Dosimetric effect of patient arm position on Cyberknife radiosurgery for spinal tumors / 北京大学学报(医学版)

OBJECTIVE@#To assess the potential dosimetric effects of arms movement in patients with Cyberknife spine tumors.@*METHODS@#In the study, 12 patients with thoracic and lumbar tumors were retrospectively selected respectively. The contour of the patient's arms was sketched and the CT density was modified to be equivalent to air in order to simulate the extreme case when the arm was completely removed from the radiation fields. The dose of simulated plan was re-calculated with the original beam parameters and compared with the original plan. The changes of V100, D95, and D90, conformity index (CI) and heterogeneity index (HI) in planning target volume (PTV), as well as Dmax, D1cc and D2cc in the spinal cord, stomach, esophagus, and intestines were analyzed by comparing with the original plans.@*RESULTS@#Compared with the original treatment plan, V100, D95, D90 and CI of PTV for the simulated plan was increased by 0.86%, 2.02%, 1.97% and 0.80% respectively, the difference was statistically significant (P < 0.05). Dmax, D1cc and D2cc of spinal cord was increased by 2.35%, 0.59% and 1.49% on average, compared with the original plan, the difference was statistically significant (P < 0.05). The difference was statistically significant only in average D2cc of stomach, which was increased by 1.70%, compared with the original plan (P < 0.05). There was no significant difference in dose change of eso-phagus and intestine between the original and simulated plans.@*CONCLUSION@#This study analyzed the most extreme arm position in spinal tumor of radiation therapy based on Cyberknife. It was found that the change of arm position had little effect on dosimetry. In addition, with the change of arm position, the dose in PTV and organ at risk (OAR) increased, but the increase was relatively small. Therefore, in some special cases where the patient really can't keep the arm position consistent during treatment, reasonable adjustment can be accepted. However, in order to ensure accurate radiotherapy, patient position should be as stable and consistent as possible.

Dosimetric analysis of volumetric modulated arc therapy and intensity modulated radiotherapy for patients undergone breast-conserving operation / 北京大学学报(医学版)

OBJECTIVE@#To compare the dosimetric differences between volumetric modulated arc therapy and intensity modulated radiotherapy for breast cancer patients after breast-conserving surgery.@*METHODS@#Ten patients who received radiotherapy after breast-conserving surgery were selected. Eclipse planning system was used to design volumetric rotating intensity-modulated (2F-RapidArc) and two field intensity-modulated radiation therapy (2F-IMRT) planning for each patient. 2F-RapidArc plans were made using two partial arcs with gantry rotation from 287°-293° to 152°-162°, and 0° to 90 ° was avoidance sector. The gantry angle of 2F-IMRT were 301°-311° and 125°-135°. The prescription dose was 46 Gy/23 fractions. All plans required 95% of the target volume receiving the prescription dose. The dose distribution of the target, organs at risk, machine unit (MU) and treatment time were compared.@*RESULTS@#2F-RapidArc and 2F-IMRT plans' uniformity index was 1.12±0.02 and 1.11±0.03 (P=0.282), respectively; conformal index was 0.80±0.03 and 0.65±0.04 (P<0.001), respectively. V110 of plan target volume was 20.98%±14.47% and 10.43%±10.49% (P=0.030), respectively. Compared with the 2F-IMRT, 2F-RapidArc plans had a higher dosimetric parameters for left lung: V5 (48.06%±17.32% vs. 24.23%±6.56%,P=0.001), V10 (28.89±9.28 vs.17.07±4.78%,P=0.004), Dmean [(9.70±2.14) Gy vs. (6.86±1.77) Gy, P=0.002], increased the double lung: V5 (22.85%±7.55% vs. 11.01%± 2.95%,P=0.001), V10 (13.16%±4.33% vs. 7.76%± 2.16%, P=0.006), Dmean [(4.66±0.95) Gy vs. (3.17±0.82) Gy, P=0.001], reduced the left lung: V40 (3.58%±1.46% vs. 6.19%±3.04%, P=0.006), reduced the double lung: V40 (1.61%±0.64% vs. 2.81%± 1.39%,P=0.005), increased cardiac: V5 (39.3%±17.19% vs. 8.79%±4.24%, P<0.001), V10 (21.31%±13.8% vs. 5.73%±3.42%, P=0.002), V20 (7.80%±6.08% vs. 4.05%±2.85%,P=0.018), Dmean [(0.64±0.25) Gy vs. (0.29±1.39) Gy,P<0.001],reduced the heart: V40(0.50%±0.40% vs. 1.86%±1.94%,P=0.037),increased the contralateral breast Dmean [(1.63±1.26) Gy vs. (0.09±0.05) Gy, P=0.004]. Compared with 2F-IMRTplan, 2F-RapidArc increased the treatment time [(132.9±7.2) s vs. (140.3±11.6) s, P=0.030]. Both the machine units were almost the same [(467.0±30.4) MU vs. (494.7±44.9) MU, P=0.094].@*CONCLUSION@#Both 2F-RapidArc and 2F-IMRT plans could reach the clinical requirements. 2F-RapidArc had a better conformal index, reduced the high dose area, but increased the low dose regions of the lung, heart, body area, and increased the average dose of the contralateral breast. The treatment time of 2F-RapidArc was longer than that of 2F-IMRT, and the MU of 2F-RapidArc and 2F-IMRT plans were almost the same.

Dosimetric Study of Biliary Stent Loaded with RadioactiveI Seeds / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>A novel radioactive 125I seed-loaded biliary stent has been used for patients with malignant biliary obstruction. However, the dosimetric characteristics of the stents remain unclear. Therefore, we aimed to describe the dosimetry of the stents of different lengths - with different number as well as activities of 125I seeds.</p><p><b>METHODS</b>The radiation dosimetry of three representative radioactive stent models was evaluated using a treatment planning system (TPS), thermoluminescent dosimeter (TLD) measurements, and Monte Carlo (MC) simulations. In the process of TPS calculation and TLD measurement, two different water-equivalent phantoms were designed to obtain cumulative radial dose distribution. Calibration procedures using TLD in the designed phantom were also conducted. MC simulations were performed using the Monte Carlo N-Particle eXtended version 2.5 general purpose code to calculate the radioactive stent's three-dimensional dose rate distribution in liquid water. Analysis of covariance was used to examine the factors influencing radial dose distribution of the radioactive stent.</p><p><b>RESULTS</b>The maximum reduction in cumulative radial dose was 26% when the seed activity changed from 0.5 mCi to 0.4 mCi for the same length of radioactive stents. The TLD's dose response in the range of 0-10 mGy irradiation by 137Cs γ-ray was linear: y = 182225x - 6651.9 (R2=0.99152; y is the irradiation dose in mGy, x is the TLDs' reading in nC). When TLDs were irradiated by different energy radiation sources to a dose of 1 mGy, reading of TLDs was different. Doses at a distance of 0.1 cm from the three stents' surface simulated by MC were 79, 93, and 97 Gy.</p><p><b>CONCLUSIONS</b>TPS calculation, TLD measurement, and MC simulation were performed and were found to be in good agreement. Although the whole experiment was conducted in water-equivalent phantom, data in our evaluation may provide a theoretical basis for dosimetry for the clinical application.</p>