Background: Multiple beams are generally used with an increased possibility that the beam axis intersects the treatment table. Treatment tabletops are commonly made of carbon fiber due to its high mechanical strength and rigidity, low specific density, extremely light and low radiation beam attenuation properties. Purpose of this paper is investigated the dose changes in the buildup region and beam attenuation by a carbon fiber tabletop for high energy 6- and 18-MV photon beams.  Materials and Methods: Measurements were performed for 10 cm × 10 cm and 20 cm × 20 cm field sizes. The surface dose and percentage depth doses (%DD) were measured by a Markus parallel plate chamber at a source-surface distance (SSD) of 100 cm for 6 MV and 18 MV photon beams. Attenuation measurements were made at the solid-water phantom for gantry angles of 0^o and 180^o rotation of the beam. Results: A carbon fiber tabletop increases the surface dose from 12.87% to 86.65% for 10 cm x 10 cm and from 8.72% to 71.16% for 20 cm × 20 cm field at 6 and 18 MV, respectively. The surface dose with the carbon fiber tabletop in an open field (0^o) increases with field size. Conclusion: The carbon fiber tabletop causes a substantially increased surface dose, and also significantly decreases the skin-sparing effect, which is clinically important. The dosimetric effect of the tabletop may be higher, especially for the intensity-modulated radiation therapy depending on the beam orientation.
 

Background: Several high-precision stereotactic radiation therapy modalities are currently used in clinical settings. We aimed to evaluate whether the CyberKnife (CK) or TrueBeam (TB) radiation treatment systems were more appropriate for treating targets of various morphologies according to the physical properties of each device.  Materials and Methods: Spheres (diameter = 5–50 mm), as well as triangular prisms and cubes (length of a side = 10–50 mm), were used as virtual targets for each treatment delivery system. A phantom with dosimetry film was irradiated to evaluate the flatness and gradient of the radiation treatment from each modality. Results: The homogeneity index (HI) for the spherical targets was significantly higher (dose distribution was more homogeneous) using the TB than when using the CK (1.9 vs. 1.4; p = 0.002). There were no significant differences between treatment modalities in the HI for more complex shapes. The HI increased monotonically as the virtual target diameter increased for the CK (p = 0.048). The flatness parameter was lower for the TB than for the CK (1.4 vs. 1.1; p < 0.001). Conclusion: The CK is particularly robust for delivering therapeutic radiation to small targets, while the TB is more suitable for targets with a simple shape or when the HI is a critical treatment factor.
 

 

Background: The optimal radiation dose for oral cavity cancers treated with retrograde superselective intra-arterial chemoradiotherapy (SIACRT) is unclear. The aim of the present study was to evaluate the treatment outcome and toxicity in patients treated with <60 Gy compared with those treated with ≥60 Gy to provide evidence for determining the optimal dose. Materials and Methods: Between January 2009 and December 2013, 159 oral cavity cancer patients were treated with SIACRT with curative intent at a single institution. One hundred and twenty-nine patients received ≥60 Gy and 30 received <60 Gy. Local control (LC), disease-free survival (DFS), overall survival (OS), and toxicity were compared. Propensity score matching was performed to reduce bias. Results: The median follow-up period was 48 months (range, 2–88 months). LC (<60 Gy vs. ≥60 Gy, 81.5% vs. 86.1% at 3 years, p = 0.534), DFS (68.8% vs. 72.4% at 3 years, p = 0.816), and OS (85.9% vs. 72.3% at 3 years, p = 0.132) were comparable between the two groups. There was also no difference in toxicity. However, the median overall treatment period was significantly shorter in the <60 Gy cohort (39 days vs. 49 days, p < 0.0001). Conclusion: The radiation dose may be reduced to <60 Gy when treating oral cavity cancers with SIACRT.

The treatment results of intensity-modulated stereotactic radiotherapy (IM-SRT) by volumetric-modulated arc therapy (VMAT) for intramedullary cervical spinal cord metastases (IMCSCM) in two cases were presented. Case 1: A 76-year-old woman showed left-sided motor weakness and left arm pain and dysesthesia due to IMCSCM at C [cervical] 6-7 (located a little to the left laterally) with multiple small brain metastases from thyroid carcinoma.  Multiple brain metastases were successfully treated by stereotactic radiosurgery (SRS). In addition, IMCSCM was treated by IM-SRT. Case 2: A 48-year-old man presented with asymptomatic IMCSCM at C2 (located a little to the right laterally) after conventional whole brain radiotherapy (WBRT) and multiple sessions of SRS/SRT for multiple brain metastases from lung adenocarcinoma. IMCSCM was treated by IM-SRT. In both cases 39 Gy in 13 fractions (without PTV [planning target volume] margin, D95%=95% dose) was delivered to the IMCSCM (0.3 ml and 0.5 ml in volume respectively) by coplanar 2-full circular arc VMAT. The maximum dose to the tumor was 46.3 Gy in case 1 and 47.1 Gy in case 2. IMCSCM in both cases shrank markedly without adverse effects during the follow-up period of 32 months and 8 months respectively. The symptoms of the extremities in case 1 were subsided completely until the patient’s death at 34 months after SRT from lung metastasis. In case 1 IMCSCM had been thought to be a relatively radioresistant thyroid carcinoma metastasis. In case 2 IMCSCM was near the field of the prior WBRT. However, both tumors were successfully treated without adverse effects by VMAT IM-SRT.

Background: The purpose of this study was to investigate the dosimetric characteristics of a new type of two-dimensional diode detector array used for quality assurance of stereotactic radiosurgery (SRS). Materials and Methods: The devices used in this study were the SRS MapCHECK detector and the StereoPHAN. The detector has 1013 diode detectors over an area of 77 x 77 mm². The reproducibility, dose linearity, dose rate dependencies, output factors (OPFs) and angular dependencies were investigated as dosimetric characteristics. The OPFs were measured and compared between AP and PA direction ranging from 0.5 x 0.5 to 7 x 7 cm². The angular dependencies were measured using 19 gantry angles. Results: The dose reproducibility and linearities showed sufficient performance of 6 MV and 10 MV. At 40 MU/min, there was a 1.3% difference from the ionization chamber measurements. For the flattening filter-free beam, there was no dose rate dependency from the 400 MU/minute to 2400 MU/minute, and the variation was within 0.5%. For small irradiation fields of 1 cm or less, the measured value of the SMC differed in AP and PA directions by up to 4.5%. The maximum gantry angle dependency of the detector was 5.3%. A maximum difference of -3.1% occurred between the measurements and TPS calculations. Conclusion: Results indicate that the new 2D diode detector is stable and useful for QA and end-to-end testing of SRS due to its excellent dose characteristics, high resolution and ease of handling when combined with the StereoPHAN.

Background: Chronic long-term irradiation of mice with low dose-rate (20 mGy/day) gamma rays significantly shortened their life spans due to neoplasms and significant suppression of their ability to eliminate transplanted tumors. Materials and Methods: Mice exposed to chronic 20 mGy/day gamma rays for 400 days and housed in an enriched environment (EE) were compared with those housed in a standard environment. Results: We demonstrate that an EE significantly ameliorates the suppression of transplanted tumors in mice exposed to chronic low dose-rate gamma rays. Peripheral blood analysis revealed that the proportions of some immune cells were increased by EE housing. Additionally, the number and activity of natural killer (NK) cells in the peripheral blood increased with EE housing, indicating that NK cells may be involved in enhancing the ability to reject transplanted tumors. Conclusion: To our knowledge, this is the first study to report that the adverse effects, such as the suppression of tumor rejection activity of chronic low dose-rate irradiation exposure, may be alleviated by EE housing, which suggests the possibility that the adverse effects of irradiation may be mitigated by changes in lifestyle.