Retrospective evaluation of pediatric cranio-spinal axis irradiation plans with the Hi-ART tomotherapy system

Helical tomotherapy (HT) can be used for the delivery of cranio-spinal axis irradiation (CSAI) without the need for beam matching of conventional linac-based external beam irradiation. The aim of this study is to retrospectively evaluate HT plans used for treatment in nine patients treated with CSAI. Helical tomotherapy cranio-spinal axis irradiation (HT-CSAI) plans were created for each patient. Average length along the cranio-spinal axis of the PTV was 65.6 cm with a range between 53 and 74 cm. Treatment planning optimization and plan evaluation parameters were obtained from the HT planning station for each of the nine patients. PTV coverage by the 95% isodose surface ranged between 98.0 to 100.0% for all nine patients. The clinically acceptable dose variation within the PTV or tolerance range was between 0.7 and 2.5% for all nine patients. Doses to the organs at risk were clinically acceptable. An increasing length along the longitudinal axis of the PTV did not consistently increase the beam-on time indicating that using a larger jaw width had a greater impact on treatment time. With a larger jaw width it is possible to substantially reduce the normalized beam-on treatment time without compromising plan quality and sparing of organs at risk. By using a larger jaw width or lower modulation factor or both, normalized beam-on times were decreased by up to 61% as compared to the other evaluated treatment plans. From the nine cases reported in this study the minimum beam-on time was achieved with a jaw width of 5.0 cm, pitch of 0.287 and a modulation factor of 2.0. Large and long cylindrical volumes can be effectively treated with helical tomotherapy with both clinically acceptable dose distribution and beam-on time.     

Helical tomotherapy for parotid gland tumors

PURPOSE: To investigate helical tomotherapy (HT) intensity-modulated radiotherapy (IMRT) as a postoperative treatment for parotid gland tumors. METHODS AND MATERIALS: Helical tomotherapy plans were developed for 4 patients previously treated with segmental multileaf collimator (SMLC) IMRT. A primary planning target volume (PTV64) and two secondary PTVs (PTV60, PTV54) were defined. The clinical goals from the SMLC plans were applied as closely as possible to the HT planning. The SMLC plans included bolus, whereas HT plans did not. RESULTS: In general, the HT plans showed better target coverage and target dose homogeneity. The minimum doses to the desired coverage volume were greater, on average, in the HT plans for all the targets. Minimum PTV doses were larger, on average, in the HT plans by 4.6 Gy (p = 0.03), 4.8 Gy (p = 0.06), and 4.9 Gy (p = 0.06) for PTV64, PTV60, and PTV54, respectively. Maximum PTV doses were smaller, on average, by 2.9 Gy (p = 0.23), 3.2 Gy (p = 0.02), and 3.6 Gy (p = 0.03) for PTV64, PTV60, and PTV54, respectively. Average dose homogeneity index was statistically smaller in the HT plans, and conformity index was larger for PTV64 in 3 patients. Tumor control probabilities were higher for 3 of the 4 patients. Sparing of normal structures was comparable for the two techniques. There were no significant differences between the normal tissue complication probabilities for the HT and SMLC plans. CONCLUSIONS: Helical tomotherapy treatment plans were comparable to or slightly better than SMLC plans. Helical tomotherapy is an effective alternative to SMLC IMRT for treatment of parotid tumors.     

Dose–volume and biological-model based comparison between helical tomotherapy and (inverse-planned) IMAT for prostate tumours

BACKGROUND AND PURPOSE: Helical tomotherapy (HT) and intensity-modulated arc therapy (IMAT) are two arc-based approaches to the delivery of intensity-modulated radiotherapy (IMRT). Through plan comparisons we have investigated the potential of IMAT, both with constant (conventional or IMAT-C) and variable (non-conventional or IMAT-NC, a theoretical exercise) dose-rate, to serve as an alternative to helical tomotherapy. MATERIALS AND METHODS: Six patients with prostate tumours treated by HT with a moderately hypo-fractionated protocol, involving a simultaneous integrated boost, were re-planned as IMAT treatments. A method for IMAT inverse-planning using a commercial module for static IMRT combined with a multi-leaf collimator (MLC) arc-sequencing was developed. IMAT plans were compared to HT plans in terms of dose statistics and radiobiological indices. RESULTS: Concerning the planning target volume (PTV), the mean doses for all PTVs were similar for HT and IMAT-C plans with minimum dose, target coverage, equivalent uniform dose (EUD) and tumour control probability (TCP) values being generally higher for HT; maximum dose and degree of heterogeneity were instead higher for IMAT-C. In relation to organs at risk, mean doses and normal tissue complication probability (NTCP) values were similar between the two modalities, except for the penile bulb where IMAT was significantly better. Re-normalizing all plans to the same rectal toxicity (NTCP=5%), the HT modality yielded higher TCP than IMAT-C but there was no significant difference between HT and IMAT-NC. The integral dose with HT was higher than that for IMAT. CONCLUSIONS: with regards to the plan analysis, the HT is superior to IMAT-C in terms of target coverage and dose homogeneity within the PTV. Introducing dose-rate variation during arc-rotation, not deliverable with current linac technology, the simulations result in comparable plan indices between (IMAT-NC) and HT.     

Tomotherapeutic stereotactic body radiation therapy: Techniques and comparison between modalities

Presentation and comparison of tomotherapeutic intensity-modulated techniques for planning and delivery of stereotactic body radiation therapy. Serial tomotherapeutic SBRT has been planned and delivered at our institution since 8/2001. Since 12/2005, 12 patients have been treated using a helical tomotherapy unit. For these 12 patients both helical and serial tomotherapy plans were computed and clinically approved. Techniques and considerations of tomotherapy SBRT planning, associated image-guidance, and delivery are presented. The respective treatment plans were compared based on dosimetric parameters as well as time to develop a treatment plan and delivery times. Also the associated quality of megavoltage CT (MVCT) image-guidance inherent to the helical tomotherapy unit was assessed. Tumor volumes averaged 9.3, 9.8, and 58.7 cm3 for liver, lung, and spinal targets. Helical and serial tomotherapy plans showed comparable plan quality with respect to maximum and average doses to the gross tumor and planning target volumes. Time to develop helical tomotherapy plans averaged 3.5 h while serial tomotherapy planning consistently required less than one hour. Treatment delivery was also slower using helical tomotherapy, with differences of less than 10 min between modalities. MVCT image-guidance proved satisfactory for bony and lung targets, but failed to depict liver lesions, owing to poor soft-tissue contrast. SBRT planning and delivery is clinically feasible using either tomotherapeutic modality. While treatment planning time was consistently shorter and more readily accomplished in a standardized approach using the serial tomotherapy modality, actual plan quality and treatment delivery times are grossly comparable between the modalities. MVCT volumetric image-guidance, was observed to be valuable for thoracic and spinal target volumes, whereas it proved challenging for liver targets.     

Dosimetric comparisons of helical tomotherapy treatment plans and step-and-shoot intensity-modulated radiosurgery treatment plans in intracranial stereotactic radiosurgery

PURPOSE: To evaluate dose conformity, dose homogeneity, and dose gradient in helical tomotherapy treatment plans for stereotactic radiosurgery, and compare results with step-and-shoot intensity-modulated radiosurgery (IMRS) treatment plans. METHODS AND MATERIALS: Sixteen patients were selected with a mean tumor size of 14.65 +/- 11.2 cm3. Original step-and-shoot IMRS treatment plans used coplanar fields because of the constraint of the beam stopper. Retrospective step-and-shoot IMRS plans were generated using noncoplanar fields. Helical tomotherapy treatment plans were generated using the tomotherapy planning station. Dose conformity index, dose gradient score index, and homogeneity index were used in plan intercomparisons. RESULTS: Noncoplanar IMRS plans increased dose conformity and dose gradient, but not dose homogeneity, compared with coplanar IMRS plans. Tomotherapy plans increased dose conformity and dose gradient, yet increased dose heterogeneity compared with noncoplanar IMRS plans. The average dose conformity index values were 1.53 +/- 0.38, 1.35 +/- 0.15, and 1.26 +/- 0.10 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The average dose homogeneity index values were 1.15 +/- 0.05, 1.13 +/- 0.04, and 1.18 +/- 0.09 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The mean dose gradient score index values were 1.37 +/- 19.08, 22.32 +/- 19.20, and 43.28 +/- 13.78 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The mean treatment time in tomotherapy was 42 +/- 16 min. CONCLUSIONS: We were able to achieve better dose conformity and dose gradient in tomotherapy plans compared with step-and-shoot IMRS plans for intracranial stereotactic radiosurgery. However, tomotherapy treatment time was significantly larger than that in step-and-shoot IMRS.     

Assessment of extended-field radiotherapy for stage IIIC endometrial cancer using three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and helical tomotherapy

PURPOSE: To perform a dosimetric comparison of three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and helical tomotherapy (HT) plans for pelvic and para-aortic RT in postoperative endometrial cancer patients; and to evaluate the integral dose (ID) received by critical structures within the radiation fields. METHODS AND MATERIALS: We selected 10 patients with Stage IIIC endometrial cancer. For each patient, three plans were created with 3D-CRT, IMRT, and HT. The IMRT and HT plans were both optimized to keep the mean dose to the planning target volume (PTV) the same as that with 3D-CRT. The dosimetry and ID for the critical structures were compared. A paired two-tailed Student t test was used for data analysis. RESULTS: Compared with the 3D-CRT plans, the IMRT plans resulted in lower IDs in the organs at risk (OARs), ranging from -3.49% to -17.59%. The HT plans showed a similar result except that the ID for the bowel increased 0.27%. The IMRT and HT plans both increased the IDs to normal tissue (see Table 1 and text for definition), pelvic bone, and spine (range, 3.31-19.7%). The IMRT and HT dosimetry showed superior PTV coverage and better OAR sparing than the 3D-CRT dosimetry. Compared directly with IMRT, HT showed similar PTV coverage, lower Ids, and a decreased dose to most OARs. CONCLUSION: Intensity-modulated RT and HT appear to achieve excellent PTV coverage and better sparing of OARs, but at the expense of increased IDs to normal tissue and skeleton. HT allows for additional improvement in dosimetry and sparing of most OARs.     

Intensity-modulated radiation therapy (IMRT) dosimetry of the head and neck: a comparison of treatment plans using linear accelerator-based IMRT and helical tomotherapy

PURPOSE: To date, most intensity-modulated radiation therapy (IMRT) delivery has occurred using linear accelerators (linacs), although helical tomotherapy has become commercially available. To quantify the dosimetric difference, we compared linac-based and helical tomotherapy-based treatment plans for IMRT of the oropharynx. METHODS AND MATERIALS: We compared the dosimetry findings of 10 patients who had oropharyngeal carcinoma. Five patients each had cancers in the base of the tongue and tonsil. Each plan was independently optimized using either the CORVUS planning system (Nomos Corporation, Sewickly, PA), commissioned for a Varian 2300 CD linear accelerator (Varian Medical Systems, Palo Alto, CA) with 1-cm multileaf collimator leaves, or helical tomotherapy. The resulting treatment plans were evaluated by comparing the dose-volume histograms, equivalent uniform dose (EUD), dose uniformity, and normal tissue complication probabilities. RESULTS: Helical tomotherapy plans showed improvement of critical structure avoidance and target dose uniformity for all patients. The average equivalent uniform dose reduction for organs at risk (OARs) surrounding the base of tongue and the tonsil were 17.4% and 27.14% respectively. An 80% reduction in normal tissue complication probabilities for the parotid glands was observed in the tomotherapy plans relative to the linac-based plans. The standard deviation of the planning target volume dose was reduced by 71%. In our clinic, we use the combined dose-volume histograms for each class of plans as a reference goal for helical tomotherapy treatment planning optimization. CONCLUSIONS: Helical tomotherapy provides improved dose homogeneity and normal structure dose compared with linac-based IMRT in the treatment of oropharyngeal carcinoma resulting in a reduced risk for complications from focal hotspots within the planning target volume and for the adjacent parotid glands.     

鼻咽癌螺旋断层放疗与常规加速器调强放疗的剂量学比较

目的 通过比较鼻咽癌螺旋断层放疗与常规直线加速器静态调强治疗计划,研究其剂量学特性.方法 选10例鼻咽癌患者的CT图像,统一勾画靶区及正常器官后,分别传输至螺旋断层放疗、常规调强放疗逆向调强计划系统.统一给予肿瘤靶区(pGTV、PTVnd)处方剂量70 Gy分33次,亚临床病灶区(PTV1)60 Gy分33次,预防照射区(PTV2)54 Gy分33次.正常器官限制体积与剂量为腮腺V35＜50%,脑干＜54 Gy,脊髓＜45 Gy,晶体＜9 Gy等.对两组数据进行配对t检验.结果 两组计划均有较好靶区处方剂量分布,但螺旋断层放疗组的均匀性好于常规调强放疗组;PTV1平均剂量(63.84 Gy)也显著低于常规调强放疗组(70.30 Gy);腮腺平均剂量较常规常规调强放疗组低5.3Gy,V30及V35显著低于常规调强放疗组;喉-气管-食管的最大剂量也较常规调强放疗组明显降低.结论 在鼻咽癌调强放疗中,螺旋断层放疗较常规直线加速器静态调强放疗有更好的剂量均匀性及更陡峭的剂量梯度,并可更好地保护正常器官.     

Comparing step-and-shoot IMRT with dynamic helical tomotherapy IMRT plans for head-and-neck cancer

PURPOSE: The goal of this planning study was to compare step-and-shoot intensity-modulated radiotherapy (IMRT) plans with helical dynamic IMRT plans for oropharynx patients on the basis of dose distribution. METHODS AND MATERIALS: Five patients with oropharynx cancer had been previously treated by step-and-shoot IMRT at the University Medical Centre Utrecht, The Netherlands, applying five fields and approximately 60-90 segments. Inverse planning was carried out using Plato, version 2.6.2. For each patient, an inverse IMRT plan was also made using Tomotherapy Hi-Art System, version 2.0, and using the same targets and optimization goals. Statistical analysis was performed by a paired t test. RESULTS: All tomotherapy plans compared favorably with the step-and-shoot plans regarding sparing of the organs at risk and keeping an equivalent target dose homogeneity. Tomotherapy plans in particular realized sharper dose gradients compared with the step-and-shoot plans. The mean dose to all parotid glands (n = 10) decreased on average 6.5 Gy (range, -4 to 14; p = 0.002). The theoretical reduction in normal tissue complication probabilities in favor of the tomotherapy plans depended on the parotid normal tissue complication probability model used (range, -3% to 32%). CONCLUSION: Helical tomotherapy IMRT plans realized sharper dose gradients compared with the clinically applied step-and shoot plans. They are expected to be able to reduce the parotid normal tissue complication probability further, keeping a similar target dose homogeneity.     

ArcCHECK系统在食管癌螺旋断层放疗计划验证中的应用

目的 探讨ArcCHECK系统在食管癌断层治疗旋转照射和固定野照射计划验证中的应用,总结相关经验。方法 对32例不同部位食管癌分别制作Helical旋转照射和Direct固定野照射验证计划,并通过ArcCHECK测量、分析,对比验证结果通过率。分析靶体积与计划验证通过率的相关性。将靶体积较小的治疗验证计划分别放在ArcCHECK模体中心和外周探测点处,分析验证通过率差异。结果 Helical计划验证通过率高于Direct计划(P<0.01),其靶体积与验证通过率的相关系数分别为-0.364和-0.042,P值分别为0.041和0.819。Helical计划采用3%/2mm标准时,高剂量区放在模体中心和外周探测点处测得的通过率不同(P=0.005),后者通过率更高;采用3%/3mm标准时与Direct计划的3%/3m、3%/2mm标准的相近(P均>0.05)。结论 Helical计划验证通过率普遍高于Direct计划,原因可能与ArcCHECK探测器的角度响应以及因更多参考点受到低剂量辐射而未参与计算有关,另外还可能跟Direct计划对断层治疗剂量控制系统要求更高有关。在Helical验证计划中,当采用3%/3mm标准时,靶体积越大,验证时出现较低通过率的可能性增加,但相关系数较低。验证计划的高剂量区位于模体中心或者探测点处都可以实现计划验证,综合考量建议放在模体等中心处。     

乳腺癌保乳术后螺旋断层治疗技术的剂量学研究

目的 研究乳腺癌保乳术后患者应用固定野调强放疗(FF-IMRT)和螺旋断层治疗(HT)计划的剂量学差异。方法 选择10例左侧乳腺癌保乳术后IMRT患者,CT模拟定位、勾画靶区及危及器官,对同一CT图像设计FF-IMRT计划和HT计划。配对t检验两种计划靶区及危及器官剂量分布及照射时间差异。结果 与FF-IMRT计划相比,HT计划的100%PTV覆盖度增加(P=0.000),105%PTV覆盖度降低(P=0.000),平均剂量(D_mean)降低(P=0.002),均匀指数(HI)、适形指数(CI)增加(P=0.001、0.023)。HT计划的患侧肺剂量体积V₅、V₁₀、V₂₀、V₃₀、V₄₀、D_mean分别降低28%、30%、35%、46%、61%、32%(P=0.000),双肺的分别降低30%、28%、34%、46%、62%、26%(P=0.000),心脏的和最大剂量(D_max)分别降低57%、59%、71%、82%、91%、45%和12%(P=0.000~0.002),健侧乳腺D_mean、D_max分别增加0.9、3.0 Gy (P=0.000、0.000),健侧肺的分别增加0.42、2.70 Gy (P=0.000、0.000)。HT计划照射时间明显高于FF-IMRT计划(11.98 min:5.96 min,P=0.000)。结论 左侧如乳腺癌HT计划的靶区均匀性和适形度均优于FF-IMRT计划,危及器官可获得等同于或优于FF-IMRT计划的剂量分布,可作为新照射方式用于乳腺癌保乳术后患者。     

A dosimetric comparison of non-coplanar IMRT versus Helical Tomotherapy for nasal cavity and paranasal sinus cancer.

PURPOSES: To determine if there are clinically significant differences between the dosimetry of sinus tumors delivered by non-coplanar LINAC-based IMRT techniques and Helical Tomotherapy (HT). HT is capable of delivering highly conformal and uniform target dosimetry. However, HT lacks non-coplanar capability, which is commonly used for linear accelerator-based IMRT for nasal cavity and paranasal sinus tumors. METHODS AND MATERIALS: We selected 10 patients with representative early and advanced nasal cavity and paranasal sinus malignancies treated with a preoperative dose of 50 Gy/25 fractions without coverage of the cervical lymphatics for dosimetric comparison. Each plan was independently optimized using either Corvus inverse treatment planning system, commissioned for a Varian 2300 CD linear accelerator with 1cm multileaf collimator (MLC) leaves, or the HT inverse treatment planning system. A non-coplanar seven field technique was used in all Corvus plans with five mid-sagittal fields and two anterior oblique fields as described by Claus et al. [F. Claus, W. De Gersem, C. De Wagter, et al., An implementation strategy for IMRT of ethmoid sinus cancer and bilateral sparing of the optic pathways, Int J Radiat Oncol Biol Phys 51 (2001) 318-331], whereas only coplanar beamlets were used in HT planning. Dose plans were compared using DVHs, the minimum PTV dose to 1cm3 of the PTV, a uniformity index of planned treatment volume (PTV), and a comprehensive quality index (CQI) based on the maximum dose to optical structures, parotids and the brainstem which were deemed as the most critical adjacent structures. RESULTS: Both planning systems showed comparable PTV dose coverage, but HT had significantly higher uniformity (p<0.01) inside the PTV. The CQI for all organs at risk were equivalent except ipsilateral lenses and eyes, which received statistically lower dose from HT plans (p<0.01). CONCLUSIONS: Overall HT provided equivalent or slightly better normal structure avoidance with a more uniform PTV dose for nasal cavity and paranasal sinus cancer treatment than non-coplanar LINAC-based IMRT. The disadvantage of coplanar geometry in HT is apparently counterbalanced by the larger number of fields.     

胸膜间皮瘤螺旋断层调强放疗与两种容积旋转调强放疗计划的剂量学评估

目的 比较螺旋断层调强放疗（helical tomotherapy, HT）和基于两种加速器的容积旋转调强放疗（volumetric modulated arc therapy, VMAT）在恶性胸膜间皮瘤放疗中的剂量学差异。方法 回顾性分析10 例无法手术的胸膜间皮瘤患者CT图像,采用Elekta Synergy（S-VMAT）和Elekta Axesse加速器（A-VMAT）进行VMAT放疗计划以及螺旋断层放疗系统完成HT放疗计划的设计,要求95%的计划靶区（PTV）达到处方剂量60 Gy。 比较3种计划在靶区适形度指数（CI）、均匀性指数（HI）、最大剂量（Dmax）、最小剂量（Dmin）、平均剂量（Dmean）以及危及器官 （OARs）剂量体积参数方面的差异。结果HT计划的Dmax、Dmean显著低于S VMAT和A VMAT（P＜0.001,P=0.002）,而Dmin和CI的差异均无统计学意义（P＞0.05）。此外,HT计划的靶区HI显著优于S-VMAT和A-VMAT （1.04±0.01 vs. 1.11±0.03 vs. 1.09±0.02, P＜0.001）;CI也优于后两者,但差异无统计学意义（0.80±0.07 vs. 0.71±0.12 vs. 0.75±0.08, P＞0.05）。3组计划的OARs剂量体积参数的差异均无统计学意义（P＞0.05）。与HT计划比较,S-VMAT和A-VMAT计划的平均实施时间大幅减少[（11.11±3.75）min vs.（3.27±1.65）min vs.（2.57±1.66）min,P＜0.05]。结论 VMAT计划在靶区覆盖度与均匀性方面略逊于HT,但治疗时间明显缩短,有利于提高患者治疗过程中的舒适度和重复性。     

Tomotherapy planning of small brain tumours.

Helical tomotherapy (HT) combines a rotating intensity modulated fan beam with integrated CT imaging for high precision radiotherapy. HT plans for 12 patients with small brain tumours were compared with five other radiotherapy techniques. Proton techniques gave overall the best results, while HT was shown to produce better target dose uniformity (average SD=1.3%) and kept irradiation of organs at risk as good as other photon methods.     

Intensity modulated and three-dimensional conformal radiation therapy plans for oropharyngeal cancer: a comparison of their sensitivity to set-up errors and uncertainties

We compared the effect of set-up error and uncertainty on two radiation therapy treatment plans for head and neck cancer: one using intensity modulated radiation therapy (IMRT) and one using conventional three-dimensional conformal radiation therapy (3D-CRT). We used a Pinnacle3 (Philips Medical Systems, Markham, Ontario) system to create the two treatment plans (7-beam IMRT and 5-beam 3D-CRT) for the same volumetric data set, based on the objectives and constraints defined in the Radiation Therapy Oncology Group H-0022 protocol. In both plans, the dose-volume constraints for the targets and the organs at risk (oars) were met as closely as the beam geometries would allow. Monte Carlo-based simulations of set-up error and uncertainty were performed in three orthogonal directions for 840 simulated "courses of treatment" for each plan. A systematic error (chosen from distributions characterized by standard deviations ranging from 0 mm to 6 mm) and random uncertainties (2 mm standard deviation) were incorporated. We used a probability approach to compare the sensitivities of the IMRT and the 3D-CRT plans to set-up error and uncertainty in terms of equivalent uniform dose (EUD) to targets and oars.Based on the EUD analysis, the targets and oars showed considerably greater sensitivity to set-up error with the IMRT plan than with the 3D-CRT plan. For the IMRT plan, target EUDS were reduced by 4%, 7.5%, and 10% for 2-mm, 4-mm, and 6-mm set-up errors respectively. However, even with set-up error, the mandible, spinal cord, and parotid EUDS always remained lower with the IMRT plan than with the 3D-CRT plan.We conclude that, when quantified by EUD, IMRT-plan doses to oars and targets are more sensitive to set-up error than are 3D-CRT-plan doses. However, as judged by the differences between target and OAR doses, IMRT retains its superiority over 3D-CRT, even in the presence of set-up error.