Analysis of Predictive Factors for Lung Injury after Forward-Planned Intensity-Modulated Radiotherapy in Whole Breast Irradiation / 한국유방암학회지

PURPOSE: This study was performed to assess frequency, timings of occurrence, and predictors of radiologic lung damage (RLD) after forward-planned intensity-modulated radiotherapy (FIMRT) for whole breast irradiation. METHODS: We retrospectively reviewed medical records of 157 breast cancer patients and each of their serial chest computed tomography (CT) taken 4, 10, 16, and 22 months after completion of breast radiotherapy (RT). FIMRT was administered to whole breast only (n=152), or whole breast and supraclavicular regions (n=5). Dosimetric parameters, such as mean lung dose and lung volume receiving more than 10 to 50 Gy (V10-V50), and clinical parameters were analyzed in relation to radiologic lung damage. RESULTS: In total, 104 patients (66.2%) developed RLD after whole breast FIMRT. Among the cases of RLD, 84.7% were detected at 4 months, and 15.3% at 10 months after completion of RT. More patients of 47 or younger were found to have RLD at 10 months after RT than patients older than the age (11.7% vs. 2.9%, p=0.01). In univariate and multivariate analyses, age >47 and V40 >7.2% were significant predictors for higher risk of RLD. CONCLUSION: RLD were not infrequently detected in follow-up CT after whole breast FIMRT. More detected cases of RLD among younger patients are believed to have developed at later points after RT than those of older patients. Age and V40 were significant predictors for RLD after whole breast intensity-modulated radiotherapy.

Implementation and Evaluation of the Electron Arc Plan on a Commercial Treatment Planning System with a Pencil Beam Algorithm / 의학물리

Less execution of the electron arc treatment could in large part be attributed to the lack of an adequate planning system. Unlike most linear accelerators providing the electron arc mode, no commercial planning systems for the electron arc plan are available at this time. In this work, with the expectation that an easily accessible planning system could promote electron arc therapy, a commercial planning system was commissioned and evaluated for the electron arc plan. For the electron arc plan with use of a Varian 21-EX, Pinnacle3 (ver. 7.4f), with an electron pencil beam algorithm, was commissioned in which the arc consisted of multiple static fields with a fixed beam opening. Film dosimetry and point measurements were executed for the evaluation of the computation. Beam modeling was not satisfactory with the calculation of lateral profiles. Contrary to good agreement within 1% of the calculated and measured depth profiles, the calculated lateral profiles showed underestimation compared with measurements, such that the distance-to-agreement (DTA) was 5.1 mm at a 50% dose level for 6 MeV and 6.7 mm for 12 MeV with similar results for the measured depths. Point and film measurements for the humanoid phantom revealed that the delivered dose was more than the calculation by approximately 10%. The electron arc plan, based on the pencil beam algorithm, provides qualitative information for the dose distribution. Dose verification before the treatment should be mandatory.

Estimation of Jaw and MLC Transmission Factor Obtained by the Auto-modeling Process in the Pinnacle3 Treatment Planning System / 의학물리

Radiation treatment techniques using photon beam such as three-dimensional conformal radiation therapy (3D-CRT) as well as intensity modulated radiotherapy treatment (IMRT) demand accurate dose calculation in order to increase target coverage and spare healthy tissue. Both jaw collimator and multi-leaf collimators (MLCs) for photon beams have been used to achieve such goals. In the Pinnacle3 treatment planning system (TPS), which we are using in our clinics, a set of model parameters like jaw collimator transmission factor (JTF) and MLC transmission factor (MLCTF) are determined from the measured data because it is using a model-based photon dose algorithm. However, model parameters obtained by this auto-modeling process can be different from those by direct measurement, which can have a dosimetric effect on the dose distribution. In this paper we estimated JTF and MLCTF obtained by the auto-modeling process in the Pinnacle3 TPS. At first, we obtained JTF and MLCTF by direct measurement, which were the ratio of the output at the reference depth under the closed jaw collimator (MLCs for MLCTF) to that at the same depth with the field size 10x10 cm2 in the water phantom. And then JTF and MLCTF were also obtained by auto-modeling process. And we evaluated the dose difference through phantom and patient study in the 3D-CRT plan. For direct measurement, JTF was 0.001966 for 6 MV and 0.002971 for 10 MV, and MLCTF was 0.01657 for 6 MV and 0.01925 for 10 MV. On the other hand, for auto-modeling process, JTF was 0.001983 for 6 MV and 0.010431 for 10 MV, and MLCTF was 0.00188 for 6 MV and 0.00453 for 10 MV. JTF and MLCTF by direct measurement were very different from those by auto-modeling process and even more reasonable considering each beam quality of 6 MV and 10 MV. These different parameters affect the dose in the low-dose region. Since the wrong estimation of JTF and MLCTF can lead some dosimetric error, comparison of direct measurement and auto-modeling of JTF and MLCTF would be helpful during the beam commissioning.