Abstract：
OBJECTIVE: Objective parameters for decision on adaptive radiotherapy depend on patient, tumor and treatment related factors. Present study reports geometric uncertainties occurring during high precision radiotherapy, beam fluence analysis and serial exit dose measurement as a patient-specific tool for adaptive radiotherapy.
METHODS: Serial exit dose fluence of 24 patients (at baseline and mid-treatment) undergoing IMRT/VMAT treatment were measured. Baseline and midtreatment exit dose evaluation was done using gafchromic films in predefined region of interest. Difference of volume of GTV at baseline (from simulation CT scan) and midtreatment CBCT scan was calculated (ΔGTV).
RESULTS: Population based systematic errors (mm) were 4.15, 2.26, 0.88 and random errors (mm) were 2.56, 3.69, and 2.03 in mediolateral (ML), craniocaudal (CC) and anteroposterior (AP) directions respectively. Gamma pass rate reduced with incremental shift. For a 5 mm shift, maximum deviation was found in anteroposterior axis (22.16 ± 7.50) and lowest in mediolateral axis (12.85 ± 4.95). On serial measurement of exit dose fluence, tumor shrinkage significantly influenced gamma pass rate. The mean gamma pass rate was significantly different between groups with 50% shrinkage of tumor volume (86.36 vs 96.24, P = 0.008, on multivariate analysis P = 0.026).
CONCLUSIONS: Rapid fall of gamma pass rate was observed for set up error of ≥3 mm. Serial measurement of exit dose fluence by radiochromic film is a feasible method of exit dose comparison in IMRT/VMAT, where EPID dosimetry is not available with linear accelerator configuration. Our study suggests that there is a significant difference between gamma pass rates of baseline and mid treatment exit dose fluence with greater than 50% tumor shrinkage.
METHODS: Serial exit dose fluence of 24 patients (at baseline and mid-treatment) undergoing IMRT/VMAT treatment were measured. Baseline and midtreatment exit dose evaluation was done using gafchromic films in predefined region of interest. Difference of volume of GTV at baseline (from simulation CT scan) and midtreatment CBCT scan was calculated (ΔGTV).
RESULTS: Population based systematic errors (mm) were 4.15, 2.26, 0.88 and random errors (mm) were 2.56, 3.69, and 2.03 in mediolateral (ML), craniocaudal (CC) and anteroposterior (AP) directions respectively. Gamma pass rate reduced with incremental shift. For a 5 mm shift, maximum deviation was found in anteroposterior axis (22.16 ± 7.50) and lowest in mediolateral axis (12.85 ± 4.95). On serial measurement of exit dose fluence, tumor shrinkage significantly influenced gamma pass rate. The mean gamma pass rate was significantly different between groups with 50% shrinkage of tumor volume (86.36 vs 96.24, P = 0.008, on multivariate analysis P = 0.026).
CONCLUSIONS: Rapid fall of gamma pass rate was observed for set up error of ≥3 mm. Serial measurement of exit dose fluence by radiochromic film is a feasible method of exit dose comparison in IMRT/VMAT, where EPID dosimetry is not available with linear accelerator configuration. Our study suggests that there is a significant difference between gamma pass rates of baseline and mid treatment exit dose fluence with greater than 50% tumor shrinkage.
摘要：
目的：决定自适应放疗的客观参数取决于患者，肿瘤与治疗相关因素。本研究报告了高精度放射治疗过程中出现的几何不确定性，束通量分析和连续出口剂量测量作为自适应放射治疗的患者特定工具。
方法：对24例接受IMRT/VMAT治疗的患者（在基线和中期治疗）的连续退出剂量流量进行测量。基线和中期治疗出口剂量评估是在预定义的感兴趣区域中使用gafchroming膜进行的。计算基线(来自模拟CT扫描)和中期治疗CBCT扫描的GTV体积差(ΔGTV)。
结果：基于人群的系统误差（mm）分别为4.15、2.26、0.88，而中外侧（ML）的随机误差（mm）分别为2.56、3.69和2.03，头尾（CC）和前后（AP）方向。伽马通过率随增量移位而降低。对于5毫米的位移，前后轴最大偏差（22.16±7.50），中外侧轴最小（12.85±4.95）。在出口剂量通量的连续测量中，肿瘤缩小显著影响伽玛通过率。肿瘤体积缩小50％的组之间的平均γ通过率存在显着差异（86.36vs96.24，P=0.008，多变量分析P=0.026）。
结论：对于≥3mm的设置误差，观察到伽马通过率快速下降。通过辐射变色胶片连续测量出口剂量通量是IMRT/VMAT中出口剂量比较的可行方法，其中EPID剂量测定不适用于线性加速器配置。我们的研究表明，在肿瘤缩小大于50％的情况下，基线和中期治疗退出剂量注量的伽马通过率之间存在显着差异。
方法：对24例接受IMRT/VMAT治疗的患者（在基线和中期治疗）的连续退出剂量流量进行测量。基线和中期治疗出口剂量评估是在预定义的感兴趣区域中使用gafchroming膜进行的。计算基线(来自模拟CT扫描)和中期治疗CBCT扫描的GTV体积差(ΔGTV)。
结果：基于人群的系统误差（mm）分别为4.15、2.26、0.88，而中外侧（ML）的随机误差（mm）分别为2.56、3.69和2.03，头尾（CC）和前后（AP）方向。伽马通过率随增量移位而降低。对于5毫米的位移，前后轴最大偏差（22.16±7.50），中外侧轴最小（12.85±4.95）。在出口剂量通量的连续测量中，肿瘤缩小显著影响伽玛通过率。肿瘤体积缩小50％的组之间的平均γ通过率存在显着差异（86.36vs96.24，P=0.008，多变量分析P=0.026）。
结论：对于≥3mm的设置误差，观察到伽马通过率快速下降。通过辐射变色胶片连续测量出口剂量通量是IMRT/VMAT中出口剂量比较的可行方法，其中EPID剂量测定不适用于线性加速器配置。我们的研究表明，在肿瘤缩小大于50％的情况下，基线和中期治疗退出剂量注量的伽马通过率之间存在显着差异。
