A clinical application of an automated phantom-film QA procedure for validation of IMRT treatment planning and delivery

To quantify the correlation between planned and delivered intensity-modulated radiation therapy (IMRT) dose distributions, IMRT plans for 37 prostate carcinoma patients were analyzed. IMRT treatment plans were converted into hybrid phantom plans using a commercially available treatment planning system and delivered to a specialized film phantom via a static-tomotherapy technique. The films were analyzed using a commercial film dosimetry system. Hybrid phantom axial dose maps and film images were normalized, registered to one another, and subtracted to calculate the overall relative dose difference throughout the entire film area on a pixel-by-pixel basis. The average percentage of pixels with dose-difference values greater than ± 3% among analyzed hybrid patient plans was 8.6% ± 3%. The average percentage of pixels with dose differences greater than ± 5% was 1.7% ± 1.0%. The number of pixels with more than ± 10% dose differences was negligible. An initial subset of hybrid plans was used to develop a quantitative criterion to verify for positional accuracy based on dosimetric verification of intensity map of IMRT plans for prostate patients in our institution. Plans with less than 5% of the pixels outside the ± 5% dose-difference range were accepted. This method could be implemented for other anatomical sites or treatment planning and delivery systems. © 2003 American Association of Medical Dosimetrists.     

A clinical application of an automated phantom-film QA procedure for validation of IMRT treatment planning and delivery

To quantify the correlation between planned and delivered intensity-modulated radiation therapy (IMRT) dose distributions, IMRT plans for 37 prostate carcinoma patients were analyzed. IMRT treatment plans were converted into hybrid phantom plans using a commercially available treatment planning system and delivered to a specialized film phantom via a static-tomotherapy technique. The films were analyzed using a commercial film dosimetry system. Hybrid phantom axial dose maps and film images were normalized, registered to one another, and subtracted to calculate the overall relative dose difference throughout the entire film area on a pixel-by-pixel basis. The average percentage of pixels with dose-difference values greater than ± 3% among analyzed hybrid patient plans was 8.6% ± 3%. The average percentage of pixels with dose differences greater than ± 5% was 1.7% ± 1.0%. The number of pixels with more than ± 10% dose differences was negligible. An initial subset of hybrid plans was used to develop a quantitative criterion to verify for positional accuracy based on dosimetric verification of intensity map of IMRT plans for prostate patients in our institution. Plans with less than 5% of the pixels outside the ± 5% dose-difference range were accepted. This method could be implemented for other anatomical sites or treatment planning and delivery systems. © 2003 American Association of Medical Dosimetrists.     

Treatment planning and dosimetry of a multi-axis dynamic arc technique for prostate cancer: A comparison with IMRT

Purpose Intensity-modulated radiation therapy (IMRT) allows greater dose conformity to the tumor target. However, IMRT, especially static delivery, usually requires more time to deliver a dose fraction than conventional external beam radiotherapy (EBRT). The authors have been using a “two-axis dynamic arc therapy” (2A-DAT) technique for prostate cancer treatment to make a concave dose distribution to spare the rectum and bladder while working with limited time and human resources. The objectives of this study were to (1) clinically implement the 2A-DAT technique, (2) evaluate the dosimetry in comparison with IMRT, and (3) analyze the initial treatment outcome. Materials and Methods The 2A-DAT consists of two dynamic arc therapies (DATs) with half rotation around two isocenters each in two separate symmetrical rhombi. Treatment planning is forward and on a trial-and-error basis. Thirty-four patients received 2A-DAT with a median prescribed dose of 70 Gy. Results Although inferior in dose uniformity, the 2A-DAT provided equivalent sparing of normal structures to IMRT. Daily fraction delivery time for the 34 patients ranged from 6.4 to 9.6 minutes, with an average of 7.4 minutes. Five-year survival and five-year prostate specific autigen (PSA) failure-free survival were 89.3% and 79.5%, respectively. Three patients developed grade 2 procitis. Conclusion This technique is a possible alternative to IMRT in EBRT of prostate cancer This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (C) 2002, and was presented at the 4th Shinji Takahashi Memorial International Workshop on 3D-CRT.     

A planning study of simultaneous integrated boost with forward IMRT for multiple brain metastases

The objective of this study was to evaluate the dose conformity and feasibility of whole-brain radiotherapy with a simultaneous integrated boost by forward intensity-modulated radiation therapy in patients with 1 to 3 brain metastases. Forward intensity-modulated radiation therapy plans were generated for 10 patients with 1 to 3 brain metastases on Pinnacle 6.2 Treatment Planning System. The prescribed dose was 30 Gy to the whole brain (planning target volume [PTV]_wbrt) and 40 Gy to individual brain metastases (PTV_boost) simultaneously, and both doses were given in 10 fractions. The maximum diameters of individual brain metastases ranged from 1.6 to 6 cm, and the summated PTVs per patient ranged from 1.62 to 69.81 cm³. Conformity and feasibility were evaluated regarding conformation number and treatment delivery time. One hundred percent volume of the PTV_boost received at least 95% of the prescribed dose in all cases. The maximum doses were less than 110% of the prescribed dose to the PTV_boost, and all of the hot spots were within the PTV_boost. The volume of the PTV_wbrt that received at least 95% of the prescribed dose ranged from 99.2% to 100%. The mean values of conformation number were 0.682. The mean treatment delivery time was 2.79 minutes. Ten beams were used on an average in these plans. Whole-brain radiotherapy with a simultaneous integrated boost by forward intensity-modulated radiation therapy in 1 to 3 brain metastases is feasible, and treatment delivery time is short.     

A case study of radiotherapy planning for a bilateral metal hip prosthesis prostate cancer patient.

The purpose of this report is to communicate the observed advantage of intensity-modulated radiotherapy (IMRT) in a patient with bilateral metallic hip prostheses. In this patient with early-stage low-risk disease, a dose of 74 Gy was planned in two phases--an initial 50 Gy to the prostate and seminal vesicles and an additional 24 Gy to the prostate alone. Each coplanar beam avoided the prosthesis in the beam's eye view. Using the same target expansions for each phase, IMRT and 3D-conformal radiotherapy (CRT) plans were compared for target coverage and inhomogeneity as well as dose to the bladder and rectum. The results of the analysis demonstrated that IMRT provided superior target coverage with reduced dose to normal tissues for both individual phases of the treatment plan as well as for the composite treatment plan. The dose to the rectum was significantly reduced with the IMRT technique, with a composite V 80 of 35% for the IMRT plan versus 70% for 3D-CRT plan. Similarly, the dose to the bladder was significantly reduced with a V 80 of 9% versus 20%. Overall, various dosimetric parameters revealed the corresponding 3D-CRT plan would not have been acceptable. The results indicate significant success with IMRT in a clinical scenario where there were no curative alternatives for local treatment other than external beam radiotherapy. Therefore, definitive external beam radiation of prostate cancer patients with bilateral prosthesis is made feasible with IMRT. The work described herein may also have applicability to other groups of patients, such as those with gynecological or other pelvic malignancies.     

Advantages and limitations of navigation-based multicriteria optimization (MCO) for localized prostate cancer IMRT planning

Efficacy of inverse planning is becoming increasingly important for advanced radiotherapy techniques. This study’s aims were to validate multicriteria optimization (MCO) in RayStation (v2.4, RaySearch Laboratories, Sweden) against standard intensity-modulated radiation therapy (IMRT) optimization in Oncentra (v4.1, Nucletron BV, the Netherlands) and characterize dose differences due to conversion of navigated MCO plans into deliverable multileaf collimator apertures. Step-and-shoot IMRT plans were created for 10 patients with localized prostate cancer using both standard optimization and MCO. Acceptable standard IMRT plans with minimal average rectal dose were chosen for comparison with deliverable MCO plans. The trade-off was, for the MCO plans, managed through a user interface that permits continuous navigation between fluence-based plans. Navigated MCO plans were made deliverable at incremental steps along a trajectory between maximal target homogeneity and maximal rectal sparing. Dosimetric differences between navigated and deliverable MCO plans were also quantified. MCO plans, chosen as acceptable under navigated and deliverable conditions resulted in similar rectal sparing compared with standard optimization (33.7 ± 1.8 Gy vs 35.5 ± 4.2 Gy, p = 0.117). The dose differences between navigated and deliverable MCO plans increased as higher priority was placed on rectal avoidance. If the best possible deliverable MCO was chosen, a significant reduction in rectal dose was observed in comparison with standard optimization (30.6 ± 1.4 Gy vs 35.5 ± 4.2 Gy, p = 0.047). Improvements were, however, to some extent, at the expense of less conformal dose distributions, which resulted in significantly higher doses to the bladder for 2 of the 3 tolerance levels. In conclusion, similar IMRT plans can be created for patients with prostate cancer using MCO compared with standard optimization. Limitations exist within MCO regarding conversion of navigated plans to deliverable apertures, particularly for plans that emphasize avoidance of critical structures. Minimizing these differences would result in better quality treatments for patients with prostate cancer who were treated with radiotherapy using MCO plans.     

Azygography in the study of malignant tumours of the oesophagus (author's transl)]

Up to the present time, no simple method has existed for gauging the true size of an oesophageal tumour. The intimate relations between the azygos vein and the oesophagus in the thorax between D3 and D8 justifies this new study: azygography. On the basis of 40 examinations, 13 of which were followed by surgery in patients suffering from carcinoma of the oesophagus, as was indicated by classical anatomical data, azygography made possible the evaluation of tumour extension in the mediastinum and the involvement of adjacent structures, such as the right pulmonary artery. Azygography thus aided in the precision of surgical indications and in the delineation of the volume to be irradiated. The examination is carried out by selective opacification after catheterisation via the femoral vein. Radiological findings distinguish involvement by deviation, compression, invasion, obstruction and collateral circulation. In certain cases a part of the tumour itself is opacifield by vessels with an anarchic pattern. Comparison of the results of radiological study with surgical findings shows that the examination makes it possible to predict, between the level of the third and eighth thoracic vertebrae, difficulties in or impossibility of dissection of the tumour as well as, in the case of involvement of the arch, the necessity for total oesophagectomy with additional cervical approach. The accuracy of the information obtained is certainly less valuable as far as the lower third is concerned. Non-traumatic, simple and rapid, azygography would appear to be the examination of choice in defining the exent of a tumour of the middle third of the oesophagus, as a complement to clinical findings and barium swallow, being particularly valuable in determining the volume to be irradiated or on a pre-operative assessment.     

Maximizing dosimetric benefits of IMRT in the treatment of localized prostate cancer through multicriteria optimization planning

We examine the quality of plans created using multicriteria optimization (MCO) treatment planning in intensity-modulated radiation therapy (IMRT) in treatment of localized prostate cancer. Nine random cases of patients receiving IMRT to the prostate were selected. Each case was associated with a clinically approved plan created using Corvus. The cases were replanned using MCO-based planning in RayStation. Dose-volume histogram data from both planning systems were presented to 2 radiation oncologists in a blinded evaluation, and were compared at a number of dose-volume points. Both physicians rated all 9 MCO plans as superior to the clinically approved plans (p<10^?5). Target coverage was equivalent (p = 0.81). Maximum doses to the prostate and bladder and the V50 and V70 to the anterior rectum were reduced in all MCO plans (p<0.05). Treatment planning time with MCO took approximately 60 minutes per case. MCO-based planning for prostate IMRT is efficient and produces high-quality plans with good target homogeneity and sparing of the anterior rectum, bladder, and femoral heads, without sacrificing target coverage.     

Utilization of a commercial prostate brachytherapy planning system for 3D treatment planning of ophthalmic tumors.

The 3D brachytherapy transperineal ultrasound implant (B3DTUI) program by the Multimedia Medical System has been adopted for eye plaque treatment planning. The post op CT digitization option was selected to enter the actual seed coordinates present in the eye plaque. Although the B3DTUI algorithm is designated to calculate a permanent dose values, the described procedure allows determination of the dose distribution as the dose rate values. The dose computation program utilizes updated source quantities recommended by the AAPM TG-43 formalism, such as air kerma strength, dose rate constant, radial dose function, and anisortopy factor function. As a result, more accurate dose distribution in the target is obtained than by using traditional dose computation formalism.     

Investigation for decrease of delivery time for the prostate cancer patient by modifications of treatment planning parameters in TomoTherapy planning station

The purpose of present study is to investigate the decrease of delivery time for prostate cancer patient by using the helical type accelerator, Hi-Art System. The delivery time for Hi-Art System depends on planning parameters [pitch, modulation factor (MF) and field width (FW)], which are set by the operator at the beginning of the treatment planning. If you can allow for the deterioration of the dose distribution, the delivery time is able to decrease by increasing of FW and/or by decreasing of MF. On the other hands, as the use of 5.0 cm FW tends to increase the dose for the penile bulb, enough consideration for the dose distribution is needed. In addition, pitch should be set for the gantry rotation period not to become 15 s or less to prevent the increase of delivery time.     

A systematic benchmark method for analysis and comparison of IMRT treatment planning algorithms

Tools and procedures for evaluating and comparing different intensity-modulated radiation therapy (IMRT) systems are presented. IMRT is increasingly in demand and there are numerous systems available commercially. These programs introduce significantly different software to dosimetrists and physicists than conventional planning systems, and the options often seem initially overwhelmingly complex to the user. By creating geometric target volumes and critical normal tissues, the characteristics of the algorithms may be investigated, and the influence of the different parameters explored. Overall optimization strategies of the algorithm may be characterized by treating a square target volume (TV) with 2 perpendicular beams, with and without heterogeneities. A half-donut (hemi-annulus) TV with a “donut hole” (central cylinder) critical normal tissue (CNT) on a CT of a simulated quality assurance phantom is suggested as a good geometry to explore the IMRT algorithm parameters. Using this geometry, the order of varying parameters is suggested. First is to determine the effects of the number of stratifications of optimized intensity fluence on the resulting dose distribution, and selecting a fixed number of stratifications for further studies. To characterize the dose distributions, a dose-homogeneity index (DHI) is defined as the ratio of the dose received by 90% of the volume to the minimum dose received by the “hottest” 10% of the volume. The next step is to explore the effects of priority and penalty on both the TV and the CNT. Then, choosing and fixing these parameters, the effects of varying the number of beams can be looked at. As well as evaluating the dose distributions (and DHI), the number of subfields and the number of monitor units required for different numbers of stratifications and beams can be evaluated.     

故障模式和效应分析与故障树分析方法在调强放射治疗计划设计流程中的应用

目的 运用故障模式和效应分析（failure modes and effects analysis,FMEA）与故障树分析（failure tree analysis,FTA）对调强放射治疗（intensity modulated radiotherapy,IMRT）计划设计流程进行风险评估,优化和完善质量管理方案。方法 对运用Eclipse计划系统设计IMRT计划的工作流程建立流程图。根据流程图进行FMEA分析,对每个故障模型（failure modes,FM）进行定量评估得出O、S、D值,相乘得到风险优先系数（risk priority number,RPN）。然后按照是否执行质量管理措施（quality management,QM）分为两组进行评估,并按照RPN值大小排序。最后对排序靠前的高危步骤进行FTA分析。结果 研究得出IMRT计划设计流程图,可分为10个主过程,33个子过程。FMEA分析后得出47个FM模型,未执行QM评估组中FM模型的RPN值范围为13.2~271.8,其中有27个FM模型RPN ≥ 80,18个FM模型S ≥ 8。执行QM评估组FM模型RPN值范围为11.2~158.4,其中有11个FM模型RPN ≥ 80。对执行QM评估组（101.17±66.34）和未执行QM评估组（59.54±35.64）的RPN值比较差异有统计学意义（t=8.501,P<0.05）。RPN值排序前25%的FM模型为处方剂量定义错误、计算参数设置错误、影像导入错误、计划评估确认错误等。最后对定义处方剂量和导入影像这两个高危步骤进行FTA分析。结论 FMEA和FTA分析方法具有可操作性和实用性,能够系统全面地分析IMRT计划设计流程中存在的潜在故障和风险,可帮助建立和优化放射治疗中的质量管理规范。     

A dosimetric comparison of RapidArc and IMRT with hypofractionated simultaneous integrated boost to the prostate for treatment of prostate cancer

Objective:

To compare the dosimetric results and treatment delivery efficiency among RapidArc® (Varian Medical Systems, Palo Alto, CA), 7-field intensity-modulated radiotherapy (7-f IMRT) and 9-field IMRT (9-f IMRT) with hypofractionated simultaneous integrated boost to the prostate.

Methods:

RapidArc, 7-f IMRT and 9-f IMRT plans were created for 21 consecutive patients treated for high-risk prostate cancer using the Eclipse™ treatment planning system (Varian Medical Systems). All plans were designed to deliver 70.0 Gy in 28 fractions to the prostate planning target volume (PTV) while simultaneously delivering 50.4 Gy in 28 fractions to the pelvic nodal PTV. Target coverage and sparing of organs at risk (OARs) were compared across techniques. The total number of monitor units (MUs) and the treatment time were used to assess treatment delivery efficiency.

Results:

RapidArc resulted in slightly superior conformity and homogeneity of prostate PTV, whereas all plans were comparable with respect to dose to the nodal PTV. Although OARs sparing for RapidArc and 7-f IMRT plans were almost equivalent, 9-f IMRT achieved better sparing of the rectum and bladder than RapidArc and 7-f IMRT. RapidArc provided the highest treatment delivery efficiency with the lowest MUs and shortest treatment time.

Conclusion:

RapidArc resulted in similar OAR sparing to 7-f IMRT, whereas 9-f IMRT provided the best OAR sparing. Treatment delivery efficiency is significantly higher for RapidArc.

Advances in knowledge:

This study validated the feasibility and limitations of RapidArc in the treatment of high-risk prostate cancer with complex pelvic target volumes.Radiotherapy has played an important role in the treatment of locally advanced prostate cancer. Several randomised controlled trials have demonstrated that high-dose radiotherapy improves prostate-specific antigen control, and a recently published meta-analysis [1] showed that high-dose radiotherapy is superior to conventional-dose radiotherapy in preventing biochemical or clinical failure and prostate cancer-specific death. However, dose escalation has been limited by toxicity in conventional techniques. Therefore, prostate cancer is one of the most common tumour sites treated with intensity-modulated radiation therapy (IMRT), which enables the delivery of highly conformal dose distribution to the target while reducing the dose to critical organs. IMRT also has the ability to produce inhomogeneous dose distribution, which allows for simultaneous differential dose delivery to multiple tumour targets (simultaneous integrated boost). Despite the obvious benefits of IMRT, there are some disadvantages. The potential downsides of IMRT include the increased time required for radiotherapy delivery and increased monitor units (MUs) needed compared with conventional three-dimensional conformal radiation therapy.Volumetric-modulated arc therapy (VMAT) is a relatively new rotational radiation therapy technique based on the idea of delivering IMRT with continuous dynamic modulation of the dose rate, field aperture and gantry speed. Compared with IMRT, the potential benefit of VMAT is the increase in delivery efficiency, including a shorter treatment time and a lower number of MUs.Several recent studies have compared VMAT with IMRT for prostate radiotherapy [2–13]. Although shortened treatment time is a common finding, there are inconsistencies in the dosimetric outcome. Many studies considering relatively simple target volumes that included prostate only or prostate with seminal vesicles found that VMAT achieved equal or better normal tissue sparing over IMRT [2,3,5,6,8–10,12]. However, very few studies have focused on more complex pelvic target volumes, including the prostate, seminal vesicles and pelvic lymph nodes [4,7,11,13]. Some of these studies found largely equivalent sparing of organs at risk (OARs) between VMAT and IMRT [7,13]. However, other planning studies have reported contradictory results. Yoo et al [4] noted superior OARs sparing with IMRT to VMAT. Myrehaug et al [11] found VMAT to have no consistent dosimetric advantage over IMRT. Thus, those studies have yielded mixed results. Our study aims to expand such studies to quantitatively evaluate VMAT for prostate cancer cases with complex pelvic target volumes and simultaneous integrated boost techniques.RapidArc® is one of the VMAT techniques implementing the progressive resolution optimisation algorithm in the Eclipse™ planning system by Varian Medical Systems (Palo Alto, CA). In the present study, we compare the performance of RapidArc, 7-field IMRT (7-f IMRT) and 9-field IMRT (9-f IMRT) with hypofractionated simultaneous integrated boost to the prostate for patients with high-risk prostate cancer. This study focused on the evaluation of the dosimetric results and treatment delivery efficiency.     

Toxicity and outcome of pelvic IMRT for node-positive prostate cancer

Background and purpose

This study reports on the treatment techniques, toxicity, and outcome of pelvic intensity-modulated radiotherapy (IMRT) for lymph node-positive prostate cancer (LNPPC, T1-4, c/pN1 cM0).

Patients and methods

Pelvic IMRT to 45–50.4?Gy was applied in 39?cases either after previous surgery of involved lymph nodes (n?=?18) or with a radiation boost to suspicious nodes (n?=?21) with doses of 60–70?Gy, usually combined with androgen deprivation (n?=?37). The prostate and seminal vesicles received 70–74?Gy. In cases of previous prostatectomy, prostatic fossa and remnants of seminal vesicles were given 66–70?Gy. Treatment-related acute and late toxicity was graded according to the RTOG criteria.

Results

Acute radiation-related toxicity higher than ?grade?2 occurred in 2?patients (with the need for urinary catheter/subileus related to adhesions after surgery). Late toxicity was mild (grade 1–2) after a median follow-up of 70?months. Over 50% of the patients reported no late morbidity (grade 0). PSA control and cancer-specific survival reached 67% and 97% at over ?5?years.

Conclusion

Pelvic IMRT after the removal of affected nodes or with a radiation boost to clinically positive nodes led to an acceptable late toxicity (no grade 3/4 events), thus justifying further evaluation of this approach in a larger cohort.     

Treatment planning and delivery of IMRT using 6 and 18 MV photon beams without flattening filter

In light of the increasing use of intensity modulated radiation therapy (IMRT) in modern radiotherapy practice, the use of a flattening filter may no longer be necessary. Commissioning data have been measured for a Varian 23EX linear accelerator with 6 and 18 MV photon energies without a flattening filter. Measurements collected for the commissioning of the linac included percent depth dose curves and profiles for field sizes ranging from 2×2 to 40×40 cm² as defined by the jaws and multileaf collimator. Machine total scatter factors were measured and calculated. Measurements were used to model the unflattened beams with the Pinnacle³ treatment planning system. IMRT plans for prostate, lung, brain and head and neck cancer cases were generated using the flattening filter and flattening filter-free beams. From our results, no difference in the quality of the treatment plans between the flat and unflattened photon beams was noted. There was however a significant decrease in the number of monitor units required for unflattened beam treatment plans due to the increase in linac output—approximately two times and four times higher for the 6 and 18 MV, respectively.     

直肠癌静态调强与容积旋转调强放疗计划的剂量学对比研究

目的 对比研究直肠癌术后患者应用静态调强放疗(IMRT)和容积旋转调强放疗(VMAT)的计划质量、治疗效率和剂量精度,为临床治疗技术的选择提供参考依据.方法 选择10例直肠癌术后调强放疗患者,行CT模拟定位并勾画靶区及危及器官,在同一计划系统上给予相同处方剂量和目标优化条件,分别设计5野IMRT计划和双弧VMAT计划.比较两种计划的靶区(PTV/CTV)受量、适形指数(CI)、均匀指数(HI)、危及器官(OAR)的受量、机器跳数、治疗计划执行时间,以及剂量验证通过率.结果 两种治疗计划均能满足临床剂量要求,VMAT计划的靶区剂量覆盖率略低于IMRT计划.VMAT和IMRT计划的HI分别为0.095和0.101,差异无统计学意义(t=2.61, P>0.05);而IMRT计划的CI(0.737)优于VMAT计划(0.614)(t=4.94, P<0.05),考虑为VMAT计划优化过程中对周围正常组织低剂量区受量限制过于严格,从而造成计划的适形度受到影响.VMAT计划中正常组织如膀胱、股骨头的低剂量区较之IMRT计划均有不同程度增加.VMAT和IMRT计划的平均机器跳数(MUs)分别为599和515(t=4.72, P<0.05),相应的治疗时间分别为201和304 s(t=5.83, P<0.05).使用Delta⁴对两种计划进行验证,γ通过率(选用3%/3 mm标准)分别为VMAT 93.13%和IMRT 96.00%(t=3.75, P<0.05).结论 直肠癌VMAT和IMRT 计划均可满足临床要求,VMAT计划可以显著降低治疗时间,提高治疗效率,但其疗效还需进一步临床评估.