Sparing lung tissue with virtual block method in VMAT planning for locally advanced non-small cell lung cancer

This study aimed to exploit a new virtual block method to spare normal lung tissue in VMAT planning for patients with locally advanced non-small cell lung cancer(LA-NSCLC).The previous method was used to manually restrict the angle of the beam passing through,which ignored the location and shape of large targets that varied between different slices and did not block the beamlets precisely.Unlike the previous method,this new virtual block method was used to block the beamlets when necessary by closing the multi-leaf collimator(MLC)at prerequisite angles.The algorithm for closing the MLC depended on the thickness of the beamlets passing through the lungs and avoided only the entrance radiation beamlet.Moreover,this block can be automatically contoured.A retrospective study was performed to compare the VMAT plans with and without the virtual block method for 17 LANSCLC patients,named the block plan(B-plan)/non-block plan(N-plan).All cases were selected in this study because of the large tumor size and unmet dose constraints of the lungs.In addition to the maximum dose constraint for the virtual block,B-plans adopted identical optimization parameters to N-plans for each patient.These two types of plans were compared in terms of dosimetric indices and plan scores.The results were statistically analyzed using the Wilcoxon nonparametric signed-rank test.B-plans have advantages in the following dosimetric metrics that have statistical significance(p<0.05):(1)lower V_(5)/V_(10)/D_(mean)/normal tissue complication probability(NTCP)of total lungs;(2)reductions in V_(5)/V_(10)for the contralateral lung;(3)decrease in Dmean/V_(40)of the heart;(4)decrease in esophagus V_(40);(5)reductions in Dmean,V_(5)/V_(10) of normal tissue.B-plans(82.51±7.07)achieved higher-quality scores than N-plans(80.74±7.22).The new virtual block spared the lungs as well as other normal structures in VMAT planning for LA-NSCLC.Thus,the block method may decrease the risk of radiation-related toxicity in patients.

Cage-like radiotherapy system for noncoplanar radiotherapy

The aim of this study was to design a cage-like radiotherapy system(CRTS)to further promote the clinical application of noncoplanar radiotherapy.The CRTS comprises two stands,two O-rings,several arc girders,an X-ray head,an imaging subsystem,and a treatment couch.The X-ray head rotates with O-rings around the patient’s body and slides along the arc girder.Compared with the C-arm linear accelerator(C-Linac),the clinically available spatial irradiation angle ranges(SIARs)of the CRTS for the head,chest,and abdomen were 33%,63.6%,and 62.6%larger,respectively.Moreover,according to a preliminary planning comparison based on the dose distribution simulation method,the CRTS achieved much better protection of normal tissue than the C-Linac.Furthermore,the CRTS enabled accurate noncoplanar irradiation without movement of the body being irradiated,allowed automatic control of the movements of different parts without risk of collisions,and provided continuous radiation over an angle that considerably exceeded a full turn.These advantages make CRTS very promising for noncoplanar radiotherapy.

Cerebral functional abnormalities in patients with nasopharyngeal carcinoma after radiotherapy:an observational magnetic resonance resting-state study

Background:Nasopharyngeal carcinoma (NPC) is sensitive to radiotherapy (RT).However,neurocognitive complications such as memory loss and learning and attention deficits emerge in the survivors of NPC who received RT.It remains unclear how radiation affects patient brain function.This pilot study aimed at finding cerebral functional alterations in NPC patients who have received RT.Methods:From September 2014 to December 2016,42 individuals,including 22 NPC patients and 20 normal volunteer controls in National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital,Chinese Academy of Medical Sciences,and Peking Union Medical College,were recruited in this study.All patients received resting-state functional magnetic resonance imaging scans and neurocognitive tests 1 day before the initiation of RT (baseline) and 1 day after the completion of RT;the 20 normal controls were also subjected to the same scans and tests.The amplitude of the low-frequency fluctuations (ALFF) in blood oxygen level-dependent signals and functional connectivity (FC) were used to characterize cerebral functional changes.Independent t test,paired t test,and analysis of variances were used to obtain statistical significance across groups.Results:After RT,NPC patients showed significantly decreased ALFF values in the calcarine sulcus,lingual gyrus,cuneus,and superior occipital gyrus and showed significantly reduced FC mainly in the default mode network (P < 0.05,corrected by AlphaSim).Relative to the controls,ALFF was decreased in the lingual gyrus,calcarine sulcus,cingulate cortex,medial prefrontal gyrus (P < 0.05,corrected by AlphaSim),and FC reduction was found in multiple cerebellar-cerebral regions,including the cerebellum,parahippocampus,hippocampus,fusiform gyrus,inferior frontal gyrus,inferior occipital gyrus,precuneus,and cingulate cortex (P < 0.001,corrected by AlphaSim).Conclusions:Cerebral functional alterations occur immediately after RT.This study may provide an explanation for the cognitive deficits in the morphologically normal-appearing brains of NPC patients after RT and may contribute to the understanding of the complex mechanism of RT.