TITLE:
Construction of a Simple Rectum Model Using Image Guidance in Prostate Patients Treated with 3D Conformal Radiotherapy
AUTHORS:
Marco D’Andrea, Maria Daniela Falco, Dahlia Fedele, Elisabetta Ponti, Barbara Tolu, Daniela Di Cristino, Rosaria Barbarino, Luana Di Murro, Grazia Tortorelli, Andrea Duggento, Paolo Bagalà, Maria Guerrisi, Riccardo Santoni
KEYWORDS:
Organ Motion, Prostate Cancer, Rectal Toxicity, Radiotherapy
JOURNAL NAME:
Journal of Cancer Therapy,
Vol.5 No.12,
October
14,
2014
ABSTRACT: Purpose: To evaluate the performance of a
rectum model in predicting late rectal toxicity of prostate patients undergoing
3D conformal radiation therapy while following a dietary protocol combined with
image guidance. Methods: A linear accelerator equipped with a Cone Beam
Computed Tomography (CBCT) system was used to treat 20 patients who were
following a dietary protocol. The set-up was verified by co-registering CBCT
scans with the planning CT scan (pCT). A mean dose volume histogram
() as the arithmetical mean of the rectum DVHs from each CBCT scan
was obtained. A suitably defined 3D rectum model (Average Rectum, AR) was
defined and its DVH (DVHAR) was calculated. DVHs were also evaluated
for the first five CBCT scans using both methods (5 >and
DVHAR5). The Lyman-Kutcher-Burman NTCP model with QUANTEC parameters
was used to compare the calculated DVHs. The QUANTEC dose values were used to
describe the time behaviour of the relative volumes using the Gamma
Distribution for the frequency of the relative rectum volumes at each QUANTEC
dose value. Results: No statistically
significant differences between NTCPAR5 and NTCPAR and between NTCP and NTCP were found. The best agreement
with the observed toxicity rate (0%) was obtained form DVHAR. The Gamma Distributions of the rectum
volumes at the QUANTEC dose levels were found to be highly variable among the
patients. Conclusions: Both dietary protocol and image guidance were found
effective in limiting late rectal toxicity. AR was a better predictor for late
rectal toxicity and better described the rectum volume during the treatment
course. Finally, from the Gamma
distributions, and from our toxicity data, we can suggest V75 as the best predictor of late rectal
toxicity.