Dynamic Conformal Arc Therapy Plans Research Articles

Single-isocenter multiple-target stereotactic radiosurgery for multiple brain metastases: dosimetric evaluation of two automated treatment planning systems

PurposeAutomated treatment planning systems are available for linear accelerator (linac)-based single-isocenter multi-target (SIMT) stereotactic radiosurgery (SRS) of brain metastases. In this study, we compared plan quality between Brainlab Elements Multiple Brain Metastases (Elements MBM) software which utilizes dynamic conformal arc therapy (DCAT) and Varian HyperArc (HA) software using a volumetric modulated arc therapy (VMAT) technique.Patients and methodsBetween July 2018 and April 2021, 36 consecutive patients ≥ 18 years old with 367 metastases who received SIMT SRS at UPMC Hillman Cancer San Pietro Hospital, Rome, were retrospectively evaluated. SRS plans were created using the commercial software Elements MBM SRS (Version 1.5 and 2.0). Median cumulative gross tumor volume (GTV) and planning tumor volume (PTV) were 1.33 cm3 and 3.42 cm3, respectively. All patients were replanned using HA automated software. Extracted dosimetric parameters included mean dose (Dmean) to the healthy brain, volumes of the healthy brain receiving more than 5, 8,10, and 12 Gy (V5Gy, V8Gy, V10Gy and V12Gy), and doses to hippocampi.ResultsBoth techniques resulted in high-quality treatment plans, although Element MBM DCAT plans performed significantly better than HA VMAT plans, especially in cases of more than 10 lesions). Median V12Gy was 13.6 (range, 1.87–45.9) cm3 for DCAT plans and 18.5 (2.2–62,3) cm3 for VMAT plans (p < 0.0001), respectively. Similarly, V10Gy, V8Gy, V5Gy (p < 0.0001) and median dose to the normal brain (p = 0.0001) were favorable for DCAT plans.ConclusionsBoth Elements MBM and HA systems were able to generate high-quality plans in patients with up to 25 brain metastases. DCAT plans performed better in terms of normal brain sparing, especially in patients with more than ten lesions and limited total tumor volume.

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.

Dosimetric comparison among dynamic conformal arc therapy, coplanar and non-coplanar volumetric modulated arc therapy for single brain metastasis.

In the delivery of stereotactic radiosurgery (SRS) by linear accelerator (LINAC), dynamic conformal arc therapy (DCAT) with non-coplanar beams is conventionally used. However, volumetric modulated arc therapy (VMAT) can improve target conformity, thereby decreasing the dose to organs at risk by inversed planning methods, but few studies have directly compared DCAT and VMAT with and without non-coplanar beams in patients with single brain metastasis. We therefore conducted a planning study to compare the dose distribution in DCAT, VMAT using only a coplanar arc (CoVMAT) and VMAT with non-coplanar arcs (NcVMAT) in the treatment of single brain metastasis. DCAT, CoVMAT and NcVMAT plans were created for 15 patients. The three modalities were compared in terms of target conformity, target coverage, the dose to normal brain tissue, monitor units (MUs) and beam-on time. Both conformity indices (RTOG-CI and IP-CI) as well as the D98% of the gross target volume (GTV) were significantly better in the NcVMAT plans than in the DCAT plans. Comparisons of the doses to normal brain tissue revealed that the V20Gy, V15Gy, V12Gy, V10Gy and V5Gy were significantly smaller in the NcVMAT plans than in the plans based on the other two modalities. The MUs of the DCAT and NcVMAT plans were larger than those of the CoVMAT plans, and the beam-on time was longer in the NcVMAT and CoVMAT plans than in the DCAT plans. Compared to the CoVMAT and DCAT plans, NcVMAT plans significantly improved target conformity and reduced the doses to normal brain tissue at V20Gy, V15Gy, V12Gy, V10Gy and V5Gy.

Treating lung cancer with dynamic conformal arc therapy: a dosimetric study

BackgroundLung cancer patients are often in poor physical condition, and a shorter treatment time would reduce their discomfort. Dynamic conformal arc therapy (DCAT) offers a shorter treatment time than conventional 3D conformal radiotherapy (3D CRT) and is usually available even in departments without inverse planning possibilities. We examined its suitability as a treatment modality for lung cancer patients.MethodsOn a cohort of 35 lung cancer patients, relevant dosimetric parameters were compared in respective DCAT and 3D CRT treatment plans. Radiochromic film dosimetry in an anthropomorphic phantom was used to compare both DCAT and 3D CRT dose distributions against their planned counterparts.ResultsIn comparison with their 3D CRT counterparts, DCAT plans equal or exceed the agreement between the calculated dose and the dose measured using film dosimetry. In dosimetric comparison, DCAT performed significantly better than 3D CRT in dose conformity to PTV and the number of monitor units used per plan, and significantly worse in dose homogeneity, mean lung dose and lung volume exposed to 5 Gy or more (V5Gy). No significant difference was found in the V20Gy value to lung, dose to 1 cm3 of spinal cord, and the mean dose to oesophagus. Improvements in V20Gy and V5Gy were found to be negatively correlated. DCAT plans differ from 3D CRT by exhibiting a moderate negative correlation between target volume sphericity and dose homogeneity.ConclusionsWith respect to the agreement between the planned and the irradiated dose distribution, DCAT appears at least as reliable as 3D CRT. In specific conditions concerning the patient anatomy and treatment prescription, DCAT may yield more favourable dosimetric parameters. On average, however, conventional 3D CRT usually obtains better dosimetric parameters. We can thus only recommend DCAT as a complementary technique to the conventional 3D CRT.

A dosimetric and treatment efficiency evaluation of stereotactic body radiation therapy for peripheral lung cancer using flattening filter free beams.

To investigate potential dosimetric benefits and treatment efficiency of dynamic conformal arc therapy (DCA), intensity modulated radiation therapy (IMRT), and double partial arcs Rapidarc (RA) techniques in the treatment of early-stage peripheral lung cancer using stereotactic body radiotherapy (SBRT) with flattening filter free (FFF) beams. Twenty early-stage peripheral lung cancer patients were selected. For each patient, DCA, IMRT and RA plans were created to meet Radiation Therapy Oncology Group (RTOG) 0915 objectives with 48 Gy covering 95% of the planning target volume (PTV) in 4 fractions. PTV coverage, organs at risk (OARs) doses, planning time, monitor units (MU) and treatment time were evaluated. RA was significantly better than DCA for PTV coverage. RA provided a lower V32Gy to chest wall and less V20Gy to lung over those of DCA and IMRT. For other OARs, there is no significant difference among all three techniques. DCA plans showed significantly less planning time, shorter treatment time and lower MU number than those of RA and IMRT. RA provides a superior dosimetric benefit to DCA and IMRT in the treatment of early-stage lung cancer using SBRT with FFF beams. Considering the MU number, planning time and treatment efficiency, DCA technique is an effective treatment strategy.

SU-E-T-62: Cardiac Toxicity in Dynamic Conformal Arc Therapy, Intensity-Modulated Radiation Therapy and Volumetric Modulated Arc Therapy of Lung Cancers

Purpose: The cardiac toxicity for lung cancer patients, each treated with dynamic conformal arc therapy (DAT), intensity-modulated radiation therapy (IMRT), or volumetric modulated arc therapy (VMAT) is investigated. Methods: 120 lung patients were selected for this study: 25 treated with DAT, 50 with IMRT and 45 with VMAT. For comparison, all plans were generated in the same treatment planning system, normalized such that the 100% isodose lines encompassed 95% of planning target volume. The plan quality was evaluated in terms of homogeneity index (HI) and 95% conformity index (%95 CI) for target dose coverage and mean dose, maximum dose, V3 0 Gy as well as V5 Gy for cardiac toxicity analysis. Results: When all the plans were analyzed, the VMAT plans offered the best target coverage with 95% CI = 0.992 and HI = 1.23. The DAT plans provided the best heart sparing with mean heart dose = 2.3Gy and maximum dose = 11.6Gy, as compared to 5.7 Gy and 31.1 Gy by IMRT as well as 4.6 Gy and 30.9 Gy by VMAT. The mean V30Gy and V5Gy of the heart in the DAT plans were up to 11.7% lower in comparison to the IMRT and VMAT plans. When the tumor volume was considered, the VMAT plans spared up to 70.9% more doses to the heart when the equivalent diameter of the tumor was larger than 4cm. Yet the maximum dose to the heart was reduced the most in the DAT plans with up to 139.8% less than that of the other two plans. Conclusion: Overall, the VMAT plans achieved the best target coverage among the three treatment modalities, and would spare the heart the most for the larger tumors. The DAT plans appeared advantageous in delivering the least maximum dose to the heart as compared to the IMRT and VMAT plans.

SU-E-T-631: A Systematic Study on Dosimetric Impact of Grid Size and Angular Interval in Dynamic Conformal Arc Technique for Lung SBRT

Purpose: To systematically evaluate the dosimetric impact of grid size and angular increment, in stereotactic body radiation therapy(SBRT) using dynamic conformal arc therapy (DCAT) technique. Methods: DCAT plans were obtained with varying grid size (2, 3, and 4 mm) and angular increment (5, 10, and 20°) for various planning target volumes (PTVs). As 95% of PTV volume is covered with the prescribed dose,dose variation from coarser grid size was compared to 2 mm grid size with assuming the latter could provide calculated dose accurate enough in practical aspect. The impact of angular increment variation on any organ at risk (OAR) was evaluated with placing the spinal cord in a set of 8 different locations (5 cm and 7 cm distance from the isocenter and 5°, 10°, and 20° of azimuthal angle with respect to the a location chosen as zero angle in axial plane). Results: Compared to 2 mm grid size, 3 mm grid size showed increases ranging from 2 to 3%, 2%, and 1 to 2% in monitor units, the maximum dose of the PTV, and the maximum dose of the spinal cord, respectively. For 4 mm grid size, the amount of increase was larger (4 to 7%, 4 to 6%, and 4 to 6%, respectively). When compared to 5° angular increment, dose variation with 10° increment was less than 2%, but 20° increment caused significant variations reaching up to 10% and 24% for 5 cm and 7 cm distant volume. Conclusions: Dosimetric impact of planning parameters would guide planners to use appropriate parameters with possible dose uncertainty in DCAT. With coarse grid size, planners are expected to choose lower isodose line for PTV coverage, resulting in patient overdose. Significantly inaccurate prediction of OAR dose could be made with coarse angular increment depending on location of OAR.

Evaluation of the dynamic conformal arc therapy in comparison to intensity‐modulated radiation therapy in prostate, brain, head‐and‐neck and spine tumors

To evaluate dynamic conformal arc therapy (DAT) dose distribution and clinical applicability in comparison to intensity‐modulated radiotherapy (IMRT) in different types of tumors and locations, twelve patients with prostate cancer with no node involvement and three patients with single tumors in the pituitary, in the neck and in the thoracic spinal region treated with IMRT, were retrospectively planned with DAT using Eclipse (V8.1). The prostate cases were also planned with three‐dimensional conformal radiation therapy (3DCRT). Dose distributions were evaluated through comparisons of dose‐volumetric histograms and in‐house IMRT protocol constraints, as well as validated via ion chamber array measurements. DAT plans for prostate showed a statistically comparable achievement of tumor conformity and dose sparing for bladder and rectum when compared to IMRT. Dose on femoral heads were similar to those achieved using 3DCRT. DAT could be planned with similar results to those obtained in IMRT for the dose constraints of the defined structures by using a 360° arc for the brain lesion and several arcs including noncoplanar ones for the head‐and‐neck and spinal tumors. Experimental validation of the calculated dose distributions via gamma analysis of composite distributions for DAT provided that more than 95% of the pixels satisfy the criteria 3 mm–3%, which was similar to that of IMRT. The average number of monitor units was approximately five times lower than IMRT. In conclusion, DAT is capable of providing conformal dose distributions to the targets accomplishing many of the IMRT dose constraints simultaneously. Experimental dose‐validation accuracy, ease of planning and reduced treatment times make DAT both acceptable and attractive for clinical use.PACS numbers: 87.55.D‐, 87.55.dk, 87.55.Qr, 87.56.bd, 87.56.Fc, 87.53.Kn, 87.55. de, 87.55.kd

SU-FF-T-587: Evaluation of the Dynamic Conformal Arc Therapy as An Alternative to Intensity-Modulated Radiation Therapy in Prostate, Brain, Head-And-Neck, and Spine Tumors

Purpose: To evaluate the dynamic conformal arc therapy (DAT) dose distribution and clinical applicability in comparison to intensity‐modulated radiotherapy(IMRT) in different types of tumors and locations. Methods and Materials: Twelve patients with prostate cancer with no node involvement and three patients with single tumors in the pituitary, in the neck, and in the thoracic spinal region, treated with IMRT, were retrospectively planned with DAT using Eclipse (V8.1). The prostate cases were also planned with three‐dimensional static conformal technique (3DST). Dose distributions were evaluated through comparisons in dose‐volumetric histograms and in‐house IMRT protocol constraints for all the involved techniques. A dose measurement system was used to evaluate the accuracy of calculated dose distributions. Results: DAT plans for prostate showed a statistically comparable achievement of tumor conformity and dose sparing for bladder and rectum when compared to IMRT.Dose on femoral heads were similar to those achieved using 3DST. DAT could be planned with close results to those obtained in IMRT for the dose constraints of the defined structures by using a 360°‐arc for the brain lesion and several arcs including non‐coplanar ones for the head‐and‐neck and spinal tumors. The accuracy of experimental validation of the calculated dose distributions with DAT was similar to that of IMRT. The average number of monitor units for our DAT plans were 5 times lower than IMRT.Conclusions: The dose distribution evaluation showed that DAT is a reasonable alternative to IMRT for single tumors, accomplishing many of the IMRT constraints used in standard protocols. Moreover, the significant fewer number of monitor units used in DAT compared to IMRT reduce both the planning and the treatment times, providing not only cost savings but also better opportunities of more accurate results of treatment delivery. Conflict of interest: This study is partially supported by a Varian Research Grant.

Comparative dosimetric study of three-dimensional conformal, dynamic conformal arc, and intensity-modulated radiotherapy for brain tumor treatment using Novalis system

Purpose: To investigate the dosimetric differences among three-dimensional conformal radiotherapy (3D-CRT), dynamic conformal arc therapy (DCAT), and intensity-modulated radiotherapy (IMRT) for brain tumor treatment. Methods and Materials: Fifteen patients treated with Novalis were selected. We performed 3D-CRT, DCAT, and IMRT plans for all patients. The margin for the planning target volume (PTV) was 1 mm, and the specific prescription dose was 90% for all plans. The target coverage at the prescription dose, conformity index (CI), and heterogeneity index were analyzed for all plans. Results: For small tumors (PTV ≤2 cm 3 ), the three dosimetric parameters had approximate values for both 3D-CRT and DCAT plans. The CI for the IMRT plans was high. For medium tumors (PTV >2 to ≤100 cm 3 ), the three plans were competitive with each other. The IMRT plans had a greater CI, better target coverage at the prescription dose, and a better heterogeneity index. For large tumors (PTV >100 cm 3 ), the IMRT plan had good target coverage at the prescription dose and heterogeneity index and approximate CI values as those in the 3D-CRT and DCAT plans. Conclusion: The results of our study have shown that DCAT is suitable for most cases in the treatment of brain tumors. For a small target, 3D-CRT is useful, and IMRT is not recommended. For larger tumors, IMRT is superior to 3D-CRT and very competitive in sparing critical structures, especially for big tumors.

SU-FF-T-350: A Comparative Dosimetric Study of Three-Dimensional Conformal, Dynamic Conformal Arc, and Intensity Modulated Radiation Therapy for Brain Tumor Treatment

Purpose: To investigate dosimetric differences among three‐dimensional conformal (3D‐CRT), dynamic conformal arc therapy (DCAT) and intensity modulated radiotherapy(IMRT) for braintumortreatment for a broad range of braintumor volumes and shapes in an effort to determine whether a preferred method can be identified based upon pre‐treatment characteristics. Method and Materials: Fifteen patients treated with Novalis were selected. We performed 3D‐CRT, DCAT and IMRT plans for all the cases. The beam numbers in 3D‐CRT or IMRT plans were the same as the arc numbers in the DCAT plans, and the gantry angle of each beam in 3D‐CRT or IMRT plans was the middle angle of each arc in the DCAT plans. The PTV margin was re‐chosen as 1mm, and the specific prescription dose was re‐set to 90% for all the plans. The target coverage at prescription dose (TV90%), conformity index (CI) and heterogeneity index (HI) were used to compare the different plans. V50% and V80% of the organs at risk (OAR) were also calculated. Results: For small braintumors (PTV⩽2cc), three dosimetric parameters had approximate values for both 3D‐CRT and DCAT plans ( TV 90% ¯ ∼93%, CI ¯ ∼1.7, HI ¯ ∼1.4) . The CI for IMRT plans was high ( CI ¯ =3) . For medium braintumors (2cc<PTV⩽100cc), the three plans were competitive with each other. IMRT plans had higher CI and better TV90% and HI. For large braintumors (PTV⩾100cc), IMRT plan had nearly perfect TV90% and HI and the approximate CI values as those in both 3D‐CRT and DCAT plans. Conclusions: DCAT is suitable for most cases in the treatment of braintumors. For a small target, 3D‐CRT is still useful, and IMRT is not recommended. For larger braintumors,IMRT is superior to 3D‐CRT, and very competitive in sparing critical structures near the target, especially for the treatment of a big braintumor.