The Radiological Physics Center (RPC) developed two heterogeneous anthropomorphic quality assurance phantoms for use in verifying the accuracy of radiation delivery: one for intensity-modulated radiation therapy (IMRT) to the pelvis and the other for stereotactic body radiation therapy (SBRT) to the thorax. The purpose of this study was to describe the design and development of these two phantoms and to demonstrate the reproducibility of measurements generated with them. The phantoms were built to simulate actual patient anatomy. They are lightweight and water-fillable, and they contain imageable targets and organs at risk of radiation exposure that are of similar densities to their human counterparts. Dosimetry inserts accommodate radiochromic film for relative dosimetry and thermoluminesent dosimetry capsules for absolute dosimetry. As a part of the commissioning process, each phantom was imaged, treatment plans were developed, and radiation was delivered at least three times. Under these controlled irradiation conditions, the reproducibility of dose delivery to the target TLD in the pelvis and thorax phantoms was 3% and 0.5%, respectively. The reproducibility of radiation-field localization was less than 2.5 mm for both phantoms. Using these anthropomorphic phantoms, pelvic IMRT and thoracic SBRT radiation treatments can be verified with a high level of precision. These phantoms can be used to effectively credential institutions for participation in specific NCI-sponsored clinical trials.

Process data reconciliation and gross error detection have been the subject of many recent publications, for which Tamhane and Mah (1985) and Mah (1987) have provided a thorough review. Analytical solutions to linear data reconciliation problems can be obtained efficiently, for instance, by matrix projection (Crowe et al., 1983). However, solving general data reconciliation problems with nonlinear constraints invariably requires some type of iterative procedure. In this note, an iterative procedure is developed that makes use of Crowe's matrix projection and for the first time combines a quasi-Newton update with the Gauss-Newton scheme for solving nonlinear data reconciliation problems.Using the Lagrange method, Britt and Leucke (1973) developed the normal equations for nonlinear parameter estimation. More recently, Stephenson and Shewchuk (1986) and Serth et al. (1 987) also based their data reconciliation problems on the normal equations. Although straightforward, the approaches based on solving the system of normal equations suffer from two drawbacks. First, the size of the problem may be unduly large due to the Lagrange multipliers; second, first-order derivatives of the constraints appear in the normal equations and have to be calculated for every iteration.Crowe (1986) extended his method of matrix projection to bilinear constraints with an iterative procedure for determining one of the variables in the bilinear terms. Unfortunately, this procedure is too specific to be useful for more general cases.Knepper and Gorman (1980) proposed a Gauss-Newton iterative algorithm and, in order to reduce computational effort, suggested using old derivatives of constraints until the constraints are satisfied (i.e., the constant-direction approach). HLowever, their algorithm is limited to problems with no more constraints than measured variables and the constant-direction approach is characterized by slow convergence. Knepper and Glorman applied the theory of generalized inverses to solve the linearized subproblem. Crowe (private communication, 1987) presented a more general method based on matrix projection (Crowe et al., f983). The latter not only effectively reduces the problem size but also removes the restriction that no more constraints than measured variables be handled. In this note, a Broyden-type update (Broyden, 1965) is proposed to replace the old derivatives so that the rate of convergence can be improved without repeatedly evaluating the derivatives. Crowe's Iterative SchemeA general data reconciliation problem is defined aswhere f is an m vector of functions, x is an n vector of measured variables, u is an r vector of unmeasured variables, and Z is the variance-covariance matrix of measurements 2, or some weighting matrix. The sizes of these vectors are related by n + r 2 m > r z 0. Linearizing the constraint functions f around Xk and v k gives where Bk and Pk denote, respectively, the ( m x n) and ( m x r ) matrices of the derivatives offwith respect to x and v evaluated a t xk and v k .Following Crowe ...

The purpose of this study was to determine the dose to the contralateral breast during accelerated partial breast irradiation (APBI) and to compare it to external beam‐published values. Thermoluminescent dosimeter (TLD) packets were used to measure the dose to the most medial aspect of the contralateral breast during APBI simulation, daily quality assurance (QA), and treatment. All patients in this study were treated with a single‐entry, multicatheter device for 10 fractions to a total dose of 34 Gy. A mark was placed on the patient's skin on the medial aspect of the opposite breast. Three TLD packets were taped to this mark during the pretreatment simulation. Simulations consisted of an AP and Lateral scout and a limited axial scan encompassing the lumpectomy cavity (miniscan), if rotation was a concern. After the simulation the TLD packets were removed and the patients were moved to the high‐dose‐rate (HDR) vault where three new TLD packets were taped onto the patients at the skin mark. Treatment was administered with a Nucletron HDR afterloader using Iridium‐192 as the treatment source. Post‐treatment, TLDs were read (along with the simulation and QA TLD and a set of standards exposed to a known dose of 6 MV photons). Measurements indicate an average total dose to the contralateral breast of 70 cGy for outer quadrant implants and 181 cGy for inner quadrant implants. Compared to external beam breast tangents, these results point to less dose being delivered to the contralateral breast when using APBI.PACS number: 87.55.D‐

Purpose: To determine the dose to the contralateral breast during Accelerated Partial Breast Irradiation (APBI) treatment, simulation and daily QA, and to compare it to external beam published values. Methods: TLD‐100 packets were used to measure the dose to the most medial aspect of the contralateral breast during APBI simulation, daily QA, and treatment. Patient measurements were used as opposed to phantom data so as to measure more clinically relevant data that includes variability in patient size and geometry. All patients in this study were treated with a SAVI interstitial applicator for ten fractions to a total dose of 3.4Gy. Measurements were made for two or three fractions of the treatment course using three packets of TLD‐100 for each measurement. A mark was placed on the patient's skin on the medial aspect of the opposite breast. Three TLD packets were taped to this mark during the pre‐treatment simulation. Simulations and QA were conducted in our CT suite and consisted of an AP and Lateral scout or a mini scan if rotation was a concern. After the simulation the TLD packets were removed and the patients was moved to the HDR vault where three new TLD packets were taped onto the patient at the skin mark. Treatment was administered with a Nucletron HDR afterloader using Iridium 192 as the treatment source. Post treatment, the TLD were read (along with the simulation and QA TLD and a set of standards exposed to a known dose of 6 MV photons). Results: Measurements indicate a worst case exposure to the contrlateral breast of less than 250cGy. As would be expected, inner quadrant implants Result in higher dose than outer quadrants. Conclusion: Compared to external beam breast tangents, these results point to less dose to the contralateral breast when using APBI.

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