Objective:To evaluate the protection of small bowel and bladder by Contoura carbon fiber belly board in patients with rectal cancer undergoing postoperative radiotherapy and the position deviation during radiotherapy. Methods: This study enrolled 45 consecutive patients with rectal cancer who had undergone prior surgery. Twenty patients who applied the belly board were defined as group A, and the other 25 patients were defined as group B. All the patients received threE-dimensional conformal radiation therapy(3D-CRT), and the prescriptive radiation dosage of 95% of planning target volume (PTV) was 50 Gy/25 times. Patients in group A underwent two sets of CT scans as follows: group A1, prone alone; group A2, prone with the use of the belly board. The radiation dosage and radiated volume in PTV, small bowel, and bladder were observed by dosE-volume histograms. Ten patients were selected randomly from group A and group B, respectively. Their position deviation during radiotherapy was measured by double exposure field verification system. The acute radiation reactions of all patients were observed and recorded during radiotherapy. Results: No significant difference was found in the total PTV and total volume of small bowel and bladder and mean irradiation dosage to PTV between groups A1 and A2. The mean irradiation dosage to the small bowel and bladder, the volume of small bowel irradiated at 10%-100% dose levels, and the volume of bladder irradiated at 30%-100% dose levels, were significantly decreased in group A2. The difference was significant. Compared with group B, the right-left and superior-inferior position deviations were significantly reduced in group A. The difference was significant (P<0.05). The anterior-posterior position deviation was also reduced, but the difference was not significant (P=0.705). The incidence of grade 3 or more adverse reactions were 15% (3/20) in group A and no patient broke off or stopped treatment; the incidence of grade 3 or more adverse reactions was 24% (6/25) in group B, and two patients broke off the treatment because of severe adverse reaction. One patient terminated the treatment. Conclusions: The Contoura carbon fiber belly board can reduce the irradiation dosage and volume of small bowel and bladder in patients with rectal cancer undergoing postoperative radiotherapy. The position deviation has better reproducibility and the acute radiation reactions are tolerable. It is worthy of application in clinic.

Objective:To build a predictive model for symptomatic radiation pneumonitis(RP) using the pretreatment CT radiomics features, clinical and dosimetric data of lung cancer patients by using machine learning method.Methods:A retrospective analysis of 103 lung cancer patients who underwent radiotherapy in the Affiliated Hospital of Jiangnan University from November 2018 to April 2020 was performed. Total normal lung tissues were segmented as an interested volume in pretreatment CT images, and then 250 radiomics features were extracted. The correlations of RP and clinical or dosimetric features were firstly investigated with univariate analysis. Then all clinical data, dosimetric data and CT radiomics features were collected and considered as predictors for modeling of RP grade ≥ 2. Features were selected through LASSO machine learning method, and the predictive model was built. Finally, nomogram for risk of RP were obtained according to the selected features.Results:The result of univariate analysis showed that symptomatic RP was significantly correlated with lung dosimetric parameters including mean lung dose (MLD), V20 Gy and V30 Gy( t=2.20, 2.34 and 2.93, P<0.05). Four features, including lung dose volume percentage V30 Gyand three radiomics features, entropy feature of GLCM, mean and median feature of wavelet histogram were selected among all clinical, dosimetric features and radiomics features. AUC of the predicted model obtained from selected features reached 0.757. For convenient clinical use, the nomogram were obtained, and then personalized RP risk prediction and early intervention could be performed according to this nomogram. Conclusions:Pretreatment CT radiomics and dosimetric features can be used in predicting symptomatic RP, which will be useful for advanced intervention treatment.

Objective To evaluate the effect of the thickness and area of the cavity between bolus and skin upon the dose deposition in the shallow tissues.Methods The linear accelerator head model of 6 MV X ray was constructed using Geant4,which simulated the accelerator working condition of 10 cm× 10 cm field and recorded the information of emergent particles as phase space file.A water phantom of 30 × 30 × 30 cm3 was designed at the SAD level.A 30 cm × 30 cm × 1 cm water film was constructed adjacent to or with different cavities to the upper surface of the phantom.The phase space file was utilized as particle source to simulate the particle transport process.The axis depth dose distribution and lateral dose profiles in the center area of the field at a depth of 1 mm,5 mm,9 mm,15 mm and 21 mm of the phantom were obtained,respectively.The simulated data obtained from water film with different cavities were compared with those of adjacent to the water phantom.Results When the cavity was ≤ 5 mm,the cavity exerted slight effect.When the thickness was increased,the maximum dose depth (Dmax) was increased,the PDD at Dmax (PD Dmax) became less,the depth of influenced lateral dose profiles was increased and the dose in the center area was decreased.Along with the increase of cavity area,the Dmax was initially increased and then decreased,the PD Dmax was at first decreased and subsequently increased,the depth of influenced lateral dose profile was initially increased and then decreased,the dose in the center area was first decreased and subsequently increased.The lateral dose profile distant from the cavity or located at a depth ≥ 15 mm was almost not affected by the cavity.Conclusion The thickness of the cavity between bolus and skin should be less than 5 mm and the cavity area should be small as possible.

Objective To investigate the effect of cavity thickness, area and distance under the bolus upon the dose in the superficial tissues. Methods An accelerator model was constructed based on Geant4.The model accuracy was validated by the comparison of the calculated data with the measured data. A 30×30×30 cm3 water phantom with the upper surface located at the isocenter level and a 30×30×1 cm3 water film were constructed. Different models with the water film close to or different cavities with the water phantom were established. Under the 10×10 cm2 field with 6 MV X-ray beam,the central axis depth dose distribution and the lateral dose profiles at a depth of 0. 1 cm ( profile1) of the models with different cavities were calculated. The calculated data of different model with the water film close to or different cavities with the water phantom were statistically compared. Results When the cavity thickness was ≤ 0. 5 cm, the cavity exerted slight effect upon the depth of maximum dose ( Dmax ) and superficial dose. As the cavity thickness was increased,the Dmax was also increased,the PDD at 0. 1 cm ( PDD1) was decreased rapidly and the profile1 was increased from the cavity center to the edge. Along with the increase of cavity area,the Dmax was initially increased and then decreased,whereas the PDD1 was first decreased followed by an increase. When the cavity area was small,the profile1 was gradually increased from the cavity center to the edge. When the cavity area was large,the profile1 was initially decreased and subsequently increased. When the distance was ≥0. 2 cm,it was qualified for the clinical requirement and it exerted no effect when the distance was≥1. 0 cm. The profile1 distant from the cavity was not affected. Conclusion The cavity under the bolus should be minimized to reduce the cavity thickness,area and distance as possible.

Objective To research the effect of cavity under Bolus to anisotropic analytical algorithm (AAA) on calculation precision of dose in shallow tissue based on Monte Carlo method;Methods A 30 cm × 30 cm × 30 cm water phantom with the upper surface was constructed which was located at the source-axis distance (SAD) of the medical linear accelerator and the center as well as coincided with the central axis of the radiation field in Eclipse treatment panning system. Above the water phantom, a water film of 1 cm thick with or without different cavities was constructed or. AAA was used to calculate the dose distribution on the central axis and the x-axis of different depth of the water model with different cavities respectively. The accelerator model, the same water phantom and the water film were constructed and the dose distributions of the same positions were calculated with Geant4. Based on the Geant4 calculation result, the calculation precision of AAA with different cavity were compared;Results For cavities with area of 2 cm × 2 cm, if the thickness is smaller than 0.5 cm, the AAA calculation error is about 2%. with the cavity thickness increase, the AAA would overestimate the dose in the shallow area under the cavity. With the cavity area increase, the area where AAA overestimate the shallow dose gradually moved out until near the edge of the radiation field, and the calculation error on the central area gradually reduced until there is basically no error. Conclusions The shallow dose would be increased according to the cavity size when planning with AAA; If there are cavities with large volume, it is better to reposition.