Experimental assessment of out‐of‐field dose components in high energy electron beams used in external beam radiotherapy

Abstract

The purpose of this work was to experimentally investigate the out‐of‐field dose in a water phantom, with several high energy electron beams used in external beam radiotherapy (RT). The study was carried out for 6, 9, 12, and 18 MeV electron beams, on three different linear accelerators, each equipped with a specific applicator. Measurements were performed in a water phantom, at different depths, for different applicator sizes, and off‐axis distances up to 70 cm from beam central axis (CAX). Thermoluminescent powder dosimeters (TLD‐700) were used. For given cases, TLD measurements were compared to EBT3 films and parallel‐plane ionization chamber measurements. Also, out‐of‐field doses at 10 cm depth, with and without applicator, were evaluated. With the Siemens applicators, a peak dose appears at about 12–15 cm out of the field edge, at 1 cm depth, for all field sizes and energies. For the Siemens Primus, with a 10×10cm2 applicator, this peak reaches 2.3%, 1%, 0.9% and 1.3% of the maximum central axis dose (Dmax) for 6, 9, 12 and 18 MeV electron beams, respectively. For the Siemens Oncor, with a 10×10cm2 applicator, this peak dose reaches 0.8%, 1%, 1.4%, and 1.6% of Dmax for 6, 9, 12, and 14 MeV, respectively, and these values increase with applicator size. For the Varian 2300C/D, the doses at 12.5 cm out of the field edge are 0.3%, 0.6%, 0.5%, and 1.1% of Dmax for 6, 9, 12, and 18 MeV, respectively, and increase with applicator size. No peak dose is evidenced for the Varian applicator for these energies. In summary, the out‐of‐field dose from electron beams increases with the beam energy and the applicator size, and decreases with the distance from the beam central axis and the depth in water. It also considerably depends on the applicator types. Our results can be of interest for the dose estimations delivered in healthy tissues outside the treatment field for the RT patient, as well as in studies exploring RT long‐term effects.PACS number(s): 87.53.Bn, 87.56.bd, 87.56.J‐

AAPM TG158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

“…The characteristics of the nontarget dose from electron therapy are starkly different than those from photon therapy, and the magnitude of the nontarget dose from electron therapy is highly dependent on accelerator manufacturer, as shown in Fig. , and even based on specific applicator type . While out‐of‐field doses generally decrease with distance from the edge for electron therapy, this is less pronounced than for photon therapy (particularly for Elekta and Siemens accelerators), and the dose may show regions of increase, particularly around 20 cm from the field edge.…”

“…While out‐of‐field doses generally decrease with distance from the edge for electron therapy, this is less pronounced than for photon therapy (particularly for Elekta and Siemens accelerators), and the dose may show regions of increase, particularly around 20 cm from the field edge. The majority of the out‐of‐field dose is from scattered electrons, particularly scattered primary electrons or Compton scattered electrons originating in the lower trimmer . The increase in dose at ~20 cm from the field edge arises from scattered electrons originating from the rounded surface of the MLC .…”

Influence of growth hormone therapy on the occurrence of a second neoplasm in survivors of childhood cancer

“…Hospital physicists obtained radiotherapy and patient data from technical radiotherapy records for all included patients who received radiotherapy. For each of these patients, radiation treatment was reconstructed using a commercialized Treatment Planning System (TPS), Isogray®, in which patient images were replaced by anthropomorphic phantoms mimicking the anatomical dimensions of the patient in which the main organs of interest were contoured (16,17,18,19). Details about the methods have been previously described (20).…”

Experimental validatıon of peripheral dose distribution of electron beams for eclipse electron Monte Carlo algorithm

“…Alabdoaburas et al 17 measured the peripheral dose of electron beams by thermoluminescent dosimeter and EBT3 film for a Varian-type applicator. They found that the out-of-field dose from electron beams increases with the beam energy and the applicator size, and decreases with the distance from the beam central axis and the depth in water.…”