An anthropomorphic phantom study of effect of lung tumor size and location on dosimetric parameters

Objective： The aim of the study was to study the effect of the size and location of tumors on the normal lung dose-volume parameters for lung cancer. Methods： Three spheres with diameters of 2, 3 and 4 cm made of tissue-equivalent materials used for simulating tumors were inserted into the upper lobe, middle lobe, lower lobe of the right lung, upper lobe, lower lobe of the left lung of the Rando phantom, respectively. Five-field simplified IMRT （slMRT） planning were designed. The prescribed dose was 60 Gy/2 Gy/30 f, 99% of the planning target volume received this dose. Dose-volume parameters of normal lung tissues including relative volume of lung receiving 〉 5, 10, 20, 30 and 50 Gy （V5, Vl0, V2o, V30, V50）, and mean lung dose （MLD） were analyzed and compared. Results： For the dose-volume parameters, the diameter and the position of the tumor had a significant effect （P 〈 0.05）. With the diameter expanding from 2 to 3 cm, the parameters associated with tumor lying in various lobes increased by a range between 3.83%-125.38%, while the parameters linked with tumors on different lobes increased by a range between 10.46%-51.46% with the diameter expanding from 3 to 4 cm. Conclusion： Location and size of sphere-like tumor have an obvious effect on dose-volume parameters. Knowing about the degree of influence will help oncologists and physicists better evaluate treatment planning, then the probability of radiation pneumonitis can be reduced.

Dosimetric risk factors for radiation esophagitis in patients with breast cancer following regional nodal radiation

BACKGROUND Radiation esophagitis(RE)is one of the most common clinical symptoms of regional lymph node radiotherapy for breast cancer.However,there are fewer studies focusing on RE caused by hypofractionated radiotherapy(HFRT).AIM To analyze the clinical and dosimetric factors that contribute to the development of RE in patients with breast cancer treated with HFRT of regional lymph nodes.METHODS Between January and December 2022,we retrospectively analysed 64 patients with breast cancer who met our inclusion criteria underwent regional nodal intensity-modulated radiotherapy at a radiotherapy dose of 43.5 Gy/15F.RESULTS Of the 64 patients in this study,24(37.5%)did not develop RE,29(45.3%)developed grade 1 RE(G1RE),11(17.2%)developed grade 2 RE(G2RE),and none developed grade 3 RE or higher.Our univariable logistic regression analysis found G2RE to be significantly correlated with the maximum dose,mean dose,relative volume 20-40,and absolute volume(AV)20-40.Our stepwise linear regression analyses found AV30 and AV35 to be significantly associated with G2RE(P<0.001).The optimal threshold for AV30 was 2.39 mL[area under the curve(AUC):0.996;sensitivity:90.9%;specificity:91.1%].The optimal threshold for AV35 was 0.71 mL(AUC:0.932;sensitivity:90.9%;specificity:83.9%).CONCLUSION AV30 and AV35 were significantly associated with G2RE.The thresholds for AV30 and AV35 should be limited to 2.39 mL and 0.71 mL,respectively.