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Minato-ku, Japan

Purpose: A coefficient of a treatment margin model for anisotropic systematic positioning errors has been calculated in Cartesian coordinate system based on van Herk's analytical formulation.Methods: Three-dimensional (3D) patient population distribution was formulated in Cartesian coordinate system to model anisotropic systematic positioning errors. Analytical 3D integration with anisotropic standard deviations Σ;'s and the following Newton's method yielded the coefficient of van Herk's systematic positioning error model in Cartesian coordinate system.Results: The treatment margins for the anisotropic systematic errors in Cartesian coordinate system were 2.1 Σ; for 90% patient population coverage and 2.4 Σ; for 95% patient population coverage.Conclusions: It was found that the treatment margins for anisotropic systematic positioning errors in Cartesian coordinate system were smaller than those for the isotropic model in spherical coordinate system for a given patient population coverage probability. © 2011 American Association of Physicists in Medicine.

Ashino Y.,Elekta KK
Japanese Journal of Clinical Radiology | Year: 2013

The number of patients with cancer who receive radiotherapy has been steadily increasing over time. This is partially due to the benefits of radiotherapy, which is "minimally invasive and allows patients to maintain a high QOL" and heightened public awareness that this treatment is a "highly-targeted therapy". This trend has gained even more momentum since the Cancer Control Act came into effect in April 2007. In addition, ongoing improvements and the addition of medical reimbursement have contributed to the renewal of equipment and stable provision of radiotherapy, having more than one linac installed at designated facilities. In the history of radiotherapy, Treatment Planning System (TPS) have played an important role in improving radiation treatment. TPS has contributed to achieving, in a multifaceted way, a situation where the planned dose distribution has become identical to the real dose distribution. Efforts have been made to bring about technological innovations in medical linear accelerators (linac) including attempts to reduce size, but compared with these in TPS, no marked changes in technology occurred. In the 1990s, however, it became imperative to realize full digital using digital output of TPS. IMRT is the latest treatment technology produced using digitally controlled linac. Japanese researchers tend to view IMRT as an advanced form of conformal radiotherapy. However, it is indisputable that digital control is far superior to analogue control in terms of the assurance and verification accuracy. It is worth considering that instantaneous high-dose-rate radiotherapy leads to shortening treatment time, hypo-fractionated radiotherapy and a new application of the relative biological effectiveness (RBE) as a significant variable. The Flattening Filter Free (FFF) technology will make this instantaneous high-dose-rate radiotherapy available. FFF linac would produce less scatter, and therefore potentially less dose to structure outside the treatment field, e.g. contralateral breast and whole body dose. While patient positioning and immobilization (intrafraction motion) become critical since miss-positioning of the patient may quickly lead to a misadministration of the prescribed dose. There will be new uses of concurrent imaging and therapeutic radiation delivery and more precise determinations of the actual location and numbers of clonogenic stem cells and hypoxic cell that must be inactivated to achieve local control and potential cure.

Sakumi A.,University of Tokyo | Shiraishi K.,University of Tokyo | Onoe T.,University of Tokyo | Yamamoto K.,University of Tokyo | And 4 more authors.
Journal of Radiation Research | Year: 2012

We have successfully created a single arc volumetric modulated arc therapy (VMAT) plan for treating post-surgical left breast/chest wall and regional nodes using Elekta multileaf collimator (MLC). Dose volume histograms (DVHs) were compared between the VMAT plans and conventional tangential beam plans using a field-in-field technique, leading to significant DVH advantages in the VMAT plans. The difference between Elekta VMAT and Varian RapidArc due to different MLC designs was discussed in terms of the number of arcs required to cover a large target, highlighting a single arc capability of Elekta VMAT for a large target volume which may be less sensitive to unexpected organ motion during dose delivery.

Takahashi W.,University of Tokyo | Yamashita H.,University of Tokyo | Saotome N.,University of Tokyo | Iwai Y.,Elekta KK | And 3 more authors.
Radiation Oncology | Year: 2012

Background: The purpose of this study was to compare dose distributions from three different algorithms with the x-ray Voxel Monte Carlo (XVMC) calculations, in actual computed tomography (CT) scans for use in stereotactic radiotherapy (SRT) of small lung cancers.Methods: Slow CT scan of 20 patients was performed and the internal target volume (ITV) was delineated on Pinnacle 3. All plans were first calculated with a scatter homogeneous mode (SHM) which is compatible with Clarkson algorithm using Pinnacle 3treatment planning system (TPS). The planned dose was 48 Gy in 4 fractions. In a second step, the CT images, structures and beam data were exported to other treatment planning systems (TPSs). Collapsed cone convolution (CCC) from Pinnacle 3, superposition (SP) from XiO, and XVMC from Monaco were used for recalculating. The dose distributions and the Dose Volume Histograms (DVHs) were compared with each other.Results: The phantom test revealed that all algorithms could reproduce the measured data within 1% except for the SHM with inhomogeneous phantom. For the patient study, the SHM greatly overestimated the isocenter (IC) doses and the minimal dose received by 95% of the PTV (PTV95) compared to XVMC. The differences in mean doses were 2.96 Gy (6.17%) for IC and 5.02 Gy (11.18%) for PTV95. The DVH's and dose distributions with CCC and SP were in agreement with those obtained by XVMC. The average differences in IC doses between CCC and XVMC, and SP and XVMC were -1.14% (p = 0.17), and -2.67% (p = 0.0036), respectively.Conclusions: Our work clearly confirms that the actual practice of relying solely on a Clarkson algorithm may be inappropriate for SRT planning. Meanwhile, CCC and SP were close to XVMC simulations and actual dose distributions obtained in lung SRT. © 2012 Takahashi et al; licensee BioMed Central Ltd.

Shiraishi K.,University of Tokyo | Futaguchi M.,University of Tokyo | Haga A.,University of Tokyo | Sakumi A.,University of Tokyo | And 6 more authors.
BioMed Research International | Year: 2014

Time-averaged intreatment prostate localization errors were calculated, for the first time, by three-dimensional prostate image cross-correlation between planning CT and intrafraction kilovoltage cone-beam CT (CBCT) during volumetric modulated arc therapy (VMAT). The intrafraction CBCT volume was reconstructed by an inhouse software after acquiring cine-mode projection images during VMAT delivery. Subsequently, the margin between a clinical target volume and a planning target volume (PTV) was obtained by applying the van Herk and variant formulas using the calculated localization errors. The resulting PTV margins were approximately 2 mm in lateral direction and 4 mm in craniocaudal and anteroposterior directions, which are consistent with the margin prescription employed in our facility. © 2014 Kenshiro Shiraishi et al.

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