Characteristics and dosimetric impact of intrafraction motion during peripheral lung cancer stereotactic radiotherapy: is a second midpoint cone beam computed tomography of added value?

Background: In our department, during lung stereotactic body radiation therapy (SBRT), all patients receive an intra-fractional midpoint cone beam computed tomography (CBCT). This study aimed to quantify the benefit of adding a second midpoint CBCT over a course of peripheral lung SBRT. Materials and methods: Six-hundred-sixty-four CBCTs from 166 patients were retrospectively analyzed. Treatments were based on the internal target volume (ITV) approach. An isotropic 0.5 cm margin was used to create the planning target volume (PTV) around the ITV. The prescribed dose was 48 Gy in 4 fractions to the PTV. Patients were divided into two groups: patients for whom the 3D-intra-fractional-variation (IFV) was < 0.5 cm (105 patients) and patients with at least one 3D-IFV ≥ 0.5 cm (high-risk groups). Plans simulating the dosimetric impact of the IFV were created as follows: the original 2 arcs (ARC) were copied into a new plan consisting of 4 times ARC1 and 4 times ARC2. The delivery of ARC1 was always assumed to have occurred with the isocenter initially coordinated, whereas the positions of ARC2 were modified for each arc by the measured the 3D-IFV. Results: For the PTV, we obtained: D99% (Gy) = 45.2 vs. 48.2 Gy (p < .0001); Dmean = 53 vs. 54 Gy (p < .0001) for the reconstructed vs. planned dose values, respectively. For the ITV, the changes are less pronounced: D99%(Gy) = 52.2 vs. 53.6 Gy (p =.0007); Dmean = 56 vs. 56.8 Gy (p =.0144). The V48 Gy (%)-ITV coverage did not statistically change between the delivered vs. planned dose (p =.1803). Regarding the organs at risk for both groups, dose-volume-histograms were near-identical. Conclusion: We demonstrated that a single CBCT is sufficient and reliable to manage the IFV during peripheral lung SBRT

Dosimetric Impact of Intrafraction Motion During Peripheral Lung Cancer Stereotactic Radiotherapy: Is a Second Cone Beam Computed Tomography of Added Value?

PURPOSE/OBJECTIVE(S): In our department, during lung SBRT, all patients (regardless of tumor location) receive an additional intra-fractional CBCT, allowing us to adjust the beam delivery accordingly to the intra-fractional variation (IFV). It is to be expected that each IFV exceeding the planning target volume (PTV) margins could lead to potential discrepancies between planned and delivered plans. A posteriori robust dosimetric evaluation will help us to quantify the actual impact on the target's volumes coverage. MATERIALS/METHODS: Six hundred sixty-four CBCTs from 166 consecutives free-breathing lung SBRT patients were retrospectively analyzed. Treatments were based on the internal target volume (ITV) approach with a 4D-CT at simulation and performed using volumetric modulated arc therapy. An isotropic 0.5 cm margin was used to create the PTV around the ITV. The prescribed dose was 48 Gy in 4 fractions to the PTV (80% isodose line). Patients were divided into two groups: patients for whom the 3D-IFV was below 0.5 cm (low-risk group: 105 patients, 573/664 fractions) and patients with at least one 3D-IFV ≥ 0.5 cm (high-risk group: 61 patients, 91/664 fractions). Plans simulating the dosimetric impact of the IFV were created as follows: the original two arcs were copied into a new plan consisting of 4 times ARC1 and 4 times ARC2. The delivery of ARC1 was always assumed to have occurred with the isocenter coordinates as those in the original plan, whereas the positions of ARC2 were modified for each arc by the measured the 3D displacement for that fraction according to the intra-fraction CBCT. RESULTS: The IFV reduces both the minimal (D99%) and mean (Dmean) dose to both the PTV and the ITV. For the PTV, we obtained: D99(%) = 45.2 vs 48.2 Gy (P 0.5 cm was observed for 3 and 4 fractions, respectively. Regarding the organs at risk (D99%; Dmean; Dmax): for both the low- and high-risk groups, dose-volume histograms were near-identical (no significant difference). CONCLUSION: Although IFV results in a significant change between the delivered vs planned dose distributions for the PTV (D99%; V48Gy; Dmean) and on the ITV (D99%; Dmean), the V48Gy-ITV coverage did not statistically change. Based on our data we demonstrated that a single CBCT is sufficient and reliable to manage the IFV during peripheral lung SBRT.SCOPUS: ar.jDecretOANoAutActifinfo:eu-repo/semantics/publishe

Characteristics and dosimetric impact of intrafraction motion during peripheral lung cancer stereotactic radiotherapy: is a second midpoint cone beam computed tomography of added value?

In our department, during lung stereotactic body radiation therapy (SBRT), all patients receive an intra-fractional midpoint cone beam computed tomography (CBCT). This study aimed to quantify the benefit of adding a second midpoint CBCT over a course of peripheral lung SBRT. Six-hundred-sixty-four CBCTs from 166 patients were retrospectively analyzed. Treatments were based on the internal target volume (ITV) approach. An isotropic 0.5 cm margin was used to create the planning target volume (PTV) around the ITV. The prescribed dose was 48 Gy in 4 fractions to the PTV. Patients were divided into two groups: patients for whom the 3D-intra-fractional-variation (IFV) was < 0.5 cm (105 patients, low risk group) and patients with at least one 3D-IFV ≥ 0.5 cm (61 patients, high-risk group). Plans simulating the dosimetric impact of the IFV were created as follows: the original 2 arcs (ARC ) were copied into a new plan consisting of 4 times ARC 1 and 4 times ARC 2. The delivery of ARC 1 was always assumed to have occurred with the isocenter initially coordinated, whereas the positions of ARC 2 were modified for each arc by the measured the 3D-IFV. For the PTV, we obtained: D99% (Gy) = 45.2 . 48.2 Gy (p < 0.0001); Dmean = 53 . 54 Gy (p < .0001) for the reconstructed . planned dose values, respectively. For the ITV, the changes are less pronounced: D99% (Gy) = 52.2 . 53.6 Gy (p = 0.0007); Dmean = 56 . 56.8 Gy (p = 0.0144). The V48 Gy(%)-ITV coverage did not statistically change between the delivered . planned dose (p = 0.1803). Regarding the organs at risk for both groups, dose-volume-histograms were near-identical. We demonstrated that a single CBCT is sufficient and reliable to manage the IFV during peripheral lung SBRT

Unintended dose to the lower axilla in adjuvant radiotherapy for breast cancer: Differences between tangential beam and VMAT.

To evaluate dosimetric differences in unintended dose to the lower axilla between 3D-standard (3DCRT), tangential beam forward intensity modulated radiotherapy (F-IMRT) and volumetric modulated arc therapy (VMAT). The objective is to evaluate whether results of clinical trials, such as the ACOSOG-Z011 trial, that evaluated omission of axillary clearance can be extrapolated towards more conformal techniques like VMAT. Twenty-five consecutive patients treated with whole breast radiotherapy alone (WBRT) using a F-IMRT technique were identified. Three additional plans were created for every patient: one plan using a single 270° arc (VMAT 1x270°), another using two small ≤90° opposing arcs (VMAT 2x < 90°) and thirdly a 3DCRT plan without F-IMRT. Axillary levels I-II were contoured after the treatment plans were made. The volume of the axilla level I that was covered by the 50% isodose (V50%) was significantly higher for VMAT 2x < 90° (71.3 cm, 84% of structure volume, p < 0.001) and VMAT 1x270° (68.8 cm, 81%, p < 0.01) compared to 3DCRT (60.3 cm, 71%) and F-IMRT (60.8 cm, 72%). The V50% to the axilla level II, however, was low for all techniques: 12.3 cm (12%); 8.9 cm (9%); 4.3 cm (4%); 4.4 cm (4%) for VMAT 2x < 90°, VMAT 1x270°, 3DCRT, F-IMRT, respectively. For the higher doses (V90% and above), no clinically relevant differences were seen between the different modalities. WBRT treatments with VMAT do not lead to a significant reduction of the unintended axillary dose in comparison with a tangential beam setup. Hence, concerning tumor control, VMAT can be applied to clinical situations similar to the Z0011 trial. The intermediate axillary dose is higher with VMAT, but the clinical consequence of this difference on toxicity is unknown