| Abstract |
During radiotherapy all healthy organs are exposed to ionizing radiation regardless of their position in relation to the radiation field. This fact results in the increase of the possibility of secondary cancer after the radiotherapy. In the case of Hodgkin lymphoma there are not sufficient data in the literature regarding the radiation dose and second cancer risk at healthy organs. The aim of this research is a) to determine the dose to healthy organs that are partially in or out of the radiation fields, for Hodgkin lymphoma patients, using the IFRT and ISRT techniques and b) to estimate the risk of secondary cancer.
Organs partially in the treatment field
Data were obtained from patients that received 3d conformal radiotherapy with the IFRT and ISRT techniques. Patients that were irradiated in anatomic regions above and below the diaphragm were included. The Organ Equivalent Dose (OED), as it was suggested by the group of Schneider et al, and the Lifetime Attributable Risk (LAR) were determined. All calculations were performed with the use of three different models: the mechanistic, plateau and bell shaped models. The organs that were examined for radiotherapy treatment above the diaphragm were the breast, lungs, thyroid gland, pharynx, oral cavity and esophagus. Respectively for treatment below the diaphragm the organs were the colon, rectum and bladder. The calculated risk with the above methods was compared to the cancer risk of population that has not been exposed to ionizing radiation. All calculations were performed for patients of the age of 20, 30 and 40.
The range of OED was calculated to 0.63 – 8.53 and 0.63 – 7.26 with the IFRT and ISRT techniques respectively for radiotherapy in anatomic regions above the diaphragm. Respectively for anatomic regions below the diaphragm the range was 0.18 – 7.64 and 0.80 – 4.95. The cancer risk after radiotherapy above the diaphragm was calculated to 0.5% – 8.0% with the IFRT technique and 0.5% - 5.2% with the ISRT technique. Respectively the cancer risk after radiotherapy below the diaphragm was calculated to 0.1% – 13.0% with the IFRT technique and 0.5% - 8.4% with the ISRT technique.
For radiotherapy in anatomic regions above the diaphragm the biggest benefit of ISRT over IFRT technique is observed in breast and lungs whereas for radiotherapy in anatomic regions below the diaphragm is observed in colon and rectum. For the bladder it was estimated that the cancer risk with the ISRT technique is higher than the risk with the IFRT technique, though this risk is smaller than the risk of population not exposed to ionizing radiation.
Out of field organs
The average dose to organs that are out of the treatment field for Hodgkin Lymphoma patients was determined with Monte Carlo calculations using a human body model created by relative software. The head of a 6MV linear accelerator was simulated. The treatment of Hodgkin lymphoma patients at mediastinum, pelvis and axillary region with the ISRT/IFRT techniques was simulated. For cancer risk estimation the reference model of BEIR VII was used. The average dose was calculated to organs that are out of the treatment field and are defined in ICRP-103. The cancer risk after radiotherapy at the mediastinum was estimated for the colon, stomach, bladder, liver, thyroid gland and prostate. Respectively for radiotherapy at the pelvis the cancer risk was estimated for the stomach, lungs, liver, breast, ovaries, testicles and thyroid gland. For radiotherapy at the axillary region cancer risk was estimated for the colon, stomach, bladder, liver, thyroid gland, breast, ovaries, testicles and prostate. All cancer risk estimations were performed for patients of 20, 30 and 40 years old. Finally the estimated cancer risk was compared to the cancer risk of population not exposed to ionizing radiation. The range of the average dose to out of field organs after mediastinum, pelvis and axillary region radiotherapy with the IFRT technique was calculated to 7.5-481, 5.0-774.5 and 5.0-594 mGy respectively. The respective ranges for the ISRT technique were 2.0-246, 3.0-300.5 and 2.5-234 mGy. The thyroid gland presents the highest cancer risk after mediastinum radiotherapy for both men and women patients. For pelvis radiotherapy the highest risk is observed in breast for women and stomach for men. For radiotherapy at the axillary region the highest risk was found to be the thyroid gland for men and the breast for women. In all cases the use of ISRT technique resulted in the decrease of cancer risk in comparison to the IFRT. Finally, in all out of field organs the cancer risk was smaller than the respective risk of the not exposed to ionizing radiation population.
|
Ακτινοθεραπεία σε λεμφώματα Hodgkin : υπολογισμός της δόσης ακτινοβολίας σε υγιή όργανα με τη μέθοδο Monte carlo και εκτίμηση του σχετιζόμενου κινδύνου καρκινογένεσης
