Evaluation of IMRT parameters for head and neck cancer
Abstract
Head and neck (H&N) cancer is one of the most common human cancers, with a global incidence of 500,000 cases per year. The American Cancer Society estimates that there will be more than 55,000 Americans diagnosed with H&N cancer each year. About two-thirds of this group will receive radiation therapy during their lifetime. Treatment options for H&N cancer patients are surgery, chemotherapy, radiation therapy, and/or a combination of all these modalities. The main steps involved in the treatment of cancer patients with radiation therapy are: simulation, target and normal tissue delineation, treatment planning and optimization, plan evaluation and treatment delivery. Intensity Modulated Radiation Therapy (IMRT) is a mode of external beam radiation therapy where intensity of the beam is modulated to provide adequate coverage to planning target volume (PTV) while preferentially sparing organs at risk (OARs). It is regarded as the gold standard for radiation treatment of H&N cancer. Although it has been over two decades since the inception of IMRT in the clinic, the overall cure rate for H&N cancer patients is still less than 50%. The main contributing factors to these treatment failures are in the difficulties associated with controlling local and regional disease. Specifically, two major issues related to H&N IMRT are: loco-regional failure and survival (failure of local tumor control), resulting in a high recurrence rate; and normal tissue toxicity (acute and chronic) due to higher radiation dosage to normal tissues beyond repair. It seems that the loco-regional failures of H&N cancer patients are due to geographical miss and insufficient dose, or a combination of both, whereas the normal tissue toxicities are due to the irradiation of non-target structures, i.e., OARs. The goal of H&N IMRT is to irradiate the cancerous cells with minimal damage to OARs. This can be accomplished by the accurate estimation of gross tumor volume (GTV) and OARs, optimum PTV delineation, better fluence optimization and dose calculation that could provide a better overall survival and hence, improve quality of care for these patients. The goal of this thesis work is to optimize these IMRT treatment parameters to maximize the Tumor Control Probability (TCP) and minimize Normal Tissue Complication Probability (NTCP) as recommended by ICRU-83. To achieve this goal, three main steps are explored in the thesis. The first part of this thesis is focused on improvement in the estimation of volume (targets and organs) definition accuracy to avoid any geographical miss of cancers (target volumes) while excluding normal tissue in target volumes. In the second part of this thesis, a treatment planning strategy is explored to determine an optimum margin for the PTV and OAR expansion by using image-guidance. In the final part of this thesis, optimization and dosimetric accuracy in terms of grid size calculation for H&N IMRT is described. Future research will concentrate on additional improvements in TCP and NTCP by accurately defining target volume with aid of functional imaging (e.g, PET) and possibly dose escalation to radiation-resistant and hypoxic tumors by using differential dose painting.
Degree
Ph.D.
Advisors
Stantz, Purdue University.
Subject Area
Medicine|Medical imaging
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