Scintillating fiber based in-vivo dose monitoring system to the rectum in proton therapy of prostate cancer: A Geant4 Monte Carlo simulation

Abstract

Purpose: To construct a dose monitoring system based on an endorectal balloon coupled to thin scintillating fibers to study the dose to the rectum in proton therapy of prostate cancer. Method: A Geant4 Monte Carlo toolkit was used to simulate the proton therapy of prostate cancer, with an endorectal balloon and a set of scintillating fibers for immobilization and dosimetry measurements, respectively. Results: A linear response of the fibers to the dose delivered was observed to within less than 2%. Results obtained show that fibers close to the prostate recorded higher dose, with the closest fiber recording about one-third of the dose to the target. A 1/r 2 (r is defined as center-to-center distance between the prostate and the fibers) decrease was observed as one goes toward the frontal and distal regions. A very low dose was recorded by the fibers beneath the balloon which is a clear indication that the overall volume of the rectal wall that is exposed to a higher dose is relatively minimized. Further analysis showed a relatively linear relationship between the dose to the target and the dose to the top fibers (total 17), with a slope of (-0.07 ± 0.07) at large number of events per degree of rotation of the modulator wheel (i.e., dose). Conclusion: Thin (1 mm × 1 mm), long (1 m) scintillating fibers were found to be ideal for real time in-vivo dose measurement to the rectum during proton therapy of prostate cancer. The linear response of the fibers to the dose delivered makes them good candidates as dosimeters. With thorough calibration and the ability to define a good correlation between the dose to the target and the dose to the fibers, such dosimeters can be used for real time dose verification to the target.

Dosimetric study of RapidArc plans and conventional intensity modulated radiotherapy for prostate cancer involving seminal vesicles and pelvis lymph nodes

“…Although our study focused on photon therapy, proton therapy is also another option to treat the prostate cancer in external beam radiotherapy. 22,23 Proton therapy can produce excellent dose distribution because protons have finite range and sharp distal fall-off at the end of proton beam path. Vargas et al 24 and Rana et al 25 demonstrated that proton therapy is better at sparing rectum and bladder when compare to the photon therapy.…”

A portable secondary dose monitoring system using scintillating fibers for proton therapy of prostate cancer: A Geant4 Monte Carlo simulation study

“…The details of the simulation developed are described in the previous paper. 20 For the secondary dose monitoring system, three detectors were constructed around the water phantom. From the beam's eye view, two detectors were placed in the lateral directions and one in the distal.…”

“…This work follows a recent paper that focused in the dose distribution near and in the prostate gland. 20 In the previous paper, a dose monitoring system was constructed to study the dose delivered to the rectal wall in the proton therapy of prostate cancer. The simulation included thin scintillating fibers attached to an endorectal balloon to record the dose delivered to the balloon surface.…”