Treatment/Prognosis Flashcards
What doses are typically prescribed when using monotherapy with I-125, Pd-103, and Cs-131?
Doses typically prescribed for BT monotherapy:
I-125: 140–160 Gy
Pd-103: 110–125 Gy
Cs-131: 115 Gy
What can be done to place sources into the tissues surrounding the prostate to provide extracapsular coverage?
In order to reliably place sources into tissues surrounding the prostate, a possible technical solution is to place linked seeds embedded in Vicryl sutures in the peripheral portions of the prostate.
What is the post-implant evaluation process for LDR BT?
Generally CT-based study performed immediately after BT or ∼30 days after. Goals are:
- Verify that the target volume rcvd Rx dose
- Establish that normal tissues did not rcv excessive dose
- Serve as feedback on the quality of the implant process
- Assess dose within the target volume (Davis et al., Brachytherapy 2017)
In prostate LDR BT, what is the D90 and V100 and what are the recommended values for these parameters?
In prostate LDR BT, the D90 refers to the min dose in the hottest 90% of the post-implant prostate volume (given as a % of the Rx dose). The goal D90 is >90% of the Rx dose. The V100 refers to the volume of the prostate receiving 100% of the Rx dose. The goal V100 is >90%. Although D90 and V100 are strongly correlated, D90 is used to describe how hot or cold an implant is with respect to the Rx dose and V100 is used to describe how well the implant covers the desired target.
In prostate BT, why is the D90 parameter used and not the D100?
D90 is used instead of D100 to evaluate post-implant dosimetry b/c retrospective studies have identified D90 as a better predictor of long-term biochemical control. D90 may be a better predictor of outcomes b/c it is less sensitive to small differences in the way a prostate is contoured b/t users on post-implant CTs. (Potters et al., IJROBP 2001)
In prostate BT, what are the RV100 and the UV150?
RV100 is the volume of the rectum in cc’s receiving 100% of the Rx dose. UV150 is the volume of the urethra receiving 150% of the Rx dose.
What are the goals for RV100 and UV150 in prostate BT planning?
Reasonable goals are to limit RV100 to <1 cc and UV150 to <5%.
What isotope is typically used in HDR BT for prostate cancer?
Ir-192 is typically used for HDR BT to treat prostate cancer.
What is the half-life for Ir-192?
The half-life for Ir-192 is 73.8 days.
What are common dose/fractionation schedules for HDR BT monotherapy?
No consensus on dose/fractionation. Common fractionation schemes include: 34 Gy in 4 fx; 36–38 Gy in 4 fx; 31.5 Gy in 3 fx; 26 Gy in 2 fx.
What about single-fx HDR monotherapy?
Single-fx HDR monotherapy is investigational but some results are promising. A phase II trial by Hoskin et al. randomized pts to 19–20 Gy × 1, 13 Gy × 2, or 10.5 Gy × 3. There was no difference in bRFS b/t the arms, with 4-yr bRFS of 94% for single fx (Radiother Oncol 2017). Krauss et al. reported 3-yr bRFS of 93% for 19 Gy × 1 (IJROBP 2017). In the trial by Prada et al., 6-yr bRFS was worryingly low (66%) after 19 Gy × 1, tempering some enthusiasm for single-fx HDR (Radiother Oncol 2016). Toxicity results are encouraging. (Morton et al., Radiother Oncol 2017)
What studies have compared EBRT + BT boost vs. EBRT + EBRT boost in intermediate- and high-risk prostate cancer?
Several. ASCENDE-RT trial (Morris et al., IJROBP 2017): 398 men, 69% with high-risk Dz, were randomized to ADT + 3D conformal EBRT (46 Gy/23 fx whole pelvis WP), prostate boost to 78 Gy/39 fx) vs. ADT + WP EBRT + LDR boost (I-125, min peripheral dose 115 Gy). After median f/u of 6.5 yrs, LDR boost associated with significantly lower rates of biochemical failure (7-yr bRFS 86% vs. 75%) than EBRT boost with no difference in OS. A similar trial by Hoskin et al. also found no difference in OS (Radiother Oncol 2012). In general, the BT boost appears more effective for high-risk pts. A BT boost is allowed on the currently accruing RTOG 0924.
What about BT as salvage after EBRT failure?
LR after EBRT occurs in up to 15% (Zumsteg et al., J Urol 2015). Salvage BT is potentially curative Tx. Key selection criteria from RTOG 0526 trial of salvage LDR BT: Bx-confirmed LR with no extraprostatic Dz on imaging, recurrence >30 mos after EBRT, American Urological Association (AUA) score <15, and pre-salvage PSA <10. Phase II trial of HDR BT at MSKCC reported 5-yr bRFS 68% (Yamada et al., Brachytherapy 2014). The Princeton Radiation Oncology experience using 4–6 mos of neoadj, concurrent, and adj ADT plus salvage BT (LDR or HDR) reported 5-yr bRFS of 79% and 5-yr freedom from late grade 3 GU toxicity of 85% with no late grade ≥2 GI toxicity. (Baumann et al., Brachytherapy 2017)
What is the long-term biochemical control for low-risk pts after LDR monotherapy?
Long-term bRFS rates of 86%–98% have been reported. (Davis et al., Brachytherapy 2017)
What is the data comparing the efficacy of I-125 vs. Pd-103 for prostate BT?
I-125 and Pd-103 appear similarly efficacious. The Seattle Isotope trial randomized low-risk prostate cancer pts to I-125 vs. Pd-103 and found no difference in 3-yr bRFS (89% vs. 91%, p = 0.76) and no differences in morbidity. (Wallner K et al., IJROBP 2003)
