Physical derivation of nomograms in permanent prostate brachytherapy
Received 10 February 2009; received in revised form 1 July 2009; accepted 7 July 2009. published online 21 October 2009.
Abstract
Purpose
To demonstrate the physical origin of nomograms in permanent prostate brachytherapy, by using the correlation between fractional integral target dose (FITD) and target volume.
Methods and Materials
The integral dose (ID) E delivered by unit activity is given by the integration of 4πr2D(r)/r2dr×1.44T1/2 using the point source model from AAPM TG43. If A is the total activity implanted, then total ID will be A×E. Integral target dose are obtained by multiplying the prostate volume V with mean dose Dmean by definition, assuming prostate gland has a unity density. The FITD the target receives is defined as FITD=DmeanV/AE by energy conservation in the target volume. From this equation, the total activity needed to achieve given dose for a target of volume V is obtained. Results are compared with existing nomograms for 125I and 103Pd, and available clinical data for 131Cs.
Results
Agreement within 10.0% for 125I and 103Pd compared with existing nomograms for gland sizes from 18 to 80cc is observed. For 131Cs, the agreement is within 8.0% compared with available clinical data.
Conclusions
It is shown that the correlation between the FITD and target volume can be used to obtain the total activity needed to achieve prescribed dose. This correlation is inherent rather than empirical. It suggests that the correlation between fraction of energy deposition in target and target volume is the underlying physical origin for nomograms used in permanent prostate brachytherapy.
Department of Radiation Oncology, Tuomey Healthcare System, Sumter, SC
Corresponding author. Department of Radiation Oncology, Tuomey Healthcare System, 130 North Washington Street, Sumter, SC 29150. Tel.: +1-803-774-8776; fax: +1-803-778-6376.
Part of this study was presented at the 50th American Society for Therapeutic Radiology and Oncology (ASTRO) annual meeting in Boston, MA, September 21–25, 2008.
Financial disclosure/conflict of interest statement: Texin Li, none; Lynn Foutain, none; Edward Duffy, none.
ABSTRACT