Potential for higher treatment failure in obese patients: correlation of elevated body mass index and increased daily prostate deviations from the radiation beam isocenters in an analysis of 1,465 computed tomographic images.
OBJECTIVE
Recent clinical outcome studies on prostate cancer have reported the influence of patient's obesity on the biochemical failure rates after various treatment modalities. In this study, we investigated the effect of patient's physical characteristics on prostate shift in external beam radiotherapy (EBRT) and hypothesized that there maybe a correlation between patient physique and tumor shift.


METHODS
A retrospective analysis was performed using data for 117 patients who received image-guided radiation therapy (IGRT) for prostate cancer between January 2005 and April 2007. A total of 1,465 CT scans were analyzed. The standard deviations (SDs) of prostate shifts for all patients, along with patient weight, body mass index (BMI), and subcutaneous adipose-tissue thickness (SAT), were determined. Spearman rank correlation analysis was performed.


RESULTS
Of the 117 patients, 26.5% were considered normal weight, 48.7% were overweight, 17.9% were mildly obese, and 6.9% were moderately to severely obese. Notably 1.3%, 1.5%, 2.0%, and 21.2% of the respective shifts were greater than 10 mm in the left-right (LR) direction for the four patient groups, whereas in the anterior-posterior direction the shifts are 18.2%, 12.6%, 6.7%, and 21.0%, respectively. Strong correlations were observed between SAT, BMI, patient weight, and SDs of daily shifts in the LR direction (p < 0.01).


CONCLUSIONS
The strong correlation between obesity and shift indicates that without image-guided radiation therapy, the target volume (prostate with or without seminal vesicles) may not receive the intended dose for patients who are moderate to severely obese. This may explain the higher recurrence rate with conventional external beam radiation therapy.
Wong
James R
JR
Department of Radiation Oncology, The Carol G Simon Cancer Center, Morristown Memorial Hospital, Morristown, NJ 07962, USA. jackie.vizoso@atlantichealth.org
Gao
Zhanrong
Z
Merrick
Scott
S
Wilson
Paula
P
Uematsu
Minoru
M
Woo
Kevin
K
Cheng
Chee-Wai
CW
D015992:Body Mass Index; D001835:Body Weight; D006801:Humans; D008297:Male; D009068:Movement; D009765:Obesity / Q000000981:diagnostic imaging*; D010388:Pelvis; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D012189:Retrospective Studies; D012669:Seminal Vesicles / Q000000981:diagnostic imaging; D018709:Statistics, Nonparametric; D050151:Subcutaneous Fat / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000379:methods*; D017211:Treatment Failure; D001743:Urinary Bladder / Q000000981:diagnostic imaging