Dosimetric benefits of dynamic conformal arc therapy-combined with active breath-hold in lung stereotactic body radiotherapy.

To test the hypothesis that dynamic conformal arc therapy (DCAT) in Monaco, compared with volumetric modulated arc therapy (VMAT), maintains plan quality with higher delivery efficiency for lung stereotactic body radiotherapy (SBRT) and to investigate dosimetric benefits of DCAT with active breath-hold (DCAT+ABH), compared with free-breathing (DCAT+FB) for varying tumor sizes and motions. Fifty DCAT plans were used for lung SBRT. Randomly selected 17 DCAT plans were evaluated with respect to the retrospectively generated volumetric modulated arc therapy (VMAT) plans. The maximum dose at 2 cm from planning target volume (PTV) in any direction (D2cm/Rx), the ratio of 50% prescription isodose volume to the PTV (R50%), conformity index (CI), the lung volume receiving ≥20 Gy (V20), and monitor unit (MU) were evaluated. A t-test was used to evaluate the difference of plan quality between DCAT and VMAT. Internal target volume (ITV)/integrated-gross target volume (GTV) attributed by intra-fraction motion and lung V20 were stratified for DCAT+ABH and DCAT+FB across varying GTVs. DCAT maintained plan quality (p = 0.154 for D2cm/Rx, p = 0.089 for R50%, p = 0.064 for CI, and p = 0.780 for lung V20) while reducing MUs up to 30% (p <0.001) from 2748 MU (VMAT) to 1868 MU (DCAT). DCAT+ABH, compared to DCAT+FB, reduced tumor motion, resulting in 19% volume reduction of PTV and 60% reduction in lung V20, on average. The difference in lung V20 between DCAT+ABH and DCAT+FB increased as the target size increased. The DCAT is a favorable approach compared with VMAT. These results support the utility of DCAT as a routine planning platform for lung SBRT, especially when utilized with respiratory motion management using the ABH.

Lee S ，Lee D ，Verma V ，Waters D ，Oh S ，Colonias A ，Wegner R ，Pavord D ，Coopey B ，Fuhrer R ，Sohn JW ... -  《-》

A dosimetric comparison between volumetric-modulated arc therapy and dynamic conformal arc therapy in SBRT.

Stathakis S ，Narayanasamy G ，Licon AL ，Myers P ，Li Y ，Crownover R ，Papanikolaou N ... -  《-》

Improvement of conformal arc plans by using deformable margin delineation method for stereotactic lung radiotherapy.

Stereotactic body radiotherapy (SBRT) is an established treatment technique in the management of medically inoperable early stage non-small cell lung cancer (NSCLC). Different techniques such as volumetric modulated arc (VMAT) and three-dimensional conformal arc (DCA) can be used in SBRT. Previously, it has been shown that VMAT is superior to DCA technique in terms of plan evaluation parameters. However, DCA technique has several advantages such as ease of use and considerable shortening of the treatment time. DCA technique usually results in worse conformity which is not possible to ameliorate by inverse optimization. In this study, we aimed to analyze whether a simple method - deformable margin delineation (DMD) - improves the quality of the DCA technique, reaching similar results to VMAT in terms of plan evaluation parameters. Twenty stage I-II (T1-2, N0, M0) NSCLC patients were included in this retrospective dosimetric study. Noncoplanar VMAT and conventional DCA plans were generated using 6 MV and 10 MV with flattening filter free (FFF) photon energies. The DCA plan with 6FFF was calculated and 95% of the PTV was covered by the prescription isodose line. Hot dose regions (receiving dose over 100% of prescription dose) outside PTV and cold dose regions (receiving dose under 100% of prescription dose) inside PTV were identified. A new PTV (PTV-DMD) was delineated by deforming PTV margin with respect to hot and cold spot regions obtained from conventional DCA plans. Dynamic multileaf collimators (MLC) were set to PTV-DMD beam eye view (BEV) positions and the new DCA plans (DCA-DMD) with 6FFF were generated. Three-dimensional (3D) dose calculations were computed for PTV-DMD volume. However, the prescription isodose was specified and normalized to cover 95% volume of original PTV. Several conformity indices and lung doses were compared for different treatment techniques. DCA-DMD method significantly achieved a superior conformity index (CI), conformity number (CIPaddick ), gradient index (R50% ), isodose at 2 cm (D2 cm ) and external index (CΔ) with respect to VMAT and conventional DCA plans (P < 0.05 for all comparisons). CI ranged between 1.00-1.07 (Mean: 1.02); 1.00-1.18 (Mean: 1.06); 1.01-1.23 (Mean 1.08); 1.03-1.29 (Mean: 1.15); 1.04-1.29 (Mean: 1.18) for DCA-DMD-6FFF, VMAT-6FFF, VMAT-10FFF DCA-6FFF and DCA-10FFF respectively. DCA-DMD-6FFF technique resulted significantly better CI compared to others (P = 0.002; < 0.001; < 0.001; < 0.001). R50% ranged between 3.22-4.74 (Mean: 3.99); 3.24-5.92 (Mean: 4.15) for DCA-DMD-6FFF, VMAT-6FFF, respectively. DCA-DMD-6FFF technique resulted lower intermediate dose spillage compared to VMAT-6FFF, though the difference was statistically insignificant (P = 0.32). D2 cm ranged between 35.7% and 67.0% (Mean: 53.2%); 42.1%-79.2% (Mean: 57.8%) for DCA-DMD-6FFF, VMAT-6FFF respectively. DCA-DMD-6FFF have significantly better and sharp falloff gradient 2 cm away from PTV compared to VMAT-6FFF (P = 0.009). CΔ ranged between 0.052 and 0.140 (Mean: 0.085); 0,056-0,311 (Mean: 0.120) for DCA-DMD, VMAT-6FFF, respectively. DCA-DMD-6FFF have significantly improved CΔ (P = 0.002). VMAT- V20 Gy , V2.5 Gy and mean lung dose (MLD) indices are calculated to be 4.03%, 23.83%, 3.42 Gy and 4.19%, 27.88%,3.72 Gy, for DCA-DMD-6FFF and DCA techniques, respectively. DCA-DMD-6FFF achieved superior lung sparing compared to DCA technique. DCA-DMD-6FFF method reduced MUs 44% and 33% with respect to VMAT-6FFF and 10FFF, respectively, without sacrificing dose conformity (P < 0.001; P < 0.001). Our results demonstrated that DCA plan evaluation parameters can be ameliorated by using the DMD method. This new method improves DCA plan quality and reaches similar results with VMAT in terms of dosimetric parameters. We believe that DCA-DMD is a simple and effective technique for SBRT and can be preferred due to shorter treatment and planning time.

Güngör G ，Demir M ，Aydın G ，Yapıcı B ，Atalar B ，Özyar E ... -  《Journal of Applied Clinical Medical Physics》

Assessment of Monte Carlo algorithm for compliance with RTOG 0915 dosimetric criteria in peripheral lung cancer patients treated with stereotactic body radiotherapy.

Pokhrel D ，Sood S ，Badkul R ，Jiang H ，McClinton C ，Lominska C ，Kumar P ，Wang F ... -  《Journal of Applied Clinical Medical Physics》

A dosimetric comparison of three-dimensional conformal radiotherapy, volumetric-modulated arc therapy, and dynamic conformal arc therapy in the treatment of non-small cell lung cancer using stereotactic body radiotherapy.

Rauschenbach BM ，Mackowiak L ，Malhotra HK 《Journal of Applied Clinical Medical Physics》