Cancer -- Radiotherapy

Monte Carlo (MC) and Pencil Beam (PB) calculations are compared to their measured planar dose distributions using a 2-D diode array for lung Stereotactic Body Radiation Therapy (SBRT). The planar dose distributions were studied for two different phantom types: an in-house heterogeneous phantom and a homogeneous phantom. The motivation is to mimic the human anatomy during a lung SBRT treatment and incorporate heterogeneities into the pre-treatment Quality Assurance process, where measured and calculated planar dose distributions are compared before the radiation treatment. Individual and combined field dosimetry has been performed for both fixed gantry angle (anterior to posterior) and planned gantry angle delivery. A gamma analysis has been performed for all beam arrangements. The measurements were obtained using the 2-D diode array MapCHECK 2™.

Empirical methods of beam angle optimization (BAO) are tested against the BAO
that is currently employed in Eclipse treatment planning software. Creating an improved
BAO can decrease the amount of time a dosimetrist spends on making a treatment plan,
improve the treatment quality and enhance the tools an inexperienced dosimetrist can use
to develop planning techniques. Using empirical data created by experienced dosimetrists
from 69 patients treated for lung cancer, the most frequently used gantry angles were
applied to four different regions in each lung to gather an optimal set of fields that could
be used to treat future lung cancer patients. This method, given the moniker FAU BAO,
is compared in 7 plans created with the Eclipse BAO choosing 5 fields and 9 fields. The
results show that the conformality index improved by 30% or 3% when using the 5 and 9
fields. The conformation number was better by 12% from the 5 fields and 9% from the 9
fields. The organs at risk (OAR) were overall more protected to produce fewer
nonstochastic effects from the radiation treatment with the FAU BAO.

An improved method is introduced for prediction of local tumor control following lung
stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer
(NSCLC) patients using 18F-fluorodeoxyglucose positron emission tomography (18F-FDG
PET). A normalized background-corrected tumor maximum Standard Uptake Value
(SUVcmax) is introduced using the mean uptake of adjacent aorta (SUVref), instead of
the maximum uptake of lung tumor (SUVmax). This method minimizes the variations
associated with SUVmax and objectively demonstrates a strong correlation between the
low SUVcmax (< 2.5-3.0) and local control of post lung SBRT. The false positive rates
of both SUVmax and SUVcmax increase with inclusion of early (<6 months) PET scans,
therefore such inclusion is not recommended for assessing local tumor control of post
lung SBRT.