A simple and fast physics-based analytical method to calculate therapeutic and stray doses from external beam, megavoltage x-ray therapy

Abstract

State-of-the-art radiotherapy treatment planning systems provide reliable estimates of the therapeutic radiation but are known to underestimate or neglect the stray radiation exposures. Most commonly, stray radiation exposures are reconstructed using empirical formulas or lookup tables. The purpose of this study was to develop the basic physics of a model capable of calculating the total absorbed dose both inside and outside of the therapeutic radiation beam for external beam photon therapy. The model was developed using measurements of total absorbed dose in a water-box phantom from a 6 MV medical linear accelerator to calculate dose profiles in both the in-plane and cross-plane direction for a variety of square field sizes and depths in water. The water-box phantom facilitated development of the basic physical aspects of the model. RMS discrepancies between measured and calculated total absorbed dose values in water were less than 9.3% for all fields studied. Computation times for 10 million dose points within a homogeneous phantom were approximately 4 minutes. These results suggest that the basic physics of the model are sufficiently simple, fast, and accurate to serve as a foundation for a variety of clinical and research applications, some of which may require that the model be extended or simplified based on the needs of the user. A potentially important advantage of a physics-based approach is that the model is more readily adaptable to a wide variety of treatment units and treatment techniques than with empirical models.

AAPM TG 158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

“…Recent studies have developed more refined analytical models for predicting out‐of‐field dose. These models have increased complexity (i.e., more parameters), but provide improved accuracy in dose calculation and can estimate doses from IMRT treatments . Neutrons have not been included in any of these analytical models to date.…”

A review of uncertainties in radiotherapy dose reconstruction and their impacts on dose–response relationships

“…More recently, Jagetic and Newhauser [77] introduced an analytical method to calculate in-field and out-of-field doses for a 6 MV beam of an Elekta Synergy. Square field size (5 cm×5 cm and 10 cm×10 cm) measurements using a diamond detector were performed in a water tank.…”

Measurement and modeling of out-of-field doses from various advanced post-mastectomy radiotherapy techniques

“…To quantify a patient’s risk of developing radiogenic side effects after PMRT, accurate knowledge of the patient dose (both primary and stray radiation doses) is essential. It is generally accepted that commercial treatment planning systems (TPSs) severely underestimate dose at low dose regions (Jang et al , 2008; Howell et al , 2010a; Huang et al , 2013; Joosten et al , 2013; Wang and Ding, 2014; Jagetic and Newhauser, 2015). …”

“…Out-of-field dose data based on measurements or Monte Carlo simulations for static and IMRT photon fields were extensively reported in the literature (Stovall et al , 1995; Mutic and Low, 1998; Mutic and Klein, 1999; Stern, 1999; Meeks et al , 2002; Kry et al , 2005; Kry et al , 2006; Sharma et al , 2006; Wang and Xu, 2008; Bednarz and Xu, 2009; Ruben et al , 2011; Halg et al , 2012; Kaderka et al , 2012; La Tessa et al , 2012; Taddei et al , 2013; Covington et al , 2016), while analytical models of out-of-field dose from photon external therapy had only been proposed in a few studies (McParland and Fair, 1992; Taddei et al , 2013; Jagetic and Newhauser, 2015; Hauri et al , 2016). Most of the previous modeling studies focused on open beams or conventional field-in-field beams, and the modeling of IMRT beams required intensive information of each field (Hauri et al , 2016).…”