A hybrid phantom Monte Carlo-based method for historical reconstruction of organ doses in patients treated with cobalt-60 for Hodgkin's lymphoma

Abstract

Historical radiotherapy treatment plans lack 3D images sets required for estimating mean organ doses to patients. Alternatively, Monte Carlo-based models of radiotherapy devices coupled with whole-body computational phantoms can permit estimates of historical in-field and out-of-field organ doses as needed for studies associating radiation exposure and late tissue toxicities. In recreating historical patient treatments with Co based systems, the major components to be modeled include the source capsule, surrounding shielding layers, collimators (both fixed and adjustable), and trimmers as needed to vary field size. In this study, a computational model and experimental validation of the Theratron T-1000 are presented. Model validation is based upon in-field commissioning data collected at the University of Florida, published out-of-field data from the British Journal of Radiology (BJR) Supplement 25, and out-of-field measurements performed at the University of Wisconsin's Accredited Dosimetry Calibration Laboratory (UWADCL). The computational model of the Theratron T-1000 agrees with central axis percentage depth dose data to within 2% for 6 × 6 to 30 × 30 cm fields. Out-of-field doses were found to vary between 0.6% to 2.4% of central axis dose at 10 cm from field edge and 0.42% to 0.97% of central axis dose at 20 cm from the field edge, all at 5 cm depth. Absolute and relative differences between computed and measured out-of-field doses varied between ±2.5% and ±100%, respectively, at distances up to 60 cm from the central axis. The source-term model was subsequently combined with patient-morphometry matched computational hybrid phantoms as a method for estimating in-field and out-of-field organ doses for patients treated for Hodgkin's Lymphoma. By changing field size and position, and adding patient-specific field shaping blocks, more complex historical treatment set-ups can be to recreated, particularly those for which 2D or 3D image sets are unavailable.

Commissioning and dosimetric validation of a novel compensator‐based Co‐60 IMRT system for evaluating suitability to automated treatment planning

“…The compensator‐based IMRT system consists of a cobalt‐60 source and compensator arrays (Figure 1). A commercial cobalt‐60 source with a diameter of 2 cm and a height of 2 cm is designed for this research 15 . The primary collimator is designed to create a 35 × 35 cm 2 field size at 80 cm source to axis distance (SAD).…”

“…A commercial cobalt-60 source with a diameter of 2 cm and a height of 2 cm is designed for this research. 15 The primary collimator is designed to create a 35 × 35 cm 2 field size at 80 cm source to axis distance (SAD). Two pairs of movable jaws for x and y directions are placed at 31 cm and 37.1 cm from the source, respectively, for adjusting field size.…”

Advances in Computational Human Phantoms and Their Applications in Biomedical Engineering—A Topical Review

“…In 2017, Petroccia et al [118] explored the use of the UF/NCI computational phantom library [112] to represent patients historically treated with cobalt-60 gamma-rays for the treatment of Hodgkin’s lymphoma. This patient population is ideal for radiation epidemiology studies of late clinical effects for both secondary cancer and cardiac disease.…”

Four secondary malignancies, coronary artery disease, aortic atherosclerosis and severe constrictive pericarditis in a survivor of hodgkin lymphoma treated with radiation therapy: a case report

“…In the field of radiotherapy, radiation dose is measured in Gray units (Gy) where 1 Gy is the absorption of 1J of ionizing radiation energy by 1 Kg of tissue [2]; it's described that low doses of radiotherapy (<2 Gy) have been shown to be associated with both secondary cancers and a bit of cardiac toxicity, but true heart damage occurs with radiation dose above 30 Gy [2,3]. In a hybrid phantom Monte Carlo-based method for historical reconstruction of organ doses in patients treated with 60 Co for HL, it was shown that out-fielddoses were 38 % on average.…”

“…In a hybrid phantom Monte Carlo-based method for historical reconstruction of organ doses in patients treated with 60 Co for HL, it was shown that out-fielddoses were 38 % on average. Also, distances of 60 cm from the central axis of treatment fields were reported increasing the risk for second malignancies [3].…”