Correction method for the physical dose calculated using Clarkson integration at the center of the spread-out Bragg peak for asymmetric field in carbon-ion radiotherapy

Purpose: We previously proposed a calculation method using Clarkson integration to obtain the physical dose at the center of the spread-out Bragg peak (SOBP) for a treatment beam, the measurement point of which agrees with the isocenter [Tajiri et al. Med. Phys. 2013; 40: 071733−1−5]. However, at the measurement point which does not agree with the isocenter, the physical dose calculated by this method might have a large error. For this error, we propose a correction method.Materials and methods: To confirm whether the error can be corrected using in-air off axis ratio (OAR), we measured the physical dose at the center of an asymmetric square field and a symmetric square field and in-air OAR. For beams of which the measurement point does not agree with the isocenter, as applied to prostate cancer patients, the physical dose calculated using Clarkson integration was corrected with in-air OAR.Results: The maximum difference between the physical dose measured at the center of an asymmetric square field and the product of in-air OAR and the physical dose at the center of a symmetric square field was – 0.12 %. For beams as applied to prostate cancer patients, the differences between the measured physical doses and the physical doses corrected using in-air OAR were –0.17 ± 0.23%.Conclusions: The physical dose at the measurement point which does not agree with the isocenter, can be obtained from in-air OAR at the isocenter plane and the physical dose at the center of the SOBP on the beam axis

Calculation method using Clarkson integration for the physical dose at the center of the spread-out Bragg peak in carbon-ion radiotherapy

Purpose: In broad-beam carbon-ion radiotherapy performed using the heavy-ion medical accelerator in Chiba, the number of monitor units is determined by measuring the physical dose at the center of the spread-out Bragg peak (SOBP) for the treatment beam. The total measurement time increases as the number of treatment beams increases, which hinders the treatment of an increased number of patients. Hence, Kusano et al.[Jpn. J. Med. Phys. 23 (Suppl. 2), 65-68 (2003)] proposed a method to calculate the physical dose at the center of the SOBP for a treatment beam. Based on a recent study, the authors here propose a more accurate calculation method.Methods: The authors measured the physical dose at the center of the SOBP while varying the circular field size and range-shifter thickness. The authors obtained the physical dose at the center of the SOBP for an irregularly shaped beam using Clarkson integration based on these measurements.Results: The difference between the calculated and measured physical doses at the center of the SOBP varied with a change in the central angle of the sector segment. The differences between the calculated and measured physical doses at the center of the SOBP were within 1% for all irregularly shaped beams that were used to validate the calculation method.Conclusions: The accuracy of the proposed method depends on both the number of angular intervals used for Clarkson integration and the fineness of the basic data used for calculations: sampling numbers for the field size and thickness of the range shifter. If those parameters are properly chosen, the authors can obtain a calculated monitor unit number with high accuracy sufficient for clinical applications

Variation in patient position and impact on carbon-ion scanning beam distribution during prostate treatment

Purpose: We assessed the impact of changes in patient position on carbon-ion scanning beam distribution during treatment for prostate cancer.Methods: Sixty-eight patients were selected. Carbon-ion scanning dose was calculated. Two different planning target volumes (PTVs) were defined: PTV1 was the clinical target volume plus a setup margin for the anterior/lateral sides and posterior side, while PTV2 was the same as PTV1 minus the posterior side. Total prescribed doses of 34.4Gy (RBE) and 17.2Gy (RBE) were given to PTV1 and PTV2, respectively. To estimate the influence of the geometric variations on dose distribution, the dose was recalculated on the rigidly shifted single planning CT based on the 2D-3D rigid registration of the orthogonal X-ray images before and after treatment for the fraction of maximum positional changes.Results: Intrafractional patient positional change values average over all patients throughout the treatment course were less than target registration error = 2.00 mm and angular error = 1.27 deg. However, these maximum positional errors did not occur in all twelve-treatment fractions. Even though large positional changes occurred during irradiation in all treatment fractions, D95-PTV1 was over 98 % of the prescribed dose.Conclusions: Intrafractional patient positional changes occurred during treatment beam irradiation and degraded carbon-ion beam dose distribution. Our evaluation was not considered non-rigid deformations, albeit that, distribution was still within levels considered clinically acceptable.Advances in knowledge: Inter- and intra-fractional changes did not affect carbon-ion beam prostate treatment accuracy

A new approach to estimate the amount of tumor stroma as a prognostic factor using SUVmax and SUVpeak in pancreatic cancer

ObjectiveVarious parameters are used for measuring tumor glucose metabolic activity with 18F-FDG PET including measuring the single maximum pixel value within the slice with highest radioactivity concentration (SUVmax) or placing a fixed ROI in the area of the tumor with the highest level of 18F-FDG uptake (SUVpeak), which it defines as the largest possible mean value of a spherical VOI with radius 10 mm positioned within a tumor (SUVpeak10). It is said that the amount of tumor stroma correlates with prognosis of patients with cancer. We estimated the amount of tumor stroma with 18F-FDG-PET using SUVmax and SUVpeak10, and evaluated the prediction performance of the amount of tumor stroma with 18F-FDG-PET after surgery of pancreatic cancer.MethodsSixteen pre-surgery patients with either proven or suspected primary pancreatic cancer underwent 18F-FDG-PET/CT. The pathologically confirmation found out 13 malignancy in all cases. According to pathological findings, the stroma of tumors were quantitatively classified in 3 types (Scirrhous type: abundant stroma, Intermediate type: a type intermediate between the scirrhous type and the medullary type, and Medullary type: scanty stroma). We evaluated the correlation between the amount of tumor stroma and each 3 indexes, SUVmax, SUVpeak10 and SUVstroma. SUVstroma was calculated by the following equation:SUVstroma =1- [SUVpeak10] / [SUVmax]18F-FDG accumulates in tumor cells but does not accumulate so much in stromal cells. The tumor with abundant stroma might be low SUVpeak10, so SUVstroma might be high. Because the tumor cell avidly accumulates 18F-FDG but stroma does not so much.Each 3 indexes of SUV (SUVmax, SUVpeak10 and SUVstroma) were statistically compared with 3 types of stroma classification using the Mann-Whitney\u27s U test. The overall survival (OS) was calculated using Kaplan-Meier method by SUVs found statistically-significant with Mann-Whitney\u27s U test.ResultsThere was no patient with Medullary type in our cases. Statistically-significant difference was observed between Scirrhous type and Intermediate type in SUVstroma (p0.3 had markedly lower OS rate than those with SUVstroma<0.3 (0% vs. 50% p<0.05). ConclusionWe think that SUVstroma could estimate the amount of tumor stroma, and it is useful for predicting prognosis of the patients with pancreatic cancer.EANM\u2713 - Annual Congress of the European Association of Nuclear Medicin

Increased periostin associates with greater airflow limitation in patients receiving inhaled corticosteroids.

[Background]Periostin, an extracellular matrix protein, contributes to subepithelial thickening in asthmatic airways, and its serum levels reflect airway eosinophilic inflammation. However, the relationship between periostin and the development of airflow limitation, a functional consequence of airway remodeling, remains unknown. [Objective]We aimed to determine the relationship between serum periostin levels and pulmonary function decline in asthmatic patients on inhaled corticosteroid (ICS) treatment. [Methods]Two hundred twenty-four asthmatic patients (average age, 62.3 years) treated with ICS for at least 4 years were enrolled. Annual changes in FEV1, from at least 1 year after the initiation of ICS treatment to the time of enrollment or later (average, 16.2 measurements over 8 years per individual), were assessed. At enrollment, clinical indices, biomarkers that included serum periostin, and periostin gene polymorphisms were examined. Associations between clinical indices or biomarkers and a decline in FEV1 of 30 mL or greater per year were analyzed. [Results]High serum periostin levels (≥95 ng/mL) at enrollment, the highest treatment step, higher ICS daily doses, a history of admission due to asthma exacerbation, comorbid or a history of sinusitis, and ex-smoking were associated with a decline in FEV1 of 30 mL or greater per year. Multivariate analysis showed that high serum periostin, the highest treatment step, and ex-smoking were independent risk factors for the decline. Polymorphisms of periostin gene were related to higher serum periostin levels (rs3829365) and a decline in FEV1 of 30 mL or greater per year (rs9603226). [Conclusions]Serum periostin appears to be a useful biomarker for the development of airflow limitation in asthmatic patients on ICS