Abstract:
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Purpose: To evaluate the role of radioimmunoscintigraphy
(RIS) directed against prostate specific membrane antigen (PSMA) {ProstaScint}
in modifying the post-prostatectomy prostate fossa clinical target volume (CTV)
definition.
Methods and Materials: The records, image data, and treatment plans of 25
consecutive post-prostatectomy patients who received external beam radiotherapy
post-prostatectomy and who underwent an RIS scan for aiding treatment volume
definition were reviewed. A vessel registration technique developed at our
institution was implemented to project the region(s) of uptake on the RIS scan
into the planning CT scan to assist in defining the CTV. For each patient, the
CTV that would have been treated (CTV-pre) prior to this RIS/CT fusion was
compared with that defined after the fusion (CTV-post). Additionally, the
treatment plan generated using CTV-pre was compared with that using CTV-post to
quantify the effects of the CTV differences on the Bladder and Rectum dose
volume histograms (DVH's). These DVH comparisons were performed using two
standard endpoints - volume receiving > 60Gy (V60) and area under the curve
(AUC).
Results: The CTV-pre volume (in cc) was 24.4 +/- 10.2 {mean +/- standard
deviation} vs the CTV-post volume, which was 35.0 +/- 21.2 (p=0.032). The
CTV-post volume was larger than the corresponding CTV-pre volume in 18/25 (72%)
cases. The V60 results (in cc) were as follows: Rectum - ({using CTV-pre vs
CTV-post} 32.7 +/- 15.9 vs 41.0 +/- 25.1, p=0.168); Bladder - (33.9 +/- 13.0 vs
46.6 +/- 21.2, p=0.015). The AUC results (in Gy*cc) were as follows: Rectum -
(4027 +/- 1878 vs 4516 +/- 2151, p=0.396); Bladder - (4782 +/- 1584 vs 5561 +/-
1873, p=0.119). RTOG grade 2 toxicity occurred as follows: acute
gastrointestinal (GI): 8%, late GI: 36%, acute genitourinary (GU): 12%, late
GU: 12%. No grade 3 acute or late GI toxicity or grade 3 acute GU toxicity was
observed; however, grade 3 late GU toxicity occurred in 4% of the patients. No
Grade 4 GI or GU toxicity was observed.
Conclusion: Incorporating RIS-uptake was found to result in significant
modification in post-prostatectomy CTV definition. The dosimetric consequences
of the CTV modifications on the Rectum were demonstrated not to be significant.
Although the CTV modifications do not appear to adversely affect integral dose
to the Bladder, they do appear to have an affect on the volume of Bladder
receiving high doses. However, observed rates grade 3 and 4 GI and GU
toxicities were quite low, suggesting that treatment to the modified CTV is
tolerable. (A grant was
received from Cytogen Corporation.)
Jani MD, MSEE, A,
Analysis of the Impact of Radioimmunoscintigraphy on Post-Prostatectomy Radiotherapy Clinical Target Volume Definition. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3100621.html
