Background: To evaluate the dosimetric changes in the target volume and organs at risk (OARs) of patients with left breast cancer (LBC) who underwent intensity-modulated radiation therapy (IMRT) based on a deformation registration (DF) method. Methods: Sixteen patients with LBC treated with 6 MV X-ray IMRT were retrospectively analyzed. All targets included the lymph node drainage area and chest wall. All patients underwent CT for simulation of the primary positioning and repositioning. Primary and secondary treatment plans were developed using primary positioning CT (CT1) and repositioning CT (CT2) images to obtain plan(1) and plan(2), respectively. Rigid and DF of the dose distribution of plan(2) to CT1 were applied; the results were then added to the dose distribution of plan(1), yielding plan(rig) and plan(def), respectively. The dosimetric differences between the target and OAR volumes of the four plans were compared. Results: The clinical target volume of CT2 was 8.74% less than that of CT1. The planned target volume of CT2 was 11.20% less than that of CT1. The Dice similarity coefficients (DSCs) of the heart, left lung and right lung were significantly lower after than before DF (0.94 +/- 0.01 vs. 0.89 +/- 0.05, 0.96 +/- 0.01 vs. 0.91 +/- 0.03, and 0.96 +/- 0.01 vs. 0.92 +/- 0.03, respectively; t=3.83, 7.28, and 6.70, P<0.05, respectively). There were no significant differences in the dose-volume indices of the heart or left lung between plan(1) and the other plans, while the dose-volume indices were higher in plan(rig) than in plan(def). Conclusions: Because of small changes in the target and OAR volumes during radiotherapy, we suggest the first IMRT plan could be used to evaluate the dose-volume indices of the lungs and heart for these patients.

Objective To study the dosimetric effect on special reconstruction images obtained from an electrocardiograph-gated four-dimensional computed tomography (ECG 4D-CT) series and compare it with the accumulation dose assessment of ECG 4D-CT. Methods Fifteen patients underwent ECG 4D-CT scans to obtain a 4D-CT series. The 20 phase images of 0%~95% were reconstructed at intervals of 5% of the cardiac cycle by the 4D-CT series. The 4D-CT series was specially reconstructed, and the maximum intensity projection (MIP), minimum intensity projection (MinIP), average intensity projection (AIP) and sum intensity projection (SIP) were obtained. The left ventricular muscle (LV)and the anterior descending branch of the left coronary artery (LAD) were delineated on all series. The intensity-modulated radiation therapy (IMRT) plan for left breast cancer was designed on the basis of the 0% phase, and the accumulative dose (Dose-acc) of 20 phases was obtained by deformation registration. The dose-volume indexes of the LV and LAD were compared based on different CT series. Results The dose-volume indices of V5, V30, V40, Dmax and Dmean of the LV on MIP images were 3.8%, 2.0%, 0.9%, 3.8% and 1.7%, respectively (relative to the Dose-acc). There was no significant difference in V5 or Dmax between the MIP and Dose-acc (P>0.05). The change rates of Dmax on the MinIP, SIP and AIP images were 2.5%, 3.1% and 1.5%, respectively (relative to the Dose-acc) (P<0.05). Conclusion In the dose-volume evaluation of the LV, V30, V40 and Dmean obtained by MIP were essentially the same as those obtained by the Dose-acc and can be used instead of the 4D-CT series to evaluate dose-volume indexes.

Background Cardiac activity could impact the accuracy of dose assessment for the heart, pericardium and left ventricular myocardium (LVM). The purpose of this study was to explore whether it is possible to perform dose assessment by contouring the cardiac structures on specific three-dimensional computed tomography (3DCT) images to reduce the impact of cardiac activity. Methods Electrocardiograph-gated 4DCT (ECG-gated 4DCT) images of 22 patients in breath-hold were collected. MIM Maestro 6.8.2 (MIM) was used to reconstruct specific 3DCT images to obtain the Maximal intensity projection (MIP) image, Average intensity projection (AIP) image and Minimum intensity projection (Min-IP) image. The heart, pericardium and LVM were contoured in 20 phases of 4DCT images (0, 5%... 95%) and the MIP, AIP and Min-IP images. Then, a radiotherapy plan was designed at the 0% phase of the 4DCT images, and the dose was transplanted to all phases of 4DCT to acquire the dose on all phases, the accumulated dose of all phases was calculated using MIM. The dose on MIP, AIP and Min-IP images were also obtained by deformable registration of the dose. The mean dose (D-mean), V-5, V-10, V-20, V-30 and V-40 for the heart, pericardium and LVM in MIP, AIP and Min-IP images were compared with the corresponding parameters after dose accumulation. Results The mean values of the difference between the D-mean in the MIP image and the D-mean after accumulation for the heart, pericardium and LVM were all less than 1.50 Gy, and the dose difference for the pericardium and LVM was not statistically significant (p > 0.05). For dose-volume parameters, there was no statistically significant difference between V-5, V-10, and V-20 of the heart and pericardium in MIP, AIP, and Min-IP images and those after accumulation (p > 0.05). For the LVM, only in the MIP image, the differences of V-5, V-10, V-20, V-30 and V-40 were not significant compared to those after dose accumulation (p > 0.05). Conclusions There was a smallest difference for the dosimetry parameters of cardiac structures on MIP image compared to corresponding parameters after dose accumulation. Therefore, it is recommended to use the MIP image for the delineation and dose assessment of cardiac structures in clinical practice.

BACKGROUND:During intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC), the volume of the target volume and the organs at risk (OARs) will change constantly, which may lead to differences between the actual dose received and the initial planned dose. In this study, the cumulative dose of the two plans was obtained by deformable registration. This study provides an approach to evaluate the dose volume of IMRT for the NPC objective.METHODS:From July 2014 to May 2018, eighteen NPC patients who accepted simultaneous integrated boost IMRT were enrolled. All patients underwent simulation CT (CT1) and replanning CT (CT2) scans after 20-25 fractions of radiation therapy. The treatment plans were designed on CT1 and CT2 with the name of Plan1 and Plan2, respectively. The Planreg and Plandef were obtained after registering from CT2 to CT1 using rigidity and deformation technology by Velocity. Then the dose-volume indices of the tumor target volumes and OARs at Plan1, Plan2, Planrig and Plandef were compared.RESULTS:The gross tumor volume (GTV) and the left and right parotid gland volumes decreased by 20.8% (P<0.001), 36.8% (P<0.001) and 37.5% (P<0.001), respectively, from CT1 to CT2. There was no significant difference in the dose-volume index on the GTV and plan gross tumor volume (PGTV) between Plan1 and Plan2. The V30 of the left and right parotid gland and the Dmax of the brainstem, left and right eyeballs, left and right lens, and left and right optic nerves were all lower in Plan2 than in Plan1 (the average decrease was 17.0% to 60.1%). The differences in some dose-volume parameters (including Dmean, D99 of the GTV and PGTV, Dmean of the parotid glands, Dmax of the lens and optic nerves) between Plandef and Plan1 were less than 5%. The differences in some dose-volume parameters (including Dmean, D95 of the GTV and PGTV, Dmean, D50 and V30 of the parotid glands, Dmax of lens and optic nerves) between Planrig and Plan1 were less than 10%. The Dyce Similarity Coefficient of the target volume and OARs after deformation registration were higher than that after rigid registration.CONCLUSIONS:The volume of the GTV and parotid glands were decreased during the IMRT for NPC. The dose-volume indices of the GTV and the OARs in Plandef were similar to those in Plan1. Therefore, the dose-volume indices of Plan1 can be used to evaluate the efficacy of radiotherapy and to predict radioactive damage.