A comparative study of dose distribution of prostate IMRT between IMRT and VMAT models using knowledge-based planning / 中华放射肿瘤学杂志

Objective:To compare the dosimetric difference between knowledge-based planning (KBP) volumetric modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) models for predicting the dose distribution during IMRT, aiming to investigate the feasibility of VMAT model to predict the IMRT plans.Methods:Fifty prostate cancer patients who had completed radiotherapy were selected. Manual planning was performed on each selected patient to generate the corresponding IMRT and VMAT plans. The IMRT and VMAT manual plans of the 40 randomly-selected patients were adopted to generate the KBP VMAT and IMRT models. The remaining 10 patients were utilized to predict IMRT plans. VMAT library-derived IMRT model (V-IMRT) and IMRT library-derived IMRT model (I-IMRT) were generated. Dosimetric parameters related to organ-at-risks (OARs) and planning target volume (PTV) were statistically compared among the manual IMRT (mIMRT), V-IMRT and I-IMRT plans.Results:Compared with the mIMRT plan, I-IMRT could significantly better control D max of the PTV ( P=0.039), whereas V-IMRT and I-IMRT plans could better protect the bladder and bilateral femoral heads (both P<0.05). V-IMRT plan could better protect the D max of bilateral femoral heads and the D 15% of the right femoral head (both P<0.05), whereas no significant difference was observed in other OARs and PTV (all P>0.05). Conclusions:Compared with the manual plans, KBP IMRT plan has significant advantages in protecting the OARs. KBP VMAT and IMRT models are both feasible in clinical practice, which yield equivalent accuracy for predicting IMRT plan.

Systemic lupus erythematosus with extensive intracranial calcification: a case report / 中华神经科杂志

Extensive intracranial calcification is rare in patients with systemic lupus erythematosus. This article reported a patient with antiphospholipid antibody syndrome secondary to systemic lupus erythematosus, complicated with bilateral symmetrical extensive intracranial calcification. By reviewing literature, the results suggested that the flare of neuropsychiatric systemic lupus erythematosus and the presence of antiphospholipid antibodies may be risk factors for intracranial calcification. Therefore, in order to prevent the formation of intracranial calcification, it is necessary to maintain continuous disease remission and anticoagulant therapy.

Impact of accelerator operating errors on γ passing rate during dose verification of volumetric modulated arc therapy for pelvic tumors / 中华放射肿瘤学杂志

Objective:To investigate the impacts of gantry rotation angle errors, monitor unit (MU) errors, collimator and multi-leaf collimator (MLC) position errors upon the γ passing rate of dose verification in volumetric modulated arc therapy (VMAT).Methods:Ten patients with rectal cancer and 10 patients with uterine tumors were selected. The operating errors of accelerator parameters were introduced during the VMAT execution. By comparing the γ passing rates during dose verification between the simulating and original plans, the impact and sensitivity of the operating errors of each accelerator parameter on γ passing rate were analyzed.Results:When the γ criteria were set as 3%/3 mm, 3%/2 mm and 2%/2 mm, the γ passing rate decreasing gradient was less than 7.0% after the introduction of gantry rotation angle, MU and collimator position errors, respectively. However, after the reverse, opposite, and co-directional motion errors of the MLC blades on both sides were introduced, the γ passing rate decreasing was less than 19.13 %, 18.53%, 0.19 %; 19.87%, 20.01%, 0.42 % and 23.11%, 23.45%, 0.65 % for absolute dose verification, respectively.Conclusion:During VMAT, the reverse and opposite motion errors of MLC blades exert more significant effect on the γ passing rate compared with the gantry rotation angle errors, MU errors, collimator position errors and co-directional motion errors of the MLC blades. When the γ criteria of 3%/3 mm, 3%/2 mm and 2%/2 mm are adopted, the impact of accelerator operating errors upon the γ passing rate is strengthened in sequence. Therefore, when performing dose verification for a specific patient, appropriate γ criteria should be chosen and absolute dose verification should be taken as the reference index to evaluate the consistency between the calculated and measured dose distribution.

The dosimetric impacts of accelerator operation error on the volumetric modulated arc therapy for cervical cancer / 中华放射医学与防护杂志

Objective To investigate the dosimetric effect of accelerator gantry rotation angle errors, collimator and multileaf collimator ( MLC) leaf position errors on volumetric-modulated arc therapy ( VMAT) for cervical cancer. Methods A total of 10 patients with cervical cancer were selected. The plan. Trail file of each clinical plan was extracted from the Pinnacle3 V9. 2 planning system of USA Philips, then the operating parameters of tach control point were read and modified by Matlab programs, and thus the operating error of the accelerator was simulated. Results In this paper, it was discovered that systematic accelerator gantry rotation angle errors, systematic collimator position errors and systematic MLC shift errors which led to the maximum changes of the PTV dose limit were 0. 16％, 0. 46％ and 0. 57％, respectively, and the maximum changes of the dose limit of organs at risk ( OAR) were 0. 38％, -1. 32％ and -0. 44％, respectively. When the systematic MLC gap width errors were ± 0. 5, ± 1 and ± 2 mm, respectively, the maximum changes of PTV dose were 2. 11％, 3. 04％ and 6. 03％, respectively, while the maximum changes of the OAR average dose were 2. 17％, 3. 92％ and 7. 97％, respectively. Furthermore, the dose limits of PTV and OAR showed a strong linear correlation with MLC open or close errors(t=21. 201～90. 562,P<0. 05). If actual errors of each parameter of accelerator were introduced, the maximum changes of PTV and OAR dose limits were 0. 16％ and 1. 30％, respectively, and conformity index (CI) and homogeneity index (HI) were barely changed. Conclusions No significant effect was found for systematic accelerator gantry rotation angle errors, systematic collimator position errors and systematic MLC shift errors for cervical cancer VMAT patients. However, there is a high sensitivity to dose distribution for MLC open or close errors. Therefore, it is necessary to pay more attention on the quality control of the accelerator running in particular MLC position errors to ensure the therapeutic accuracy.