Image -guided adaptive radiotherapy for prostate and head-and-neck cancers

In the current practice of radiation therapy, daily patient alignments have been based on external skin marks or on bone. However, internal organ variation (both motion and volumetric changes) between treatment fractions can displace the treatment target, causing target underdosage and normal tissue overdosage. In order to deliver the radiation treatment as planned, more accurate knowledge of the daily internal anatomy was needed. Additionally, treatments needed to adapt to these variations by either shifting the patient to account for the daily target position or by altering the treatment plan. ^ In this dissertation, the question of whether inter-fractional variations in internal patient anatomy combined with external set-up uncertainties produced measurable differences between planned and delivered doses for prostate and head-and-neck cancer patients was investigated. Image-guided adaptive treatment strategies to improve tumor coverage and/or reduce normal tissue dose were examined. Treatment deliveries utilizing various alignment procedures for ten prostate cancer patients and eleven head-and-neck cancer patients, each of whom received multiple CT scans over the course of treatment, were simulated. ^ The largest prostate dose losses between planning and delivery were correlated with anterior/posterior and superior/inferior prostate displacement. Daily bone alignment sufficiently maintained target coverage for 70% of patients, ultrasound for 90%, and CT for 100%. A no-action-level correction protocol, which corrected the daily bone alignment for the systematic internal displacement of the prostate based on a pre-determined number of CT image sets, successfully improved the prostate and seminal vesicle dosimetric coverage. Three CT image sets were sufficient to accurately correct the bone alignment scheme for the prostate internal systematic shifts. ^ For head-and-neck cancer patient treatment, setup uncertainties and internal organ variations did not greatly affect the target dose coverage, but did increase the parotid gland dose. Bone alignment provided a lower delivered parotid gland dose, but daily adaptive treatment replanning provided the best normal tissue sparing. ^ External set-up uncertainty and inter-fractional anatomic variation negatively affected the delivered dose distribution for both prostate cancer and H\u26N cancer patients. This dissertation has shown that adapting for inter-fractional internal anatomic variations improved tumor coverage for prostate cancer and educed normal tissue dose for H\u26N cancer.