The purpose of this report is to provide detailed guidance on the dosimetry of the INTRABEAM® (Carl Zeiss Medical AG, Jena, Germany) electronic brachytherapy (eBT) system as it stands at the present time. This report has been developed by the members of American Association of Physicists in Medicine (AAPM) Task Group 292 and endorsed by the AAPM. Members of AAPM Task Group 292 on Electronic‐Brachytherapy Dosimetry have reviewed pertinent publications and user manuals regarding the INTRABEAM system dosimetry and manufacturer‐supplied dose calculation protocols. Formal written correspondence with Zeiss has also provided further clarification. Dose‐rate calculations for the INTRABEAM system are highly dependent on choice of dosimetry protocol. Even with careful protocol selection, large uncertainties remain due to the incomplete characterization of the ionization chambers used for verification with respect to their energy dependence as well as manufacturing variations. There are two distinct sets of dose‐rate data provided by Zeiss for the INTRABEAM system. One dataset (Calibration V4.0) is representative of the physical dose surrounding the source and the other dataset (TARGIT) has been adjusted to be consistent with a clinical trial named TARGIT (TARGeted Intraoperative RadioTherapy). The adjusted TARGIT doses are quite dissimilar to the physical doses, with differences ranging from 14% to 30% at the surface of a spherical applicator, depending on its diameter, and up to a factor of two at closer distances with the smaller needle applicators. In addition, ion chamber selection and associated manufacturing tolerances contribute to significant additional uncertainties. With these substantial differences in dose rates and their associated uncertainties, it is important for users to be aware of how each value is calculated and whether it is appropriate to be used for the intended treatment. If users intend to deliver doses that are the same as they were in 1998 at the onset of the TARGIT trial, then the TARGIT dose‐rate tables should be used. The Calibration V4.0 dose rates may be more appropriate to use for applications other than TARGIT trial treatments, since they more closely represent the physical doses being delivered. Users should also be aware of the substantial uncertainties associated with the provided dose rates, which are due to beam hardening, chamber geometry, and selection of the point‐of‐measurement for a given ionization chamber. This report serves to describe the details and implications of the manufacturer‐recommended dosimetry formalism for users of the INTRABEAM system.

Purpose: Synchrony is a motion management system available on the Radixact linear accelerator that utilizes kilovoltage (kV) radiographs to track target motion and synchronize the delivery of radiation with the motion. Proper management of this imaging dose requires accurate quantification. The purpose of this work was to use Monte Carlo (MC) simulations to quantify organ‐specific patient doses from these images for various patient anatomies.Methods: Point doses in water were measured per TG‐61 for three beam qualities commonly used on the Radixact. The point doses were used to benchmark a model of the imaging system built using the Monte Carlo N‐Particle (MCNP) transport code. Patient computed tomography (CT) datasets were obtained for 5 patients and 100 planar images were simulated for each patient. Patient dose was calculated using energy deposition mesh tallies.Results: The MCNP model was able to accurately reproduce the measured point doses, with a median dose difference of less than 1%. The median dose (D_50%) to soft tissue from 100 radiographs among the 5 patient cases ranged from 2.0 to 4.6 mGy. The max dose (D_1%) to soft tissue ranged from 6.2 to 31.0 mGy and the max dose to bony structures ranged from 20.2 to 71.7 mGy. These doses can be scaled to estimate total patient dose throughout many fractions.Conclusions: Patient dose is largely dependent on imaging protocol, patient size, and treatment parameters such as fractionation and gantry period. Organ doses from 100 radiographs (an approximate number for one fraction) on the Radixact are slightly less than the doses from Tomo MVCT setup images. Careful selection of clinical protocols and planning parameters can be used to minimize risk from these images.

Objective . Pencil beam scanning (PBS) proton therapy target dose conformity can be improved with energy layer-specific collimation. One such collimator is the dynamic collimation system (DCS), which consists of four nickel trimmer blades that intercept the scanning beam as it approaches the lateral extent of the target. While the dosimetric benefits of the DCS have been demonstrated through computational treatment planning studies, there has yet to be experimental verification of these benefits for composite multi-energy layer fields. The objective of this work is to dosimetrically characterize and experimentally validate the delivery of dynamically collimated proton therapy with the DCS equipped to a clinical PBS system. Approach . Optimized single field, uniform dose treatment plans for 3 × 3 × 3 cm ³ target volumes were generated using Monte Carlo dose calculations with depths ranging from 5 to 15 cm, trimmer-to-surface distances ranging from 5 to 18.15 cm, with and without a 4 cm thick polyethylene range shifter. Treatment plans were then delivered to a water phantom using a prototype DCS and an IBA dedicated nozzle system and measured with a Zebra multilayer ionization chamber, a MatriXX PT ionization chamber array, and Gafchromic™ EBT3 film. Main results . For measurements made within the SOBPs, average 2D gamma pass rates exceeded 98.5% for the MatriXX PT and 96.5% for film at the 2%/2 mm criterion across all measured uncollimated and collimated plans, respectively. For verification of the penumbra width reduction with collimation, film agreed with Monte Carlo with differences within 0.3 mm on average compared to 0.9 mm for the MatriXX PT. Significance . We have experimentally verified the delivery of DCS-collimated fields using a clinical PBS system and commonly available dosimeters and have also identified potential weaknesses for dosimeters subject to steep dose gradients.