背景:为了改善危险器官(OAR)的保留,动态轨迹放射治疗(DTRT)通过动态表和准直器旋转在光束打开期间扩展VMAT。然而,尚未进行有关台架(GT)旋转梯度对DTRT计划质量影响的全面调查。
目的:根据剂量计划质量,研究用户定义的GT旋转梯度对DTRT计划计划质量的影响,剂量测定鲁棒性,可交付性,和交货时间。
方法:DTRT的动态轨迹由GT和机架-准直器路径描述。通过最小化OAR与计划目标体积(PTV)的重叠来确定GT路径。通过两个相邻控制点(G=|Δtableangle/Δ龙门角度|$G=|\\Delta{\mathrm{table\angle}}/\\Delta{\mathrm{table\angle}}/\\Delta{\mathrm{龙门\angle}}}|Δa的最大变化(G\$})创建四个DTRT计划,具有不同的最大G&ΔG:Gmax${G}_{max}$&ΔGmax${{\\Delta}}{G}_{max}$=0.5&0.125(DTRT-1),1和0.125(DTRT-2),3和0.125(DTRT-3)和3和1(DTRT-4),包括3-4个动态轨迹,对于头部和颈部和大脑区域的三个临床动机病例(A,B,andC).创建每个案例的参考VMAT计划。对于所有计划,计划质量进行评估和比较。剂量测定计划质量通过目标覆盖率来评估,一致性,和OAR保留。剂量稳健性针对横向±3mm$\\pm3\\{\\mathrm{mm}}$之间的系统和随机患者设置不确定性进行评估,纵向,和垂直方向,和动态旋转机器部件中的±4○$\\pm4^\\circ\\$之间的机器不确定性(龙门,table,准直器旋转)。记录交货时间。通过对所有计划的日志文件分析来评估TrueBeam上的可交付性和交付准确性,并通过一种情况的胶片测量进行额外验证。所有剂量计算均基于蒙特卡洛。
结果:使用用户定义的Gmax&ΔGmax${G}_{max}\\&{{\\Delta}}{G}_{max}{G}_{max}$对DTRT计划流程的扩展已成功演示。随着Gmax和ΔGmax${G}_{max}\\&{{\\Delta}}{G}_{max}$,轻微(情况C,Dmean,parotidl。${D}_{表示,\\腮腺\\l.}$:最高为-1Gy)和实质性(案例A,D0.03cm3,opticnerver。${D}_{0.03c{m}^3,\\视神经\\r.}$:最高-9.3Gy,案例Dmean,brain$\\{D}_{表示,\\brain}$:高达-4.7Gy)与VMAT相比,观察到OAR节省的改善,同时保持类似的目标覆盖率。所有计划都在TrueBeam上交付。对于龙门架,记录在日志文件中的预期和实际机器位置值偏离<0.2°,表和准直器旋转。胶片测量与剂量计算的一致性>96%(2%全局/2mmγ通过率)。随着Gmax和ΔGmax${G}_{max}\\&{{\\Delta}}{G}_{max}$,与VMAT和DTRT-1相比,递送时间延长<2分钟/轨迹(DTRT-4)。案例A和B的DTRT计划和案例C计划的VMAT计划揭示了所考虑的不确定性的最佳剂量稳健性。
结论:针对头颈部和脑部区域的3例病例,全面研究了GT旋转梯度对DTRT计划质量的影响。增加此梯度的自由度可提高剂量测定计划的质量,但以增加所调查案例的交付时间为代价。没有观察到GT旋转梯度对剂量测定鲁棒性的明显依赖性。
BACKGROUND: To improve organ at risk (OAR) sparing, dynamic trajectory radiotherapy (DTRT) extends VMAT by dynamic table and collimator rotation during beam-on. However, comprehensive investigations regarding the impact of the gantry-table (GT) rotation gradient on the DTRT plan quality have not been conducted.
OBJECTIVE: To investigate the impact of a user-defined GT rotation gradient on plan quality of DTRT plans in terms of dosimetric plan quality, dosimetric robustness, deliverability, and delivery time.
METHODS: The dynamic trajectories of DTRT are described by GT and gantry-collimator paths. The GT path is determined by minimizing the overlap of OARs with planning target volume (PTV). This approach is extended to consider a GT rotation gradient by means of a maximum gradient of the path ( G m a x ${G}_{max}$ ) between two adjacent control points ( G = | Δ table angle / Δ gantry angle | $G = | \\Delta {{\\mathrm{table\\ angle}}/\\Delta {\\mathrm{gantry\\ angle}}} |$ ) and maximum absolute change of G ( Δ G m a x ${{\\Delta}}{G}_{max}$ ). Four DTRT plans are created with different maximum G&∆G: G m a x ${G}_{max}$ & Δ G m a x ${{\\Delta}}{G}_{max}$ = 0.5&0.125 (DTRT-1), 1&0.125 (DTRT-2), 3&0.125 (DTRT-3) and 3&1(DTRT-4), including 3-4 dynamic trajectories, for three clinically motivated cases in the head and neck and brain region (A, B, and C). A reference VMAT plan for each case is created. For all plans, plan quality is assessed and compared. Dosimetric plan quality is evaluated by target coverage, conformity, and OAR sparing. Dosimetric robustness is evaluated against systematic and random patient-setup uncertainties between ± 3 mm $ \\pm 3\\ {\\mathrm{mm}}$ in the lateral, longitudinal, and vertical directions, and machine uncertainties between ± 4 ∘ $ \\pm 4^\\circ \\ $ in the dynamically rotating machine components (gantry, table, collimator rotation). Delivery time is recorded. Deliverability and delivery accuracy on a TrueBeam are assessed by logfile analysis for all plans and additionally verified by film measurements for one case. All dose calculations are Monte Carlo based.
RESULTS: The extension of the DTRT planning process with user-defined G m a x & Δ G m a x ${G}_{max}\\& {{\\Delta}}{G}_{max}$ to investigate the impact of the GT rotation gradient on plan quality is successfully demonstrated. With increasing G m a x & Δ G m a x ${G}_{max}\\& {{\\Delta}}{G}_{max}$ , slight (case C, D m e a n , p a r o t i d l . ${D}_{mean,\\ parotid\\ l.}$ : up to-1Gy) and substantial (case A, D 0.03 c m 3 , o p t i c n e r v e r . ${D}_{0.03c{m}^3,\\ optic\\ nerve\\ r.}$ : up to -9.3 Gy, caseB, D m e a n , b r a i n $\\ {D}_{mean,\\ brain}$ : up to -4.7Gy) improvements in OAR sparing are observed compared to VMAT, while maintaining similar target coverage. All plans are delivered on the TrueBeam. Expected and actual machine position values recorded in the logfiles deviated by <0.2° for gantry, table and collimator rotation. The film measurements agreed by >96% (2%global/2 mm Gamma passing rate) with the dose calculation. With increasing G m a x & Δ G m a x ${G}_{max}\\& {{\\Delta}}{G}_{max}$ , delivery time is prolonged by <2 min/trajectory (DTRT-4) compared to VMAT and DTRT-1. The DTRT plans for case A and B and the VMAT plan for case C plan reveal the best dosimetric robustness for the considered uncertainties.
CONCLUSIONS: The impact of the GT rotation gradient on DTRT plan quality is comprehensively investigated for three cases in the head and neck and brain region. Increasing freedom in this gradient improves dosimetric plan quality at the cost of increased delivery time for the investigated cases. No clear dependency of GT rotation gradient on dosimetric robustness is observed.