Tomotherapy and Other Innovative IMRT Delivery Systems

Department of Human Oncology, University of Wisconsin–Madison, Madison, Wisconsin, United States
Seminars in Radiation Onchology (Impact Factor: 4.03). 11/2006; 16(4):199-208. DOI: 10.1016/j.semradonc.2006.04.002
Source: PubMed


Fixed-field treatments, delivered using conventional clinical linear accelerators fitted with multileaf collimators, have rapidly become the standard form of intensity-modulated radiotherapy (IMRT). Several innovative nonstandard alternatives also exist, for which delivery and treatment planning systems are now commercially available. Three of these nonstandard IMRT approaches are reviewed here: tomotherapy, robotic linear accelerators (CyberKnife, Accuray Inc., Sunnyvale, CA), and standard linear accelerators modulated by jaws alone or by their jaws acting together with a tertiary beam-masking device. Rationales for the nonstandard IMRT approaches are discussed, and elements of their delivery system designs are briefly described. Differences between fixed-field IMRT dose distributions and the distributions that can be delivered by using the nonstandard technologies are outlined. Because conventional linear accelerators are finely honed machines, innovative design enhancement of one aspect of system performance often limits another facet of machine capability. Consequently the various delivery systems may prove optimal for different types of treatment, with specific machine designs excelling for disease sites with specific target volume and normal structure topologies. However it is likely that the delivery systems will be distinguished not just by the optimality of the dose distributions they deliver, but also by factors such as the efficiency of their treatment process, the integration of their onboard imaging systems into that process, and their ability to measure and minimize or compensate for target movement, including the effects of respiratory motion.

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Available from: Minesh P Mehta, Feb 18, 2015
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    • "Our findings are corroborated in a study comparing HT and VMAT in delivering conventionally fractionated radiotherapy in several body sites by Rong et al, which demonstrated improved target dose homogeneity and lower doses to more critical structures in the HT plans [28]. This is mainly due to the increased freedom of intensity modulation created by delivering image-guided IMRT under synchronous gantry rotation and couch motion with HT [13], [25]. "
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    ABSTRACT: Helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) are both advanced techniques of delivering intensity-modulated radiotherapy (IMRT). Here, we conduct a study to compare HT and partial-arc VMAT in their ability to spare organs at risk (OARs) when stereotactic ablative radiotherapy (SABR) is delivered to treat centrally located early stage non-small-cell lung cancer or lung metastases. 12 patients with centrally located lung lesions were randomly chosen. HT, 2 & 8 arc (Smart Arc, Pinnacle v9.0) plans were generated to deliver 70 Gy in 10 fractions to the planning target volume (PTV). Target and OAR dose parameters were compared. Each technique's ability to meet dose constraints was further investigated. HT and VMAT plans generated essentially equivalent PTV coverage and dose conformality indices, while a trend for improved dose homogeneity by increasing from 2 to 8 arcs was observed with VMAT. Increasing the number of arcs with VMAT also led to some improvement in OAR sparing. After normalizing to OAR dose constraints, HT was found to be superior to 2 or 8-arc VMAT for optimal OAR sparing (meeting all the dose constraints) (p = 0.0004). All dose constraints were met in HT plans. Increasing from 2 to 8 arcs could not help achieve optimal OAR sparing for 4 patients. 2/4 of them had 3 immediately adjacent structures. HT appears to be superior to VMAT in OAR sparing mainly in cases which require conformal dose avoidance of multiple immediately adjacent OARs. For such cases, increasing the number of arcs in VMAT cannot significantly improve OAR sparing.
    Full-text · Article · Apr 2013 · PLoS ONE
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    • "The use of helical tomotherapy (HT) can provide different geometric flexibility and modulation techniques over standard IMRT. Such superior control of dose distribution could allow for better dose uniformity within the target and/ or sparing of organs at risk [5]. "
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    ABSTRACT: Purpose To determine the safety and efficacy of hypofractionated intensity modulated radiation therapy (Hypo-IMRT) using helical tomotherapy (HT) with concurrent low dose temozolomide (TMZ) followed by adjuvant TMZ in patients with glioblastoma multiforme (GBM). Methods and materials Adult patients with GBM and KPS > 70 were prospectively enrolled between 2005 and 2007 in this phase I study. The Fibonacci dose escalation protocol was implemented to establish a safe radiation fractionation regimen. The protocol defined radiation therapy (RT) dose level I as 54.4 Gy in 20 fractions over 4 weeks and dose level II as 60 Gy in 22 fractions over 4.5 weeks. Concurrent TMZ followed by adjuvant TMZ was given according to the Stupp regimen. The primary endpoints were feasibility and safety of Hypo-IMRT with concurrent TMZ. Secondary endpoints included progression free survival (PFS), pattern of failure, overall survival (OS) and incidence of pseudoprogression. The latter was defined as clinical or radiological suggestion of tumour progression within three months of radiation completion followed by spontaneous recovery of the patient. Results A total of 25 patients were prospectively enrolled with a median follow-up of 12.4 months. The median age at diagnosis was 53 years. Based on recursive partitioning analysis (RPA) criteria, 16%, 52% and 32% of the patients were RPA class III, class IV and class V, respectively. All patients completed concurrent RT and TMZ, and 19 patients (76.0%) received adjuvant TMZ. The median OS was 15.67 months (95% CI 11.56 - 20.04) and the median PFS was 6.7 months (95% CI 4.0 – 14.0). The median time between surgery and start of RT was 44 days (range of 28 to 77 days). Delaying radiation therapy by more than 6 weeks after surgery was an independent prognostic factor associated with a worse OS (4.0 vs. 16.1 months, P = 0.027). All recurrences occurred within 2 cm of the original gross tumour volume (GTV). No cases of pseudoprogression were identified in our cohort of patients. Three patients tolerated dose level I with no dose limiting toxicity and hence the remainder of the patients were treated with dose level II according to the dose escalation protocol. Grade 3–4 hematological toxicity was limited to two patients and one patient developed Grade 4 Pneumocystis jiroveci pneumonia. Conclusion Hypo-IMRT using HT given with concurrent TMZ is feasible and safe. The median OS and PFS are comparable to those observed with conventional fractionation. Hypofractionated radiation therapy offers the advantage of a shorter treatment period which is imperative in this group of patients with limited life expectancy.
    Full-text · Article · Feb 2013 · Radiation Oncology
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    • "Helical Tomotherapy is a radiation delivery technique, which is able to create highly conformal dose distributions in target volume. HT was designed as an integrated system for volumetric IGRT and IMRT [9]. Reproducibility of patient positioning is especially important in highly conformal radiotherapy techniques such as HT. "
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    ABSTRACT: Radiation therapy plays a central role in the management of many childhood malignancies and Helical Tomotherapy (HT) provides potential to decrease toxicity by limiting the radiation dose to normal structures. The aim of this article was to report preliminary results of our clinical experience with HT in pediatric malignancies. In this study 66 consecutive patients younger than 14 years old, treated with HT at our center between January 2006 and April 2010, have been included. We performed statistical analyses to assess the relationship between acute toxicity, graded according to the RTOG criteria, and several clinical and treatment characteristics such as a dose and irradiation volume. The median age of patients was 5 years. The most common tumor sites were: central nervous system (57%), abdomen (17%) and thorax (6%). The most prevalent histological types were: medulloblastoma (16 patients), neuroblastoma (9 patients) and rhabdomyosarcoma (7 patients). A total of 52 patients were treated for primary disease and 14 patients were treated for recurrent tumors. The majority of the patients (72%) were previously treated with chemotherapy. The median prescribed dose was 51 Gy (range 10-70 Gy). In 81% of cases grade 1 or 2 acute toxicity was observed. There were 11 cases (16,6%) of grade 3 hematological toxicity, two cases of grade 3 skin toxicity and one case of grade 3 emesis. Nine patients (13,6%) had grade 4 hematological toxicity. There were no cases of grade 4 non-hematological toxicities. On the univariate analysis, total dose and craniospinal irradiation (24 cases) were significantly associated with severe toxicity (grade 3 or more), whereas age and chemotherapy were not. On the multivariate analysis, craniospinal irradiation was the only significant independent risk factor for grade 3-4 toxicity. HT in pediatric population is feasible and safe treatment modality. It is characterized by an acceptable level of acute toxicity that we have seen in this highly selected pediatric patient cohort with clinical features of poor prognosis and/or aggressive therapy needed. Despite of a dosimetrical advantage of HT technique, an exhaustive analysis of long-term follow-up data is needed to assess late toxicity, especially in this potentially sensitive to radiation population.
    Full-text · Article · Aug 2011 · Radiation Oncology
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