Evaluation of Delivered Dose Changes During Radiation Therapy

Abstract

The influence of changes in the thickness of the irradiated tissue block during radiotherapy on the error in dose delivery was assessed by dosimetry in vivo. In 55 cases of head and neck cancers, entrance and exit doses and the irradiated volume sizes were measured during the first and the twentieth fractions. The real and hypothetical midline doses (i.e. midline doses calculated when the entrance dose is considered as a planned one) were calculated. The average size of irradiated volume was smaller after 20 fractions. The mean of midline dose dosimetric errors during the twentieth fraction was larger (overdosage) than that during the first fraction. These means were compared and statistically significant differences were found. Our results confirm the value of in vivo dosimetry as an appropriate tool for detecting errors in delivered dose provoked by changes in irradiated volume dimensions and show the necessity to check irradiated volume thickness during the treatment.

Development of Transmission Dose Estimation Algorithm for in vivo Dosimetry in High Energy Radiation Treatment

“…They also found error was over 10% in more than half of the occasions of human error. Miszczyk et al reported that significant overdose was caused by reduction of tumor volume after 20 sessions of radiation treatment in head and neck cancer patients 7 ). So, to avoid error from various origin and maintain good quality assurance, the confirmation of actually delivered dose to the patient (in vivo dosimetry) for every treatment session is needed.…”

Influence of interfraction motion on margins for radiotherapy of gastric cancer

“…Some authors have observed a correlation between positioning errors and patients' weight loss. 18 According to calculations, the interfractional motion increased along the x-axis during treatment, which could correlate with patient weight loss. Better patient preparation as well as remaining relaxed during treatment affects the correct positioning.…”