Neutron equivalent doses and associated lifetime cancer incidence risks for head & neck and spinal proton therapy

Abstract

In this work we have simulated the absorbed equivalent doses to various organs distant to the field edge assuming proton therapy treatments of brain or spine lesions. We have used computational whole-body (gender-specific and age-dependent) voxel phantoms and considered six treatment fields with varying treatment volumes and depths. The maximum neutron equivalent dose to organs near the field edge was found to be approximately 8 mSv Gy(-1). We were able to clearly demonstrate that organ-specific neutron equivalent doses are age (stature) dependent. For example, assuming an 8-year-old patient, the dose to brain from the spinal fields ranged from 0.04 to 0.10 mSv Gy(-1), whereas the dose to the brain assuming a 9-month-old patient ranged from 0.5 to 1.0 mSv Gy(-1). Further, as the field aperture opening increases, the secondary neutron equivalent dose caused by the treatment head decreases, while the secondary neutron equivalent dose caused by the patient itself increases. To interpret the dosimetric data, we analyzed second cancer incidence risks for various organs as a function of patient age and field size based on two risk models. The results show that, for example, in an 8-year-old female patient treated with a spinal proton therapy field, breasts, lungs and rectum have the highest radiation-induced lifetime cancer incidence risks. These are estimated to be 0.71%, 1.05% and 0.60%, respectively. For an 11-year-old male patient treated with a spinal field, bronchi and rectum show the highest risks of 0.32% and 0.43%, respectively. Risks for male and female patients increase as their age at treatment time decreases.

Assessment of the Risk for Developing a Second Malignancy From Scattered and Secondary Radiation In Radiation Therapy

“…Whole-body computational phantoms can play an important role when combined with Monte-Carlo dose calculations to simulate scattered or secondary doses (e.g., neutron doses) to organs. Such phantoms provide the geometries to assess adult and pediatric organ doses where whole-body CTs are not available (Zacharatou Jarlskog and Paganetti 2008; Athar and Paganetti 2009, 2011). Many models representing adult male and female as well as children have been developed, mostly from segmented whole-body images (Xu and Eckerman 2009).…”

“…Various studies have used whole-body patient phantoms and Monte-Carlo simulations to calculate OFV organ doses in radiation therapy (Jiang et al 2005; Fontenot et al 2008, 2009; Zacharatou Jarlskog et al 2008; Athar and Paganetti 2009; Newhauser et al 2009; Taddei et al 2009; Athar et al 2010). Based on such simulations the risks for developing a second malignancy in patients have been estimated (Jiang et al 2005; Brenner and Hall 2008; Zacharatou Jarlskog and Paganetti 2008; Athar and Paganetti 2009; Newhauser et al 2009; Taddei et al 2009; Athar et al 2010).…”

Spot scanning proton therapy minimizes neutron dose in the setting of radiation therapy administered during pregnancy

“…The value decreased significantly with lower beam energy and increasing distance of fetus from the field edge. There are other studies of out‐of‐field secondary neutron both with Monte Carlo (MC) calculations or experimental measurements that could be used to estimate the neutron H to the fetus for passive scattering and uniform scanning beams 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 . However, most of these studies were made for a specific proton beam configuration, and the reported values of neutron H vary markedly because of different machine designs, experimental setups, and measurement instruments.…”

Peripheral doses in radiotherapy: A comparison between IMRT, VMAT and Tomotherapy

“…It is well known that some of the patients treated with ionizing radiations (either X-ray based or with charged particles), can later develop a treatment induced secondary malignancy in organs located at a distance from the original tumor (Althar and Paganetti, 2009;Fontenot et al, 2009;Hall et al, 2003;Newhauser et al, 2009;Kry et al, 2005;Sharma et al, 2008;Xu et al, 2008). It is therefore very important to establish the doses that are absorbed in those distant organs.…”