Measurements of the neutron dose equivalent for various radiation qualities, treatment machines and delivery techniques in radiation therapy

Abstract

In radiation therapy, high energy photon and proton beams cause the production of secondary neutrons. This leads to an unwanted dose contribution, which can be considerable for tissues outside of the target volume regarding the long term health of cancer patients. Due to the high biological effectiveness of neutrons in regards to cancer induction, small neutron doses can be important. This study quantified the neutron doses for different radiation therapy modalities. Most of the reports in the literature used neutron dose measurements free in air or on the surface of phantoms to estimate the amount of neutron dose to the patient. In this study, dose measurements were performed in terms of neutron dose equivalent inside an anthropomorphic phantom. The neutron dose equivalent was determined using track etch detectors as a function of the distance to the isocenter, as well as for radiation sensitive organs. The dose distributions were compared with respect to treatment techniques (3D-conformal, volumetric modulated arc therapy and intensity-modulated radiation therapy for photons; spot scanning and passive scattering for protons), therapy machines (Varian, Elekta and Siemens linear accelerators) and radiation quality (photons and protons). The neutron dose equivalent varied between 0.002 and 3 mSv per treatment gray over all measurements. Only small differences were found when comparing treatment techniques, but substantial differences were observed between the linear accelerator models. The neutron dose equivalent for proton therapy was higher than for photons in general and in particular for double-scattered protons. The overall neutron dose equivalent measured in this study was an order of magnitude lower than the stray dose of a treatment using 6 MV photons, suggesting that the contribution of the secondary neutron dose equivalent to the integral dose of a radiotherapy patient is small.

Late radiation toxicity in Hodgkin lymphoma patients: proton therapy's potential

“…This was deemed negligible for this work considering that the secondary neutron dose during spot scanned delivery of a proton beam has been modeled and measured 34 , 35 . The effective neutron dose outside the target for actively scanned protons was measured to be on the order of mSv/Gy delivered for a prostate treatment case (35) .…”

“…This was deemed negligible for this work considering that the secondary neutron dose during spot scanned delivery of a proton beam has been modeled and measured 34 , 35 . The effective neutron dose outside the target for actively scanned protons was measured to be on the order of mSv/Gy delivered for a prostate treatment case (35) . Neutron dose is affected by heterogeneity in the path of the primary proton beam, the incident proton beam energy, and energy and position of neutrons generated, all of which are factors determined by the anatomical aspects of a proton treatment.…”

“…Hodgkin lymphoma (HL) is the second most commonly diagnosed cancer among adolescents and young adults in the 12-29 age group. (1) Treatment for early stage HL in Quebec in 2010 comprised two to four cycles of anthracycline-containing chemotherapy followed by involved field radiotherapy (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36). In such cases, five-year overall survival is expected to approach approximately 95%.…”

Experimental evaluation of neutron dose in radiotherapy patients: Which dose?

“…Finally, dose equivalents evaluated using both methods [Eq. (9)] and normalized to treatment Gy can be found in Fig. 5.…”

“…3 In summary, from the experimental point of view, organ dose equivalent is the only possible quantity to evaluate from dose equivalent at a point. This approach has been followed, for example, by Hälg et al, 9 Mesoloras et al, 10 Moyers et al, 11 and Wroe et al 12 In contrast, equivalent doses were calculated in works where peripheral dose evaluation was performed by MC simulations, for example, in the works of Taddei et al 13 and Newhauser et al 14 However, the evaluation of dose equivalent entails the added difficulty of Q calculation (not always explained in the literature), which could require a full MC simulation specific of each irradiation condition and which presents high uncertainties. On the other hand, the "immeasurable" quantity organ-equivalent dose (paragraph 228, Ref.…”