Monte Carlo calculated beam quality correction factors for high energy electron beams.

PURPOSE: As the dosimetry protocol TRS 398 is being revised and the ICRU report 90 provides new recommendations for density correction as well as the mean ionization energies of water and graphite, updated beam quality correction factors kQ are calculated for reference dosimetry in electron beams and for independent validation of previously determined values. METHODS: Monte Carlo simulations have been performed using EGSnrc to calculate the absorbed dose to water and the dose to the active volumes of ionization chambers SNC600c, SNC125c and SNC350p (all Sun Nuclear, A Mirion Medical Company, Melbourne, FL). Realistic clinical electron beam spectra were used to cover the entire energy range of therapeutic electron accelerators. The Monte Carlo simulations were validated by measurements on a clinical linear accelerator. With regards to the cylindrical chambers, the simulations were performed according to the setup recommendations of TRS 398 and AAPM TG 51, i.e. with and without consideration of a reference point shift by rcav/2. RESULTS: kQ values as a function of the respective beam quality specifier R50 were fitted by recommended equations for electron beam dosimetry in the range of 5 MeV to 18 MeV. The fitting curves to the calculated values showed a root mean square deviation between 0.0016 and 0.0024. CONCLUSION: Electron beam quality correction factors kQ were calculated by Monte Carlo simulations for the cylindrical ionization chambers SNC600c and SNC125c as well as the plane parallel ionization chamber SNC350p to provide updated data for the TRS 398 and TG 51 dosimetry protocols.

Heart toxicity from breast cancer radiotherapy : Current findings, assessment, and prevention.

BACKGROUND: Late cardiac toxicities caused by (particularly left-sided) breast radiotherapy (RT) are now recognized as rare but relevant sequelae, which has prompted research on risk structure identification and definition of threshold doses to heart subvolumes. The aim of the present review was to critically discuss the clinical evidence on late cardiac reactions based on dose-dependent outcome reports for mean heart doses as well as doses to cardiac substructures. METHODS: A literature review was performed to examine clinical evidence on radiation-induced heart toxicities. Mean heart doses and doses to cardiac substructures were focused upon based on dose-dependent outcome reports. Furthermore, an overview of radiation techniques for heart protection is given and non-radiotherapeutic aspects of cardiotoxicity in the multimodal setting of breast cancer treatment are discussed. RESULTS: Based on available findings, the DEGRO breast cancer expert panel recommends the following constraints: mean heart dose <2.5 Gy; DmeanLV (mean dose left ventricle) < 3 Gy; V5LV (volume of LV receiving ≥5 Gy) < 17%; V23LV (volume of LV receiving ≥23 Gy) < 5%; DmeanLAD (mean dose left descending artery) < 10 Gy; V30LAD (volume of LAD receiving ≥30 Gy) < 2%; V40LAD (volume of LAD receiving ≥40 Gy) < 1%. CONCLUSION: In addition to mean heart dose, breast cancer RT treatment planning should also include constraints for cardiac subvolumes such as LV and LAD. The given constraints serve as a clinicians' aid for ensuring adequate heart protection. The individual decision between sufficient protection of cardiac structures versus optimal target volume coverage remains in the physician's hand. The risk of breast cancer-specific mortality and a patient's cardiac risk factors must be individually weighed up against the risk of radiation-induced cardiotoxicity.