Performance of auto-planning for VMAT hypofractionated left whole-breast irradiation with simultaneous integrated boost.

Retrospective analysis of volumetric modulated arc therapy plans for hypofractionated left whole-breast irradiation with simultaneous integrated boost to assess the performance of the auto-planning (AP) engine. Fifteen treatment plans, produced using manual optimization planning approach (MP) were replanned using (AP) approach. Dose-volume parameters were defined to quantify the quality of concurrent treatment plans assessing target coverage and sparing organs at risk (OARs). The Wilcoxon Signed Rank test was used for statistical comparison of all results obtained from the use of the 2 approaches. Dose coverage for both PTVs, PTVbreast, and PTVboost, were similar with AP showing slightly significantly better results for the homogeneity index for both PTVs, for D98% of PTVbreast and D2% of PTVboost. AP plans provided a significant reduction of dose for ipsilateral lung and contralateral lung. No significant differences were observed for heart and contralateral breast. A percentage difference of -14.0% was found for the mean dose of left coronary artery between AP plans and MP plans. Despite increase of total MU by 4.3% for AP plans, planning time resulted about half of that of the MP approach. Although PTVs doses were similar between MP and AP plans, AP plans generally spared OARs significantly better than MP plans. Furthermore, the shortest AP treatment plan time approach was attractive with respect to the workload.

DVHs evaluation in brain metastases stereotactic radiotherapy treatment plans.

PURPOSE: The aim of this work is to report a retrospective study of radiobiological indicators based on Dose-Volume Histograms analysis obtained by stereotactic radiotherapy treatments. METHODS AND MATERIALS: Fifty-five patients for a total of sixty-seven brain metastases with a mean target volume of 8.49 cc were treated by Dynamic Conformal Arc Therapy (DCAT) and Intensity-Modulated Stereotactic Radiotherapy (IMRST). The Delivered prescription dose was chosen on the basis of tumor size and location so as to ensure a 100% isodose coverage to the target volume. RESULTS: The treatment plans reported a mean value of 10% and 2.19% for the inhomogeneity and conformal index, respectively. The F factor showed we overdosed sixty-three patients delivering an additional 7% dose more than calculated values. The radiobiological parameters: TCP and NTCP showed a complete tumor control limiting the organs at risk damage. CONCLUSION: One goal of stereotactic radiotherapy is to design a treatment plan in which the steep dose gradient achievable minimizes the amount of radiation delivered outside the tumor region. This technique allows to deliver a much larger dose to the target without exceeding the radiation-related tolerance of normal tissues and improving patients' quality of life.

On-line image guidance for frameless stereotactic radiotherapy of lung malignancies by cone beam CT: comparison between target localization and alignment on bony anatomy.

INTRODUCTION: Free-breathing stereotactic radiotherapy for lung malignancies requires reliable prediction of respiratory motion and accurate target localization. A protocol was adopted for reproducibility and reduction of respiratory motion and for target localization by CBCT image guidance. Tumor respiratory displacements and tumor positioning errors relative to bony anatomy alignment are analyzed. MATERIALS AND METHOD: Image guided SRT was performed for 99 lung malignancies. Two groups of patients were considered: group A did not perform any breathing control; group B controlled visually their respiratory cycle and volumes on an Active Breathing Coordinator (ABC) monitor during the acquisition of simulation CT and CBCT, and treatment delivery. GTV on end inhale and exhale CT data sets were fused in an ITV and the extent of tumor motion evaluated between these 2 phases. A pre-treatment CBCT was acquired and aligned to the reference CT using bony anatomy; for tumor positioning the ITV contour on the reference CT was matched to the visible tumor on CBCT. Interobserver variability of tumor positioning was evaluated. ITV and CBCT tumor dimensions were compared. RESULTS: 3D tumor breathing displacement (mean+/-SD) was significantly higher for group A (14.7+/-9.9 mm) than for group B (4.7+/-3.1 mm). The detected differences between tumor and bony structure alignment below 3 mm were 68% for group B and 45% for group A, reaching statistical significance. Interobserver variability was 1.7+/-1.1 mm (mean+/-SD). Dimensions of tumor image on CBCT were consistent with ITV dimensions for group B (max difference 14%). CONCLUSIONS: The adopted protocol seems effective in reducing respiratory internal movements and margin. Tumor positioning errors relative to bony anatomy are also reduced. However bony anatomy as a surrogate of the target may still lead to some relevant positioning errors. Target visualization on CBCT is essential for an accurate localization in lung SRT.

Bladder radiotherapy treatment: A retrospective comparison of 3-dimensional conformal radiotherapy, intensity-modulated radiation therapy, and volumetric-modulated arc therapy plans.

To examine tumor׳s and organ׳s response when different radiotherapy plan techniques are used. Ten patients with confirmed bladder tumors were first treated using 3-dimensional conformal radiotherapy (3DCRT) and subsequently the original plans were re-optimized using the intensity-modulated radiation treatment (IMRT) and volumetric-modulated arc therapy (VMAT)-techniques. Targets coverage in terms of conformity and homogeneity index, TCP, and organs׳ dose limits, including integral dose analysis were evaluated. In addition, MUs and treatment delivery times were compared. Better minimum target coverage (1.3%) was observed in VMAT plans when compared to 3DCRT and IMRT ones confirmed by a statistically significant conformity index (CI) results. Large differences were observed among techniques in integral dose results of the femoral heads. Even if no statistically significant differences were reported in rectum and tissue, a large amount of energy deposition was observed in 3DCRT plans. In any case, VMAT plans provided better organs and tissue sparing confirmed also by the normal tissue complication probability (NTCP) analysis as well as a better tumor control probability (TCP) result. Our analysis showed better overall results in planning using VMAT techniques. Furthermore, a total time reduction in treatment observed among techniques including gantry and collimator rotation could encourage using the more recent one, reducing target movements and patient discomfort.

Tissue heterogeneity in IMRT dose calculation for lung cancer.

The aim of this study was to evaluate the differences in accuracy of dose calculation between 3 commonly used algorithms, the Pencil Beam algorithm (PB), the Anisotropic Analytical Algorithm (AAA), and the Collapsed Cone Convolution Superposition (CCCS) for intensity-modulated radiation therapy (IMRT). The 2D dose distributions obtained with the 3 algorithms were compared on each CT slice pixel by pixel, using the MATLAB code (The MathWorks, Natick, MA) and the agreement was assessed with the γ function. The effect of the differences on dose-volume histograms (DVHs), tumor control, and normal tissue complication probability (TCP and NTCP) were also evaluated, and its significance was quantified by using a nonparametric test. In general PB generates regions of over-dosage both in the lung and in the tumor area. These differences are not always in DVH of the lung, although the Wilcoxon test indicated significant differences in 2 of 4 patients. Disagreement in the lung region was also found when the Γ analysis was performed. The effect on TCP is less important than for NTCP because of the slope of the curve at the level of the dose of interest. The effect of dose calculation inaccuracy is patient-dependent and strongly related to beam geometry and to the localization of the tumor. When multiple intensity-modulated beams are used, the effect of the presence of the heterogeneity on dose distribution may not always be easily predictable.

Analysis of salivary flow and dose-volume modeling of complication incidence in patients with head-and-neck cancer receiving intensity-modulated radiotherapy.

PURPOSE: To investigate dose-volume effects of salivary flow and the functional recovery over time, using salivary function data and different models of normal tissue complication probability (NTCP). METHODS AND MATERIALS: A total of 59 patients with head-and-neck cancer treated with intensity-modulated radiotherapy (IMRT) were analyzed in the present study. The toxicity was evaluated using the Radiation Therapy Oncology Group (RTOG) scale and salivary flows, both unstimulated (USF) and stimulated (SSF). The assessments were done before radiotherapy (RT) and at 3, 6, 12, 18, and 24 months after RT. Grade 3 toxicity was the primary endpoint. Analyses of toxicity incidence at 3, 6, and 12 months after RT were performed by both the Lyman-Kutcher-Burman (LKB) and relative seriality (S) models. RESULTS: A significant correlation was found between the incidence of Grade 3 toxicity and the incidence of patients with a reduction in SSF to <25% of the pre-RT value. Better correlations resulted between the RTOG toxicity score and the dosimetric parameters, compared with USF/SSF. The TD(50), assessed by the LKB model, was 21.4, 27.8, and 41.6 Gy at 3, 6, and 12 months after RT, respectively. The TD(50), assessed by the S model, was 20.0, 26.3, and 40.0 Gy at 3, 6, and 12 months after RT, respectively. CONCLUSION: Recovery of salivary gland function vs. time after RT took place mostly within 1 year after RT. The RTOG Grade 3 was a reliable score to perform the NTCP modeling. The choice of NTCP model had no influence on the accuracy of predictions.