ABSTRACT
Objective To investigate the dosimetric characteristics of hippocampal?avoidance prophylactic cranial irradiation ( HA?PCI ) in fixed?field intensity?modulated radiotherapy ( IMRT ) and volumetric modulated arc therapy ( VMAT) and the feasibility and risks of hippocampal avoidance. Methods Prophylactic cranial irradiation (PCI) was performed for 16 patients with localized small cell lung cancer ( SCLC) who were treated in our hospital from January to August, 2014, and achieved complete response ( CR) after chemoradiotherapy, with a prescribed dose of 25 Gy in 10 fractions. CT localization image was fused with brain MRI image to contour the hippocampus on the fused image, and the boundary of the hippocampus was extended 5 mm outward to form the area for reduced dose. IMRT and VMAT plans with hippocampal avoidance were developed separately, and the dose distribution in the whole brain, the hippocampus, and the 5?mm area outside the hippocampus was evaluated for these two plans. Independent?samples t test was applied to evaluate the difference between the two groups. Results The mean hippocampal volume in the 16 patients was 2. 76 cm3 ( range 2. 56 ?3. 01 cm3 ) . The mean radiation dose ( Dmean ) in the hippocampus during IMRT and VMAT was 9. 04± 0. 20 Gy and 10. 32± 0. 28 Gy, respectively, reduced by 66. 0% and 61. 2%, respectively, compared with the prescribed dose ( P=0. 55);Dmean in the area for reduced dose during IMRT and VMAT was 13. 57± 0. 90 Gy and 14. 86± 0. 60 Gy, respectively, reduced by 49. 0% and 44. 1%, respectively, compared with the prescribed dose (P=0. 88). Conclusions HA?PCI in IMRT and VMAT meets the clinical requirements, and can reduce the dose in the hippocampus while ensuring the whole?brain radiation dose, and therefore can be applied in PCI and provide a technical support to protect the patient’ s neurocognitive function.
ABSTRACT
Objective To compare the performances of Monaco and Pinnacle treatment planning systems (TPS) for volumetric modulated arc therapy (VMAT) optimization regarding lung cancer.The TPS was compared in terms of dose distributions,treatment delivery parameters and quality control results.Methods For 20 patients,including 10 cases of left lung cancer and l0 cases of right lung cancer,two VMAT plans were generated for each case:one with Monaco 3.0 TPS and the other with Pinnacle 9.2 TPS.Two plans were compared among plan dosimetrie distribution.conformity index and homogeneity index of the targets,the average dose,maximum dose,minimum dose and interested dose volume histograms of organs at risk(OAR,and delivery time and MUs of the therapy plans,the accuracy of treatment plans dose verification.Results Monaco provided better PTV coverage than Pinnacle (t =5.927-12.034,P ＜ 0.05) except Dminof PTV.Monaco had a worse sparing effect on lung than Pinnacle (t =3.545-7.485,P ＜0.05) except V10of diseased side lung and V5of total lung.In addition,Monaco had a better sparing effect on heart(t =2.836-4.011,P ＜0.05).Monaco had fewer delivery time(t =9.780,P ＜0.05)and MUs(t =5.304,P ＜0.05)of the therapy plans,and the pass rate of QA was better than Pinnacle(t =4.937,P ＜ 0.05).Conclusions For lung cancer patients,VMAT treatment plans obtained with Monaco and Pinnacle could offer clinically acceptable dose distributions.Pinnacle might have a better sparing effect on lung and fewer delivery time and MUs of the therapy plans.Monaco had a better PTV coverage and heart sparing.Moreover,Monaco had better accuracy of treatment plans dose verification.
ABSTRACT
Objective To explore the effect of horizontal beam on IMRT plan for lung cancer.Methods Totally 18 patients were enrolled,including 10 cases of left lung cancer and 8 cases of right lung cancer.Two intensity modulated radiation therapy (IMRT) plans were generated:one was the normal IMRT plan and another was the IMRT plan including a horizontal beam (H-IMRT).MUs,sub-field and the dose distribution of target and organs at risk (OARs) were compared.Results There were no statistically significant differences between two plans in D Dminand D of PTV,the V30 and D of the ipsilateral lung,V20 and V30 of the contralateral lung,and V30 of the total lung.When the horizontal beam was added,the PTV heterogeneity index (HI) and conformity index (CI) were significantly increased (t=-9.33,10.88,P＜0.05),the other dose index in lung was inferior (t =-1.55--7.58,P＜ 0.05),whleheart sparing were clearly better (t =1.84-3.99,P＜0.05),the number of MUs and segments were less(t =12.57,3.19,P ＜ 0.05).Conclusions IMRT in the treatment of lung cancer can further improve the PTV coverage when the horizontal beam is added.However,the increasing lung volume of low dose irradiation is not conducive to lung protection.
ABSTRACT
Objective To explore the influence of the number and orientation of the beams on the optimization of IMRT plan.Methods Four IMRT plans were designed for 9 patients with cervical cancer,and 7 and 15 fields were applied.The 15-field plans had 30 segments and the 7-field plans had 55 segments.The initial beam angle degrees were 0° and 180°,respectively.Dose delivery time,MUs of plans,the dose distributions of the targets,organs at risk and normal tissues were analyzed and compared in the plans.Results Compared the plans with different beam directions under the same amount,no difference of the irradiation dosimetry in the target and organs at risk was found,except for irradiation dosimetry received by the 7-field 180° small intestine was about 4％ higher than the other three plans(F=6.164,P＜0.05).The terms of the volume of organs at risk got high dose irradiation(V40 and V30 of the rectum and bladder,V40 of the small intestine),which was similar in the 7-and 15-field plans.V20 and Dmean of organs at risk were significantly smaller(F=3.665-10.503,P＜0.05)in the 15-field plans.The 15-field plans needed a little longer treatment time(F=0.312,P＜0.05)and HI was slightly worse (F=12.933,P＜0.05),but the number of MUs was significantly reduced(F=4.650,P＜0.05).Conclusions Increasing the beam number will offset the negative impact of sub field reduction and get the similar dose distribution result.