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Purpose: To investigate how single or fractionated doses of radiation change the microenvironment in transgenic adenocarcinoma of the mouse prostate (TRAMP)-C1tumors with respect to vascularity, hypoxia, and macrophage infiltrates. Experimental Design: Murine prostate TRAMP-C1 tumors were grown in C57BL/6J mice to 4 mm tumor diameter and were irradiated with either 25 Gy in a single dose or 60 Gy in 15 fractions. Changes in vascularity, hypoxia, and macrophage infiltrates were assessed by immunohistochemistry and molecular assays. Results: Tumor growth was delayed for 1week after both radiation schedules. Tumor microvascular density (MVD) progressively decreased over a 3-week period to nadirs of 25% and 40% of unirradiated tumors for single or fractionated treatment, respectively. In accord with the decrease in MVDs, mRNA levels of endothelial markers, such as CD31, endoglin, and TIE, decreased over the same time period after irradiation. Central dilated vessels developed surrounded by avascularized hypoxic regions that became infiltrated with aggregates of CD68+ tumorassociated macrophages, reaching a maximum at 3 weeks after irradiation. Necrotic regions decreased and were more dispersed. Conclusion: Irradiation of TRAMP-C1tumors with either single or fractionated doses decreases MVD, leading to the development of disperse chronic hypoxic regions, which are infiltrated with CD68+ tumor-associated macrophages. Approaches to interfere in the development of these effects are promising strategies to enhance the efficacy of cancer radiotherapy.

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The purpose of this study was to assess the feasibility of using a multiple partial volumetric‐modulated arcs therapy (MP‐VMAT) technique on the left breast irradiation and to evaluate the dosimetry and treatment efficiency. Ten patients with left‐sided breast cancer who had been treated by whole breast irradiation were selected for the treatment plan evaluation by using six partial volumetric modulated arcs. Each arc consisted of a 50° gantry rotation. The planning target volumes and the normal organs, including the right breast, the bilateral lungs, left ventricle, heart, and unspecified tissue, were contoured on the CT images. Dose‐volume histograms were generated and the delivery time for each arc was recorded. The PTV received greater than 95% of the V95 for all cases, and the maximum dose was within ±1% of 110% of the prescription dose. The mean homogeneity index (HI) was 10.61±0.99, and mean conformity index (CI) was 1.21±0.03. The mean dose, V5, V10, V25, and V30 of the heart were 7.61±1.38 Gy, 59.73% ±15.87%, 24.39% ±6.82%, 2.52% ±1.11%, and 1.57% ±0.71%, respectively. The volume of the left ventricle receiving 25 Gy was 5.15% ±2.23%. The total lung mean dose was 5.57±0.36 Gy, with V5 of 25.39% ±3.88% and V20 of 5.66% ±0.89%. The right breast received a mean dose of 2.13±0.22 Gy, with V5 of 1.83% ±1.22% and V10 of 0.04% ±0.12%. The mean dose of unspecified tissue was 5.34±0.37 Gy and V5 was 22.23% ±1.57%. The volume of the unspecified tissue receiving 50 Gy was 0.50% ±0.14%. The mean delivery time for each arc was 13.9 seconds. The average MU among ten patients was 511 MU (range 443 to 594 MUs). The MP‐VMAT technique for the left‐sided breast cancer patients achieved adequate target dose coverage while maintaining low doses to organs‐at‐risk, and therefore reduced the potential for induction of second malignancy and side effects. The highly efficient treatment delivery would be beneficial for improving patient throughput, providing patient comfort, and achieving precise treatment with the breathing control system.PACS number: 87.55.‐x, 87.55.D‐, 87.55.dk

Bing-Shen Huang for his pertinent comments on unirradiated liver volume to standard liver volume ratio calculation.

Background: Medical physicists are essential members of the radiation oncology team. Given the increasing complexity of radiotherapy delivery, it is important to ensure adequate training and staffing. The aim of the present study was to update a similar survey from 2008 and assess the situation of medical physicists in the large and diverse Asia Pacific region.

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