The Dilemma of Target Delineation with PET/CT in Radiotherapy Planning for Malignant Tumors

Currently there are many unanswered questions concerning contouring a target with PET/CT in radiotherapy planning. Who should contour the PET volume-the radiation oncologist or the nuclear medicine physician？ Which factors will contribute to the dual-observer variability between them？ What should be taken as the optimal SUV threshold to demarcate a malignant tumor from the normal tissue？ When the PET volume does not coincide with the local area CT findings, which portion should be contoured as the target？ If a reginal lymph node,draining area or a remote region is shown to be PET positive but CT negative, or PET negative but CT positive, how is the target identified and selected？ Further studies concerning the relationship between PET/CT and the cancerous tissue are needed. The long-term clinical results showing an increased therapeutic ratio will finally verify the applicability of guidelines to contour the target with PET/CT in radiotherapy planning.

Application of a novel computer-assisted surgery system in percutaneous nephrolithotomy:A controlled study

BACKGROUND Most complex renal stones are managed primarily with percutaneous nephrolithotomy(PCNL).However,PCNL is still a great challenge for surgeons because of poor comprehension on complex adjacent structures.Novel techniques are required to assist in planning and navigation.AIM To apply and evaluate the Hisense computer-assisted surgery(CAS)system in PCNL.METHODS A total of 60 patients with complex renal stones were included.Thirty patients in the CAS group had three-dimensional(3 D)virtual models constructed with the CAS system.The model assisted in planning and navigating in the CAS system.Thirty patients in the control group planned and navigated as standard PCNL,without the application of the CAS system.Success rate of one attempt,operation time,initial stone-free rate,decrease in hemoglobin,and complications were collected and analyzed.RESULTS There were no statistically significant differences in the baseline characteristics or planning characteristics.The success rate of one puncturing attempt(90%vs 67%,P=0.028)and the initial stone-free rate(87%vs 63%,P=0.037)were significantly higher in the CAS group.However,there were no statistically significant differences in the operation time(89.20±29.60 min vs 92.33±33.08 min,P=0.859)or in the decrease in hemoglobin(11.07±8.32 g/L vs 9.03±11.72 g/L,P=0.300)between the CAS group and the control group.No statistically significant differences in the incidence of complications(Clavien-Dindo grade≥2)were found.CONCLUSION Compared with standard PCNL,CAS-assisted PCNL had advantages in terms of the puncturing success rate and stone-free rate.The Hisense CAS System was recommended to assist in preoperative planning and intraoperative navigation for an intuitive,precise and convenient PCNL.

A multiphase direct aperture optimization for inverse planning in radiotherapy

Optimization of the inverse planning becomes critical because it follows the invention of intensity modulated radiotherapy(IMRT) to shorten the previous "trial-and-error" treatment process and increase efficiency.In this paper, the inverse planning is used to direct aperture optimization in the ARTS(Accurate/Advanced Radiotherapy System). The objective function was quadratic, both tolerance and dose-volume constraint types are supported. The memory efficient conjugate gradient algorithm is used to cope with its large data.Furthermore, to fully exploit the solution space, a shortest path sub-procedure is coupled into the whole algorithm, thus giving further possibility decreasing the objective function. Two clinical cases are tested, indicating that the applicability of this algorithm is promising to clinical usage.

Dose Distributions in Simulated Electron Radiotherapy with Intraoral Cones Using Treatment Planning System

Aim: This study aims to evaluate the difference between depth data from an intraoral cone and a conventional irradiation tube calculated using a treatment planning system (TPS), and that measured using an intraoral cone for electron radiotherapy. Background: A TPS is only compatible with conventional irradiation tubes. However, such systems are not suitable for determining dose distributions when a special cone is employed. Materials and Methods: Dose distributions were calculated using the beam data for mounted intraoral cones using a TPS. Then, the dose distribution by field size was calculated for a low-melting-point lead alloy using the beam data for a mounted conventional tube. The calculated data were evaluated against the measured intraoral-cone depth data based on the dose and depth differences. Results: The calculated data for the intraoral cone case did not match the measured data. However, the depth data obtained considering the field size determined for the lead alloy using the conventional tube were close to the measured values for the intraoral cone case. The difference in the depth at which the absorbed dose was 50% of the maximum value of the percentage depth dose was less than ±4 mm for the generalized Gaussian pencil beam convolution algorithm and less than ±1 mm for the electron Monte Carlo algorithm. Conclusion: It was found that the measured and calculated dose distributions were in agreement, especially when then electron Monte Carlo algorithm was used. Thus, the TPS can be employed to determine dose distributions for intraoral cone applications.

Complex Target Volume Delineation and Treatment Planning in Radiotherapy for Malignant Pleural Mesothelioma (MPM)

Introduction: Radiotherapy alone or combined with surgery and/or chemotherapy is being investigated in the treatment of malignant pleural mesothelioma (MPM). This study aimed to simulate a Volumetric Modulated Arc Therapy (VMAT) treatment of a patient with MPM. Materials and Methods: CT images from a patient with intact lungs were imported via DICOM into the Pinnacle3 treatment planning (TP) system (TPS) and used as a model for MPM to delineate organs at risk (OAR) and both clinical and planning target volumes (CTV and PTV) with a margin of 5 mm. Elekta Synergy with 6 MV photons and 80 leafs MLCi2 was employed. VMAT plans were generated using two coplanar arcs with gantry rotation angles of 178° - 182°, the collimator angles of each arc were set to 90°, Octavius® 4D 729 was employed for quality assurance while the calculated and measured doses were compared using VeriSoft. Results: A TP was achieved. The Gamma volume analysis with criteria of 3 mm distance to agreement and 3% dose difference yielded the gamma passing rate = 99.9%. The reference isodose was 42.75 Gy with the coverage constraints for the PTV D95 and V95 = 95.0% of 45 Gy. The remaining dosimetric parameters met the recommendations from the clinically acceptable guidelines for the radiotherapy of MPM. Conclusion: Using well-defined TV and VMAT, a consistent TP compared to similar ones from publications was achieved. We obtained a high agreement between the 3D dose reconstructed and the dose calculated.

Comparative Study between Field-in-Field and IMRT Techniques in Prostate Cancer Radiotherapy: A Treatment Planning Study

Introduction: Field-in-Field (FIF) and Intensity Modulated Radiation Therapy (IMRT) are two advanced radiation therapy planning techniques. Both of them are being used to achieve the same two related aims which are, to expose the targeted tumor to the full radiation dose and to spare the nearby normal tissues (or organs) from being exposed to high amounts of radiation more than its tolerance dose limits. FIF is a forward planning while IMRT is an inverse planning and FIF is a forward IMRT. Aim: The purpose of this study was to compare between Field-in-Field and IMRT techniques in prostate cancer radiotherapy. Method: A treatment planning system supporting both inverse and forward planning facilities is used. Ten prostate cancer patients were planned with both FIF and IMRT planning techniques. Doses received by the Planning Target Volume (PTV) and Organs at Risk (OARs) were compared in the two methods quantitatively from Dose Volume Histograms (DVHs) and qualitatively from (axial cuts). Results: The results showed that the IMRT planning technique achieved better dose coverage to the PTV than the FIF planning technique but, except RT and LT Femoral Heads, FIF achieved a better protection to the Rectum and the Bladder (OARs) than IMRT. Conclusions: The results showed that the inverse planning based IMRT technique is better and recommended in the prostate cancer radiotherapy than the FIF technique.

The Impact of Risk-Based Cancer Care Planning on the Complications and Self-Care Ability of Cervical Cancer Patients Undergoing Radiotherapy

Objective:To explore the impact of the application and implementation of risk-based cancer care planning in patients with cervical cancer radiotherapy on the complications and self-care ability of patients.Method:This study recruited selected patients who came for cervical cancer radiotherapy in a tertiary hospital in Xianyang City,Shaanxi Province from November 2020 to November 2021.One hundred patients were recruited.Nursing management was carried out,and cancer care planning under the concept of conventional care and risk were applied.The effects of different nursing methods on patients were compared and analyzed.Results:The patients in the experimental group had higher scores of self-care ability and lower complication rate.All data were significantly different from those of the control group(P<0.05),and the nursing effect on the experimental group was better.Conclusion:The application and implementation of the risk-based cancer care planning in patients who received cervical cancer radiotherapy has significant clinical effects,which is beneficial to reduce the incidence of patients’adverse reactions and promote patient recovery.

Volumetric-modulated arc therapy vs c-IMRT in esophageal cancer:A treatment planning comparison

AIM： To compare the volumetric-modulated arc ther- apy （VMAT） plans with conventional sliding window intensity-modulated radiotherapy （c-IMRT） plans in esophageal cancer （EC）. METHODS： Twenty patients with EC were selected, including 5 cases located in the cervical, the upper, the middle and the lower thorax, respectively. Five plans were generated with the eclipse planning sys- tem： three using c-IMRT with 5 fields （5F）, 7 fields （7F） and 9 fields （gF）, and two using VMAT with a single arc （1A） and double arcs （2A）. The treatment plans were designed to deliver a dose of 60 Gy to the plan-ning target volume （PTV） with the same constrains in a 2.0 Gy daily fraction, 5 d a week. Plans were normal- ized to 95% of the PTV that received 100% of the pre- scribed dose. We examined the dose-volume histogram parameters of PTV and the organs at risk （OAR） such as lungs, spinal cord and heart. Monitor units （MU） and normal tissue complication probability （NTCP） of OAR were also reported. RESULTS： Both c-IMRT and VMAT plans resulted in abundant dose coverage of PTV for EC of different Io- cations. The dose conformity to PTV was improved as the number of field in c-IMRT or rotating arc in VMAT was increased. The doses to PTV and OAR in VMAT plans were not statistically different in comparison with c-IMRT plans, with the following exceptions： in cervical and upper thoracic EC, the conformity index （CI） was higher in VMAT （1A 0.78 and 2A 0.8） than in c-IMRT （5F 0.62, 7F 0.66 and 9F 0.73） and homogeneity was slightly better in c-IMRT （7F 1.09 and 9F 1.07） than in VMAT （1A 1,1 and 2A 1.09）, Lung V30 was lower in VMAT （1A 12.52 and 2A 12.29） than in c-IMRT （7F 14.35 and 9F 14.81）. The humeral head doses were significantly increased in VMAT as against c-IMRT. In the middle and lower thoracic EC, CI in VMAT （1A 0.76 and 2A 0.74） was higher than in c-IMRT （5F 0.63 Gy and 7F 0.67 Gy）, and homogeneity was almost similar between VMAT and c-IMRT. V20 （2A 21.49 Gy vs 7F 24.59 Gy and 9F 24.16 Gy） and V30 （2A 9.73 Gy vs 5F 12.61 Gy, 7F 11.5 Gy and 9F 11.37 Gy） of lungs in VMAT were lower than in c-IMRT, but low doses to lungs （V5 and Vl0） were increased. V30 （1A 48.12 Gy vs 5F 59.2 Gy, 7F 58.59 Gy and 9F 57.2 Gy）, V40 and V50 of heart in VMAT was lower than in c-IMRT. MUs in VMAT plans were significantly reduced in comparison with c-IMRT, maximum doses to the spinal cord and mean doses of lungs were similar between the two techniques. NTCP of spinal cord was 0 for all cases. NTCP of lungs and heart in VMAT were lower than in c-IMRT. The advantage of VMAT plan was enhanced by doubling the arc. CONCLUSION： Compared with c-IMRT, VMAT, especial- ly the 2A, slightly improves the OAR dose sparing, such as lungs and heart, and reduces NTCP and MU with a better PTV coverage.

Auto-planning技术用于胸中段食管癌调强放疗的可行性

目的探讨Auto-planning技术用于食管癌调强放疗计划设计的可行性。方法选取24例食管癌放疗病例,用Pinnacle 3计划系统设计自动治疗计划(ap-IMRT)和人工计划(m-IMRT),比较两种不同计划的剂量体积直方图(DVH),用配对t检验分析靶区和危及器官受照剂量的差异。结果肿瘤靶区GTV的D_(min)(t=-2.233,P=0.036)、均匀性指数HI(t=2.205,P=0.038),计划靶区PTV的D 98(t=-2.241,P=0.035)、HI(t=2.543,P=0.018)、适形度指数CI(t=-2.497,P=0.020),左肺V 20(t=4.412,P=0.000)、V_(30)(t=5.243,P=0.000),心脏V 30(t=2.546,P=0.018)、V_(40)(t=2.404,P=0.025)、D_(mean)(t=2.565,P=0.017),以上参数均是ap-IMRT计划优于m-IMRT。脊髓最大受照剂量D_(max)(t=-1.891,P=0.045),m-IMRT计划优于ap-IMRT。结论ap-IMRT靶区剂量分布能够达到较好均匀性和适形度,且能更地保护并行器官,但对串行器官脊髓的保护欠佳。

Using CT imaging to delineate the prostatic apex for radiation treatment planning

Background and Objective: In computed tomography (CT)-based radiotherapy planning for prostate cancer, it is difficult to precisely delineate the prostatic apex because of its relationship with the urogenital diaphragm and bulbospongiosus musculature. In this retrospective study, we analyzed the magnetic resonance imaging (MRI) and CT scans of the patients with prostate cancer to investigate the relationship between the prostatic apex and the anatomic structure visible on CT, and to provide evidence for localizing the prostatic apex in radiotherapy planning. Methods: MRI and CT scans of 108 patients with prostate cancer were analyzed to measure the distances between the prostatic apex and the bottom of ischial tuberosities, the bottom of obturator foramen, the bottom of pubic symphysis, and the bulb of the penis. The volume of the prostate was measured to analyze its relationship with the localization of the prostatic apex. Results: The prostatic apex was located (13.1 ± 3.3) mm above the bulb of the penis, (11.0 ± 5.4) mm above the bottom of the obturator foramen, (31.3 ± 5.5) mm above the ischial tuberosities, and (7.1 ± 4.7) mm above the bottom of the symphysis pubis. There was no correlation between the size of the prostate and the localization of the prostatic apex. Conclusions: The variance of the distance between the prostatic apex and the bulb of the penis is smaller than that of the distance between the apex and bony anatomy. Delineating the target to 6 mm above the bulb of the penis can cover the prostatic apex in 95% of the patients with prostate cancer, delineating to the bottom of obturator foramen can cover the prostatic apex in 100% of the patients.

Effect of Non-Delineated Normal Volumes in IMRT Treatment for Left Breast Cancer: A Treatment Planning Study

Introduction: Intensity Modulated Radiation Therapy (IMRT) planning dose calculation process depends on IMRT dose constraints. So, if there was any structure along the treatment beam path not delineated, it would not be taken into account during that calculation process. During IMRT routine practical work, it is noticed that there are some non-delineated normal tissue volumes that received un-aimed dose. Aim: The purpose of this study was to study the effect of unusually delineated normal volumes in IMRT treatment for left sided breast cancer. Method: Ten left sided breast cancer patients were planned with IMRT inverse planning system. The unusually delineated normal volumes were delineated and taken into account in IMRT dose constraints as an Organ at Risk. Doses received by that volume were compared in the two methods quantitatively from Dose Volume Histograms (DVHs) and qualitatively from (axial cuts). Results: The results showed that doses received by the unusually delineated volume when they were delineated and taken into account in IMRT dose constraints were significantly higher than when they were not. Conclusions: The results showed that for IMRT planning technique used for treating left-sided breast cancer, all of the normal tissues/structures that are closed to the treatment targets must be delineated and taken into account in the IMRT planning dose constraints.

Dosimetric Effects Due to Inter-Observer Variability of Organ Contouring When Utilizing a Knowledge-Based Planning System for Prostate Cancer

Purpose: Radiotherapy is a widely accepted standard of care for early-stage prostate cancer, and it is believed that the plan quality and treatment outcome are associated with contour accuracy of both the target and organs-at-risk (OAR). The purposes of this study are to 1) assess geometric and dosimetric uncertainties due to inter-observer contour variabilities and 2) evaluate the effectiveness of geometric indicators to predict target dosimetry in prostate radiotherapy. Methods: Twenty prostate patients were selected for this retrospective study. Five experienced clinicians created unique structure sets containing prostate, seminal vesicles, bladder, and rectum for each patient. A fully automated script and knowledge-based planning routine were utilized to create standardized and unbiased plans that could be used to evaluate changes in isodose distributions due to inter-observer variability in structure segmentation. Plans were created on a “gold-standard” structure set, as well as on each of the user-defined structure sets. Results: Inter-observer variability of contours during structure segmentation was very low for clearly defined organs such as the bladder but increased for organs without well-defined borders (prostate, seminal vesicles, and rectum). For plans generated with the user-defined structure sets, strong/moderate correlations were observed between the geometric indicators for target structure agreement and target coverage for both low-risk and intermediate-risk patient groups, while OAR indicators showed no correlation to final dosimetry. Conclusions: Target delineation is crucial in order to maintain adequate dosimetric coverage regardless of the associated inter-observer uncertainties in OAR contours that had a limited impact upon final dosimetry.

Comparison between 4D robust optimization methods for carbon-ion treatment planning

Intensity-modulated particle therapy(IMPT)with carbon ions is comparatively susceptible to various uncertainties caused by breathing motion,including range,setup,and target positioning uncertainties.To determine relative biological effectiveness-weighted dose(RWD)distributions that are resilient to these uncertainties,the reference phase-based four-dimensional(4D)robust optimization(RP-4DRO)and each phase-based 4D robust optimization(EP-4DRO)method in carbon-ion IMPT treatment planning were evaluated and compared.Based on RWD distributions,4DRO methods were compared with 4D conventional optimization using planning target volume(PTV)margins(PTV-based optimization)to assess the effectiveness of the robust optimization methods.Carbon-ion IMPT treatment planning was conducted in a cohort of five lung cancer patients.The results indicated that the EP-4DRO method provided better robustness(P=0.080)and improved plan quality(P=0.225)for the clinical target volume(CTV)in the individual respiratory phase when compared with the PTV-based optimization.Compared with the PTV-based optimization,the RP-4DRO method ensured the robustness(P=0.022)of the dose distributions in the reference breathing phase,albeit with a slight sacrifice of the target coverage(P=0.450).Both 4DRO methods successfully maintained the doses delivered to the organs at risk(OARs)below tolerable levels,which were lower than the doses in the PTV-based optimization(P<0.05).Furthermore,the RP-4DRO method exhibited significantly superior performance when compared with the EP-4DRO method in enhancing overall OAR sparing in either the individual respiratory phase or reference respiratory phase(P<0.05).In general,both 4DRO methods outperformed the PTV-based optimization in terms of OAR sparing and robustness.

自动计划RapidPlan优化模块在鼻咽癌调强计划中的可行性应用

目的:通过比较常规调强计划与自动优化计划间的差异,探讨自动计划RapidPlan优化模块在鼻咽癌调强计划应用中的可行性。方法:选取60例经临床验证的优质鼻咽癌计划进行分析和特征提取,先建立一个特定的自动优化模型,然后用此模型对另外的15例鼻咽癌计划进行测试,比较这15例经模型测试优化后形成的自动计划与用常规调强优化的计划间的差异。采用SPSS 22.0版软件分别对两组计划的各主要参数行配对样本t检验分析。结果:自动优化产生的计划得到的剂量分布更佳;且自动优化比常规调强优化效率更高,自动计划的优化平均时间比常规调强计划缩短33.67%(P=0.001),优化次数也从平均3.5次降到2.2次(P=0.000);自动优化比常规调强优化的计划执行效率更高,MU值平均值减少376 MU,平均减少原来的14.8%(P=0.000)。结论:基于解剖特性和先验知识的自动计划模块,即RapidPlan优化模块,通过建立优化模型,设置优化参数,产生的鼻咽癌调强计划,可以达到比常规调强计划更佳的靶区剂量分布结果,并且更好地降低正常组织的剂量,同时获得比常规调强计划更高的优化效率和计划执行效率,在鼻咽癌的调强计划优化中是切实可行的。

CADPLAN(helios)调强放疗计划的绝对剂量验证

目的:验证CADPLAN(helios)设计的病人调强放射治疗(IMRT)计划的绝对剂量准确性,保证IMRT治疗计划临床实施的正确性。方法:利用美国Varian 23-EX医用直线加速器6MV-X射线,根据经国家计量院校准过的0.6 cc电离室在体部模体中校准0.01 cc电离室;根据病人的CT图像资料,使用CADPLAN(helios)三维治疗计划系统设计出病人IMRT计划,并移置到模体中,重新计算出体模中过等中心点横截面上的剂量分布。将模体移放到加速器治疗床上,调用模体IMRT计划对模体进行照射。使用0.01 cc电离室测量出体模中等中心点及其周围两个感兴趣点上的吸收剂量,然后与模体计划中的计算值相比较。结果:空间三点绝对吸收剂量的测量值与计划值的偏差小于5%。结论:在准确、合理配置CADPLAN(helios)计划系统基础数据的情况下,利用它设计出的IMRT计划是可信的。

AiPlan放射治疗计划系统的临床剂量学测试

目的对AiPlan三维放射治疗计划系统(Treatment Planning System,TPS)进行临床剂量学验证,以检验AiPlan系统在临床正常使用条件下的有效性和安全性。方法随机选取60例在Pinnacle计划系统上已完成放射治疗计划设计的患者,将60例患者的CT图像及RT Structures通过DICOM网络传输至AiPlanTPS,并应用AiPlan系统对60例临床病例重新进行放射治疗计划设计。分别对Pinnacle和AiPan两组放射治疗计划进行绝对点剂量以及二维面剂量验证,同时比较两组放射治疗计划等中心及附近层面剂量分布情况,运用统计学方法对两组计划剂量验证结果进行分析。结果 AiPlanTPS能够实现逆向调强放射治疗计划设计所需的各项功能;经AiPlan系统设计的60例放射治疗计划均能满足临床剂量要求;绝对点剂量误差范围为-3.27%~3.98%,二维面剂量验证Gamma通过率为97.5%±2.8%,该结果与Pinnacle系统计划验证结果相比无统计学差异(t=0.149、1.858,P=0.882、0.068)。结论 Aiplan三维TPS在剂量计算精度上达同类进口产品相似水平,能够满足临床要求。

Comparison of Dosiology between Three Dimensional Conformal and Intensity-modulated Radiotherapies (5 and 7 fields) in Gastric Cancer Post-surgery

The purpose of this study was to compare the dose distribution of intensity-modulated ra- diotherapy （IMRT） in 7 and 5 fields as well as 3-D conformal radiotherapy （3D-CRT） plans for gastric cancer using dosimetric analysis. In 15 patients with gastric cancer after D1 resection, dosimetric pa- rameters for IMRT （7 and 5 fields） and 3D-CRT were calculated with a total dose of 45 Gy （1.8 Gy/day） These parameters included the conformal index （CI）, homogeneity index （HI）, maximum dose spot for the planned target volume （PTV）, dose-volume histogram （DVH） and dose distribution in the organs at risk （OAR）, mean dose （Dmean）, maximal dose （Dmax） in the spinal cord, percentage of the normal liver volume receiving more than 30 Gy （V30） and percentage of the normal kidney volume receiving more than 20 Gy （V20）. IMRT （7 and 5 fields） and 3D-CRT achieved the PTV coverage. However, IMRT presented significantly higher CI and HI values and lower maximum dose spot distribution than 3D-CRT （P=0.001）. For dose distribution of OAR, IMRT had a significantly lower Dmean and Dmax in spinal cord than 3D-CRT （P=-0.009）. There was no obvious difference in V30 of liver and V20 of kidney between IMRT and 3D-CRT, but 5-field IMRT showed lower Dmean in the normal liver than other two plans （P=0.001）. IMRT revealed favorable tumor coverage as compared to 3D-CRT and IMRT plans. Specifically, 5-field IMRT plan was superior to 3D-CRT in protecting the spinal cord and liver, but this superiority was not observed in the kidney. Further studies are needed to compare differences among the three approaches.

Influence of Position and Radiation Technique on Organs at Risk in Radiotherapy of Rectal Cancer

The influence of the position and radiation technique on the organs at risk（OARs） in radiotherapy of rectal cancer was evaluated. The relationship between the volume of irradiated small bowel（VSB） and acute bowel toxicity was determined. A total of 97 cases of rectal cancer were retrospectively randomized to receive radiotherapy with the designated treatment positions and radiation plans. Among 64 patients in the supine position, 32 patients were given three-dimensional conformal radiotherapy（3DCR） and 32 patients were subjected to intensity-modulated radiation therapy（IMRT） respectively. The rest 33 patients were treated with 3DCRT in the prone position with a belly board. The VSB was calculated for doses from 5 to 45 Gy at an interval of 5 Gy. With prescription dose in planned target volume（PTV） of 50 Gy, the dose distribution, conformal index for PTV（CIPTV）, dose-volume histogram（DVH） of OARs, the correlation of VSB and the acute toxicity were compared. The results were shown as follows：（1） Among the 3 methods, there were no differences in PTV＇s converge including V95 and D95;（2） For IMRT under a supine position, CIPTV was closest to 1, the mean dose of small bowel decreased（P〈0.05）, and the mean VSB from V30 to V45 significantly decreased（P〈0.05）.（3） For 3DCRT with a belly board under a prone position, the mean dose and the mean VSB from 40 to 45 Gy were less than those for 3DCRT under a supine position（P〈0.05）;（4） Mean proportion of VSB was significantly greater in the patients experiencing diarrhea grade 2-4 than in those with diarrhea grade 0-1 at dose levels from V30 to V45（P〈0.05）. It was concluded that for the radiotherapy of rectal cancer, IMRT technique might decrease the high-dose VSB to reduce the risk of acute injury. 3DCRT with a belly board under a prone position is superior to 3DCRT under a supine position, which could be a second choice for radiation of rectal cancer.

直肠癌术前同步推量RapidPlan模型用于术后单一处方计划优化的改造测试

目的:测试直肠癌术前同步推量RapidPlan模型用于术后单一处方计划优化的可行性,探索改造和拓展已有模型的应用方法。方法:(1)对现有直肠癌术前同步推量41.8 Gy(PTV)/50.6 Gy(PGTV)RapidPlan模型进行改造;(2)复制直肠癌术后单一PTV处方临床计划18例(45 Gy的7例,50 Gy的11例),保持布野条件、能量、加速器配置及原有剂量算法等不变,将PTV分别匹配模型中的PGTV和PTV,预测可实现的DVH区间并重新优化;(3)将自动计划靶区剂量归一至与临床计划相似后比较各剂量学参数。结果:单一处方靶区匹配模型中的PTV会导致严重的剂量热区,匹配PGTV的RapidPlan计划质量和临床计划相似或略好,但其危及器官剂量学参数的标准差均小于临床计划。结论:直肠癌术前同步推量Rapid Plan模型可用于术后单一处方放疗计划的自动优化并且其质量一致性更好,但需将单一靶区匹配给模型中最高处方剂量对应的靶区结构。

Predicting Delivery Error Using a DICOM-RT Plan for Volumetric Modulated Arc Therapy

The purpose of this study was to investigate the prediction of mechanical error using DICOM-RT plan parameters for volumetric modulated arc therapy (VMAT). We created plans for gantry rotation arcs of 360° and 180° (full-arc and half-arc VMAT) for six maxillary sinus cancer cases using a Monaco treatment planning system, and delivered the doses with a linear accelerator. We calculated DICOM-RT plan parameters, including gantry, multileaf collimator (MLC) positions and Monitor Units (MU). We compared plans with regard to gantry angle per MU (degrees/MU) and MLC travel per MU (mm/MU) for each segment. Calculated gantry angle/MLC position speeds and errors were evaluated by comparison with the log file. On average, the half-arc VMAT plan resulted in 47% and 35% fewer degrees/MU and mm/MU than the full-arc VMAT plan, respectively. The root mean square (r.m.s.) gantry and MLC speeds showed a linear relationship with calculated degrees/MU and mm/MU, with coefficients of determination (R2) of 0.86 and 0.72, respectively. The r.m.s. gantry angle and MLC position errors showed a linear relationship with calculated degrees/MU and mm/MU with R2 of 0.63 and 0.76, respectively. Deviations from plan parameters were related to mechanical error for VMAT, and provided quantitative information without the need for VMAT delivery. These parameters can be used in the selection of treatment planning.