Alternative methods for intensity-modulated radiation therapy inverse planning and dose delivery

A large number of IMRT systems are currently being marketed. Many of these systems appear to be unique, and manufacturers often emphasize design differences as they argue the merits of their particular approach. This paper focuses on highlighting the underlying feature that is intrinsically part of all IMRT systems. On the other hand, major differences often appear at the implementation stage for dose delivery. Such variations are evident because each manufacturer has a unique approach to balancing the issues of treatment time, leakage radiation reaching the patient's total body, aperture approximation of the ideal intensity maps, increasing the angles of approach for the treatment fields, integration of on-line imaging, selection of treatment distance, availability of different photon energies, and overall system complexity (i.e., cost). How these different issues are handled in the process of system design affects the relative advantages and disadvantages that appear in the final product. This paper takes the approach of dividing the various IMRT methods into categories that are divided roughly along the lines of the technique used during dose delivery to approximate the intensity patterns. Other features of each system are included under these sub-sections.     

Spinal cord planning risk volumes for intensity-modulated radiation therapy of head-and-neck cancer

PURPOSE: To assess planning organ at risk volume (PRV) margins of the spinal cord in intensity-modulated radiotherapy (IMRT) of oropharyngeal cancers, by modeling the effect of geometric uncertainties to estimate the probability of the spinal cord receiving a particular dose. METHODS AND MATERIALS: Five patients with oropharyngeal cancer were treated by IMRT with simultaneous doses of 66 Gy (gross disease) and 54 Gy (subclinical disease) in 30 fractions. Spinal cord doses were limited to 45 Gy. The probability, due to random and systematic patient positioning uncertainties (3-mm standard deviation), of the cord receiving a particular dose was determined. The effect of an on-line setup correction protocol was also modeled. RESULTS: The mean probability of a maximum spinal cord dose of 45 Gy was 1%, with a 6-mm PRV margin. The mean probability of a maximum dose exceeding 40 Gy was 37% (range, 13-77%); this probability is reduced with a setup correction protocol. CONCLUSION: A spinal cord PRV generated with a 6-mm margin leads to a 99% probability of maintaining the maximum spinal cord dose below 45 Gy. The application of an on-line setup correction protocol reduces the cord dose by approximately 5 Gy.     

Clinical and financial issues for intensity-modulated radiation therapy delivery

Intensity-modulated radiation therapy (IMRT) is a term applied to a new technology that uses nonuniform radiation beams to achieve conformal dose distributions. This article reviews the use of a commercial system, the Peacock system, which uses a special multileaf collimator (MIMiC) to deliver the dose distribution using arc therapy and segmented fields, similar to a moving strip. Although initially designed for stereotactic radiosurgery, this system has been employed to treat various body sites. More than 300 patients have been treated at our institution in the past 4 years, mainly for cranial, head-and-neck, and prostate tumors. Presently, we treat 40 to 45 patients per day with this technology using two linear accelerators operating with 10 MV and 15 MV x-rays, as Peacock has become a standard therapy procedure. Cases are presented that show the unique ability of IMRT to deliver conformal dose distributions. Why this type of technology can become a standard procedure and why it is cost-effective therapy for both the institution and the patient are discussed.     

Four-dimensional computed tomography-based treatment planning for intensity-modulated radiation therapy and proton therapy for distal esophageal cancer

PURPOSE: To compare three-dimensional (3D) and four-dimensional (4D) computed tomography (CT)-based treatment plans for proton therapy or intensity-modulated radiation therapy (IMRT) for esophageal cancer in terms of doses to the lung, heart, and spinal cord and variations in target coverage and normal tissue sparing. METHODS AND MATERIALS: The IMRT and proton plans for 15 patients with distal esophageal cancer were designed from the 3D average CT scans and then recalculated on 10 4D CT data sets. Dosimetric data were compared for tumor coverage and normal tissue sparing. RESULTS: Compared with IMRT, median lung volumes exposed to 5, 10, and 20 Gy and mean lung dose were reduced by 35.6%, 20.5%, 5.8%, and 5.1 Gy for a two-beam proton plan and by 17.4%, 8.4%, 5%, and 2.9 Gy for a three-beam proton plan. The greater lung sparing in the two-beam proton plan was achieved at the expense of less conformity to the target (conformity index [CI], 1.99) and greater irradiation of the heart (heart-V40, 41.8%) compared with the IMRT plan(CI, 1.55, heart-V40, 35.7%) or the three-beam proton plan (CI, 1.46, heart-V40, 27.7%). Target coverage differed by more than 2% between the 3D and 4D plans for patients with substantial diaphragm motion in the three-beam proton and IMRT plans. The difference in spinal cord maximum dose between 3D and 4D plans could exceed 5 Gy for the proton plans partly owing to variations in stomach gas filling. CONCLUSIONS: Proton therapy provided significantly better sparing of lung than did IMRT. Diaphragm motion and stomach gas-filling must be considered in evaluating target coverage and cord doses.     

Issues in optimization for planning of intensity-modulated radiation therapy

The clinical use of intensity-modulated radiation therapy (IMRT) is expanding rapidly in academic and, more recently, in community-based radiotherapy centers due to a high level of clinician interest, improving reimbursement patterns, and the availability of the tools required to plan and deliver IMRT plans. These tools include inverse planning optimization algorithms and linear accelerator control systems with automated, multifield delivery capabilities. The hazards of this new technology are due primarily to the nonintuitive nature of the inverse planning process and the highly complex methods of delivery required for IMRT dose delivery. Important efforts are being made to define the required quality assurance for these computer-optimized IMRT plans and to find ways to reduce their complexity without reducing the quality of the resulting plans. By minimizing the complexity of these dose plans, one also minimizes the treatment time and the probability of dose delivery errors. Methods of optimization and evaluation of dose plans and practical considerations in inverse planning are discussed. In addition, this article points out the potential hazards of inverse-planned IMRT and discusses methods by which the complexity of these plans might be reduced.     

两种调强放疗计划设计模式的比较

目的分步设计和直接子野优化是设计静态调强放疗计划的两种模式,本研究比较两种计划模式的特点。方法采用两种模式分别设计10例前列腺癌和10例鼻咽癌患者的调强计划。在射野方向和优化条件相同、最终目标函数值相近的前提下,比较两种计划设计模式下的剂量体积直方图(DVH)、靶区和危及器官的剂量、子野数、机器跳数(MU)、以及治疗时间。结果两种计划设计模式制定的计划均满足临床要求,剂量分布基本一致,DVH相似。与分步设计模式相比,直接子野优化模式使前列腺癌计划的子野数减少34%,MU减少23%,治疗时间缩短32%(即3.5 min);在鼻咽癌计划中,使总子野数减少59%,但MU增加9%,节省治疗时间49%(即13.8 min)。结论与分步模式相比,直接子野优化模式可显著减少子野数目,缩短治疗时间,降低机器磨损。但该模式MU的变化与治疗部位有关。     

调强放射治疗自动计划技术的研究进展

逆向调强放疗（intensity-modulated radiation therapy,IMRT）技术在保证靶区接收足够照射剂量的同时极大地降低了正常组织的受照剂量。在IMRT治疗计划的设计过程中,需要进行多次尝试与优化才能在提高靶区覆盖率与减少正常组织受照剂量的矛盾中找到平衡点。这种常规的计划设计过程十分繁杂,而且很大程度上依赖于设计者自身的经验,缺乏统一的规范和评判标准。因此,如果可以在复杂的优化过程之前就利用某些方法（例如自动计划算法）预测出最终的计划结果,将会提高计划的设计效率和质量。该研究将对放射治疗中自动计划技术的研究进展做一综述。     

In vivo measurements with MOSFET detectors in oropharynx and nasopharynx intensity-modulated radiation therapy

PURPOSE: To evaluate the feasibility of in vivo measurements with metal oxide semiconductor field effect transistor (MOSFET) dosimeters for oropharynx and nasopharynx intensity-modulated radiation therapy (IMRT). METHODS AND MATERIALS: During a 1-year period, in vivo measurements of the dose delivered to one or two points of the oral cavity by IMRT were obtained with MOSFET dosimeters. Measurements were obtained during each session of 48 treatment plans for 21 patients, all of whom were fitted with a custom-made mouth plate. Calculated and measured values were compared. RESULTS: A total of 344 and 452 measurements were performed for the right and left sides, respectively, of the oral cavity. Seventy percent of the discrepancies between calculated and measured values were within +/-5%. Uncertainties were due to interfraction patient positions, intrafraction patient movements, and interfraction MOSFET positions. Nevertheless, the discrepancies between the measured and calculated means were within +/-5% for 92% and 95% of the right and left sides, respectively. Comparison of these discrepancies and the discrepancies between calculated values and measurements made on a phantom revealed that all differences were within +/-5%. CONCLUSION: Our experience demonstrates the feasibility of in vivo measurements with MOSFET dosimeters for oropharynx and nasopharynx IMRT.     

调强放疗与三维适型放疗同步化疗治疗宫颈癌的临床疗效比较

目的探讨调强放射治疗(IMRT)与三维适型放疗(3D-CRT)联合同步化疗治疗子宫颈癌的临床疗效。方法选取2012年5月至2014年5月间深圳市人民医院收治的105例Ⅱb～Ⅲb期子宫颈癌患者,根据放疗方式不同分为观察组53例和对照组52例。观察组患者采用IMRT联合含顺铂同步化疗的治疗方式,对照组患者采用3D-CRT联合含顺铂同步化疗,比较两组患者治疗后缓解率、不良反应及5年复发率。结果治疗后,观察组患者缓解率为96. 2%,对照组为94. 2%,两组比较,差异无统计学意义(P>0. 05)。治疗后,两组患者均出现不同程度的白细胞下降、贫血、血小板下降、恶心、呕吐、放射性膀胱炎和放射性直肠炎等不良反应,观察组患者白细胞下降、放射性膀胱炎及放射性直肠炎发生率均低于对照组,差异均有统计学意义(均P <0. 05)。治疗后,观察组患者5年内总复发率为17. 0%,对照组为38. 5%,观察组低于对照组,差异有统计学意义(P <0. 05)。结论IMRT联合同步化疗治疗子宫颈癌患者,可降低白细胞下降、放射性膀胱炎及放射性直肠炎等不良反应发生率,降低5年局部复发率,提高患者5年内生存质量。     

Role of intensity-modulated radiation therapy in gastrointestinal cancer

Intensity-modulated radiation therapy (IMRT) represents a powerful advance in the planning and delivery of radiation therapy owing to its ability to deliver highly conformal treatment doses while sparing normal tissues. Dosimetric studies have shown the feasibility and theoretical benefit of treating with IMRT over 3D-conformal radiation therapy in gastrointestinal malignancies. Early clinical experience with IMRT in the treatment of gastric, pancreatic, rectal and anal cancers corroborates the dosimetric analyses, with some series reporting lower normal tissue toxicities. This article reviews the radiobiological, physical, technical and clinical aspects of IMRT for gastric, pancreatic, rectal and anal cancer, and summarizes the dosimetric and outcome studies to date.     

肝脏肿瘤不同调强放疗计划的剂量学对比

目的:应用放射治疗计划系统比较四种肝癌动态调强放疗计划的靶区及肝组织的剂量学分布,探讨最佳的布野模式.方法:共研究15例行调强放疗的肝脏肿瘤患者,对每例患者分别制定两种共面野计划和两种非共面野计划.评估的剂量学参数包括:PTV的适形指数(CI)和均匀指数(HI),正常肝脏接受≥40、30、20、10体积的百分数(V40、V30 、V20、V10),正常肝脏的平均剂量(MDTNL)以及脊髓和肾脏的剂量分布.结果:非共面野调强计划相对于共面调强计划而言,可在不影响靶区剂量分布的情况下,明显降低正常肝脏组织的平均剂量,对肝脏的V10、V20、V30具有明显优势,而对肝脏V40,脊髓和肾脏的剂量分布无明显影响.结论:在肝脏肿瘤的放射治疗过程中,非共面野调强计划可能在减少肝组织的受照剂量,降低放射性肝病发生的危险性上具有一定优势.     

Treatment planning for conformal proton radiation therapy

Clinical results from various trials have demonstrated the viability of protons in radiation therapy and radiosurgery. This has motivated a few large medical centers to design and build expensive hospital based proton facilities based proton facilities (current cost estimates for a proton facility is around 100 million US dollars). Until this development proton therapy was done using retrofitted equipment originally designed for nuclear experiments. There are presently only three active proton therapy centers in the United States, 22 worldwide. However, more centers are under construction and being proposed in the US and abroad. The important difference between proton and x-ray therapy is in the dose distribution. X-rays deposit most of their dose at shallow depths of a few centimeters with a gradual decay with depth in the patient. Protons deliver most of their dose in the Bragg peak, which can be delivered at most clinically required depths followed by a sharp fall-off. This sharp falloff makes protons sensitive to variations in treatment depths within patients. Treatment planning incorporates all the knowledge of protons into a process, which allows patients to be treated accurately and reliably. This process includes patient immobilization, imaging, targeting, and modeling of planned dose distributions. Although the principles are similar to x-ray therapy some significant differences exist in the planning process, which described in this paper. Target dose conformality has recently taken on much momentum with the advent of intensity modulated radiation therapy (IMRT) with photon beams. Proton treatments provide a viable alternative to IMRT because they are inherently conformal avoiding normal tissue while irradiating the intended targets. Proton therapy will soon bring conformality to a new high with the development of intensity modulated proton therapy (IMPT). Future challenges include keeping the cost down, increasing access to conventional proton therapy as well as the clinical implementation of IMPT. Computing advances are making Monte Carlo techniques more accessible to treatment planning for all modalities including proton therapy. This technique will allow complex delivery configurations to be properly modeled in a clinical setting.     

Disease-control rates following intensity-modulated radiation therapy for small primary oropharyngeal carcinoma

BACKGROUND: The purpose of this study was to assess the ability of intensity-modulated radiation therapy (IMRT) to achieve favorable disease-control rates while minimizing parotid gland doses in patients treated for small primary tumors of the oropharynx. METHODS AND MATERIALS: We retrospectively identified all patients who received IMRT as treatment for a small (<4 cm) primary tumor of the oropharynx between October 2000 and June 2002. Tumor characteristics, IMRT parameters, and patient outcomes were assessed. RESULTS: Fifty-one patients met the criteria for our study. All patients had treatment to gross disease with margin (CTV1), and all but 1 had treatment to the bilateral necks. The most common treatment schedule (39 patients) was a once-daily fractionation of prescribed doses of 63-66 Gy to the CTV1 and 54 Gy to subclinical sites, delivered in 30 fractions. Twenty-one patients (40%) had gastrostomy tubes placed during therapy; in 4 patients, the tube remained in place for more than 6 months after completion of IMRT. The median follow-up was 45 months. The 2-year actuarial locoregional control, recurrence-free, and overall survival rates were 94%, 88%, and 94%, respectively. CONCLUSIONS: These preliminary data suggest that treatment with IMRT results in favorable locoregional control of small primary oropharynx tumors. IMRT did not appear to have a more favorable acute toxicity profile in this group with respect to the use of a feeding tube; however, the mean dose of radiation delivered to the parotid gland by IMRT was decreased, because 95% of patients had a mean dose of <30 Gy to at least one gland.     

41例局部晚期不可手术胰腺癌三维适形或调强放疗的临床分析

目的 分析局部晚期胰腺癌以放疗为主的治疗结果.方法 搜集2007年12月前近8年初治局部晚期胰腺癌临床资料,共1例,均为2002AJCC分期Ⅲ期.采用三维适形或调强放疗,单纯放疗11例,同步放化疗30例.结果 全组中位生存时间和1年总生存率分别为9.2个月和23%.疗前KPS评分≥80、无区域淋巴结转移和放疗后达完全缓解或部分缓解者提示可获得更好生存期,其中位生存时间分别为11.1个月:5.8个月(χ2=7.50,P=0.006)、10.8个月:6.5个月(χ2=5.67,P=0.017)和19.5个月:9.1个月(χ2=7.28,P=0.007).同步化疗的加入较单纯放疗有提高生存的趋势(χ2=3.25,P=0.072).放疗末总临床获益者18例,主要为腹痛缓解17例(41%).无4级血液学毒性及3级非血液学毒性发生.结论 三维适形或调强放疗局部晚期胰腺癌副反应低,可提高临床获益.疗前KPS较高、无区域淋巴结转移和疗后达完全缓解或部分缓解者可望获得较好疗效,加同步化疗有提高生存率趋势.