宫颈癌术后螺旋断层放疗与常规加速器调强放疗的剂量学比较

目的 研究宫颈癌术后螺旋断层放疗(helical tomotherapy,HT)与常规静态调强放疗(IMRT)的剂量学特点。方法 采用10例宫颈癌术后患者CT图像,统一勾画靶区及危及器官(膀胱、直肠、小肠及双侧股骨头),分别传输至HT计划系统和IMRT计划系统,比较两组计划剂量体积直方图、适形度指数(CI)、均匀指数(HI)和危及器官所接受的照射剂量和体积,统一给予阴道残端60 Gy/25次,亚临床病灶50 Gy/25次,同时限定膀胱、直肠、小肠、股骨头等危及器官受照射剂量与体积。统一应用50 Gy处方剂量评价和比较CI和HI。结果 HT组适形指数(0.94±0.03)和均匀指数(1.28±0.02)均明显好于IMRT组(0.85±0.01和1.36±0.03)(t =5.12和-6.34, P<0.01);HT组PTV平均剂量为51.77Gy显著低于IMRT组54.53Gy(t =-8.01, P<0.05);HT组膀胱、直肠和小肠最大剂量、平均剂量、V₃₀、V₄₀和V₅₀照射体积均显著低于IMRT组;HT组左、右侧股骨头最大剂量、平均剂量、V₃₀和V₄₀照射体积均显著低于IMRT组。结论 HT与IMRT计划均有较好的靶区剂量分布,但HT组在适形指数、均匀指数及对周围危及器官的保护均比IMRT组有明显优势。     

Inverse-planned, dynamic, multi-beam, intensity-modulated radiation therapy (IMRT): A promising technique when target volume is the left breast and internal mammary lymph nodes

The purpose of this study was to determine the optimum beam number and orientation for inverse-planned, dynamic intensity-modulated radiation therapy (IMRT) for treatment of left-sided breast cancer and internal mammary nodes (IMNs) to improve target coverage while reducing cardiac and ipsilateral lung irradiation. Computed tomography (CT) data was used from 5 patients with left-sided breast cancer in whom the heart was close to the chest wall. The planning target volume (PTV) was the full breast plus ipsilateral IMNs. Two geometric beam arrangements were investigated, 240° and 190° sector angles, and the number of beams was increased from 7 to 9 to 11. Dose comparison metrics included: PTV homogeneity and conformity indices (HI, CI), heart V30, left lung V20, and mean doses to surrounding structures. To assess clinical application, the IMRT plans with 11 beams equally spaced in a 190° sector angle were compared to conventional plans. Treatment times were modeled. The 190° IMRT plans improved PTV HI and CI and reduced mean dose to the heart, lungs, contralateral breast, and total healthy tissue (all p < 0.05) compared to a 240° sector angle. The 11-beam plan significantly improved PTV HI and CI, heart V30, left lung V20, and healthy tissue V5 compared to a 7-beam plan (all p < 0.05). The 11-beam plan reduced heart V30 and left lung V20 (p < 0.05) without compromising PTV coverage, compared to a 9-beam plan. Compared to a conventional plan, the IMRT class solution significantly improved PTV HI and CI (both p < 0.01), heart V30 (p = 0.01), and marginally reduced left lung V20 (p = 0.07) but increased contralateral breast and lung mean dose (p < 0.001) and healthy tissue V5 (p < 0.001). An 11-beam 190° sector angle IMRT technique as a class solution is clinically feasible.     

Helical tomotherapy for radiotherapy in esophageal cancer: a preferred plan with better conformal target coverage and more homogeneous dose distribution.

We compare different radiotherapy techniques-helical tomotherapy (tomotherapy), step-and-shoot IMRT (IMRT), and 3-dimensional conformal radiotherapy (3DCRT)-for patients with mid-distal esophageal carcinoma on the basis of dosimetric analysis. Six patients with locally advanced mid-distal esophageal carcinoma were treated with neoadjuvant chemoradiation followed by surgery. Radiotherapy included 50 Gy to gross planning target volume (PTV) and 45 Gy to elective PTV in 25 fractions. Tomotherapy, IMRT, and 3DCRT plans were generated. Dose-volume histograms (DVHs), homogeneity index (HI), volumes of lung receiving more than 10, 15, or 20 Gy (V(10), V(15), V(20)), and volumes of heart receiving more than 30 or 45 Gy (V(30), V(45)) were determined. Statistical analysis was performed by paired t-tests. By isodose distributions and DVHs, tomotherapy plans showed sharper dose gradients, more conformal coverage, and better HI for both gross and elective PTVs compared with IMRT or 3DCRT plans. Mean V(20) of lung was significantly reduced in tomotherapy plans. However, tomotherapy and IMRT plans resulted in larger V(10) of lung compared to 3DCRT plans. The heart was significantly spared in tomotherapy and IMRT plans compared to 3DCRT plans in terms of V(30) and V(45). We conclude that tomotherapy plans are superior in terms of target conformity, dose homogeneity, and V(20) of lung.     

Inverse-planned, dynamic, multi-beam, intensity-modulated radiation therapy (IMRT): A promising technique when target volume is the left breast and internal mammary lymph nodes

The purpose of this study was to determine the optimum beam number and orientation for inverse-planned, dynamic intensity-modulated radiation therapy (IMRT) for treatment of left-sided breast cancer and internal mammary nodes (IMNs) to improve target coverage while reducing cardiac and ipsilateral lung irradiation. Computed tomography (CT) data was used from 5 patients with left-sided breast cancer in whom the heart was close to the chest wall. The planning target volume (PTV) was the full breast plus ipsilateral IMNs. Two geometric beam arrangements were investigated, 240° and 190° sector angles, and the number of beams was increased from 7 to 9 to 11. Dose comparison metrics included: PTV homogeneity and conformity indices (HI, CI), heart V30, left lung V20, and mean doses to surrounding structures. To assess clinical application, the IMRT plans with 11 beams equally spaced in a 190° sector angle were compared to conventional plans. Treatment times were modeled. The 190° IMRT plans improved PTV HI and CI and reduced mean dose to the heart, lungs, contralateral breast, and total healthy tissue (all p < 0.05) compared to a 240° sector angle. The 11-beam plan significantly improved PTV HI and CI, heart V30, left lung V20, and healthy tissue V5 compared to a 7-beam plan (all p < 0.05). The 11-beam plan reduced heart V30 and left lung V20 (p < 0.05) without compromising PTV coverage, compared to a 9-beam plan. Compared to a conventional plan, the IMRT class solution significantly improved PTV HI and CI (both p < 0.01), heart V30 (p = 0.01), and marginally reduced left lung V20 (p = 0.07) but increased contralateral breast and lung mean dose (p < 0.001) and healthy tissue V5 (p < 0.001). An 11-beam 190° sector angle IMRT technique as a class solution is clinically feasible.     

Treatment and Dosimetric Advantages Between VMAT, IMRT, and Helical TomoTherapy in Prostate Cancer

We investigated the possible treatment and dosimetric advantage of volumetric modulated arc therapy (VMAT) over step-and-shoot intensity-modulated radiation therapy (step-and-hhoot IMRT) and helical tomotherapy (HT). Twelve prostate cancer patients undergoing VMAT to the prostate were included. Three treatment plans (VMAT, step-and-shoot IMRT, HT) were generated for each patient. The doses to clinical target volume and 95% of planning target volume were both ≥78 Gy. Target coverage, conformity index, dose to rectum/bladder, monitor units (MU), treatment time, equivalent uniform dose (EUD), normal tissue complication probability (NTCP) of targets, and rectum/bladder were compared between techniques. HT provided superior conformity and significantly less rectal volume exposed to 65 Gy and 40 Gy, as well as EUD/NTCP of rectum than step-and-shoot IMRT, whereas VMAT had a slight dosimetric advantage over step-and-shoot IMRT. Notably, significantly lower MUs were needed for VMAT (309.7 ± 35.4) and step-and-shoot IMRT (336.1 ± 16.8) than for HT (3368 ± 638.7) (p < 0.001). The treatment time (minutes) was significantly shorter for VMAT (2.6 ± 0.5) than step-and-shoot IMRT (3.8 ± 0.3) and HT (3.8 ± 0.6) (p < 0.001). Dose verification of VMAT using point dose and film dosimetry met the accepted criteria. VMAT and step-and-shoot IMRT have comparable dosimetry, but treatment efficiency is significantly higher for VMAT than for step-and-shoot IMRT and HT.     

Effect of beam arrangement on oral cavity dose in external beam radiotherapy of nasopharyngeal carcinoma

This study compared the oral cavity dose between the routine 7-beam intensity-modulated radiotherapy (IMRT) beam arrangement and 2 other 7-beam IMRT with the conventional radiotherapy beam arrangements in the treatment of nasopharyngeal carcinoma (NPC). Ten NPC patients treated by the 7-beam routine IMRT technique (IMRT-7R) between April 2009 and June 2009 were recruited. Using the same computed tomography data, target information, and dose constraints for all the contoured structures, 2 IMRT plans with alternative beam arrangements (IMRT-7M and IMRT-7P) by avoiding the anterior facial beam and 1 conventional radiotherapy plan (CONRT) were computed using the Pinnacle treatment planning system. Dose-volume histograms were generated for the planning target volumes (PTVs) and oral cavity from which the dose parameters and the conformity index of the PTV were recorded for dosimetric comparisons among the plans with different beam arrangements. The dose distributions to the PTVs were similar among the 3 IMRT beam arrangements, whereas the differences were significant between IMRT-7R and CONRT plans. For the oral cavity dose, the 3 IMRT beam arrangements did not show significant difference. Compared with IMRT-7R, CONRT plan showed a significantly lower mean dose, V30 and V-40, whereas the V-60 was significantly higher. The 2 suggested alternative beam arrangements did not significantly reduce the oral cavity dose. The impact of varying the beam angles in IMRT of NPC did not give noticeable effect on the target and oral cavity. Compared with IMRT, the 2-D conventional radiotherapy irradiated a greater high-dose volume in the oral cavity.     

子宫颈癌术后调强放疗照射野设计的探讨

目的 通过对子宫颈癌调强放疗各种布野方案的比较,探讨符合临床要求的最佳照射方案。方法 对10例子宫颈癌患者采用调强治疗方案,处方剂量为46 Gy,分次量为2 Gy。每位患者做6个不同的治疗计划,分别为5野、7野、9野均分照射,初始入射角度选用0°和180°。分别计算比较靶区的覆盖度、均匀性、适形度各项指标。结果 7野和9野的靶区适形度基本一致,7野的均匀性最好,5野靶区覆盖度也能达到要求,但适形度和均匀度都次于7、9野;9野IMRT计划与5野IMRT计划相比没有减少正常组织的受照剂量,但增加了子野数和照射的总跳数,延长了治疗时间。结论 在子宫颈癌的调强放疗中,综合考虑各种物理和生物因素,建议在设计照射野时尽量选择7野照射。     

Dosimetric comparison of vaginal vault brachytherapy vs applicator-guided stereotactic body radiotherapy with volumetric modulated arc therapy and helical tomotherapy for endometrium cancer patients

We performed this dosimetric study to compare a nonstandard volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) techniques with high-dose rate (HDR) brachytherapy (BRT) plan of vaginal vault in patients with postoperative endometrial cancer (EC). Twelve postoperative patients with early stage EC were included in this study. Three plans were performed for each patient; dosimetric and radiobiological comparisons were made using dose-volume histograms and equivalent dose for determining the planning target volume (PTV) coverages in brachytherapy and external beam radiotherapy, and organs-at-risk (OARs) doses between three different delivery techniques. All the plans achieved adequate dose coverage for PTV; however, the VMAT plan yielded better dose conformity, and the HT plan showed better homogeneity for target volume. With respect to the OARs, the bladder D_2cc was significantly lower in the BRT plan than in the VMAT and HT plans, with the highest bladder D_2cc value being observed in the HT plan. However, no difference was observed in the rectum D_2cc of the three plans. Other major advantages of the BRT plan over the VMAT and HT plans were the relatively lower body integral doses and femoral head doses as well as the fact that the integral doses were significantly lower in the BRT plan than in the VMAT and HT plans. This is the first dosimetric comparison of vaginal vault treatment for EC with BRT, VMAT, and HT plans. Our analyses showed the feasibility of stereotactic body radiotherapy technique as an alternative to HDR-BRT for postoperative management of EC patients.     

Nasopharyngeal carcinoma radiotherapy with hybrid technique

The aim of the study was to investigate the effect of the Hybrid technique which was created by combining of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for the treatment of nasopharyngeal cancer (NPC) patients. 7 to 9 field IMRT, triple arc VMAT, and Hybrid plans were generated for 10 advanced stage NPC patients. The homogeneity index (HI) and the conformity index (CI) of planning target volumes (PTVs) were calculated for each technique to evaluate the plan quality. The techniques were compared in terms of plan quality, sparing of organs at risk (OARs), monitor units (MUs), and delivery time. Hybrid technique significantly improved the target dose homogeneity and the conformity for PTV70 and PTV60 compared to IMRT and VMAT. Hybrid plans significantly reduced the maximum dose of the brainstem sparing compared to the VMAT plans and also improved the sparing of spinal cord compared to IMRT and VMAT. The MUs and the delivery time of Hybrid plans were found to be between values for IMRT and VMAT plans. Hybrid technique can be useful when IMRT and VMAT techniques are not adequate alone in the treatment of NPC patients.     

The effect of the target-organ geometric complexity on the choice of delivery between RapidArc and sliding-window IMRT for nasopharyngeal carcinoma

We attempted to assess the effect of target-organ geometric complexity on the plan quality of sliding-window intensity-modulated radiotherapy (IMRT), double-arc (RA2), and triple-arc (RA3) RapidArc volumetric-modulated arc radiotherapy for nasopharyngeal carcinoma (NPC). Plans for 9-field sliding-window IMRT, RA2, and RA3 were optimized for 36 patients with NPC ranging from T1 to T4 tumors. Initially the patients were divided into 2 groups, with group A representing the most simple early stage (T1 and T2) cases, whereas group B represented the more complex advanced cases (T3 and T4). Evaluation was performed based on target conformity, target dose homogeneity, organ-sparing capability, and delivery efficiency. Based on the plan quality results, a subgroup of advanced cases, group B2, representing the most demanding task was distinguished and reported separately from the rest of the group B cases, B1. Detailed analysis was performed on the anatomic features for each group of cases, so that planners can easily identify the differences between B1 and B2. For the group A cases, RA3 plans were superior to the IMRT plans in terms of organ sparing, whereas target conformity and dose homogeneity were similar. For the group B1 cases, the RA3 plans produced almost equivalent plan quality as the IMRT plans. For the group B2 cases, for most of which large target volumes were adjacent to (5 mm or less) and wrapping around the brain stem, RA2 and RA3 were inferior to the IMRT regarding both target dose homogeneity and conformity. RA2 plans were slightly inferior to IMRT and RA3 plans for most cases. The plan comparison results depend on the target to brain stem distances and the target sizes. The plan quality results together with the anatomic information may allow the evaluation of the 3 treatment options before actual planning.     

Inverse Planning – a Comparative Intersystem and Interpatient Constraint Study

PURPOSE: To compare commercial treatment-planning systems (TPS) for inverse planning (IP) and to assess constraint variations for specific IMRT indications. MATERIAL AND METHODS: For IP, OTP, XiO and BrainSCAN were used and step-and-shoot intensity-modulated radiotherapy (IMRT) delivery was assumed. Based on identical constraints, IP was performed for a prostate, head and neck, brain, and gynecologic case. IMRT plans were compared in terms of conformity/homogeneity, dose-volume histograms (DVHs), and delivery efficiency. For ten patients each of a class of indications, constraint variations were evaluated. RESULTS: IMRT plans were comparable concerning minimum target dose, homogeneity, conformity, and maximum doses to organs at risk. Larger differences were seen in dose gradients outside the target, monitor units, and segment number. Using help structures proved efficient to shape isodoses and to reduce segmentation workload. For IMRT class solutions, IP constraint variations depended on anatomic site. CONCLUSION: IP systems requiring doses as input and having objective functions based on physical parameters had a very similar performance. Constraint templates can be established for a class of IMRT indications.     

Volumetric-modulated arc therapy in postprostatectomy radiotherapy patients: A planning comparison study

The purpose of this study was to compare postprostatectomy planning for volumetric-modulated arc therapy (VMAT) with both single arc (SA) and double arcs (DA) against dynamic sliding window intensity-modulated radiotherapy (IMRT). Ten cases were planned with IMRT, SA VMAT, and DA VMAT. All cases were planned to achieve a minimum dose of 68 Gy to 95% of the planning target volume (PTV) and goals to limit rectal volume >40 Gy to 35% and >65 Gy to 17%, and bladder volumes >40 Gy to 50% and >65 Gy to 25%. Plans were averaged across the 10 patients and compared for mean dose, conformity, homogeneity, rectal and bladder doses, and monitor units. The mean dose to the clinical target volume and PTV was significantly higher (p<0.05) for SA compared with DA or IMRT. The homogeneity index was not significantly different: SA = 0.09; DA = 0.08; and IMRT = 0.07. The rectal V40 was lowest for the DA plan. The rectal V20 was significantly lower (p<0.05) for both the VMAT plans compared with IMRT. There were no significant differences for bladder V40 or rectal and bladder V65. The IMRT plans required 1400 MU compared with 745 for DA and 708 for SA. This study shows that for equivalent dose coverage, SA and DA VMAT plans result in higher mean doses to the clinical target volume and PTV. This greater dose heterogeneity is balanced by improved low-range rectal doses and halving of the monitor units.     

Dosimetric evaluation of automatic and manual plans for early nasopharyngeal carcinoma to radiotherapy

To investigate dosimetric differences and plan qualities between manual plans and automatic plans for nasopharyngeal carcinoma (NPC) in early stage, and provide better options to maximize the benefits. Sixteen cases diagnosed with early NPC were retrospectively investigated. Conventional step and shoot IMRT with 7-fields and full arc volumetric-modulated arc therapy (VMAT) with double arcs were manually generated by experienced planners and automatically generated by Auto-Planning module in Pinnacle³ respectively, such as IMRT manual-planning (mIMRT), IMRT auto-planning (aIMRT), VMAT manual-planning (mVMAT), and VMAT auto-planning (aVMAT) for each patient. Target coverage, organs at risk sparing, monitor units, and planning times were compared and evaluated. All parameters of plans are able to fulfill International Commission on Radiation Units and Measurements repor (ICRU) 83 recommendations. Automatic plans are comparable or superior to manual plans without time-consuming planning process. The CI and HI for PTVs are better in aVMAT when compared with aIMRT and mVMAT, but those are similar between aIMRT and mVMAT. Automatic plans not only have superior dose homogeneity and conformity in PTVs, but also have better sparing for spinal cord or slightly reduce the doses received by other OARs, while the VMAT plans have better sparing for brain stem, especially the aVMAT plans. However, Dmax, V30, and V40 of brain stem are similar between aIMRT and mVMAT without significant difference. The monitor units and planning time for treatment plans have been significantly decreased through automatic planning technique. The automatic VMAT plan has greater clinical advantages and should be recommended to a better option for treating NPC in early stage, while automatic IMRT would be preferentially considered instead of manual VMAT.     

直肠癌术前放疗中三维适形放疗与调强适形放疗的剂量学比较分析

目的 比较三维适形放疗(3D-CRT)与5野、7野调强适形放疗(IMRT)的剂量分布,以探讨IMRT对直肠癌术前放疗的价值。方法 对10例术前新辅助放化疗直肠癌患者,分别设计3D- CRT、5野IMRT、7野IMRT计划,应用剂量体积直方图(DVH),比较3种治疗计划的靶区适形度指数(CI)、不均匀性指数(HI)和正常器官受量。结果 适形度指数(CI)7野IMRT计划＞5野IMRT＞3D- CRT,不均匀性指数(HI)5野IMRT计划＞7野IMRT＞3D- CRT。5野、7野IMRT计划比3D- CRT均可以减少高剂量照射小肠、膀胱、股骨头体积,7野IMRT计划比5野可以减少高剂量照射的骨髓和膀胱的体积。结论 直肠癌术前放疗中IMRT计划在靶区剂量适形度方面均优于3D- CRT计划,对正常组织的保护也存在明显的优势。7野IMRT计划较5野IMRT计划技术有更好的剂量适形度与剂量均匀性。     

Improvement of treatment plans developed with intensity-modulated radiation therapy for concave-shaped head and neck tumors

PURPOSE: To improve dose conformity and normal tissue sparing in patients with concave-shaped head and neck cancers by using tomotherapy and static step-and-shoot intensity-modulated radiation therapy (IMRT) and by comparing results with those of three-dimensional (3D) conformal radiation therapy (CRT) and two-dimensional (2D) radiation therapy. MATERIALS AND METHODS: Treatment planning in 10 patients with concave-shaped head and neck tumors was performed by using tomotherapy and step-and-shoot IMRT, 3D CRT, and 2D techniques. IMRT plans were modified by placing "virtual critical structures" in regions outside the target where hot spots occurred. These modified plans were used for comparison because they provided better dose conformity. Critical structures were the spinal cord, the parotid glands, and the mandible. Comparisons were performed by means of dose-volume histograms, clinical target volume (CTV), target covered by 95% isodose (D(95%)), dose received by 5% of the critical structure volume (D(5%)), maximum dose, mean dose, and normal tissue complication probability for critical structures. RESULTS: Original IMRT plans showed more conformal dose distributions than those in 3D CRT and 2D plans. However, hot spots developed in the posterior and anterior neck. Introduction of virtual critical structures in IMRT plans resulted in removal of these hot spots without affecting target coverage. Modified IMRT plans also demonstrated better CTV coverage than that in 3D CRT and 2D plans. The average D(95%) was 97.3% with tomotherapy, 97.1% with step-and-shoot IMRT, 84.7% with 3D CRT, and 69.4% with 2D techniques. D(5%) for the spinal cord changed from approximately 45 Gy with 3D plans and 46 Gy with 2D plans to approximately 28 Gy with IMRT. CONCLUSION: IMRT demonstrated better target coverage and sparing of critical structures than that of 3D CRT and 2D techniques. Use of virtual critical structures resulted in removal of hot spots around the spinal cord.