Abstract
To develop dose optimization schemes of breast balloon brachytherapy using a stepping of Ir192 HDR source.There is a considerable underdosage (11%–13%) of PTV due to anisotropy of a stationary source in breast balloon brachytherapy. We improved the PTV coverage by varying multiple dwell positions and weights. We assumed that the diameter of spherical balloons varied from 4.0 cm to 5.0 cm, that the PTV was a 1‐cm thick spherical shell over the balloon (reduced by the small portion occupied by the catheter path), and that the number of dwell positions varied from 2 to 13 with 0.25‐cm steps, oriented symmetrically with respect to the balloon center. By assuming that the perfect PTV coverage can be achieved by spherical dose distributions from an isotropic source, we developed an optimization program to minimize two objective functions defined as: (1) the number of PTV‐voxels having more than 10% difference between optimized doses and spherical doses, and (2) the difference between optimized doses and spherical doses per PTV‐voxel.The optimal PTV coverage occurred when applying 8–11 dwell positions with weights determined by the optimization scheme. Since the optimization yields ellipsoidal isodose distributions along the catheter, there is relative skin sparing for cases with source movement approximately tangent to the skin. We also verified the optimization in CT‐based treatment planning systems.Our volumetric dose optimization for PTV coverage showed close agreement to linear or multiple‐points optimization results from the literature. The optimization scheme provides a simple and practical solution applicable to the clinic.PACS number: 87.55.de
Highlights
91 Chang Hyun Choi, et al.: Dose optimization...that it eliminates residual foci of tumor near the surgical bed by delivering adequate doses in one week, while reducing doses to normal tissues
It is known that part of the planning target volume (PTV) is underdosed due to anisotropy of the source.[7,8,9] Recent Monte Carlo studies[9,10,11] have shown that doses to the PTV and the skin in the early trials have been overestimated by neglecting the lack of scatter and the attenuation by contrast media in the balloon
Our volumetric dose optimization showed a close PTV-dose volume histograms (DVH) agreement with the results obtained using linear or multiple-points optimization in the literature.[7,8,11] All of these suggest that 11%– 13% of the PTV does not receive the prescription dose, primarily due to anisotropy, and propose multiple dwell positions for an improved PTV coverage
Summary
91 Chang Hyun Choi, et al.: Dose optimization...that it eliminates residual foci of tumor near the surgical bed by delivering adequate doses in one week, while reducing doses to normal tissues. It is known that part of the planning target volume (PTV) is underdosed due to anisotropy of the source.[7,8,9] Recent Monte Carlo studies[9,10,11] have shown that doses to the PTV and the skin in the early trials have been overestimated by neglecting the lack of scatter and the attenuation by contrast media in the balloon This presented two issues: that skin erythema seen in the early trials occurred at lower doses than previously thought, and that the PTV below the skin and along the source axis may not be adequately treated.[11] On the other hand, recent studies[8, 12] have shown that dose optimization by using multiple dwell positions along the balloon catheter can produce better isodose surfaces enclosing the PTV. Conformal plans optimized by using multiple dwell positions and dwell times are suggested by a recent research protocol (NSABP B39/RTOG 0413), in clinical practice most cases are treated with a stationary source (i.e. a single dwell position)
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