Dosimetry for Organs at Risk With and Without Use of Perirectal Hydrogel Spacer in Prostate Cancer Patients Treated With SBRT
ASTRO Poster Library. Fried D. Sep 24, 2017; 191652; 2559 Topic: Genitourinary Cancer
Daniel Fried
Daniel Fried
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D. B. Fried1, R. S. DuBose1, K. Johnson1, M. Cogdell1, J. A. Gersh2, and J. M. Kilburn2; 1Gibbs Cancer Center & Research Institute, Greer, SC, 2Gibbs Cancer Center, Spartanburg, SC, United States


Perirectal spacing with placement of biomaterials between the posterior prostate and the anterior rectum has shown promise in reducing the radiation dose received by the rectal wall when used in the setting of conventionally fractionated radiation therapy. The use of SBRT for treatment of low risk and favorable intermediate risk prostate cancer continues to increase. However, there is little data describing the use of perirectal hydrogel spacer (PHS) with SBRT in the treatment of prostate cancer. This is a retrospective comparison of dosimetric parameters for normal structures in patients treated without PHS compared to those treated with PHS.


28 patients with low risk or favorable intermediate risk prostate cancer were treated with CyberKnife (CK) SBRT (3625 cGy in 5 fractions) prior to initiation of a PHS program. Since introducing a PHS program we have treated 66 patients with CK including PHS. In this analysis we compare dosimetric characteristics of these patients with regard to bowel, bladder and penile bulb dose. Mean values were compared with 2-sided t-tests.


The volume of rectum receiving at least 3440 cGy was 0.99 cc with PHS (range 0.00 cc – 2.32 cc) compared to 2.48 cc (range 1.22 cc – 3.37 cc) without PHS (p = 0.0000). The mean maximum dose received by 10% of the rectum (D10) and mean D20 were significantly lower in the PHS group compared to the non-PHS group, 2666 cGy and 2165 cGy compared to 3044 cGy (p = 0.0000) and 2459 cGy (p = 0.0001). The mean D50 was not significantly different between the 2 groups, 1090 cGy with PHS compared to 1140 cGy without (p = 0.47). With regard to bladder dose, none of the differences between mean doses achieved statistical significance, but all favored the PHS group numerically. The mean D10 for the bladder was 2623 cGy with PHS compared to 2952 cGy without (p = 0.12) and the mean D50 was 1209 cGy with PHS compared to 1313 cGy without (p = 0.08). Penile bulb mean doses were significantly less for all dosimetric parameters among PHS patients compared with non-PHS patients. Mean maximum point dose to the penile bulb was 3035 cGy with PHS compared to 2264 cGy without (p = 0.0000). The mean volume of penile bulb receiving 2000 cGy or higher was 0.43 cc with PHS compared to 1.78 cc without (p = 0.0000).


PHS application resulted in improved dosimetry for rectal endpoints pertinent to high radiation dose regions that are likely to confer long-term toxicity. In addition, penile bulb dosimetry was significantly improved with use of PHS. Although the numerical improvements in bladder dose were not statistically significant, there was a suggestion of decreased dose endpoints.  Use of PHS may promote not only sparing of the rectum, but also result in decreased dose to other organs at risk including the penile bulb and bladder.

AuthorDisclosure: D.B. Fried: None. R.S. DuBose: None. K. Johnson: None. M. Cogdell: None. J.A. Gersh: None. J.M. Kilburn: None.
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