Whole‐body dose equivalent including neutrons is similar for 6 MV and 15 MV IMRT, VMAT, and 3D conformal radiotherapy

Abstract

Purpose This study investigates the difference in whole‐body dose equivalent between 6 and 15 MV image‐guided radiotherapy (IGRT) for the treatment of a rhabdomyosarcoma in the prostate. Methods A previously developed model for stray radiation of the primary beam was improved and used to calculate the photon dose and photon energy in the out‐of‐field region for a radiotherapy patient. The dose calculated by the treatment planning system was fused with the model‐calculated out‐of‐field dose, resulting in a whole‐body photon dose distribution. The peripheral neutron dose equivalent was calculated using an analytical model from the literature. A daily cone beam CT dose was added to the neutron and photon dose equivalents. The calculated 3D dose distributions were compared to independent measurements conducted with thermoluminescence dosimeters and an anthropomorphic phantom. The dose contributions from the IGRT treatments of three different techniques applied with two nominal X‐ray energies were compared using dose equivalent volume histograms (DEVHs). Results The calculated and measured out‐of‐field whole‐body dose equivalents for the IGRT treatments agreed within (9 ± 10) % (mean and type A SD). The neutron dose equivalent was a minor contribution to the total out‐of‐field dose up to 50 cm from the isocenter. Further from the isocenter, head leakage was dominating inside the patient body, whereas the neutron dose equivalent contribution was important close to the surface. There were small differences between the whole‐body DEVHs of the 6 and 15 MV treatments applied with the same technique, although the single scatter contributions showed large differences. Independent of the beam energy, the out‐of‐field dose of the volumetric‐modulated arc therapy (VMAT) treatment was significantly lower than the dynamic intensity‐modulated radiation therapy (IMRT) treatment. Conclusion The calculated whole‐body dose helped to understand the importance of the dose contributions in different areas of the patient. Regarding radiation protection of the patient for IGRT treatments, the choice of beam energy is not important, whereas the treatment technique has a large influence on the out‐of‐field dose. If the patient is treated with intensity‐modulated beams, VMAT should be used instead of dynamic IMRT in terms of radiation protection of the patient. In general, the developed models for photon and neutron dose equivalent calculation can be used for any patient geometry, tumor location, and linear accelerator.

Dosimetric comparison of coplanar and non-coplanar volumetric-modulated arc therapy in head and neck cancer treated with radiotherapy

“…The Conformity Index (CI RTOG ) [15][16][17], isodose line covering 95% of the volume within PTV (ID 95% ), Dose Homogeneity Index (DHI) [15][16][17], Homogeneity Index (HI RTOG ) [15][16][17], conformity number (CN) [15][16][17][18], low dose volume and OAR coverage in both the plans were analyzed. Total monitor units (MU) per fraction, IMRT ratio, i.e., total MU per cGy prescription dose [19][20][21][22][23], and the integral dose to patients [24,25] were noted and compared. The dose covering a percentage of the structure's volume (D % ) and the volume of the structure receiving a certain dose (V % or V Gy ) were used for dosimetric evaluation and planning purposes.…”

Feasibility of a GATE Monte Carlo platform in a clinical pretreatment QA system for VMAT treatment plans using TrueBeam with an HD120 multileaf collimator

“…41 As monitor unit (MU) in the use of IMRT or VMAT is usually higher than that in conventional RT, effect of neutron dose in IMRT and VMAT has been studied and reported. [42][43][44][45] Peripheral dose of thermal neutron in VMAT with 10 MV was less than 100 micro-Gray of kerma equivalent. 45 All the mean energies of the photon simulated in this study were less than 10 MeV and only 0.08% for 10 MV was over 10 MeV, we did not consider effect of the neutron dose in film measurement.…”

A nomogram for predicting late radiation-induced xerostomia among locoregionally advanced nasopharyngeal carcinoma in intensity modulated radiation therapy era

“…Moreover, VMAT has more beam entry angles and supports the simultaneous variation in MLC leaf positions, gantry rotation speed and dose rate, resulting in great reductions in monitor units and treatment delivery time per fraction by transforming IMRT into VMAT for head and neck cancer [ 24 ]. Lower MU has its advantages such as the potential decrease in total body dose due to leakage and scattering from MLCs [ 25 , 26 ]. Extra low-dose areas may have potential protective effects on other oral cavity accessory glands [ 12 ].…”