Modeling correlation indices between bladder and Foley's catheter balloon dose with CT-based planning using limited CT slices in intracavitary brachytherapy for carcinoma of cervix.
OBJECTIVE
To derive and validate an index to correlate the bladder dose with the catheter balloon dose using limited computed tomography (CT) slices.


METHODS
Applicator geometry reconstructed from orthogonal radiographs were back-projected on CT images of the same patients for anatomy-based dosimetric evaluation. The correlation indices derived using power function of the catheter balloon dose and the bladder volume dose were validated in 31 patients with cervical cancer.


RESULTS
There was significant correlation between International Commission on Radiation Units (ICRU)-38 balloon reference dose (Dr) and the dose received by 25% bladder volume (D(25)) (P< 0.0001). Significant correlation was also found between the reference dose of mid-balloon point (D(rm)) and the dose to D(25) (P < 0.0001). Average percentage difference [100 x (observed index - expected index)/ expected index] of observed value of I'25 (index for the dose to D25 bladder with respect to mid-balloon reference point) from that of expected value was 0.52%, when the index was modeled with reference dose alone. Similarly the average percentage difference for I'10cc (index for the dose to 10 cc volume of bladder with respect to mid balloon point) was 0.84%. When this index was modeled with absolute bladder volume and reference dose, standard deviation of the percentage difference between observed and expected index for D(rm) reduced by approximately 2% when compared to D(r).


CONCLUSIONS
For clinical applications, correlation index modeled with reference dose and volume predicts dose to absolute volume of bladder. Correlation index modeled with reference dose gives a good estimate of dose to relative bladder volume. From our study, we found D(rm) to be a better indicator of bladder dose than D(r).
Oinam
Arun S
AS
Department of Radiotherapy, Postgraduate Institute of Medical Education and Research, Chandigarh, India. oarunsingh@rediffmail.com
Goda
Jayant Sastri
JS
Dubey
Sidharth
S
Bhardwaj
Anup
A
Patel
Firuza D
FD
D001706:Biopsy; D001918:Brachytherapy / Q000379:methods*; D002404:Catheterization; D005260:Female; D006801:Humans; D011446:Prospective Studies; D011859:Radiography / Q000379:methods; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D014057:Tomography, X-Ray Computed / Q000379:methods*; D001743:Urinary Bladder / Q000473:pathology*; D002583:Uterine Cervical Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy*