Thesis Defense: Dynamic Optimization of Fractionation Schedules in Radiation Therapy


Event Speaker: 

Jagdish Ramakrishnan

Event Location: 


Event Date/Time: 

Thursday, May 9, 2013 - 3:30pm



In radiation therapy, the fractionation schedule, i.e. the total number
of treatment days and the dose delivered per day, plays an important
role in treatment outcome. Conventional radiation therapy procedures
deliver an equal dose to the tumor every day over the course of 30-40
days. In this thesis, we investigate the improvement in treatment
effectiveness when dynamically optimizing the fractionation scheme.

In the first part of the thesis, we consider delivering a different dose
each day depending on the observed patient anatomy. Given that a fixed
prescribed dose must be delivered to the tumor over the course of the
treatment, such an approach results in a lower cumulative dose to a
radio-sensitive organ-at-risk when compared to that resulting from
standard fractionation. We use the dynamic programming algorithm to
solve the problem exactly. When using a physical dose model, we
characterize the structure of an optimal policy and develop heuristic
policies based on this structure. Next, we suggest an approach which
both optimizes the fraction size and selects a treatment plan from a
plan library. Computational results from patient datasets suggest that
such a spatio-temporal approach is beneficial.

In the second part of the thesis, we analyze the effect of repopulation
on the optimal fractionation scheme. We are primarily motivated by
accelerated tumor repopulation towards the end of radiation treatment,
which is believed to play a role in treatment failure for some tumor
sites. A dynamic programming framework is developed to determine the
optimal fractionation scheme based on a model of cell kill due to
radiation and tumor growth in between treatment days. We prove that the
optimal dose fractions are increasing over time. We find that faster
tumor growth suggests shorter overall treatment duration. In addition,
the presence of accelerated repopulation suggests larger dose fractions
later in the treatment to compensate for the increased tumor proliferation.

Thesis Committee: Dimitri P. Bertsekas, Thomas Bortfeld [s], David Craft
[s], John N. Tsitsiklis [s]
[s] = Supervisor