摘要
目的 假定125I粒子植入术后肿瘤每月以20%速度退缩时，研究等间距与周边密集、中间稀疏2种布源方式对剂量的影响。方法 利用计算机三维治疗计划系统（TPS）勾画4 cm×5 cm的圆柱形肿瘤，根据布源方式不同分为等间距组和周边密集、中间稀疏组，以处方剂量125 Gy载入放射性活度1.85×107Bq 125I粒子行术前计划。假设125I粒子植入肿瘤后肿瘤高不变，直径每月以20%的速度缩小，粒子随肿瘤均匀向心性集中，分别计算125I粒子植入术后0、1、2、3个月时90%靶体积吸收剂量（D90）、90%处方剂量覆盖体积占靶体积的百分比（V90）、150%处方剂量覆盖体积占靶体积的百分比（V150）。结果 等间距组载入粒子85颗，植入0、1、2、3个月后的D90分别为126.20、130.41、133.82和139.48 Gy，V90分别为97.0%、98.1%、99.3%和100%，V150分别为70.2%、69.9%、71.1%和71.5%；周边密集、中间稀疏组植入粒子75颗，植入0、1、2、3个月后的D90分别为126.46、125.41、123.50和128.83 Gy，V90分别为95.2%、95.7%、94.9%和97.6%，V150分别为52.8%、60.4%、62.7%和59.3%。结论 当肿瘤直径每个月以20%速度退缩时，粒子等间距分布时肿瘤预期吸收剂量逐渐增加；周边密集、中间稀疏的布源方式肿瘤预期吸收剂量不变，且高剂量区范围明显小于等间距布源。
Objective To study the dosimetric effect of two source patterns, including equal spacing and peripheral dense intermediate sparse by assuming a tumor shrinking speed of 20% per month after 125I seed implantation.Methods A virtual cylindrical tumor with 4 cm in height and 5 cm in diameter was contoured on a three-dimensional treatment planning system （TPS）. Two groups of preoperative plans were made with 1.85×107 Bq 125I seeds using two source patterns respectively. It was assumed that the tumor height was unchanged, while the diameter of tumor would decrease at a speed of 20% per month, and the locations of seeds would concentrate towards the tumor core. The 90% target volume dose （D90）, the ratio of 90% isodose volume over the target volume （V90）, and the ratio of 150% isodose volume over the target volume （V150） were calculated at 0, 1, 2, 3 months after 125I implantation respectively.Results In equal spacing group, 85 seeds were implanted. The values of D90 were 126.20, 130.41, 133.82 and 139.48 Gy after 0, 1, 2 and 3 months respectively. The values of V90 were 97.0%, 98.1%, 99.3% and 100%, while those of V150 were 70.2%, 69.9%, 71.1% and 71.5%. The dense in-periphery and sparse-in the middle group was loaded with 75 seeds. The D90 values were 126.46, 125.41, 123.50 and 128.83 Gy, the V90 95.2%, 95.7%, 94.9% and 97.6%, and the V150 52.8%, 60.4%, 62.7% and 59.3% after 0, 1, 2 and 3 months, respectiviely.Conclusions When the tumor diameter reduces at a rate of 20% per month after 125I seed implantation, the expected tumor dose absorption will gradually increase using the equal spacing sources pattern. However, the expected dose does not vary with source distribution of dense-in the-surrounding and sparse-in-middle, which also reduces high dose volume more than the equal spacing pattern.
出处
《中华放射医学与防护杂志》
CAS
CSCD
北大核心
2017年第9期713-716,共4页
Chinese Journal of Radiological Medicine and Protection
