Volumetric Modulated Arc Therapy Irradiation Research Articles

Experimental Validation of an Analytical Program and a Monte Carlo Simulation for the Computation of the Far Out-of-Field Dose in External Beam Photon Therapy Applied to Pediatric Patients.

BackgroundThe out-of-the-field absorbed dose affects the probability of primary second radiation-induced cancers. This is particularly relevant in the case of pediatric treatments. There are currently no methods employed in the clinical routine for the computation of dose distributions from stray radiation in radiotherapy. To overcome this limitation in the framework of conventional teletherapy with photon beams, two computational tools have been developed—one based on an analytical approach and another depending on a fast Monte Carlo algorithm. The purpose of this work is to evaluate the accuracy of these approaches by comparison with experimental data obtained from anthropomorphic phantom irradiations.Materials and MethodsAn anthropomorphic phantom representing a 5-year-old child (ATOM, CIRS) was irradiated considering a brain tumor using a Varian TrueBeam linac. Two treatments for the same planned target volume (PTV) were considered, namely, intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). In all cases, the irradiation was conducted with a 6-MV energy beam using the flattening filter for a prescribed dose of 3.6 Gy to the PTV. The phantom had natLiF : Mg, Cu, P (MCP-N) thermoluminescent dosimeters (TLDs) in its 180 holes. The uncertainty of the experimental data was around 20%, which was mostly attributed to the MCP-N energy dependence. To calculate the out-of-field dose, an analytical algorithm was implemented to be run from a Varian Eclipse TPS. This algorithm considers that all anatomical structures are filled with water, with the exception of the lungs which are made of air. The fast Monte Carlo code dose planning method was also used for computing the out-of-field dose. It was executed from the dose verification system PRIMO using a phase-space file containing 3x109 histories, reaching an average standard statistical uncertainty of less than 0.2% (coverage factor k = 1 ) on all voxels scoring more than 50% of the maximum dose. The standard statistical uncertainty of out-of-field voxels in the Monte Carlo simulation did not exceed 5%. For the Monte Carlo simulation the actual chemical composition of the materials used in ATOM, as provided by the manufacturer, was employed.ResultsIn the out-of-the-field region, the absorbed dose was on average four orders of magnitude lower than the dose at the PTV. For the two modalities employed, the discrepancy between the central values of the TLDs located in the out-of-the-field region and the corresponding positions in the analytic model were in general less than 40%. The discrepancy in the lung doses was more pronounced for IMRT. The same comparison between the experimental and the Monte Carlo data yielded differences which are, in general, smaller than 20%. It was observed that the VMAT irradiation produces the smallest out-of-the-field dose when compared to IMRT.ConclusionsThe proposed computational methods for the routine calculation of the out-of-the-field dose produce results that are similar, in most cases, with the experimental data. It has been experimentally found that the VMAT irradiation produces the smallest out-of-the-field dose when compared to IMRT for a given PTV.

Evaluation of a generalized knowledge-based planning performance for VMAT irradiation of breast and locoregional lymph nodes-Internal mammary and/or supraclavicular regions.

To evaluate the performance of eleven Knowledge-Based (KB) models for planning optimization (RapidPlantm (RP), Varian) of Volumetric Modulated Arc Therapy (VMAT) applied to whole breast comprehensive of nodal stations, internal mammary and/or supraclavicular regions. Six RP models have been generated and trained based on 120 VMAT plans data set with different criteria. Two extra-structures were delineated: a PTV for the optimization and a ring structure. Five more models, twins of the previous models, have been created without the need of these structures. All models were successfully validated on an independent cohort of 40 patients, 30 from the same institute that provided the training patients and 10 from an additional institute, with the resulting plans being of equal or better quality compared with the clinical plans. The internal validation shows that the models reduce the heart maximum dose of about 2 Gy, the mean dose of about 1 Gy and the V20Gy of 1.5 Gy on average. Model R and L together with model B without optimization structures ensured the best outcomes in the 20% of the values compared to other models. The external validation observed an average improvement of at least 16% for the V5Gy of lungs in RP plans. The mean heart dose and for the V20Gy for lung IPSI were almost halved. The models reduce the maximum dose for the spinal canal of more than 2 Gy on average. All KB models allow a homogeneous plan quality and some dosimetric gains, as we saw in both internal and external validation. Sub-KB models, developed by splitting right and left breast cases or including only whole breast with locoregional lymph nodes, have shown good performances, comparable but slightly worse than the general model. Finally, models generated without the optimization structures, performed better than the original ones.

Deep Inspiration Breath-Hold (DIBH) for Locoregional Breast Irradiation using Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Proton Therapy (IMPT): A Dosimetric Comparison to Cardiac Substructure

Conventional breast irradiation with tangent fields poses cardiotoxicity risks but recent techniques significantly reduce heart exposure, such as rotational intensity modulated radiation therapy or proton therapy. This study evaluates the potential of deep inspiration breath-hold (DIBH) combination with volumetric modulated arc therapy (VMAT) and intensity modulated proton therapy (IMPT) for further cardiac sparing, at the cardiac substructure level. Following breast conserving surgery, 14 left-sided breast cancer patients treated with free breathing (FB)-VMAT (n = 7) or DIBH-VMAT (n = 7) were retrospectively included. Patients were treated to a dose of 51.8Gy to the whole left breast, 50.4 Gy to the axillary and internal mammary nodes, and 63 Gy to the tumor bed. Pencil beam scanning plans were generated on the initial simulation FB or DIBH computed tomography scans with similar PTV coverage constraints. The endpoint was the mean dose to the heart, to the cardiac cavities, to the left ventricle walls and to the coronary arteries. Table 1 presents the mean doses to cardiac substructures using VMAT and IMPT, with or without DIBH. When combined with VMAT, DIBH significantly reduces dose to nearly all cardiac substructures and to all coronary artery segments. In contrast, when combined with IMPT, DIBH does not show any dosimetric benefit. FB-IMPT significantly spares cardiac substructures compared with DIBH-VMAT. Contrasting with VMAT irradiation where DIBH significantly reduces doses delivered to nearly all cardiac substructures, DIBH does not seem to demonstrate a dosimetric benefit when combined with IMPT. DIBH is thus probably unnecessary for locoregional breast irradiation with IMPT.Abstract 2091; TableStructureVMAT (mean dose Gy)IMPT (mean dose Gy)Free BreathingDIBHp valueFree BreathingDIBHp valueHeart7.123.500.010.800.320.05Left ventricle7.403.19<0.010.090.220.09Anterior wall12.475.23<0.010.260.720.18Apical wall12.384.390.010.400.880.20Lateral wall6.603.37<0.010.040.160.02Inferior wall4.131.65<0.02<0.010.010.47Septal wall6.622.77<0.030.020.010.36Right ventricle7.053.55<0.040.790.070.14Left auricle3.971.910.02<0.01<0.010.08Right auricle3.892.440.040.060.030.13Left main coronary artery6.342.85<0.010.02<0.010.37Left anterior descending artery21.198.32<0.012.481.650.47Proximal segment12.995.170.040.190.290.63Mid segment24.1010.88<0.014.003.130.68Distal segment23.528.370.012.151.380.35Circumflex artery5.122.540.03<0.01<0.010.11Proximal segment7.343.090.02<0.010.010.22Distal segment4.532.410.06<0.01<0.010.10Right coronary artery5.402.870.010.030.060.62Proximal segment6.454.580.220.060.140.59Mid segment4.152.270.050.01<0.010.29Distal segment3.011.170.01<0.01<0.010.36Posterior descending segment6.151.560.01<0.01<0.010.18Author Disclosure: P. Loap: None. F. Goudjil: None. B. Baron: None. M. Ribeiro: None. A. Fourquet: None. Y. Kirova: None. Open table in a new tab

Optimized stereotactic volumetric modulated arc therapy as an alternative to brachytherapy for vaginal cuff boost. A dosimetric study

We evaluate the role of stereotactic body radiotherapy using volumetric modulated arc therapy (VMAT) technique as an alternative to high-dose rate brachytherapy (HDR-BT) in the treatment of vaginal cuff in postoperative endometrial cancer. CT scans of 8 patients were used in this study. The clinical target volume (CTV) was defined as the 0.5 cm tissue around the applicator (then subtracting the applicator). Total dose was 30Gy delivered in 5 fractions. In HDR-BT, dose was prescribed at a distance of 0.5 cm from the surface applicator. For VMAT irradiation, a planning target volume (PTV) was obtained from CTV by an expansion of 3 mm. Two VMAT plans were generated using a full arc rotation. The first plan was optimized with an anatomy-based optimization module (PO-VMAT) using a 1mm multileaf collimator beam margin to enhance dose heterogeneity and dose fallout outside the target. The second plan was generated with a full-inverse planning module (FI-VMAT). Conformity (CI100, CI50, CI25), gradient (GI) indexes, and integral doses were calculated. To account for various dose heterogeneity distributions we calculated the equivalent uniform dose (EUD) using the Niemerko model. A Kruskal-Wallis analysis of variance followed by Dunn’s-type multiple comparisons was performed. Dose distributions were more heterogeneous with HDR-BT: Dmean was 144.2% of prescription dose for CTV in HDR-BT and 118.5 and 108.6% for PTV in PO-VMAT and FI-VMAT, respectively. The mean values of EUD for CTV were 136.9%, 130.0 %, and 111.0% of prescription dose in HDR-BT, PO-VMAT, and FI-VMAT plans, respectively. GI indexes were 2.81, 3.41, and 4.14 for HDR-BT, PO-VMAT, and FI-VMAT, respectively. Near-maximal doses (D0.1cc) for rectum and bladder were significantly higher in HDR-BT plans compared to PO-VMAT and FI-VMAT plans (rectum: 131.2% vs112.8% vs 112.0%, respectively; bladder: 129.2% vs 108.7%, and 109.8%, respectively). PO-VMAT plans were able to mimic the HDR-BT dose distribution, showing a successful capability of highly conformal dose distribution, EUD values similar to HDR-BT, and steep dose-gradient outside PTV, then providing a reasonable alternative to brachytherapy.

A study of dose verification and comparison for complex irradiation field with high dose rate radiation by using a 3D N-isopropylacrylamide gel dosimeter

This study aimed to investigate dosimeter characteristics by using a photon beam with and without the flattening filter of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) by using a 3D N-isopropylacrylamide (NIPAM) polymer gel. A self-developed optical computed tomography scheme was used to measure the dose distribution. Gamma evaluation was performed between the dose distribution calculated by a treatment planning system and the measured dose distribution by using the criteria of 3% dose difference and 3 mm distance to agreement. Under these criteria, the passing rates showed no significant difference between IMRT and VMAT irradiation with and without the flattening filter. All these results revealed that the NIPAM gel dosimeter was for high-dose-rate radiation and clinical-pretreatment verifications.

Effective heart-sparing whole lung irradiation using volumetric modulated arc therapy: a case report

BackgroundLate cardiovascular disease-related adverse events are one of the most common causes of premature mortality among long-term survivors of childhood cancer. As it is difficult to reduce the heart dose with traditional anteroposterior–posteroanterior field whole lung irradiation for pulmonary metastasis, improved radiation techniques are highly desirable. We report a case treated with whole lung irradiation using volumetric modulated arc therapy.Case presentationA 3-year-old Japanese girl with pulmonary metastases of Wilms’ tumor received 12 Gy in 8 fractions of whole lung irradiation using volumetric modulated arc therapy. The treatment was well tolerated, and the course was completed as planned without any toxicity. We found statistically significant reduced volumetric modulated arc therapy irradiation doses to organs at risk relative to those of the standard anteroposterior–posteroanterior field technique. The mean heart dose was 8.5 Gy for volumetric modulated arc therapy and 12.3 Gy for the anteroposterior–posteroanterior field. The doses to liver and thyroid were also more favorable with volumetric modulated arc therapy than with the anteroposterior–posteroanterior field technique. We confirmed the dosimetric advantages of volumetric modulated arc therapy over anteroposterior–posteroanterior field in whole lung irradiation in terms of superior normal organ protection.ConclusionsEffective heart sparing is possible for whole lung irradiation using volumetric modulated arc therapy. Large-scale studies using standardized procedures should be conducted to validate our results.

Log file-based patient dose calculations of double-arc VMAT for head-and-neck radiotherapy

PurposeThe log file-based method cannot display dosimetric changes due to linac component miscalibration because of the insensitivity of log files to linac component miscalibration. The purpose of this study was to supply dosimetric changes in log file-based patient dose calculations for double-arc volumetric-modulated arc therapy (VMAT) in head-and-neck cases. Methods and materialsFifteen head-and-neck cases participated in this study. For each case, treatment planning system (TPS) doses were produced by double-arc and single-arc VMAT. Miscalibration-simulated log files were generated by inducing a leaf miscalibration of ±0.5 mm into the log files that were acquired during VMAT irradiation. Subsequently, patient doses were estimated using the miscalibration-simulated log files. ResultsFor double-arc VMAT, regarding planning target volume (PTV), the change from TPS dose to miscalibration-simulated log file dose in Dmean was 0.9 Gy and that for tumor control probability was 1.4%. As for organ-at-risks (OARs), the change in Dmean was <0.7 Gy and normal tissue complication probability was <1.8%. A comparison between double-arc and single-arc VMAT for PTV showed statistically significant differences in the changes evaluated by Dmean and radiobiological metrics (P < 0.01), even though the magnitude of these differences was small. Similarly, for OARs, the magnitude of these changes was found to be small. ConclusionsUsing the log file-based method for PTV and OARs, the log file-based method estimate of patient dose using the double-arc VMAT has accuracy comparable to that obtained using the single-arc VMAT.

Reduced toxicity in the treatment of locally advanced rectal cancer: a comparison of volumetric modulated arc therapy and 3D conformal radiotherapy.

BackgroundExcellent dosimetric characteristics were demonstrated for volumetric modulated arc therapy (VMAT) in preoperative chemoradiotherapy (CRT) for locally advanced rectal cancer (LARC). In a single-center retrospective analysis, we tested whether these advantages may translate into significant clinical benefits. We compared VMAT to conventional 3D conformal radiotherapy (3DCRT) in patients, homogeneously treated according to the control arm of the CAO/ARO/AIO-04 trial.MethodsCRT consisted of pelvic irradiation with 50.4/1.8Gy by VMAT (n = 81) or 3DCRT (n = 107) and two cycles of 5-fluorouracil. Standardized total mesorectal excision surgery was performed within 4–6 weeks. The tumor regression grading (TRG) was assessed by the Dworak score. Acute and late toxicity were evaluated via the Common Terminology Criteria for Adverse Events and the Late effects of normal tissues scale, respectively. Side effects greater than or equal to grade 3 were considered high-grade.ResultsMedian follow-up was 18.3 months in the VMAT group and 61.5 months in the 3DCRT group with no differences in TRG between them (p = 0.1727). VMAT treatment substantially reduced high-grade acute and late toxicity, with 5 % versus 20 % (p = 0.0081) and 6 % vs. 22 % (p = 0.0039), respectively. With regard to specific organs, differences were found in skin reaction (p = 0.019) and proctitis (p = 0.0153).ConclusionsVMAT treatment in preoperative CRT for LARC showed the potential to substantially reduce high-grade acute and late toxicity. Importantly, we could demonstrate that VMAT irradiation did not impair short-term oncological results. We conclude, that the reduced toxicity after VMAT irradiation may pave the way for more efficient systemic therapies, and hopefully improved patient survival in the multimodal treatment of LARC.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-015-1812-x) contains supplementary material, which is available to authorized users.

In-vivo dosimetry with Gafchromic films for multi-isocentric VMAT irradiation of total marrow lymph-nodes: a feasibility study.

BackgroundTotal marrow (lymph-nodes) irradiation (TMI-TMLI) by volumetric modulated arc therapy (VMAT) was shown to be feasible by dosimetric feasibility studies. It was demonstrated that several partially overlapping arcs with different isocenters are required to achieve the desired coverage of the hematopoietic or lymphoid tissues targets and to spare the neighbouring healthy tissues. The effect of isocenter shifts was investigated with the treatment planning system but an in- vivo verification of the procedure was not carried out. The objective of this study was the in-vivo verification of the consistency between the delivered and planned doses using bi-dimensional GafChromic EBT3 films.MethodsIn a first phase a phantom study was carried out to quantify the uncertainties under controlled conditions. In a second phase three patients treated with TMLI were enrolled for in-vivo dosimetry. The dose prescription was 2Gy in single fraction. Ten arcs paired on 4-6 isocenters were used to cover the target. Cone Beam Computed Tomography (CBCT) was used to verify the patient positioning at each isocenter. GafChromic EBT3 films were placed below the patient on the top of a dedicated immobilization system specifically designed. The dose maps measured with the EBT3 films were compared with the corresponding calculations along the patient support couch. Gamma Agreement Index (GAI) with dose difference of 5% and distance to agreement of 5 mm was computed.ResultsIn the phantom study, optimal target coverage and healthy tissue sparing was observed. GAI(5%,5 mm) was 99.4%. For the patient-specific measurements, GAI(5%,5 mm) was greater than 95% and GAI (5%,3 mm) > 90% for all patients.ConclusionsIn vivo measurements demonstrated the delivered dose to be in good agreement with the planned one for the TMI-TMLI protocol where partially overlapping arcs with different isocenters are required.