Focal Boosted IMRT Treatment of Prostate Cancer to 84 Gy in 28 Fractions: Preliminary Clinical Outcomes and Dosimetry

PURPOSE/OBJECTIVE(S)

The FLAME trial reported that focal boosting of prostate tumor to 95 Gy in 35 fractions improves biochemical control. However, this treatment is not commonly used in the United States. We investigated a focally boosted treatment of 84 Gy in 28 fractions (EQD2 108 Gy, BED 252 Gy).

MATERIALS/METHODS

Between 2019-2022, men with unfavorable intermediate risk (uIR) and high risk (HR) prostate cancer were enrolled on a prospective registry and received a novel IMRT regimen. The dose levels were 84 Gy to the gross tumor volume (GTV) as defined on mpMRI (T2W and ADC) with no added margin, 70 Gy to the prostate and proximal seminal vesicles, and optional 50.4 Gy to elective pelvic lymph nodes (all 28 fractions). Patients received fiducial markers and hydrogel spacer. The treatment planning goal was to cover 95% of the GTV at 84 Gy, and also meet the target and normal tissue dosimetry criteria of the hypofractionated treatment arm of NRG-GU005. VMAT was used for treatment delivery. ADT was given at the discretion of the treating physician.

RESULTS

A total of 20 men were included in the study, 2 (10%) uIR and 18 (90%) HR. 9 (45%) tumors were GS 7, 7 (35%) were GS 8, and 4 (20%) were GS 9. There were 13 (65%) stage cT1, 4 (20%) cT2 and 3 (15%) cT3. One (5%) patient received short term ADT, 18 (95%) long term ADT, and 1 (5%) refused ADT. 18 (90%) men received elective nodal radiation. The mean baseline PSA was 25.1 (range 4.2-73.4). The median baseline IPSS score was 11.1 (IQR 4.5-12), and 4 patients had severe baseline urinary symptoms (IPSS ≥20). The mean baseline prostate volume was 57.4 cc (range 26.8-198.3). The mean volume of the 84 Gy boost target was 7.1 cc (range 2.3-15.0) and the mean proportion of the prostate boosted was 14.8% (range 2% - 47%). There were 10 (50%) men with 1 boost target, 6 (30%) with two, 3 (15%) with three, and 1 (5%) had 4 boost targets. Targets were located in peripheral zone (85%), transition zone (30%), and central zone (5%). Patients met all per-protocol normal tissue criteria of NRG-GU005, except for bladder D0.03cc. The mean±SD (Gy) rectum D15%, D25%, and D30% were 51±5, 45±5, 42±4. The mean±SD (Gy) bladder D0.03cc, D30%, D50% were 79±4, 50±8, 38±10. At a median follow up time of 21.3 months (range 7.1-38.2), no patients have developed biochemical progression, local recurrence, distant progression, or death from prostate cancer. One patient died at 18 months from metastatic colorectal cancer, unrelated to prostate cancer treatment. Acute grade 1-2 GU toxicity occurred in 13 (65%) patients, and acute grade 1-2 GI toxicity occurred in 4 (20%) patients. No patients developed grade 3+ acute or late GU or GI toxicity. Two patients required temporary foley catheter for obstruction during RT, and both had IPSS >20 at baseline. The patient who refused ADT had a PSA bounce of magnitude 2.2 ng/mL at 14 months, PSA values declined without additional treatment.

CONCLUSION

A novel 28-fraction focal boosted IMRT treatment is feasible and has an acceptable early toxicity profile. Oncologic results are promising but require longer follow up.

Role of circulating tumor cells (CTCs) in biochemical recurrence (BR) of prostate cancer

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Background: CTCs have an established role in the prognosis of metastatic prostate cancer. Little data exists regarding the role of CTCs in BR of prostate cancer. The aim of this study was to determine whether there is a correlation between the number of CTCs in men with BR with varying prostate specific antigen (PSA) and PSA doubling time (PSADT) categories. Secondary endpoints looking at correlation of the CTCs with clinical or laboratory factors (Gleason scores, testosterone, hemoglobin, alkaline phosphatase, BMI, imaging results) will also be assessed.

Methods: BR was defined as patients (pts) who have undergone primary treatment with prostatectomy or radiation or both, with rise to >/= 0.2 from a prior undetectable level for prior prostatectomy or > 2 mg/dl rise from post-nadir radiotherapy. The study was powered to detect a Pearson correlation of .46 with a sample size of 36. Eleven of planned accrual goal of 36 pts were enrolled from May to September 2010. PSADT was obtained and correlated with the CTC values, categorized as PSADT of < 3 months, 3-14.9 months and > 15 months. CTCs were evaluated in 7.5 mL of peripheral blood using the CTC CellSearch test.

Results: The median age for 11 patients was 75 y/o (range: 57-91) with a median PSA of 1.6 ng/mL (range 0.2-6.5) and testosterone levels of 309 ng/dL (range: 31–471). Gleason scores were 8 (n=1), 7 (n=5), 6 (n=2), 5 (n=3). Prostatectomy was the primary treatment in 6 pts, radiotherapy in 5 pts and Cyberknife in 1 pt. Median hemoglobin was 12.43 g/dL, BMI was 26.79 and alkaline phosphatase was 69 IU/L. PSADT varied between 3 to 55 months. All pts accrued had 0 CTC levels. The latter result translates into a 95% confidence interval upper bound of approximately .27 for the proportion of patients in this population who have non-zero CTC levels.

Conclusions: Prostate cancer pts with BR have negative blood CTCs and does not appear to correlate with PSA or PSADT. However, the limited number of patients precludes sufficient interpretation at this time and further accrual is ongoing. The absence of CTC levels in this patient population, if supported through further data collection, could emerge as an important unanticipated finding from this study. Supported by IRG-08-091-01 from ACS to GWU Cancer Institute.

No significant financial relationships to disclose.

Renal transplantation with iliac vein transposition

We evaluated a technique for implantation of right kidneys with short renal veins without the need for venous reconstruction.

METHOD

The technique of iliac vein transposition was performed in six recipients who received right kidneys with short renal veins. Two cases were living related donors, two were living unrelated, one was an autotransplant, and one was a cadaver kidney recipient. The common and external iliac veins and arteries of the recipient were thoroughly mobilized, allowing for the lateral transposition of the external iliac vein with respect to the external iliac artery. The renal vessels were subsequently implanted in an end to side fashion onto the corresponding transposed external iliac vessels. After implantation, the iliac vein remained lateral with respect to the iliac artery.

CONCLUSIONS

The technique described allows for the implantation of right kidneys without the need for venous reconstruction. Such an approach is especially useful in cases of grafts with short veins.

Use of a nasogastric tube to evacuate stone debris after ureteroscopic holmium lithotripsy

We report a case of bilateral struvite and matrix staghorn calculi in a quadriplegic man with severe upper and lower extremity contractures that prevented percutaneous nephrolithotomy. Bilateral ureteroscopic lithotripsy was performed but the "snowstorm" of particles and viscous matrix material prevented complete stone clearance with the ureteroscope alone. Irrigation and aspiration through a fluoroscopically positioned nasogastric tube allowed evacuation of stone debris, mucinous matrix, and completion of the procedure.

A model of bladder tumor xenografts in the nude rat

PURPOSE

An in vivo tumor model for the study of human urothelial carcinoma is desirable. Orthotopic xenografts are useful in order to better approximate human tumor cell behavior in situ. A prior model has been described in the nude mouse. However, its small bladder size limits both histologic characterization and the application of intravesical therapeutics. In the absence of preirradiation, orthotopic xenografts of human transitional cell carcinoma in the nude rat has not been previously reported.

MATERIALS AND METHODS

Nude rats 2 to 4 weeks of age were inoculated with 1-5 x 10(6) cells of RT4 (well differentiated papillary human bladder tumor cell line). Inoculation was performed via open cystotomy. Techniques of mucosal injury including acid treatment and cautery were explored in an effort to optimize tumor implantation and growth. Animals were sacrificed at varying intervals and histologic assessment was performed.

RESULTS

The overall rate of tumor implantation and growth was 93.4% (57 of 61). Tumors reliably grew within the muscularis and mucosal growth was seen as well. Intramuscular tumor growth was less differentiated and had a higher fraction of mitotic cells than mucosal tumor. Tumor growth was consistently seen as early as 2 weeks after inoculation which facilitates experimental trials. Distant metastasis was not observed. Mucosal injury did not increase the rate of tumor implantation.

CONCLUSION

This model is highly reproducible and will prove useful in the further study of bladder cancer progression as well as in the development of therapeutic modalities for both superficial and muscle invasive bladder carcinoma.

Technique for accurate stellar polarimetry using CCD cameras

Using a technique for CCD polarimetry, we have obtained stellar polarization data with the 0.9-m telescope on Kitt Peak and with the Tek 2048 CCD camera. Measurements of stars viewed through holes in polarizing filters serve to correct for variations in atmospheric transparency. For the brightest stars the uncertainties in the measured polarization during a single, hour-long, polarimetric sequence are 0.3-0.5%, because of the residual effects of the variations in transparency. For fainter stars we are Poisson noise limited. Our technique provides some advantages over other techniques for CCD polarimetry, primarily because it can be easily integrated into existing photometric systems.

Clathrin domains involved in recognition by assembly protein AP-2

The domains on clathrin responsible for interaction with the plasma membrane-associated assembly protein AP-2 have been studied using a novel cage binding assay. AP-2 bound to pure clathrin cages but not to coat structures already containing AP that had been prepared by coassembly. Binding to preassembled cages also occurred in the presence of elevated Tris-HCl concentrations (greater than or equal to 200 mM) which block AP-2 interactions with free clathrin. AP-2 interactions with assembled cages could also be distinguished from AP-2 binding to clathrin trimers by sodium tripolyphosphate (NaPPPi), which binds to the alpha subunit of AP-2 (Beck, K., and Keen, J. H. (1991) J. Biol. Chem. 266, 4442-4447). At concentrations of 1-5 mM, NaPPPi blocked clathrin-triskelion binding; in contrast, interactions with cages persisted in the presence of 25 mM NaPPPi. To begin to identify the region(s) of the clathrin molecule important in recognition by AP-2, clathrin cages were proteolyzed to remove heavy chain terminal domains and portions of the distal leg as well as all of the light chains. AP-2 bound to these "clipped cages"; however, unlike the interaction with native cages, binding of AP-2 to clipped cages was sensitive to the lower concentrations of both Tris-HCl and NaPPPi which disrupt interactions of AP-2 with clathrin trimers. Reconstitution of the clipped cages with clathrin light chains did not restore resistance of AP-2 binding to Tris-HCl. We conclude that one binding site for AP-2 resides on the hub and/or proximal part of the clathrin triskelion whereas a second site is likely to involve the terminal domain and/or distal leg; the second site is manifested only in the assembled lattice structure. We suggest that these two distinct binding interactions may be mediated by the two unique large subunits within the AP-2 complex, acting sequentially during assembly.