Radiation burden from secondary doses to patients undergoing radiation therapy with photons and light ions and radiation doses from imaging modalities

Ionising radiation is increasingly used for the treatment of cancer, being the source of a considerable fraction of the medical irradiation to patients. With the increasing success rate of cancer treatments and longer life expectancy of the treated patients, the issue of secondary cancer incidence is of growing concern, especially for paediatric patients who may live long after the treatment and be more susceptible to carcinogenesis. Also, additional imaging procedures like computed tomography, kilovoltage and megavoltage imaging and positron emission tomography, alone or in conjunction with radiation therapy, may add to the radiation burden associated with the risk of occurrence of secondary cancers. This work has been based on literature studies and is focussed on the assessment of secondary doses to healthy tissues that are delivered by the use of modern radiation therapy and diagnostic imaging modalities in the clinical environment. A considerable fraction of artificial radiation to the healthy organs of the patient is delivered from modern radiation therapy modalities alone or in conjunction with diagnostic imaging. Secondary doses to the healthy tissues of the patient undergoing radiation therapy can vary by several orders of magnitude, from about a few μGy to 2.5 Gy. Additionally, the absorbed doses from different diagnostic imaging techniques can contribute to the radiation burden by 6-3700 mGy assuming daily set-up verification during the whole therapy course. As the risk for secondary cancers varies most likely non-linearly with dose, it is important to assess the total radiation burden. The results of this study show that the radiation burden from secondary radiation in modern radiation therapy is significant and could be compared with that from diagnostic imaging in the case of repeated imaging sessions. (authors)