Consensus statement on tumour bed localization for radiation after oncoplastic breast surgery.

Background: Oncoplastic surgery (ops) is becoming the new standard of care for breast-conserving surgery, leading to some challenges with adjuvant radiation, particularly when accurate tumour bed (tbd) delineation is needed for focused radiation (that is, accelerated partial breast irradiation or boost radiation). Currently, no guidelines have been published concerning tbd localization for adjuvant targeted radiation after ops. Methods: A modified Delphi method was used to establish consensus by a panel of 20 experts in surgical and radiation oncology at the Canadian Locally Advanced Breast Cancer National Consensus Group and in a subsequent online member survey. Results: These are the main recommendations:■ Surgical clips are necessary and should, at a minimum, be placed along the 4 side walls of the cavity, plus 1-4 clips at the posterior margin if necessary.■ Operative reports should include pertinent information to help guide the radiation oncologists.■ Breast surgeons and radiation oncologists should have a basic understanding of ops techniques and work on "speaking a common language."■ Careful consideration is needed when determining the value of targeted radiation, such as boost, in higher-level ops procedures with extensive tissue rearrangement. Conclusions: The panel developed a total of 6 recommendations on tbd delineation for more focused radiation therapy after ops, with more than 80% agreement on each statement. All are summarized, together with the corresponding evidence or expert opinion.

Small composite field correction factors for the CyberKnife radiosurgery system: clinical and PCSR plans.

A formalism has been proposed for small and non-standard photon fields in which [Formula: see text] correction factors are used to correct dosimeter response in small fields (indiviual or composite) relative to that in a larger machine-specific reference (MSR) field. For clinical plans consisting of several fields, a plan-class specific reference (PCSR) plan can also be defined, serving as an intermediate calibration field between the MSR and clinical plans within a certain plan-class. In this work, the formalism was applied in the calculation of [Formula: see text] for 21 clinical plans delivered by the [Formula: see text] radiosurgery system, each plan employing one or two of the smallest diameter collimators: 5 mm, 7.5 mm, and 10 mm. Three detectors were considered: the Exradin A16 and A26 micro chambers, and the W1 plastic scintillator. The clinical plans were grouped into 7 plan-classes according to commonly shared characteristics. The suitability of using a PCSR plan to represent the detector response of each plan within the plan-class was investigated. Total and intermediate correction factors were calculated using the [Formula: see text] Monte Carlo user code. The corrections for the micro chambers were large, primarily due to the presence of the low-density air cavity and the volume averaging effect. The correction for the scintillator was found to be close to unity for most plans, indicating that this detector may be used to measure small clinical plan correction factors in any plan except for those using the 5 mm collimator. The PCSR plan was shown to be applicable to plan-classes comprising isocentric plans only, with plan-classes divided according to collimator size. For non-isocentric plans, the variation of [Formula: see text] as a function of the point of measurement within a single plan, as well as the high inter-plan-class variability of the correction factor, precludes the use of a PCSR plan.

Monte Carlo calculation of VMAT and helical tomotherapy dose distributions for lung stereotactic treatments with intra-fraction motion.

The aim of this study is to calculate realistic dose distributions that include the continuous deformation of organs and continuous motion of machine using 4D Monte Carlo methods for both volumetric modulated arc therapy and helical tomotherapy treatments. As part of a previous study, we presented a method to perform position-probability-sampled Monte Carlo dose calculations in the BEAMnrc and DOSXZYnrc user codes of EGSnrc. In this study, the DOSXYZnrc user code was further modified to account for the continuous intra-fraction deformation of the patient geometry. We implemented in the user code a method to update the transport grid densities as a function of time and map the energy deposited in the time dependent transport grid back to a reference grid. We provide information on the measurements performed to validate the implementation of this method and present an example of the application of the method for lung stereotactic treatments with intra-fraction motion. The results show that breathing motion is properly addressed with the internal target volume method for the cases studied.