A simple analytical model for a fast 3D assessment of peripheral photon dose during coplanar isocentric photon radiotherapy

Abstract

Considering that cancer survival rates have been growing and that nearly two-thirds of those survivors were exposed to clinical radiation during its treatment, the study of long-term radiation effects, especially secondary cancer induction, has become increasingly important. To correctly assess this risk, knowing the dose to out-of-field organs is essential. As it has been reported, commercial treatment planning systems do not accurately calculate the dose far away from the border of the field; analytical dose estimation models may help this purpose. In this work, the development and validation of a new three-dimensional (3D) analytical model to assess the photon peripheral dose during radiotherapy is presented. It needs only two treatment-specific input parameter values, plus information about the linac-specific leakage, when available. It is easy to use and generates 3D whole-body dose distributions and, particularly, the dose to out-of-field organs (as dose–volume histograms) outside the 5% isodose for any isocentric treatment using coplanar beams [including intensity modulated radiotherapy and volumetric modulated arc therapy (VMAT)]. The model was configured with the corresponding Monte Carlo simulation of the peripheral absorbed dose for a 6 MV abdomen treatment on the International Comission on Radiological Protection (ICRP) 110 computational phantom. It was then validated with experimental measurements using thermoluminescent dosimeters in the male ATOM anthropomorphic phantom irradiated with a VMAT treatment for prostate cancer. Additionally, its performance was challenged by applying it to a lung radiotherapy treatment very different from the one used for training. The model agreed well with measurements and simulated dose values. A graphical user interface was developed as a first step to making this work more approachable to a daily clinical application.

Analytical models for external photon beam radiotherapy out-of-field dose calculation: a scoping review

“…Table 1 summarizes the methods used for experimental data acquisitions in the 21 selected articles. Seven were reported as single-compartment models: the oldest ( 25 ) and the most recent model ( 57 ) belong to this category. The remaining articles were multi-compartment models with sub-models dedicated to each of the dose components.…”

“…Depending on the research groups, measurements were performed by an orthovoltage unit operated at 200 kVp and a cobalt-60 machines ( 25 ), different medical accelerators operated at 6 MV ( 20 , 53 , 57 , 61 , 64 ), 10 MV ( 20 ) and 25 MV ( 25 ). Measurements could have been made for a set of simple geometry open square and rectangular fields ( 25 , 65 ) or, for a set of reference treatment plans-specific beam settings ( 20 , 53 , 57 , 61 , 64 ).…”

“…Ionization chambers and thermoluminescent dosimeters (TLDs) are the two most commonly used types of detectors for these measurements, with similar frequencies of use, each being involved in 50% of the publications. In case of measurements in an anthropomorphic phantom, TLDs of type TLD-100 ( 20 , 53 , 57 , 61 ) or an ultra-sensitive MCP-N type TLDs ( 64 ) were employed. Diamond detectors ( 55 , 63 , 67 ) or solid-state diode dosimeter ( 67 ) were also used.…”

“…TLD100 (LiF:Mg,Ti), TLD100H (LiF:Mg,Cu,P), TLD600/700 (LiF:Mg,Ti) and TLD700H (7LiF:Mg,Cu,P) were used synergistically ( 43 , 68 ). In addition, MC simulations were performed by some groups, as a surrogate or to supplement their experimental data ( 43 , 57 , 67 ).…”

“…One approach discriminates the near field and the distant regions ( 25 , 53 , 57 , 61 , 64 ). In this case, the sector integration method, proposed by ( 42 ) and investigated by ( 69 ), was implemented by the Gustave Roussy’s group ( 25 ), whilst the group from MD Anderson Cancer Center ( 53 , 61 , 64 ) opted for the double-Gaussian description originally proposed by ( 70 ).…”