correlation with Radiation Therapy Oncology Group (RTOG) lung toxicity score: planning target volume (PTV), tumour location, primary vs. metastatic tumour, and Mean Lung Dose (in 2 Gy fractions, MLD2). Normal Tissue Complication Probability (NTCP) values were then estimated. RESULTS: The median follow-up time was 30.9 months (range 6.7-56.7). RTOG grade 0-1 toxicity was observed in 54/63 (85.7%) and grade 2-3 in 9/63 (14.3%) cases. Mean values of MLD(2) for RTOG grade 0-1 and 2-3 were respectively 11.2 Gy (95% Confidence Interval (CI) 10.1-12.3 Gy) and 20.3 Gy (95% CI 16.6-23.9 Gy). NTCP mean values for RTOG grade 0-1 and 2-3 were respectively 4% (95% CI 2-5.9%) and 37% (95% CI 11.6-62.3%). Univariate analysis, performed with t-Student test, showed a statistically significant difference between MLD(2) values in the two groups (t=5.93 and p < or = 0.001). Logistic regression analysis showed a good correlation between MLD(2) and toxicity scores 2-3 (p=0.008, odds ratio 1.5). From logistic regression relationship between the observed rates of grade 2-3 and MLD(2), a D(50)=19.8 Gy and a gamma50= 2.2 were obtained. From the sigmoid-shaped dose-response relationship between NTCP and MLD(2), a D(50)=22.4 Gy and gamma(50)= 2.2 were derived. DISCUSSION: MLD(2) is strongly associated to the risk of lung injury. Higher NTCP values are associated with a higher risk, but when comparing the expected to the observed toxicity rate, NTCP seems to underestimate the risk

Optimized Volumetric Modulated Arc Therapy Versus 3D-CRT for Early Stage Mediastinal Hodgkin Lymphoma Without Axillary Involvement: A Comparison of Second Cancers and Heart Disease Risk

Purpose: The purpose of this study was to evaluate the risks of second cancers and cardiovascular diseases associated with an optimized volumetric modulated arc therapy (VMAT) planning solution in a selected cohort of stage I/II Hodgkin lymphoma (HL) patients treated with either involved-node or involved-site radiation therapy in comparison with 3-dimensional conformal radiation therapy (3D-CRT). Methods and Materials: Thirty-eight patients (13 males and 25 females) were included. Disease extent was mediastinum alone (n=8, 21.1%); mediastinum plus unilateral neck (n=19, 50%); mediastinum plus bilateral neck (n=11, 29.9%). Prescription dose was 30 Gy in 2-Gy fractions. Only 5 patients had mediastinal bulky disease at diagnosis (13.1%). Anteroposterior 3D-CRT was compared with a multiarc optimized VMAT solution. Lung, breast, and thyroid cancer risks were estimated by calculating a lifetime attributable risk (LAR), with a LAR ratio (LARVMAT-to-LAR(3D-CRT)) as a comparative measure. Cardiac toxicity risks were estimated by calculating absolute excess risk (AER). Results: The LAR ratio favored 3D-CRT for lung cancer induction risk in mediastinal alone (P = .004) and mediastinal plus unilateral neck (P = .02) presentations. LAR ratio for breast cancer was lower for VMAT in mediastinal plus bilateral neck presentations (P = .02), without differences for other sites. For thyroid cancer, no significant differences were observed, regardless of anatomical presentation. A significantly lower AER of cardiac (P = .038) and valvular diseases (P&lt;.0001) was observed for VMAT regardless of disease extent. Conclusions: In a cohort of patients with favorable characteristics in terms of disease extent at diagnosis (large prevalence of nonbulky presentations without axillary involvement), optimized VMAT reduced heart disease risk with comparable risks of thyroid and breast cancer, with an increase in lung cancer induction probability. The results are however strongly influenced by the different anatomical presentations, supporting an individualized approach. (C) 2015 Elsevier Inc. All rights reserved

Stereotactic body radiation therapy for early stage non-small cell lung cancer: Results of a prospective trial

Patients affected with early stage (IA-IB) non-small cell lung cancer (NSCLC), deemed medically inoperable, are usually treated by conventional 3D-CRT, with poor results in terms of local tumour control and survival. Hypofractionated stereotactic body radiation therapy (SBRT) appears to be a valid alternative option, with high rates of local control and promising survival rates according to recent reported series. We herein report the final results of a prospective phase II trial of SBRT in 62 stage I NSCLC patients, homogeneously treated with three fractions of 15Gy each, given every other day during a 1 week time, up to a total dose of 45Gy; dose was prescribed to the 80%-isodose encompassing planning target volume. Patients were immobilized in a dedicated stereotactic body frame; margins around gross tumour volume were 5mm in the axial plane and 10mm in the longitudinal direction. Median age was 73.7 years. A pathologic confirmation of NSCLC was obtained in 64.5% of patients. Forty-three patients had stage IA and 19 stage IB disease. The majority of patients did not experience any toxicity; mild skin reactions, fatigue, dyspnea/cough or transient thoracic pain were recorded in approximately 10% of patients. With a median follow-up time of 28 months, 2 patients experienced an isolated local relapse, 4 an isolated nodal relapse and 15 a systemic failure. At 3 years, local control rate was 87.8%, cancer-specific survival 72.5%, overall survival 57.1%, with 8 out of 20 non-cancer related deaths. In multivariate analysis, tumour volume was associated with a better outcome. In our series, SBRT was well tolerated and confirmed its efficacy, with local control and survival rates globally superior to those reported using conventional radiotherapy. A longer follow-up is needed in order to establish a correct comparison with surgical series, and to fully ascertain a potential negative impact of SBRT on comorbidities of such a fragile patients population