Comparative dosimetric study of spot-scanning proton therapy versus volumetric-modulated radiation therapy for extrahepatic bile duct cancer.

This study aimed to compare the dose distributions and clarify the dosimetric characteristics of spot-scanning proton therapy (SSPT) and photon volumetric modulated arc therapy (VMAT) for extrahepatic bile duct cancer (EBDC). This retrospective study included 10 patients with EBDC treated with real-time image-gated SSPT. Using the simultaneous integrated boost technique, the 2 prescription dose levels for planning target volumes were 72.6 and 44 Gy, delivered in 22 fractions. Plan quality comparisons were conducted by analyzing various parameters, including homogeneity, conformity, dose to organs at risk, and normal tissue complication probability (NTCP) for radiation-induced liver damage (RILD). The target dose distributions using SSPT were almost equivalent to those achieved using photon VMAT. There was a significant reduction in all liver dose parameters, the NTCP value for RILD, and kidney dose (mean, V12 Gy, and V18 Gy) in SSPT than in photon VMAT. No significant differences were observed in the intestinal doses in the high-dose area. Thus, compared with photon VMAT, SSPT for EBDC significantly reduced radiation doses to the liver and kidneys and has shown potential clinical benefits of reduced radiation-induced toxicity.

Effective heart-sparing whole lung irradiation using volumetric modulated arc therapy: a case report.

BACKGROUND: Late cardiovascular disease-related adverse events are one of the most common causes of premature mortality among long-term survivors of childhood cancer. As it is difficult to reduce the heart dose with traditional anteroposterior-posteroanterior field whole lung irradiation for pulmonary metastasis, improved radiation techniques are highly desirable. We report a case treated with whole lung irradiation using volumetric modulated arc therapy. CASE PRESENTATION: A 3-year-old Japanese girl with pulmonary metastases of Wilms' tumor received 12 Gy in 8 fractions of whole lung irradiation using volumetric modulated arc therapy. The treatment was well tolerated, and the course was completed as planned without any toxicity. We found statistically significant reduced volumetric modulated arc therapy irradiation doses to organs at risk relative to those of the standard anteroposterior-posteroanterior field technique. The mean heart dose was 8.5 Gy for volumetric modulated arc therapy and 12.3 Gy for the anteroposterior-posteroanterior field. The doses to liver and thyroid were also more favorable with volumetric modulated arc therapy than with the anteroposterior-posteroanterior field technique. We confirmed the dosimetric advantages of volumetric modulated arc therapy over anteroposterior-posteroanterior field in whole lung irradiation in terms of superior normal organ protection. CONCLUSIONS: Effective heart sparing is possible for whole lung irradiation using volumetric modulated arc therapy. Large-scale studies using standardized procedures should be conducted to validate our results.

Correlation Between Dosimetric Parameters and Acute Dermatitis of Post-operative Radiotherapy in Breast Cancer Patients.

BACKGROUND/AIM: To examine the correlation between dosimetric parameters and acute radiation dermatitis in early breast cancer patients subjected to post-operative radiotherapy. PATIENTS AND METHODS: The data of 84 patients treated with post-operative radiotherapy were analyzed. The total prescribed dose was 50 Gy in 25 fractions over 5 weeks. Radiation dermatitis was assessed according to Common Terminology Criteria for Adverse Events v4.0. We set organ at risk whole body (from neck to abdomen examined by CT images) also as surrogate skin volume (3 mm thickness). RESULTS: A total of 28 patients showed radiation dermatitis grade equal or higher than 2 at the 50 Gy time point. These 28 patients were compared to 56 matched pair patients with grade 0-1 radiation dermatitis during the same treatment period. The mean of V5-20 and V40 in patient's whole volume and V40-50 in skin volume were significantly higher in patients who presented with acute radiation dermatitis Grades ≥2 than in the other patients who did not. The statistically most significant difference was observed for V40 for skin volume and V5 for patient whole volume. Rate of acute radiation dermatitis grade ≥2 was significantly higher for patients with V5 (whole body) >1,360 cm3 than those with V5 (whole body) <1,360 cm3 (47% vs. 27%, p=0.0353), as well as for patients with V40 (skin volume) >45 cm3 compared with those with V40 (skin volume) <45 cm3 (50% vs. 18%, p=0.0043). CONCLUSION: Dosimetric parameters were useful to predict radiation dermatitis grade ≥2. V5 (whole body) 1,360 cm3 and V40 (skin volume) 45 cm3 may be dose volume constrain for radiation dermatitis grade ≥2.

Identification of the suitable leaf margin for liver stereotactic body radiotherapy with flattening filter-free beams.

The purpose of this study is to identify the suitable leaf margin for liver stereotactic body radiotherapy (SBRT) with flattening filter-free (FFF) beams, as compared with that with flattening filter (FF) beams. SBRT treatment planning for 10 patients with liver cancer was performed using 10-MV FFF and FF beams obtained from a Varian TrueBeam (Varian Medical Systems, Palo Alto, CA) linear accelerator. Each plan was generated with the leaf margin to the planning target volume (PTV) ranging from -3 to 5 mm. The prescription dose at D95 (dose covering 95% of the volume) was 48 Gy in 4 fractions to the PTV. The following dosimetric parameters were evaluated quantitatively: homogeneity index (HI), conformity index (CI), gradient index (GI), the normal liver receiving a dose greater than or equal to 20 Gy (V20), and the mean normal liver dose. The HI for FFF and FF beams increased as the leaf margin decreased. The leaf margins that achieved the best CI and GI were 0.1 and -0.3 mm for FFF beams, and 0.1 and -0.9 mm for FF beams. The liver V20 and the mean liver dose reached their minimum values at leaf margins of -0.8 and 0.0 mm for FFF beams, and -0.8 and 0.0 mm for FF beams. The suitable leaf margin for SBRT planning did not differ significantly for FFF and FF beams. Our data showed that, for both FFF and FF beams, a leaf margin of 0 or -1 mm was optimal for liver SBRT planning in terms of both target coverage and normal tissue sparing.

Polarity correction factor for flattening filter free photon beams in several cylindrical ionization chambers.

In this study, we aimed to compare the polarity correction factor in ionization chambers for flattening filter free (FFF) photon beams and flattening filter (FF) beams. Measurements were performed with both 6 and 10 MV FFF and FF beams. Five commercial ionization chambers were evaluated: PTW TN30013; IBA Dosimetry CC01, CC04, and CC13; and Exradin A12S. Except for the CC01 ionization chamber, the other four chambers showed less than a 0.3 % difference in the polarity effect between the FFF and the FF beams. The CC01 chamber showed a strong field-size-dependence, unlike the other chambers. The polarity effect for all chambers with FFF beams did not change with the dose rate. Except in the case of the CC01 chamber, the difference in the polarity effect between FFF and FF beams was not significant.

Comparison of acute and subacute genitourinary and gastrointestinal adverse events of radiotherapy for prostate cancer using intensity-modulated radiation therapy, three-dimensional conformal radiation therapy, permanent implant brachytherapy and high-dose-rate brachytherapy.

AIMS AND BACKGROUND: To examine acute and subacute urinary and rectal toxicity in patients with localized prostate cancer monotherapeutically treated with the following four radiotherapeutic techniques: intensity-modulated radiation therapy, three-dimensional conformal radiation therapy, low-dose-rate permanent implant brachytherapy using I-125 seeds, and high-dose-rate brachytherapy. METHODS: One hundred and fifty-six patients with localized prostate cancer were distributed as follows: 57 underwent intensity-modulated radiation therapy, 35 underwent three-dimensional conformal radiation therapy, 37 underwent I-125 implant, and 27 underwent high-dose-rate brachytherapy. The prescribed doses were 70-74 Gy/35-37 fractions, 70 Gy/35 fractions, 145 Gy, and 45.5 Gy/7 fraction/4 days for intensity-modulated radiation therapy, three-dimensional conformal radiation therapy, I-125 implant, and high-dose-rate brachytherapy, respectively. Toxicities (≤6 months) were retrospectively evaluated using the Common Terminology Criteria for Adverse Events version 4.03. RESULTS: The frequency of grade 1 or 2 urinary toxicities using three-dimensional conformal radiation therapy (33/35, 94%) was significantly higher than that with high-dose-rate brachytherapy (18/27, 67%) or intensity-modulated radiation therapy (37/57, 65%) (P <0.05). The frequency of grade 1 or 2 urinary toxicities using I-125 implant was 31/37, 84%. The frequency of grade 1 or 2 gastrointestinal toxicities using three-dimensional conformal radiation therapy (17/35, 49%) was significantly higher than that using I-125 implant (4/37, 11%) or high-dose-rate brachytherapy (0/27, 0%) (P <0.05). Using intensity-modulated radiation therapy, the frequency of grade 1 or 2 gastrointestinal toxicities was 18/57 (32%), which was significantly higher than that using high-dose-rate brachytherapy (0/27, 0%) (P <0.05). Grade 3 or greater adverse events were not observed. CONCLUSIONS: Acute and subacute genitourinary toxicities were observed more frequently after three-dimensional conformal radiation therapy than after high-dose-rate brachytherapy or intensity-modulated radiation therapy. Acute and subacute gastrointestinal toxicities were seen more often after three-dimensional conformal radiation therapy than after brachytherapy (I-125 implant or high-dose-rate brachytherapy).

Radiotherapy treatment planning with contrast-enhanced computed tomography: feasibility of dual-energy virtual unenhanced imaging for improved dose calculations.

BACKGROUND: In radiotherapy treatment planning, intravenous administration of an iodine-based contrast agent during computed tomography (CT) improves the accuracy of delineating target volumes. However, increased tissue attenuation resulting from the high atomic number of iodine may result in erroneous dose calculations because the contrast agent is absent during the actual procedure. The purpose of this proof-of-concept study was to present a novel framework to improve the accuracy of dose calculations using dual-energy virtual unenhanced CT in the presence of an iodine-based contrast agent. METHODS: Simple phantom experiments were designed to assess the feasibility of the proposed concept. By utilizing a "second-generation" dual-source CT scanner equipped with a tin filter for improved spectral separation, four CT datasets were obtained using both a water phantom and an iodine phantom: "true unenhanced" images with attenuation values of 2 ± 11 Hounsfield Units (HU), "enhanced" images with attenuation values of 274 ± 23 HU, and two series of "virtual unenhanced" images synthesized from dual-energy scans of the iodine phantom, each with a different combination of tube voltages. Two series of virtual unenhanced images demonstrated attenuation values of 12 ± 29 HU (with 80 kVp/140 kVp) and 34 ± 10 HU (with 100 kVp/140 kVp) after removing the iodine component from the contrast-enhanced images. Dose distributions of the single photon beams calculated from the enhanced images and two series of virtual unenhanced images were compared to those from true unenhanced images as a reference. RESULTS: The dose distributions obtained from both series of virtual unenhanced images were almost equivalent to that from the true unenhanced images, whereas the dose distribution obtained from the enhanced images indicated increased beam attenuation caused by the high attenuation characteristics of iodine. Compared to the reference dose distribution from the true unenhanced images, the dose distribution pass rates from both series of virtual unenhanced images were greater than 90%, while those from the enhanced images were less than approximately 50-60%. CONCLUSIONS: Dual-energy virtual unenhanced CT improves the accuracy of dose distributions in radiotherapy treatment planning by removing the iodine component from contrast-enhanced images.

Dosimetry analyses comparing high-dose-rate brachytherapy, administered as monotherapy for localized prostate cancer, with stereotactic body radiation therapy simulated using CyberKnife.

The purpose of this study was to perform dosimetry analyses comparing high-dose-rate brachytherapy (HDR-BT) with simulated stereotactic body radiotherapy (SBRT). We selected six consecutive patients treated with HDR-BT monotherapy in 2010, and a CyberKnife SBRT plan was simulated for each patient using computed tomography images and the contouring set used in the HDR-BT plan for the actual treatment, but adding appropriate planning target volume (PTV) margins for SBRT. Then, dosimetric profiles for PTVs of the rectum, bladder and urethra were compared between the two modalities. The SBRT plan was more homogenous and provided lower dose concentration but better coverage for the PTV. The maximum doses in the rectum were higher in the HDR-BT plans. However, the HDR-BT plan provided a sharper dose fall-off around the PTV, resulting in a significant and considerable difference in volume sparing of the rectum with the appropriate PTV margins added for SBRT. While the rectum D5cm(3) for HDR-BT and SBRT was 30.7 and 38.3 Gy (P < 0.01) and V40 was 16.3 and 20.8 cm(3) (P < 0.01), respectively, SBRT was significantly superior in almost all dosimetric profiles for the bladder and urethra. These results suggest that SBRT as an alternative to HDR-BT in hypofractionated radiotherapy for prostate cancer might have an advantage for bladder and urethra dose sparing, but for the rectum only when proper PTV margins for SBRT are adopted.

Salvage high-dose-rate interstitial brachytherapy for locally recurrent rectal cancer: long-term follow-up results.

BACKGROUND: We retrospectively examined outcomes of salvage high-dose-rate interstitial brachytherapy (HDR-ISBT) for locally recurrent rectal cancer (LRRC). METHODS: Nine patients with LRRC were treated with salvage HDR-ISBT. Their median age was 63 years. The median maximum diameter of LRRC was 40 mm (range 20-80 mm). Adenocarcinomas were histologically confirmed in all cases. The prescribed dose was 30 Gy/5 fractions/3 days to 50 Gy/10 fractions/6 days in the combined external-beam radiotherapy group (four patients) and 54 Gy/9 fractions/5 days to 60 Gy/10 fractions/6 days in the monotherapeutic group (five patients). Median follow-up time was 90 months (range 6-221 months). RESULTS: Local control at final follow-up was achieved in five of nine patients. Of these five patients, one experienced a locally re-recurrent tumor in the vaginal wall 33 months after treatment and received re-HDR-ISBT as re-salvage treatment. The 8-year overall survival, local control, and progression-free survival rates were 56, 44, and 33 %, respectively. Based on the Common Terminology Criteria for Adverse Events ver. 4.03, the following Grade 3 adverse events were observed in three patients (≥3 months): Grade 3 skin ulceration in one patient who showed tumor invasion of the skin and whose V100 was 400 cc; Grade 3 vaginal perforation in one patient whose tumor had invaded the vaginal wall; and Grade 3 vagina-to-bladder fistula in one patient whose tumor received re-irradiation. Late adverse events above Grade 3 were not observed. CONCLUSIONS: Long-term follow-up results revealed that salvage HDR-ISBT is a promising treatment for LRRC with tolerable toxicity.

[Perceptual image dissimilarity--a novel metric for objective assessment of image quality in computed tomography with iterative reconstruction].

An iterative reconstruction (IR) technique in computed tomography (CT) is expected to play an important role in reducing the radiation dose while preserving both spatial resolution and contrast-to-noise ratio. However, images obtained by using the IR technique are known to have different visual appearances from those obtained by using the traditional filtered back-projection (FBP) reconstruction. This appearance is often figuratively described as "blocky," but it has not been objectively characterized further. In this paper, we propose a novel image quality metric, called "perceptual image dissimilarity" (PID), to characterize the visual dissimilarity between FBP and IR images. The PID was formulated as a grayscale transformation and subsequent structural similarity (SSIM)-based image quality measurement. The PID metric was validated using phantom images with three different modules. Sixty datasets, each consisting of an IR image and its corresponding noise-level-equivalent FBP image, were visually assigned "subjective dissimilarity scores" on a five level scale by six observers. The data sets were then quantitatively analyzed using both the PID and the traditional mean squared error (MSE) metrics. Our results show that the PID is highly consistent with the subjective dissimilarity score and thus delivers superior performance, whereas the MSE fails to quantify the observers' visual perception.

Gemstone spectral imaging: determination of CT to ED conversion curves for radiotherapy treatment planning.

The monochromatic images acquired by Gemstone spectral imaging (GSI) mode on the GE CT750 HD theoretically determines the computed tomography (CT) number more accurately than that of conventional scanner. Using the former, the CT number is calculated from (synthesized) monoenergetic X-ray data. We reasoned that the monochromatic image might be applied to radiotherapy treatment planning (RTP) to calculate dose distribution more accurately. Our goal here was to provide CT to electron density (ED) conversion curves with monochromatic images for RTP. Therefore, we assessed the reproducibility of CT numbers, an important factor on quality assurance, over short and long time periods for different substances at varying energy. CT number difference between measured and theoretical value was investigated. The scanner provided sufficient reproducibility of CT numbers for dose calculation over short and long time periods. The CT numbers of monochromatic images produced by this scanner had reasonable values for dose calculation. The CT to ED conversion curve becomes linear with respect to the relationship between CT numbers and EDs as the energy increases. We conclude that monochromatic imaging from a fast switching system can be applied for the dose calculation, keeping Hounsfield units (HU) stability.

A phase I study of concurrent weekly carboplatin and paclitaxel combined with intensity-modulated pelvic radiotherapy as an adjuvant treatment for early-stage cervical cancer patients with positive pelvic lymph nodes.

OBJECTIVES: The objective of this study was to determine the maximum tolerated dose (MTD) and acute dose-limiting toxicities (DLTs) of intravenous carboplatin plus paclitaxel combined with intensity-modulated pelvic radiotherapy (pelvic IMRT) as an adjuvant treatment for early-stage cervical cancer patients with positive pelvic lymph nodes. METHODS: Women with uterine cervical cancer who were treated with radical hysterectomy and pelvic lymphadenectomy and displayed positive pelvic lymph nodes were eligible for this study. The patients were postoperatively treated with pelvic IMRT (50.4 Gy). The concurrent weekly chemotherapy consisted of carboplatin (area under the curve [AUC], 2) and paclitaxel (starting at 35 mg/m² and escalating by 5 mg/m² in 3 patient cohorts). The primary end point of the escalation study was acute DLT that occurred within 30 days of the completion of radiation therapy. RESULTS: Nine patients were enrolled and treated at 2 dose levels until DLT occurred. The median age of the patients was 47 years (range, 28-66 years). The median radiotherapy treatment time was 39.5 days (range, 38-64 days). At dose level I (35 mg/m² paclitaxel), 2 grade 3 leukopenia and a neutropenia were observed, but no DLT occurred. At dose level II (40 mg/m² paclitaxel), the first patient experienced a grade 2 hypersensitive reaction, which resulted in discontinuation of planned treatment. Thus, 2 more patients were evaluated at this dose level. Of these, 1 patient experienced febrile neutropenia, which was considered to be a DLT, and the other patient experienced long-lasting grade 3 leukopenia and grade 3 neutropenia, which resulted in the discontinuation of chemotherapy for 2 weeks (a DLT). We then evaluated 3 more patients at dose level 1, but no DLT occurred. The MTD of paclitaxel and carboplatin was thus defined as 35 mg/m² and an AUC of 2.0, respectively. CONCLUSIONS: Weekly paclitaxel/carboplatin and pelvic IMRT is a reasonable adjuvant treatment regimen for cervical cancer patients after radical hysterectomy. The MTD of paclitaxel and carboplatin for future phase II trials of this regimen is 35 mg/m² and an AUC of 2.0, respectively.

Feasibility and accuracy of relative electron density determined by virtual monochromatic CT value subtraction at two different energies using the gemstone spectral imaging.

BACKGROUND: Recent work by Saito (2012) has demonstrated a simple conversion from energy-subtracted computed tomography (CT) values (ΔHU) obtained using dual-energy CT to relative electron density (RED) via a single linear relationship. The purpose of this study was to investigate the feasibility of this method to obtain RED from virtual monochromatic CT images obtained by the gemstone spectral imaging (GSI) mode with fast-kVp switching. METHODS: A tissue characterization phantom with 13 inserts made of different materials was scanned using the GSI mode on a Discovery CT750 HD. Four sets of virtual monochromatic CT images (60, 77, 100 and 140 keV) were obtained from a single GSI acquisition. When we define Δ HU in terms of the weighting factor for the subtraction α, Δ HU ≡ (1 + α)H - αL (H and L represent the CT values for high and low energy respectively), the relationship between Δ HU and RED is approximated as a linear function, a × Δ HU/1000 + b (a, b = unity). We evaluated the agreement between the determined and nominal RED. We also have investigated reproducibility over short and long time periods. RESULTS: For the 13 insert materials, the RED determined by monochromatic CT images agreed with the nominal values within 1.1% and the coefficient of determination for this calculation formula was greater than 0.999. The observed reproducibility (1 standard deviation) of calculation error was within 0.5% for all materials. CONCLUSIONS: These findings indicate that virtual monochromatic CT scans at two different energies using GSI mode can provide an accurate method for estimating RED.

Dose-volume histogram predictors of chronic gastrointestinal complications after radical hysterectomy and postoperative concurrent nedaplatin-based chemoradiation therapy for early-stage cervical cancer.

PURPOSE: The purpose of this study was to evaluate dose-volume histogram (DVH) predictors for the development of chronic gastrointestinal (GI) complications in cervical cancer patients who underwent radical hysterectomy and postoperative concurrent nedaplatin-based chemoradiation therapy. METHODS AND MATERIALS: This study analyzed 97 patients who underwent postoperative concurrent chemoradiation therapy. The organs at risk that were contoured were the small bowel loops, large bowel loop, and peritoneal cavity. DVH parameters subjected to analysis included the volumes of these organs receiving more than 15, 30, 40, and 45 Gy (V15-V45) and their mean dose. Associations between DVH parameters or clinical factors and the incidence of grade 2 or higher chronic GI complications were evaluated. RESULTS: Of the clinical factors, smoking and low body mass index (BMI) (<22) were significantly associated with grade 2 or higher chronic GI complications. Also, patients with chronic GI complications had significantly greater V15-V45 volumes and higher mean dose of the small bowel loops compared with those without GI complications. In contrast, no parameters for the large bowel loop or peritoneal cavity were significantly associated with GI complications. Results of the receiver operating characteristics (ROC) curve analysis led to the conclusion that V15-V45 of the small bowel loops has high accuracy for prediction of GI complications. Among these parameters, V40 gave the highest area under the ROC curve. Finally, multivariate analysis was performed with V40 of the small bowel loops and 2 other clinical parameters that were judged to be potential risk factors for chronic GI complications: BMI and smoking. Of these 3 parameters, V40 of the small bowel loops and smoking emerged as independent predictors of chronic GI complications. CONCLUSIONS: DVH parameters of the small bowel loops may serve as predictors of grade 2 or higher chronic GI complications after postoperative concurrent nedaplatin-based chemoradiation therapy for early-stage cervical cancer.

Anti-IL-6 receptor antibody does not ameliorate radiation pneumonia in mice.

We previously showed that early administration of monoclonal anti-interleukin-6 receptor antibody (IL-6RA) does not prevent radiation-induced lung injury in mice. The purpose of this study was to investigate whether a higher dose and longer course of IL-6RA treatment was effective in ameliorating radiation pneumonia. C57Bl/6J mice received thoracic irradiation of 12 Gy, and were intraperitoneally injected with the IL-6RA, namely MR16-1, or with control rat IgG 4 times, once immediately following exposure and then weekly from 1 to 3 weeks after irradiation. Enzyme-linked immunosorbent assays were used to analyze the plasma levels of IL-6 and serum amyloid A (SAA). Lung injury was assessed by histological staining with haematoxylin and eosin (H&E) and by measuring wet lung weight. We observed marked upregulation of IL-6 in IL-6RA-treated mice compared to the IgG-treated control group, whereas IL-6RA did not increase the production of SAA in the group receiving irradiation. However, radiation pneumonia, as evaluated by H&E staining and lung weight showed no differences between the IL-6RA-treated mice and the controls. Long-term treatment with high-dose IL-6RA does not ameliorate radiation pneumonia.

The usefulness of an independent patient-specific treatment planning verification method using a benchmark plan in high-dose-rate intracavitary brachytherapy for carcinoma of the uterine cervix.

To develop an easy independent patient-specific quality assurance (QA) method using a benchmark plan for high-dose-rate intracavitary brachytherapy for cervix cancer, we conducted benchmark treatment planning with various sizes and combinations of tandem-ovoid and tandem-cylinder applications with 'ideal' geometry outside the patient. Two-dimensional-based treatment planning was conducted based on the Manchester method. We predicted the total dwell time of individual treatment plans from the air kerma strength, total dwell time and prescription dose of the benchmark plan. In addition, we recorded the height (dh), width (dw) and thickness (dt) covered with 100% isodose line. These parameters were compared with 169 and 29 clinical cases for tandem-ovoid or tandem-cylinder cases, respectively. With regard to tandem-ovoid cases, differences in total dwell time, dh, dt and dw between benchmark and individual plans were on average -0.2% ± 3.8%, -1.0 mm ± 2.6 mm, 0.8 mm ± 1.3 mm and -0.1 mm ± 1.5 mm, respectively. With regard to tandem-cylinder cases, differences in total dwell time, dh(front) (the distance from tandem tip to tandem ring), dt and dw between benchmark and individual plans were on average -1.5% ± 3.1%, -1.5 mm ± 4.9 mm, 0.1 mm ± 1.0 mm and 0.2 mm ± 0.8 mm, respectively. Of two cases, more than 13% differences in total dwell time were observed between benchmark plans and the clinical cases, which turned out to be due to the use of the wrong source position setting. These results suggest that our method is easy and useful for independent verification of patient-specific treatment planning QA.

Quality assurance of MLC leaf position accuracy and relative dose effect at the MLC abutment region using an electronic portal imaging device.

We investigated an electronic portal image device (EPID)-based method to see whether it provides effective and accurate relative dose measurement at abutment leaves in terms of positional errors of the multi-leaf collimator (MLC) leaf position. A Siemens ONCOR machine was used. For the garden fence test, a rectangular field (0.2 20 cm) was sequentially irradiated 11 times at 2-cm intervals. Deviations from planned leaf positions were calculated. For the nongap test, relative doses at the MLC abutment region were evaluated by sequential irradiation of a rectangular field (2 20 cm) 10 times with a MLC separation of 2 cm without a leaf gap. The integral signal in a region of interest was set to position A (between leaves) and B (neighbor of A). A pixel value at position B was used as background and the pixel ratio (A/B 100) was calculated. Both tests were performed at four gantry angles (0, 90, 180 and 270°) four times over 1 month. For the nongap test the difference in pixel ratio between the first and last period was calculated. Regarding results, average deviations from planned positions with the garden fence test were within 0.5 mm at all gantry angles, and at gantry angles of 90 and 270° tended to decrease gradually over the month. For the nongap test, pixel ratio tended to increase gradually in all leaves, leading to a decrease in relative doses at abutment regions. This phenomenon was affected by both gravity arising from the gantry angle, and the hardware-associated contraction of field size with this type of machine.

Megavoltage cone beam computed tomography dose and the necessity of reoptimization for imaging dose-integrated intensity-modulated radiotherapy for prostate cancer.

PURPOSE: Megavoltage cone beam computed tomography (MV-CBCT) dose can be integrated with the patient's prescription. Here, we investigated the effects of imaging dose and the necessity for additional optimization when using intensity-modulated radiotherapy (IMRT) to treat prostate cancer. METHODS AND MATERIALS: An arc beam mimicking MV-CBCT was generated using XiO (version 4.50; Elekta, Stockholm, Sweden). The monitor units (MU) for dose calculation were determined by conforming the calculated dose to the dose measured using an ionization chamber. IMRT treatment plans of 22 patients with prostate cancer were retrospectively analyzed. Arc beams of 3, 5, 8, and 15 MU were added to the IMRT plans, and the dose covering 95% of the planning target volume (PTV) was normalized to the prescribed dose with (reoptimization) or without optimization (compensation). RESULTS: PTV homogeneity and conformality changed negligibly with MV-CBCT integration. For critical organs, an imaging dose-dependent increase was observed for the mean rectal/bladder dose (D(mean)), and reoptimization effectively suppressed the D(mean) elevations. The bladder generalized equivalent uniform dose (gEUD) increased with imaging dose, and reoptimization suppressed the gEUD elevation when 5- to 15-MU CBCT were added, although rectal gEUD changed negligibly with any imaging dose. Whereas the dose elevation from the simple addition of the imaging dose uniformly increased rectal and bladder dose, the rectal D(mean) increase of compensation plans was due mainly to low-dose volumes. In contrast, bladder high-dose volumes were increased by integrating the CBCT dose, and reoptimization reduced them when 5- to 15-MU CBCT were added. CONCLUSION: Reoptimization is clearly beneficial for reducing dose to critical organs, elevated by addition of high-MU CBCT, especially for the bladder. For low-MU CBCT aimed at bony structure visualization, compensation is sufficient.

Carbon ion irradiation suppresses metastatic potential of human non-small cell lung cancer A549 cells through the phosphatidylinositol-3-kinase/Akt signaling pathway.

We previously showed that carbon ion irradiation can inhibit the expression of the anillin (ANLN) gene, which is regulated by the activation of the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway associated with metastasis. The purpose of this study is to compare the effects of carbon ion irradiation on the PI3K/Akt signaling pathway to those of photon irradiation. Our study showed that carbon ion irradiation of human lung adenocarcinoma cells A549 decreased their invasion more effectively than photon irradiation did. We found that carbon ion irradiation reduced the nuclear localization of ANLN at lower dose, but did not affect its expression. Low-dose carbon ion irradiation also reduced the level of phosphorylated Akt compared to untreated controls, whereas photon irradiation did not. These results suggest that carbon ion irradiation effectively suppresses the metastatic potential of A549 cells by suppressing the PI3K/Akt signaling pathway.

Weekly verification of dosimetric data for virtual wedge using a 2D diode detector array.

A linac manufacturer has recommended that users measure virtual wedge (VW) angle and VW factor as a weekly quality assurance (QA) procedure. The purpose of this study was to investigate whether a 2D diode detector array (MapCHECK™) is a useful tool for the verification of dosimetric data for VW. Measurements were performed on 2 linear accelerators (4, 6, and 10 MV) at 10-cm depth for a field size of 10 × 10 cm(2) and with wedge angles of 15, 30, 45, and 60°. To verify the VW dose distributions generated by the treatment planning system (TPS), we confirmed that agreement between TPS data and measurements were ≤ 2% dose difference or 2-mm distance-to-agreement based on American Association of Physicists in Medicine Task Group Report 53 (AAPM TG-53). We present here the results of a 1-year evaluation of VW by means of a 2D diode detector array. The maximum 2-fold standard deviation of the measured wedge angle turned out to be within 1.0, and all measured VW factors to be 1.00 ± 0.03. Although >95% of the points measured for 6 and 10 MV were generally within the tolerance of the dose distribution as mentioned above, the percentage of agreement between the measured data for 4 MV and TPS data were somewhat below 90%. We also verified generally good reproducibility for the dose distribution. The 2-D diode detector array was thus found to be useful as a tool for weekly VW QA.