Assessment of carcinogenic risks in radiotherapy of non-malignant diseases

Abstract

Purpose/Objective: With the renewed interest in the treatment of benign diseases with radiotherapy, there is also concern about the risk of induction of malignancies. The carcinogenic risk can be estimated with the concept of effective dose introduced by the International Commission on Radiological Protection (ICRP). The objective of this study is to calculate effective doses for various non-malignant diseases and assess the risk for tumor induction, dependent on age and gender.Materials/Methods: According to the ICRP the average risk factor for fatal cancers is presently assumed to be 10 percent per Sv in the high dose region. The attributable lifetime risk is, however, considerably smaller at older age than earlier in life. In radiotherapy, the dose distribution will be inhomogeneous. Organ doses have been calculated using Monte Carlo radiation transport codes and anthropomorphic mathematical phantoms. The different susceptibilities for tumor induction in these organs, are approximated by tissue weighting factors. The effective dose has been derived as the sum of the products of the equivalent organ doses and their tissue weighting factors.Results: For Graves’ orbitopathy, for a square field, a target dose of 20 Gy and 5 MV photons, the effective dose is 65 mSv. Adjustment of the field to the conical outline of the orbit, with a slightly lower target dose of 16 Gy and 12 MV photons, resulted in an effective dose of 34 mSv. For radiotherapy to prevent heterotopic ossification with a target dose of 7 Gy, effective doses between 136 and 323 mSv and between 213 and 419 mSv are derived for a male and female phantom, respectively. Irradiation of the shoulder (omarthritis, target dose 12 Gy) performed in the absence or presence of thyroid protection, resulted in effective doses of 197 and 185 mSv, respectively, for the female gender. For treatment of the knee (gonarthrosis, target dose 6 Gy) the effective dose is 13 mSv.Conclusions: The calculation of effective doses for radiotherapy of benign diseases offers the possibility to optimize the irradiation procedure. On the basis of the average attributable risk factor, the estimated number of induced fatal tumors varies from 1 to 40 per 1000 patients. When irradiations are performed at older age the risk factor will be reduced by an approximate factor of three. Purpose/Objective: With the renewed interest in the treatment of benign diseases with radiotherapy, there is also concern about the risk of induction of malignancies. The carcinogenic risk can be estimated with the concept of effective dose introduced by the International Commission on Radiological Protection (ICRP). The objective of this study is to calculate effective doses for various non-malignant diseases and assess the risk for tumor induction, dependent on age and gender. Materials/Methods: According to the ICRP the average risk factor for fatal cancers is presently assumed to be 10 percent per Sv in the high dose region. The attributable lifetime risk is, however, considerably smaller at older age than earlier in life. In radiotherapy, the dose distribution will be inhomogeneous. Organ doses have been calculated using Monte Carlo radiation transport codes and anthropomorphic mathematical phantoms. The different susceptibilities for tumor induction in these organs, are approximated by tissue weighting factors. The effective dose has been derived as the sum of the products of the equivalent organ doses and their tissue weighting factors. Results: For Graves’ orbitopathy, for a square field, a target dose of 20 Gy and 5 MV photons, the effective dose is 65 mSv. Adjustment of the field to the conical outline of the orbit, with a slightly lower target dose of 16 Gy and 12 MV photons, resulted in an effective dose of 34 mSv. For radiotherapy to prevent heterotopic ossification with a target dose of 7 Gy, effective doses between 136 and 323 mSv and between 213 and 419 mSv are derived for a male and female phantom, respectively. Irradiation of the shoulder (omarthritis, target dose 12 Gy) performed in the absence or presence of thyroid protection, resulted in effective doses of 197 and 185 mSv, respectively, for the female gender. For treatment of the knee (gonarthrosis, target dose 6 Gy) the effective dose is 13 mSv. Conclusions: The calculation of effective doses for radiotherapy of benign diseases offers the possibility to optimize the irradiation procedure. On the basis of the average attributable risk factor, the estimated number of induced fatal tumors varies from 1 to 40 per 1000 patients. When irradiations are performed at older age the risk factor will be reduced by an approximate factor of three.