Estimation of absorbed dose to thyroid in patients treated with radiotherapy for various cancers.

This study is aimed at the evaluation of the absorbed dose to the thyroid gland from scattered/primary radiations in patients who have undergone radiotherapy. In this study, the skin entrance dose (SED) on the anterior neck at the level of the thyroid gland was measured using thermoluminescent dosimeters for 57 patients during radiotherapy with (60)Co teletherapy unit. Phantom dosimetry was also performed to find the correlation between the SED and the dose at the depth of the thyroid. SED of patients treated for breast cancer was 6.77±3.49 Gy and that of those with Hodgkin's disease and Ca. lung irradiation were 21.29±13.52 Gy and 28.80±14.94 Gy, respectively. SED at the level of the thyroid gland was found to be highest for patients whose thyroid gland was within the radiation field, while lowest for patients with skull irradiation. Thyroid gland is recommended to be shielded or excluded from the field whenever possible.

Investigation of the Occurrence of Human Errors in Treatment of Cancer Patients with External Beam Radiotherapy.

The main objective of clinical radiotherapy procedures is to deliver accurate doses to cancer patients. However, human errors can occur during the treatment planning and dose delivery that may result in under- or overexposure to the patient. Therefore the aim of the present study was to detect and quantify different types of errors that may occur during radiation treatment at the Nuclear Medicine, Oncology and Radiotherapy Institute (NORI) in Islamabad, Pakistan. In this context, systematic studies were carried out over an 18-month period at NORI, for which 800 patients were selected. Eight different types of human errors were detected and corrected before or during the first five radiation therapy fractions. Errors detected during the dose calculation and patient setup steps were ∼22% and ∼14% of the total incidents, respectively. Wedge/shielding blocks placement and field size settings-related errors were ∼10% and 19%, whereas source-surface distance/source-axis distance settings-related errors were ∼8%. Errors observed during treatment time/monitor unit, gantry/collimator angle settings, and counting fraction were about 7%, 9%, and 11%, respectively. Of the 105 errors detected, 28 were major errors (deviation from the prescribed daily dose ≥5%) and 77 were minor errors. The occurrence of minor and major error rates were 9.6% and 3.5%, respectively.

Quantitative analysis of the factors responsible for over or under dose of 131 I therapy patients of hyperthyroidism.

Radioiodine (131 I) therapy has been in use for more than 60 y. Several protocols have been suggested and used for prescribing the activity to be administered to the patients for the treatment of hyperthyroidism; application of these protocols may result in an under or over dose of the hyperthyroid patients. The main objective of this study was to carry out quantitative analysis of the factors responsible for possible under or over dosage of the patients. In this regard, a total of 59 patients [15 diffuse goitre (DG) and 44 nodular goitre (NG) cases] were studied. In order to compare the thyroid doses calculated by using different protocols, the dosimetric approach was followed. 131 I uptakes were measured after 24 and 48 h, respectively, by giving 0.5 MBq of 131 I to each patient. Thyroid mass and effective half-life were also calculated for each patient and the variations in the thyroid doses were analysed. According to the results 28 and 54% patients were under dosed and 72 and 46% patients were over dosed with DG and NG, respectively. The protocols, which have not taken into account the thyroid mass, multi pre-therapeutic 131 I uptakes and the effective half-life of 131 I of the individual patient, showed a higher degree of deviation from the required thyroid dose. Besides these parameters, some fundamental factors such as radiosensitivity, previous exposure to thyroid drugs and duration of the disease are recommended to be incorporated, which can certainly affect the clinical out comes.

Release criteria from hospitals of 131I thyrotoxicosis therapy patients in developing countries--case study.

The current release limit, recommended by the International Atomic Energy Agency (IAEA)(1), from hospitals of patients undergoing 131I thyrotoxicosis therapy is approximately 1100 MBq (approximately 30 mCi). Owing to the difference in socio-economic conditions, literacy rate, family system, etc., this release limit may not be applicable in most of the developing countries like Pakistan. Therefore, the prime objective of this case study was to re-evaluate the release criteria for 131I thyrotoxicosis therapy patients by taking into account their lifestyle, economic conditions and other facilities such as availability of private/public transport, etc. In this context, systematic studies were carried out and 50 patients (i.e. 35 outpatients and 15 inpatients) at the Nuclear Medicine Oncology and Radiotherapy Institute (NORI), Islamabad, were studied. Exposure rate at the surface of the body and at a distance of 1 m from the standing patient was measured. Results obtained from this study showed that the dose equivalent delivered by these patients to their family members (particularly children) and general public was higher than annual dose limits recommended by the International Commission for Radiation Protection in their report ICRP Publication 60(2). In the light of this study, it is recommended that the release activity limit of approximately 370 MBq (or dose rate level of approximately 10 microSv h-1 at 1 m from the patient) be adopted instead of approximately 1100 MBq in developing countries like Pakistan.