Experimental verification of Advanced Collapsed‐cone Engine for use with a multichannel vaginal cylinder applicator

Abstract

Model‐based dose calculation algorithms have recently been incorporated into brachytherapy treatment planning systems, and their introduction requires critical evaluation before clinical implementation. Here, we present an experimental evaluation of Oncentra® Brachy Advanced Collapsed‐cone Engine (ACE) for a multichannel vaginal cylinder (MCVC) applicator using radiochromic film. A uniform dose of 500 cGy was specified to the surface of the MCVC using the TG‐43 dose formalism under two conditions: (a) with only the central channel loaded or (b) only the peripheral channels loaded. Film measurements were made at the applicator surface and compared to the doses calculated using TG‐43, standard accuracy ACE (sACE), and high accuracy ACE (hACE). When the central channel of the applicator was used, the film measurements showed a dose increase of (11 ± 8)% (k = 2) above the two outer grooves on the applicator surface. This increase in dose was confirmed with the hACE calculations, but was not confirmed with the sACE calculations at the applicator surface. When the peripheral channels were used, a periodic azimuthal variation in measured dose was observed around the applicator. The sACE and hACE calculations confirmed this variation and agreed within 1% of each other at the applicator surface. Additionally for the film measurements with the central channel used, a baseline dose variation of (10 ± 4)% (k = 2) of the mean dose was observed azimuthally around the applicator surface, which can be explained by offset source positioning in the central channel.

Initial evaluation of Advanced Collapsed cone Engine dose calculations in water medium for I‐125 seeds and COMS eye plaques

“…As mentioned previously, since the total PSS point dose deposition kernel data is normalized to match the TG‐43 doses at 1 cm on the transverse axis internally within the OcB software, this difference is expected to propagate to the ACE data. Overall, the agreement between ACE and both TG‐43 and MCNP6 is within the uncertainties of the TPS calculations (4.7% for k = 1 for TG‐43 based planning [based on estimates from TG‐138 method]), and ~5% for ACE calculations). The 5% uncertainty in ACE calculations was determined based on single source TG‐186 level 1 commissioning results for the generic high‐dose rate Ir‐192 source .…”

Comprehensive methodology for commissioning modern 3D-image-based treatment planning systems for high dose rate gynaecological brachytherapy: A review

“…Inhomogeneity modelling accuracy: Verifies that the TPS models the inhomogeneities in GYN cases and modifies the dose distributions according to the attenuation/scattering properties of these inhomogeneities (especially applicators and shields) [10,19,26,27,30,[53][54][55]. This test is particularly important for the applicators and shields in GYN cases.…”

Impact of a commercially available model-based dose calculation algorithm on treatment planning of high-dose-rate brachytherapy in patients with cervical cancer

“…The primary dose was calculated using a ray trace of the primary photons in a grid that generates scatter energy, which is then input into the collapsed cone superposition convolution algorithm. This algorithm uses angular discretization of radiation transport directions and pre-calculated dose deposition point kernels in water, scaled to reflect the influence of inhomogeneities [ 21 – 23 ]. A material composition and density were assigned to each structure in order to use the MBDCA.…”