Absorbed dose distributions from beta‐decaying radionuclides: Experimental validation of Monte Carlo tools for radiopharmaceutical dosimetry

Abstract

Purpose This study aims to experimentally validate the Monte Carlo generated absorbed doses from the beta particles emitted by 90Y and 177Lu using radiochromic EBT3 film‐based dosimetry. Methods Line sources of 90Y and 177Lu were inserted longitudinally through blocks of low‐density polyethylene and tissue‐equivalent slabs of cortical bone and lung equivalent plastics. Radiochromic film (Gafchromic EBT3) was laser cut to accommodate orthogonal line sources of radioactivity, and the film was sandwiched intimately between the rectangular blocks to achieve charged particle equilibrium. Line sources consisted of plastic capillary tube of length (13 ± 0.1) cm, with 0.42‐mm inner diameter and a wall thickness of 0.21 mm. 90Y line sources were prepared from a solution of dissolved 90Y resin microspheres. 177Lu line sources were prepared from an aliquot of 177Lu‐DOTATATE. Film exposures were conducted for durations ranging from 10 min to 38 h. Radiochromic film calibration was performed by irradiation with 6‐MV‐bremsstrahlung x rays from a calibrated linear accelerator, in accordance with literature recommendations. Experimental geometries were precisely simulated within the GATE Monte Carlo toolkit, which has previously been used for the generation of dose point kernels. Results The mean percentage difference between measured and simulated absorbed doses were 5.04% and 7.21% for 90Y and 177Lu beta absorbed dose in the range of (0.1–10) Gy. Additionally, 1D gamma analysis using a local 10%/1 mm gamma criterion was performed to compare the absorbed dose distributions. The percentage of measurement points passing the gamma criterion, averaged over all tests, was 93.5%. Conclusions We report the experimental validation of Monte Carlo derived beta absorbed dose distributions for 90Y and 177Lu, solidifying the validity of using Monte Carlo‐based methods for estimating absorbed dose from beta emitters. Overall, excellent agreement was observed between the experimental beta absorbed doses in the linear region of the radiochromic film and the GATE Monte Carlo simulations demonstrating that radiochromic film dosimetry has sufficient sensitivity and spatial resolution to be used as a tool for measuring beta decay absorbed dose distributions.

Experimental validation of Monte Carlo dosimetry for therapeutic beta emitters with radiochromic film in a 3D‐printed phantom

“…Tiwari et al. 11 was able to measure beta energy deposition above 1 mm, and Villarreal‐Barajas et al. 14 showed the potential to measure at 0.104 mm, but found damage to their first three layers of RF, and recorded their first clean measurement at 0.416 mm.…”

“…Prior work on experimental measurement of short‐range beta emitters has shown the viability of using RF as an effective measurement tool for these radionuclides but lacks the capability to reliably measure at short distances, where a large portion of the dose is deposited for many radionuclides of interest. Tiwari et al 11 . was able to measure beta energy deposition above 1 mm, and Villarreal‐Barajas et al 14 .…”

“…Prior work on experimental measurement of shortrange beta emitters has shown the viability of using RF as an effective measurement tool for these radionuclides but lacks the capability to reliably measure at short distances, where a large portion of the dose is deposited for many radionuclides of interest. Tiwari et al 11 was able to measure beta energy deposition above 1 mm, and Villarreal-Barajas et al 14 showed the potential to measure at 0.104 mm, but found damage to their first three layers of RF, and recorded their first clean measurement at 0.416 mm. It is unclear if the geometry proposed by Villarreal-Barajas et al would be reliable at 0.416 mm or at any lower distances as only a single measurement appears to have been attempted.…”

“…The ongoing interest in these low energy beta measurements has prompted other experiments with Tiwari et al., 11 demonstrating the use of RF measurement for 90 Y and 177 Lu at distances between 1 mm and 15 mm from the source, although the first 1–2 mm of the film was impacted by delamination. Their experimental configuration showed good correlation with GEANT4 Application for Tomographic Emission (GATE) 12 MC at these distances and incorporated direct measurement of the beta, gamma, and bremsstrahlung portions of the deposited dose.…”

The effect of magnetic field strength on the positron range and projected annihilation artifact in integrated PET/MR systems: A GATE Monte Carlo study

“…The GATE MC simulation package [36][37][38] (version 7.0.0) was used to simulate the annihilation distribution of positrons in different tissue and MFs. Gate toolkit can define an MF with different strengths in the interest direction.…”