Intensity-modulated radiation therapy (IMRT) has been considered the most successful development in radiation oncology since the introduction of computed tomography into treatment planning that enabled three-dimensional conformal radiotherapy in 1980s. More than three decades have passed since the concept of inverse planning was first introduced in 1982, and IMRT has become the most important and common modality in radiation therapy. This review will present developments in inverse IMRT treatment planning and IMRT delivery using multileaf collimators, along with the associated key concepts. Other relevant issues and future perspectives are also presented.
Radiation Oncology ; Radiotherapy, Conformal

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The effect of setup uncertainties on CTV dose and the correlation between setup uncertainties and setup margin were evaluated by Monte Carlo based numerical simulation. Patient specific information of IMRT treatment plan for rectal cancer designed on the VARIAN Eclipse planning system was utilized for the Monte Carlo simulation program including the planned dose distribution and tumor volume information of a rectal cancer patient. The simulation program was developed for the purpose of the study on Linux environment using open source packages, GNU C++ and ROOT data analysis framework. All misalignments of patient setup were assumed to follow the central limit theorem. Thus systematic and random errors were generated according to the gaussian statistics with a given standard deviation as simulation input parameter. After the setup error simulations, the change of dose in CTV volume was analyzed with the simulation result. In order to verify the conventional margin recipe, the correlation between setup error and setup margin was compared with the margin formula developed on three dimensional conformal radiation therapy. The simulation was performed total 2,000 times for each simulation input of systematic and random errors independently. The size of standard deviation for generating patient setup errors was changed from 1 mm to 10 mm with 1 mm step. In case for the systematic error the minimum dose on CTV Dstat/Dmin was decreased from 100.4 to 72.50% and the mean dose Dsyst was decreased from 100.45% to 97.88%. However the standard deviation of dose distribution in CTV volume was increased from 0.02% to 3.33%. The effect of random error gave the same result of a reduction of mean and minimum dose to CTV volume. It was found that the minimum dose on CTV volume Drand/Dmin was reduced from 100.45% to 94.80% and the mean dose to CTV Drand was decreased from 100.46% to 97.87%. Like systematic error, the standard deviation of CTV dose DeltaDrand was increased from 0.01% to 0.63%. After calculating a size of margin for each systematic and random error the "population ratio" was introduced and applied to verify margin recipe. It was found that the conventional margin formula satisfy margin object on IMRT treatment for rectal cancer. It is considered that the developed Monte-carlo based simulation program might be useful to study for patient setup error and dose coverage in CTV volume due to variations of margin size and setup error.
Humans ; Rectal Neoplasms ; Statistics as Topic ; Tumor Burden ; Uncertainty

We report here on a rare case of primary malignant melanoma of the female urethra. A 69-year-old female presented at our hospital with a several month history of dysuria, poor stream, gross hematuria, intermittent blood spots, and a painful mass at the external urethral meatus. The physical examination revealed a soft, small, chestnut-sized lesion through the urethral orifice. The mass was tan colored, ulcerated, covered with necrotic tissue, and protruded from the external urethral meatus. The mass was removed by wide local excision under spinal anesthesia. The pathological diagnosis was malignant melanoma of the urethra. Computed tomography of the abdomen as well as a whole-body bone scan showed no evidence of metastasis. The patient has been free of disease for 6 months postoperatively. We discuss the clinicopathologic features and treatment of this tumor.
Abdomen ; Aged ; Anesthesia, Spinal ; Dysuria ; Female ; Hematuria ; Humans ; Melanoma ; Neoplasm Metastasis ; Physical Examination ; Rivers ; Triacetoneamine-N-Oxyl ; Ulcer ; Urethra

OBJECTIVE: We investigated the effect of optimization in dose-limiting shell method on the dosimetric quality of CyberKnife (CK) plans in treating brain metastases (BMs).METHODS: We selected 19 BMs previously treated using CK between 2014 and 2015. The original CK plans (CKoriginal) had been produced using 1 to 3 dose-limiting shells : one at the prescription isodose level (PIDL) for dose conformity and the others at lowisodose levels (10–30% of prescription dose) for dose spillage. In each case, a modified CK plan (CKmodified) was generated using 5 dose-limiting shells : one at the PIDL, another at intermediate isodose level (50% of prescription dose) for steeper dose fall-off, and the others at low-isodose levels, with an optimized shell-dilation size based on our experience. A Gamma Knife (GK) plan was also produced using the original contour set. Thus, three data sets of dosimetric parameters were generated and compared.RESULTS: There were no differences in the conformity indices among the CKoriginal, CKmodified, and GK plans (mean 1.22, 1.18, and 1.24, respectively; p=0.079) and tumor coverage (mean 99.5%, 99.5%, and 99.4%, respectively; p=0.177), whereas the CKmodified plans produced significantly smaller normal tissue volumes receiving 50% of prescription dose than those produced by the CKoriginal plans (p < 0.001), with no statistical differences in those volumes compared with GK plans (p=0.345).CONCLUSION: These results indicate that significantly steeper dose fall-off is able to be achieved in the CK system by optimizing the shell function while maintaining high conformity of dose to tumor.
Brain ; Dataset ; Methods ; Neoplasm Metastasis ; Prescriptions ; Radiosurgery