ABSTRACT
Objective:To investigate the dosimetric effects of prone immobilization devices combined with a belly board (PIDBBs) in the intensity-modulated radiotherapy (IMRT) for gynecologic cancers.Methods:A total of 20 patients with cervical or endometrial cancer treated with radiotherapy in the Third Affiliated Hospital of Sun Yat-sen University from August 2020 to June 2021 were retrospectively analyzed. Two sets of body contours were outlined for each patient. One set of body contours did not contain the immobilization devices, and the other contour set included the immobilization devices. For each patient, doses were calculated for the two sets of contours using the same 7-field IMRT plan and were recorded as Plan without and Plan with. The dosimetric difference caused by the immobilization devices was assessed by comparing the parameter values in the dose-volume histograms (DVHs) and by plan subtraction. The Gafchromic EBT3 film and anthropomorphic phantom were used to verify the calculated doses. Results:The target coverage and average dose of Plan with were lower than those of Plan without. Specifically, the V50 Gy, V49 Gy, and Dmean of planning target volume (PTV) decreased by 19.75%, 7.99%, and 2.54% ( t = 8.96, 10.49, 22.09, P < 0.01), respectively. The V40 Gy, V30 Gy, V20 Gy, V15 Gy, and Dmean of skins increased by 51.79%, 51.05%, 45.72%, 33.63% and 10.80% ( t = -2.54, -5.63, -15.57, -24.06, -13.88, P < 0.01), respectively. Doses to other organs at risk (OARs) showed no significant differences. As indicated by the EBT3 measurements, the doses to skins of the abdomen and pelvis on the anthropomorphic phantom increased by approximately 37.24% ( t = 10.86, P<0.01). Conclusions:Although PIDBBs can effectively reduce the low dose to the small intestine, the radiation attenuation caused by them can reduce the PTV coverage of radiotherapy plans and increase the doses to abdominal and pelvic skins sharply, especially for patients requiring irradiation of the groin and perineum.
ABSTRACT
Objective To compare the impact of immobilization base plates composed of 7 types of materials on the MR-simulation imaging quality used for radiotherapy,aiming to provide reference data for clinical applications.Methods Using identical T1 and T2 sequences of Siemens MR-simulator,the MR images of ACR Large Phantom were acquired on the Orfit carbon fiber laminate,polycarbonate (PC),high precision base plate (HP),Jinan Huayuxin BR,WR,KP and SP materials,respectively.The imaging quality without any plate was used as the baseline data.The following metrics were compared:1.High-contrast spatial resolution:the sharpness of 3 pairs of hole arrays was observed,which represented resolutions of 1.1 mm,1.0 mm and 0.9 mm on the LR and AP directions;2.Image intensity uniformity in terms of percent integral uniformity (PIU):PIU =100× [1-((high-low)/(high +low)];3.Low-contrast resolution:distinguishable spokes representing resolutions of 5.1％,3.6％,2.5％ and 1.4％ were recorded.According to ACR recommendations,high-contrast resolution of 1.0 mm,PIU of T1WI and T2＞82％and low-contrast spoke difference＜3 were considered as clinically acceptable.Results High-contrast T1WI and T2WI resolutions of no plate,PC plate,HP plate and KP material were all 0.9 mm,and those of the remaining materials were =worse than 0.9 mm.The T1WI and T2WI PIU of no plate was＞87％,and the PIU of carbon fiber plate was reduced by＞ 25％.The PIU decrease of remaining materials was within ±4％.Except the carbon fiber plate,the low-contrast spokes of the remaining materials were within ±3 compared with the reference.Conclusions In clinical settings,carbon fiber plate exerts the most significant effect upon the MR-simulation imaging quality,which is unsuitable for MR simulation.Imaging quality of PC and HP plates are consistent with that of no plate.BR and KP materials exert slight effect upon MR signal.The remaining materials are of potential values for the manufacture of immobilization devices and accessories.
ABSTRACT
Objective To evaluate the effect of home-made immobilization device with KV-CBCT in lung-SBRT and investigate its clinical use value.Methods Choosing 10 lung tumor patients (half centre type tumor;half peripheral type) random analysis the interfractional and intrafractional setup errors in the SBRT process by this fixed device with KV-CBCT.The concrete method is using Varian's KV-CBCT scans the patients before and after the SBRT each time,then make the registration between the reconstructed 3 d image and the planned CT image (both based on bone landmark),we then obtain the average setup errors in LR,AP and SI directions.Simultaneously,this research make contrastive analysis of setup errors among this fixed device and other fixed devices such as vacuum pad,phantom in body IMRT.All data make one-factor analysis of variance by SSPS 17.0.Results All the setup errors data was gaussian distribution,the centre type interfraction was at (0.01 ±0.32) cm (LR),(-0.08 ±0.38) cm (AP),(0.14 ±0.36) cm (SI) of the cross section,peripheral type interfraction was at (0.01 ± 0.32) cm (LR),(-0.08 ± 0.38) cm (AP),(0.14 ± 0.36) cm (SI) of the cross section (P =0.001).We found out that the average of lung tumor's setup error at all three directions have no significant difference-the largest was the AP directions (P =0.003),the second was the SI direction (P =0.003) and the smallest was the LR direction (P =0.001).The central type has no significant difference at three directions.Compare to the other fixed device,the average setup errors of our device are (0.09 ± 0.33) cm (LR),(-0.10 ± 0.44) cm (SI),(0.17 ±0.35) cm (AP) better than the report at present paper.As the interfraction setup error was small enough by using this fixed device while it has beyond the system algorithm,the registration software of system shows (0.0 ± 0.0 cm).Conclusions The range of lung tumor motion can be cut down obviously and enhance each placement accuracy,repeatability,on SBRT with home-made immobilization device.