ANALYSIS OF SET-UP ERRORS IN BREAST CANCER PATIENTS UNDERGOING EXTERNAL BEAM RADIOTHERAPYAT NATIONAL HOSPITAL ABUJA
ANALYSIS OF SET-UP ERRORS IN BREAST CANCER PATIENTS UNDERGOING EXTERNAL BEAM RADIOTHERAPYAT NATIONAL HOSPITAL ABUJA
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Date
2023-04
Authors
ONUH, ECHECHE
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Abstract
Radiotherapy plays an important role in breast cancer treatment. The main goal of radiationtherapy is to ensure tumor control while avoiding complications to the organs at risks. Uncertainty in the dose deposited in the tumor exists due to a variety of factors which include patient positioning errors. This study assessed and quantified breast cancer patients‟ set-up errors using an electronic portal imaging device and evaluated the dosimetric and biological impact in terms of generalized equivalent uniform dose (gEUD) using predictive models, such as Tumour Control Probability (TCP) and Normal Tissue Complication Probability (NTCP). About 200 breast cancer patients were considered at the Radiotherapy-Oncology department of National Hospital Abuja (NHA). Systematic and random errors were quantified, in addition,three-dimensional treatment planning was performed using CT scan images of the patients. The total prescribed dose was 5000 cGy per 25 fractions for most of the patients. The dosimetric and biological impact of these set-up errors on the target volume and the organ at risk (OARs) coverage were assessed by evaluating the Dose– Volume Histogram (DVH), gEUD, TCP and NTCP. The standard deviations (SDs) of the systematic set-up and random set-up errors were calculated for the Lateral, Anterior-Posterior and Superior-Inferior fields and were found to be 6.6055(4.477), 4.608(3.591), 11.432(8.1748) respectively. Thus, a planning target volume (PTV) margin of 5 mm was defined around the OARs, and around the clinical target volume (CTV). The toxicity of OARs was quantified using gEUD, TCP and NTCP. The data represented that NTCP values for conformal technique was one (1) for the combined lungs at D50, D75, D90 and D98 of the planning target volume (p = 0.05). In addition, NTCP values of the heart were equal to 0.99 at D50, D75, D90 and D98. The TCP outcome shows a negative and not so good correlation with calculated dose to 50%, 75%, 90% and 95% of the target volume (D95%). In conclusion, this research confirmed that more relevant and robust radiobiological parameters should be integrated with more recent dose calculation methods to obtain reliable prediction of organ at risks toxicity and avoid over/under estimating of TCP and NTCP. This is critical if medical decisions have to be based on NTCP estimations in routine practice.
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A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA, IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF DOCTORATE DEGREE OF SCIENCE IN RADIATION BIOPHYSICS, DEPARTMENT OF PHYSICS, FACULTY OF PHYSICAL SCIENCES, AHMADU BELLO UNIVERSITY, ZARIA NIGERIA