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Dose–volume histogram comparison between static 5-field IMRT with 18-MV X-rays and helical tomotherapy with 6-MV X-rays

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      Abstract

      We treated prostate cancer patients with static 5-field intensity-modulated radiation therapy (IMRT) using linac 18-MV X-rays or tomotherapy with 6-MV X-rays. As X-ray energies differ, we hypothesized that 18-MV photon IMRT may be better for large patients and tomotherapy may be more suitable for small patients. Thus, we compared dose–volume parameters for the planning target volume (PTV) and organs at risk (OARs) in 59 patients with T1–3 N0M0 prostate cancer who had been treated using 5-field IMRT. For these same patients, tomotherapy plans were also prepared for comparison. In addition, plans of 18 patients who were actually treated with tomotherapy were analyzed. The evaluated parameters were homogeneity indicies and a conformity index for the PTVs, and D2 (dose received by 2% of the PTV in Gy), D98, Dmean and V10–70 Gy (%) for OARs. To evaluate differences by body size, patients with a known body mass index were grouped by that index ( <21; 21–25; and >25 kg/m2). For the PTV, all parameters were higher in the tomotherapy plans compared with the 5-field IMRT plans. For the rectum, V10 Gy and V60 Gy were higher, whereas V20 Gy and V30 Gy were lower in the tomotherapy plans. For the bladder, all parameters were higher in the tomotherapy plans. However, both plans were considered clinically acceptable. Similar trends were observed in 18 patients treated with tomotherapy. Obvious trends were not observed for body size. Tomotherapy provides equivalent dose distributions for PTVs and OARs compared with 18-MV 5-field IMRT. Tomotherapy could be used as a substitute for high-energy photon IMRT for prostate cancer regardless of body size.

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      Volumetric modulated arc therapy for delivery of prostate radiotherapy: comparison with intensity-modulated radiotherapy and three-dimensional conformal radiotherapy.

      Volumetric modulated arc therapy (VMAT) is a novel form of intensity-modulated radiotherapy (IMRT) optimization that allows the radiation dose to be delivered in a single gantry rotation of up to 360 degrees , using either a constant dose rate (cdr-VMAT) or variable dose rate (vdr-VMAT) during rotation. The goal of this study was to compare VMAT prostate RT plans with three-dimensional conformal RT (3D-CRT) and IMRT plans. The 3D-CRT, five-field IMRT, cdr-VMAT, and vdr-VMAT RT plans were created for 10 computed tomography data sets from patients undergoing RT for prostate cancer. The parameters evaluated included the doses to organs at risk, equivalent uniform doses, dose homogeneity and conformality, and monitor units required for delivery of a 2-Gy fraction. The IMRT and both VMAT techniques resulted in lower doses to normal critical structures than 3D-CRT plans for nearly all dosimetric endpoints analyzed. The lowest doses to organs at risk and most favorable equivalent uniform doses were achieved with vdr-VMAT, which was significantly better than IMRT for the rectal and femoral head dosimetric endpoints (p < 0.05) and significantly better than cdr-VMAT for most bladder and rectal endpoints (p < 0.05). The vdr-VMAT and cdr-VMAT plans required fewer monitor units than did the IMRT plans (relative reduction of 42% and 38%, respectively; p = 0.005) but more than for the 3D-CRT plans (p = 0.005). The IMRT and VMAT techniques achieved highly conformal treatment plans. The vdr-VMAT technique resulted in more favorable dose distributions than the IMRT or cdr-VMAT techniques, and reduced the monitor units required compared with IMRT.
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        Prostate cancer radiation dose response: results of the M. D. Anderson phase III randomized trial.

        A randomized radiotherapy dose escalation trial was undertaken between 1993 and 1998 to compare the efficacy of 70 vs. 78 Gy in controlling prostate cancer. A total of 305 Stage T1-T3 patients were entered into the trial and, of these, 301 with a median follow-up of 60 months, were assessable. Of the 301 patients, 150 were in the 70 Gy arm and 151 were in the 78 Gy arm. The primary end point was freedom from failure (FFF), including biochemical failure, which was defined as 3 rises in the prostate-specific antigen (PSA) level. Kaplan-Meier survival analyses were calculated from the completion of radiotherapy. The log-rank test was used to compare the groups. Cox proportional hazard regression analysis was used to examine the independence of study randomization in multivariate analysis. There was an even distribution of patients by randomization arm and stage, Gleason score, and pretreatment PSA level. The FFF rates for the 70- and 78 Gy arms at 6 years were 64% and 70%, respectively (p = 0.03). Dose escalation to 78 Gy preferentially benefited those with a pretreatment PSA >10 ng/mL; the FFF rate was 62% for the 78 Gy arm vs. 43% for those who received 70 Gy (p = 0.01). For patients with a pretreatment PSA 10 ng/mL who were treated to 78 Gy (98% vs. 88% at 6 years, p = 0.056). Rectal side effects were also significantly greater in the 78 Gy group. Grade 2 or higher toxicity rates at 6 years were 12% and 26% for the 70 Gy and 78 Gy arms, respectively (p = 0.001). Grade 2 or higher bladder complications were similar at 10%. For patients in the 78 Gy arm, Grade 2 or higher rectal toxicity correlated highly with the proportion of the rectum treated to >70 Gy. An increase of 8 Gy resulted in a highly significant improvement in FFF for patients at intermediate-to-high risk, although the rectal reactions were also increased. Dose escalation techniques that limit the rectal volume that receives >or=70 Gy to <25% should be used.
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          Tomotherapy: a new concept for the delivery of dynamic conformal radiotherapy.

          Tomotherapy, literally "slice therapy," is a proposal for the delivery of radiation therapy with intensity-modulated strips of radiation. The proposed method employs a linear accelerator, or another radiation-emitting device, which would be mounted on a ring gantry like a CT scanner. The patient would move through the bore of the gantry simultaneously with gantry rotation. The intensity modulation would be performed by temporally modulated multiple independent leaves that open and close across the slit opening. At any given time, any leaf would be (1) closed, covering a portion of the slit, (2) open, allowing radiation through, or (3) changing between these states. This method would result in the delivery of highly conformal radiation. Overall treatment times should be comparable with contemporary treatment delivery times. The ring gantry would make it convenient to mount a narrow multisegmented megavoltage detector system for beam verification and a CT scanner on the treatment unit. Such a treatment unit could become a powerful tool for treatment planning, conformal treatment, and verification using tomographic images. The physical properties of this treatment delivery are evaluated and the fundamental design specifications are justified.
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            Author and article information

            Affiliations
            [1 ]Department of Radiology, Nagoya City University Graduate school of Medical Science , Nagoya 467–8601, Japan
            [2 ]Department of Radiology, Okazaki City Hospital , 3–1 Aza-Goshoai, Koryuzi-cho, Okazaki, Aichi 444–8553, Japan
            [3 ]Department of Radiation Oncology, Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1–1–1 Hirate-cho, Kita-ku, Nagoya, Aichi 462–8508, Japan
            [4 ]Department of Radiation Oncology, JA Suzuka Hospital , Suzuka, Mie 513–8630, Japan
            [5 ]Yokohama Cyberknife Center, Yokohama, Kanagawa 241–0014, Japan
            Author notes
            [* ]Corresponding author. Department of Radiology, Nagoya City University Graduate School of Medical Sciences, 467–8601, Japan. Tel: +81-52-853-8276; Fax: +81-52-852-5244; Email: hakihiro@ 123456gmail.com
            Journal
            J Radiat Res
            J. Radiat. Res
            jrr
            jrr
            Journal of Radiation Research
            Oxford University Press
            0449-3060
            1349-9157
            March 2015
            20 January 2015
            20 January 2015
            : 56
            : 2
            : 338-345
            25609741
            4380056
            10.1093/jrr/rru111
            rru111
            © The Author 2015. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

            This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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