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Objective:To analyze the dosimetric effects on off-center tumour treatment plan resulting from the MR-Linac-based isocenter position radiotherapy plan.Methods:The cases of 19 patients who were treated in Sun Yat-sen University Cancer Center in 2020 were collected in this study. Two different IMRT plans were designed for each patient with off-center tumor both for group A with planned isocenter position as IMRT and group B with planed target center position as geometric center. The conformity index and homogeneity index of target, the dose normal tissue and the number of MU were compared between two plans.Results:The two IMRT plans met clinical dosimetric requirements. No statistical differences were found both in homogeneity index and conformity index ( P>0.05). Also there was no differences found in doses to normal tissues. However, the MU number (1 149±903, t=2.804, P=0.012) in group A was higher than that in group B (970±652). Conclusions:It is feasible to perform MR-Linac-based off-center treatment plan.
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Objective To evaluate the dose variation of target coverage and organs at risk ( OARs) among four planning strategies using spot-scanning carbon-ion radiotherapy for non-small cell lung cancer ( NSCLC) . Methods Ten NSCLC patients utilizing gating motion control were selected to receive dose calculation over multiple acquired 4DCT images. Four optimizing strategies consisted of intensity-modulated carbon-ion therapy ( IMCT-NoAS ) , IMCT combined with internal gross tumor volume ( IGTV ) assigned muscle ( IMCT-ASM ) , single beam optimization ( SBO ) ( SBO-NoAS ) and SBO combined with IGTV assigned muscle (SBO-ASM).The initial plan was re-calculated after the 4DCT data were reviewed and then compared with the initial plan in the dosimetry. Results For re-calculation plans with two reviewing CTs,all four strategies yielded similar planning target volume ( PTV ) coverage. Merely IMCT-NoAS strategy presented with relatively significant variations in dose distribution. Dose variation for OARs between initial and re-calculated plans:for all four strategies,V20 of ipsilateral lung was increased by approximately 2. 0 Gy (relative biological effective dose,RBE),V30 of heart was increased by approximately 1. 0 Gy (RBE) for both IGTV assigned muscle strategies,whereas decreased by approximately 0. 2 Gy ( RBE) for both IGTV non-assigned muscle strategies. The maximum dose of spinal cord was changed by 2. 5 Gy ( RBE ) . Conclusions Carbon-ion radiotherapy is sensitive to the anatomic motion within the tumors along the beam path. When the tumor motion along the head-foot (H-F) direction exceeds 8 mm,SBO-ASM strategy provides better dose coverage of target. Strategies with IGTV assignment may result in dose overshoot to a position deeper than the initial planning dose distribution.
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Objective To determine whether Auto-Planning-based volumetric modulated radiotherapy(Auto-VMAT)planning can improve planning efficiency without compromising plan quality compared with current manual trial-and-error-based volumetric modulated arc therapy(Manual-VMAT) planning for patients with rectal cancer. Methods Ten patients with stage Ⅱ-Ⅲ rectal cancer who underwent Dixon surgery were enrolled as subjects. The Pinnacle 9.10 planning system was used to design Manual-VMAT and Auto-VMAT plans. Dose distribution,homogeneity index(HI),conformity index(CI), D meanvalues of different organs at risk or dose-volume histogram of regions of interest,total planning time, and manual planning time were compared between the two plans. The differences were analyzed by paired t test. Results Dosimetric prescriptions were achieved in both plans. There were no significant differences in HI or CI between the Auto-VMAT plans and the Manual-VMAT plans(0.058 vs. 0.058, P=0.972;0.921 vs. 0.940,P=0.115). Compared with the Manual-VMAT plans,the V 40,D mean,and D 50%of the bladder were significantly reduced by 25.6%, 11.5%, and 8.9%, respectively, in the Auto-VMAT plans(P=0.004,0.016,0.001);the V 40,D mean,and D 50%of the small intestine were also significantly reduced by 12.1%,5.4%,and 6.8%,respectively,in the Auto-VMAT plans(P=0.023,0.001,0.001);the V 30, D mean,and D 50%of the left and right femoral heads were slightly reduced in the Auto-VMAT plans. The Auto-VMAT plans had significantly longer total planning time but significantly shorter manual planning time than the Manual-VMAT plans(50.38 vs. 36.81 min, P= 0.000;4.47 vs. 16.94 min, P= 0.000). Conclusions Compared with the Manual-VMAT plans, the Auto-VMAT plans have substantially shorter manual planning time and improved planning efficiency.
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Objective To propose a new set of conformity indices ( CIs ) that may be useful for evaluating whether the prescribed doses to target volume and organs at risk ( OAR) in intensity-modulated radiotherapy ( IMRT ) or three-dimensional conformal radiotherapy ( 3DCRT ) plans meet clinical requirements. Methods A total of 30 patients' plans were randomly selected from the IMRT or 3DCRT plans for non-small cell lung cancer and analyzed with the newly defined CIs described in this article. The plans to be improved were selected according to the evaluating results, and two schemes were developed to improve these plans. Then, the differences in CI, Dmax , Dmin , and Dmean of the planning target volume ( PTV) , V5 and V20 of the normal lung, V30 and V40 of the heart, and Dmax of the spinal cord were investigated with the paired t-test. Results Among the 30 plans, the average volume covered by the prescribed isodose line ( VRI ) was 25% larger than the PTV, so the normal lung tissue with a volume approximately 25% of PTV was given the same dose as the target volume, and the volume covered by the prescribed isodose line in the target V ( C) R was only 75% of the volume VR. Ninety-five percent of the target volume received a full prescribed dose;only 5% of the target volume received less than the prescribed dose, but which was still within 90% of the prescribed dose. In the comparison between the original plans and the plans improved using the first scheme, CI2 , CI4 , CI5 , CI6 , and homogeneity index ( HI) were not significantly different ( P=0240-0780) , and CI1 and CI3 showed significant differences ( P=0002 and 0);Dmax , Dmin , and Dmean of the PTV, V5 and V20 of the normal lung, V30 and V40 of the heart, and Dmax of the spinal cord were not significantly different ( P=0211-0964) . In the comparison between the original plans and the plans improved using the second scheme, CI2 , CI4 , and CI5 were not significantly different ( P=0308, 0308, and 0106 ) , CI1 , CI3 , CI6 , and HI showed significant differences ( P= 0001-0014);Dmax , Dmin , and Dmean of the PTV, V5 and V20 of the normal lung, and Dmax of the spinal cord showed significant differences ( P=0008-0036 ) , and V30 and V40 of the heart were not significantly different ( P=0083 and 0080) . Conclusions The new set of CIs proposed in this paper may be a good tool for evaluating the conformity of the target and the prescribed dose to OAR and thus developing better individualized treatment plans.
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Objective To propose a new set of conformity indices ( CIs ) that may be useful for evaluating whether the prescribed doses to target volume and organs at risk ( OAR) in intensity-modulated radiotherapy ( IMRT ) or three-dimensional conformal radiotherapy ( 3DCRT ) plans meet clinical requirements. Methods A total of 30 patients' plans were randomly selected from the IMRT or 3DCRT plans for non-small cell lung cancer and analyzed with the newly defined CIs described in this article. The plans to be improved were selected according to the evaluating results, and two schemes were developed to improve these plans. Then, the differences in CI, Dmax , Dmin , and Dmean of the planning target volume ( PTV) , V5 and V20 of the normal lung, V30 and V40 of the heart, and Dmax of the spinal cord were investigated with the paired t-test. Results Among the 30 plans, the average volume covered by the prescribed isodose line ( VRI ) was 25% larger than the PTV, so the normal lung tissue with a volume approximately 25% of PTV was given the same dose as the target volume, and the volume covered by the prescribed isodose line in the target V ( C) R was only 75% of the volume VR. Ninety-five percent of the target volume received a full prescribed dose;only 5% of the target volume received less than the prescribed dose, but which was still within 90% of the prescribed dose. In the comparison between the original plans and the plans improved using the first scheme, CI2 , CI4 , CI5 , CI6 , and homogeneity index ( HI) were not significantly different ( P=0240-0780) , and CI1 and CI3 showed significant differences ( P=0002 and 0);Dmax , Dmin , and Dmean of the PTV, V5 and V20 of the normal lung, V30 and V40 of the heart, and Dmax of the spinal cord were not significantly different ( P=0211-0964) . In the comparison between the original plans and the plans improved using the second scheme, CI2 , CI4 , and CI5 were not significantly different ( P=0308, 0308, and 0106 ) , CI1 , CI3 , CI6 , and HI showed significant differences ( P= 0001-0014);Dmax , Dmin , and Dmean of the PTV, V5 and V20 of the normal lung, and Dmax of the spinal cord showed significant differences ( P=0008-0036 ) , and V30 and V40 of the heart were not significantly different ( P=0083 and 0080) . Conclusions The new set of CIs proposed in this paper may be a good tool for evaluating the conformity of the target and the prescribed dose to OAR and thus developing better individualized treatment plans.
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ObjectiveTo compare planning quality,treatment efficiency and delivery accuracy for initial treated nasopharyngeal carcinoma (NPC) with step & shoot intensity modulated radiation therapy (ssIMRT) and volumetric modulated arc therapy (VMAT).These results will help make a clinic choice of the therapeutical technique.MethodsTwenty-six NPC cases were planned with the same dose prescription and objective constrains by means of 9-field ss-IMRT and VMAT respectively.Compare:( 1 ) plan dosimetric distribution,conformity index and homogeneity index of the targets,the average dose,maximum dose and interested dose-volume histograms of organs at risk (OAR) et al;(2) delivery times of the therapy plans ;(3) the accuracy of treatment plans dose verification.ResultsBoth therapeutical plans can achieve the clinic dosimetric demands.Compared to ss-IMRT,VMAT had less inferior target coverage.The CI and HI of the PGTV was 0.57 and 0.08 ( ss-IMRT),0.48 and 0.12 (VMAT) respectively ( t =-4.52,- 8.33,P =0.000,0.000).Except of brain stem,VMAT had higher mean dose and maximum dose of OARs than ss-IMRT (t=-9.57 - -3.71,P=0.000 -0.001).The spinal cord D1cc and parotids D50％ were increased by 11.9％ and 6.5％ averagely.The treatment times of ss-IMRT and VMAT were 803.7 s and 389.3 s respectively (t =24.12,P =0.000),while V MAT decreasing by 51.6％.The pass ratios of γ (3mm,3％ ) from the dose verification were 99.4％ (ss-IMRT) and 98.0％ (VMAT) respectively ( t =5.19,P =0.000).ConclusionsThe dose distribution of VMAT for initial treated nasopharyngeal carcinoma can achieve the clinic demands,but slightly worse than 9-field ss-IMRT.VMAT has the advantage of high efficiency and dosimetric accuracy.