Using a 'vector rotation' technique and 'parallel geometry' utility to calculate the equivalent dose rate from a patient undergoing nuclear medicine procedures.

A dose calculation for a person who has been in contact with a patient undergoing Nuclear medicine procedures can be performed by using Merged Phantom Tool (MPT). In this study, we are upgrading the MPT to help users easily merge phantoms at any axis and with any angle using the "vector rotation" technique. The segmented structure information of the contact's phantom is also included in the calculation using the GEANT4 "parallel geometry" utility. The calculation is applied to a case of a male cancer patient lying on a bed who has used I-131, and a caregiver standing beside the patient. The equivalent dose to the thyroid of the caregiver is calculated at 0.3, 0.5, 0.8 and 1m away from the patient, as the caregiver is standing near the patient's abdomen, chest and neck area. The results show that the dose to the thyroid of the contact greatly depends on his standing position and that there are clear differences between the results calculated with the point source and those calculated with the patient source. In summary, using activity distributions in the patient's body as well as the right communication circumstance helps to calculate the optimal dose for people who have been in contact with patients.

Dosimetric and Monte Carlo verification of jaws-only IMRT plans calculated by the Collapsed Cone Convolution algorithm for head and neck cancers.

AIM: The aim of this study is to verify the Prowess Panther jaws-only intensity modulated radiation therapy (JO-IMRT) treatment planning (TP) by comparing the TP dose distributions for head-and-neck (H&N) cancer with the ones simulated by Monte Carlo (MC). BACKGROUND: To date, dose distributions planned using JO-IMRT for H&N patients were found superior to the corresponding three-dimensional conformal radiotherapy (3D-CRT) plans. Dosimetry of the JO-IMRT plans were also experimentally verified using an ionization chamber, MapCHECK 2, and Octavius 4D and good agreements were shown. MATERIALS AND METHODS: Dose distributions of 15 JO-IMRT plans of nasopharyngeal patients were recalculated using the EGSnrc Monte Carlo code. The clinical photon beams were simulated using the BEAMnrc. The absorbed dose to patients treated by fixed-field IMRT was computed using the DOSXYZnrc. The simulated dose distributions were then compared with the ones calculated by the Collapsed Cone Convolution (CCC) algorithm on the TPS, using the relative dose error comparison and the gamma index using global methods implemented in PTW-VeriSoft with 3%/3 mm, 2%/2 mm, 1%/1 mm criteria. RESULTS: There is a good agreement between the MC and TPS dose. The average gamma passing rates were 93.3 ± 3.1%, 92.8 ± 3.2%, 92.4 ± 3.4% based on the 3%/3 mm, 2%/2 mm, 1%/1 mm criteria, respectively. CONCLUSIONS: According to the results, it is concluded that the CCC algorithm was adequate for most of the IMRT H&N cases where the target was not immediately adjacent to the critical structures.

ADDING TWO NEW CONTACT CIRCUMSTANCES TO 'MERGED PHANTOM TOOL' AND A TECHNIQUE TO CONVERT STRUCTURE INFORMATION SEGMENTED BY THE CARIMAS SOFTWARE INTO GEANT4 GEOMETRY.

Two new contact circumstances called 'stand-lie' and 'front-rear' are implemented to the merged phantom tool. To allow more flexibility for users when they calculate the dose for a volume of interest (VOI) with arbitrary geometry, an optional utility to convert segmented structure information from the CARIMAS software into parallel geometry of GEANT4 is provided. The effective dose for a person who has been in contact with a male patient being treated for thyroid cancer with 131I is calculated for four circumstances: opposite, side by side, stand-lie and front-rear. The biggest dose is the 'opposite' circumstance and the smallest one is the 'stand-lie' circumstance. Using the dose distribution in the patient's body and applying the right circumstance should be done to optimise the dose calculation for the contact person.

Calculating equivalent dose received from a patient undergoing nuclear medicine procedure by merge phantoms tool and GAMOS/Geant4 6.0.0 software.

PURPOSE: This report introduces a tool for merging two voxel phantoms to calculate the deposited dose that a person receives from a patient undergoing Nuclear medicine procedures. MATERIALS AND METHODS: The phantoms must be converted to the text format used by GEANT4 to treat DICOM images via the GAMOS utilities. The Merge Phantoms Tool can merge two phantoms in two different cases: standing either side by side or opposite. The merged phantom is also in text format and is subsequently input back into GAMOS to calculate the equivalent dose that a person receives from a patient. The equivalent doses to the eyes of people in contact are calculated in a case where a patient was administered 185 MBq of 18F-FDG during a PET examination. RESULTS: The corresponding doses when the two phantoms are standing opposite are greater than those when they are standing side by side and smaller than those from point and tube source calculated by Sumi Yokoyama at any distance. CONCLUSIONS: The Merge phantoms tool and GAMOS software can be used to calculate the deposited dose that a person receives from a patient. An accurate dose calculation can be used for radiation protection, or deciding whether a patient can be released from isolation if the dose is small even in a close contact.

Quality assurance of the jaws only-intensity modulated radiation therapy plans for head-and-neck cancer.

Intensity-modulated radiation therapy (IMRT) is a treatment technique which has become routine in developed countries. In most centers this technique is delivered with multi-leaf collimators (MLCs). However, the use of MLCs is not mandatory. Several oncology centres in developing countries are still using linear accelerators (LINAC) without MLCs, and can potentially deliver IMRT plans with the use of collimator jaws. In this report, we present the results of quality assurance of this Jaws-Only-IMRT (JO-IMRT) technique in treating nasopharyngeal carcinoma (NPC) patients. Twenty-five plans of nasopharyngeal patients were randomly chosen. For each patient, a JO-IMRT plan was generated and a series of pre-treatment verification measurements was performed including (1) point dose measurement with an ionization chamber, (2) planar dose measurement with a 2D-array detector and (3) 3-dimensional dose measurement using a rotatable phantom with a 2D-array detector. The average differences between the measured and TPS-calculated point doses were found to be 1.26±0.77%, which is within the institution's dose constraint limits. For the planar dose and 3D dose measurements, the average gamma index based on 3%/3mm criteria were 96.77±2.33% and 94.72±2.67%, respectively. Our measurements showed that the JO-IMRT treatment plans applied to the H&N patients were accurate for the treatment delivery based on our established pass criteria.