Effect of edema, relative biological effectiveness, and dose heterogeneity on prostate brachytherapy

Journal Article · Sat Apr 15 04:00:00 EDT 2006 · Medical Physics

DOI:https://doi.org/10.1118/1.2181294· OSTI ID:20775102

Wang, Jian Z; Mayr, Nina A; Nag, Subir; Montebello, Joseph; Gupta, Nilendu; Samsami, Nina; Kanellitsas, Christos ^[1]

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1. Department of Radiation Medicine, The Ohio State University, Columbus, Ohio 43210 (United States)

Many factors influence response in low-dose-rate (LDR) brachytherapy of prostate cancer. Among them, edema, relative biological effectiveness (RBE), and dose heterogeneity have not been fully modeled previously. In this work, the generalized linear-quadratic (LQ) model, extended to account for the effects of edema, RBE, and dose heterogeneity, was used to assess these factors and their combination effect. Published clinical data have shown that prostate edema after seed implant has a magnitude (ratio of post- to preimplant volume) of 1.3-2.0 and resolves exponentially with a half-life of 4-25 days over the duration of the implant dose delivery. Based on these parameters and a representative dose-volume histogram (DVH), we investigated the influence of edema on the implant dose distribution. The LQ parameters ({alpha}=0.15 Gy{sup -1} and {alpha}/{beta}=3.1 Gy) determined in earlier studies were used to calculate the equivalent uniform dose in 2 Gy fractions (EUD{sub 2}) with respect to three effects: edema, RBE, and dose heterogeneity for {sup 125}I and {sup 103}Pd implants. The EUD{sub 2} analysis shows a negative effect of edema and dose heterogeneity on tumor cell killing because the prostate edema degrades the dose coverage to tumor target. For the representative DVH, the V{sub 100} (volume covered by 100% of prescription dose) decreases from 93% to 91% and 86%, and the D{sub 90} (dose covering 90% of target volume) decrease from 107% to 102% and 94% of prescription dose for {sup 125}I and {sup 103}Pd implants, respectively. Conversely, the RBE effect of LDR brachytherapy [versus external-beam radiotherapy (EBRT) and high-dose-rate (HDR) brachytherapy] enhances dose effect on tumor cell kill. In order to balance the negative effects of edema and dose heterogeneity, the RBE of prostate brachytherapy was determined to be approximately 1.2-1.4 for {sup 125}I and 1.3-1.6 for {sup 103}Pd implants. These RBE values are consistent with the RBE data published in the literature. These results may explain why in earlier modeling studies, when the effects of edema, dose heterogeneity, and RBE were all ignored simultaneously, prostate LDR brachytherapy was reported to show an overall similar dose effect as EBRT and HDR brachytherapy, which are independent of edema and RBE effects and have a better dose coverage.

• OSTI ID: 20775102
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 4 Vol. 33; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
BRACHYTHERAPY
CARCINOMAS
DOSE RATES
DOSIMETRY
EDEMA
IODINE 125
PALLADIUM 103
PROSTATE
RADIATION DOSE DISTRIBUTIONS
RADIATION DOSES
RADIATION SOURCE IMPLANTS
RBE
TUMOR CELLS