5-year outcomes after PBRT at a single, high-volume, PBRT center


We have previously reported on the very good, albeit unremarkable, outcomes of proton beam radiation therapy (PBRT) as administered at the University of Florida Jacksonville. We now have their 5-year analysis on a much larger data set, the largest so far in the modern era.

Bryant et al. report on their retrospective analysis of the records of 1,327 men consecutively treated between 2006 and 2010. Almost all of them (98 percent) were treated with at least 78 GyE and those treated with hypofractionated doses were excluded.  To ensure comparable data, 113 patients were excluded for lack of adequate follow-up and use of adjuvant chemotherapy. Other key patient characteristics included:

  • Low risk: 42 percent
  • Intermediate risk: 44 percent
  • High risk: 14 percent
  • 15 percent had concurrent ADT, mostly among high-risk patients
  • 55 percent had radiation to seminal vesicles
  • 3 percent had IMRT radiation to pelvic lymph nodes (although all patients were node negative) and were excluded from the toxicity analysis

Cancer Control

After an average (median) follow-up of 5.3 years, the 5-year freedom from biochemical failure by risk group was:

  • Low risk: 99 percent
  • Intermediate risk: 96 percent
    • 95 percent if there was only one intermediate-risk factor
    • 90 percent if there were two or more intermediate-risk factors
  • High risk: 74 percent
    • 80 percent if there was only one high-risk factor
    • 32 percent if there were two or more high-risk factors
    • 87.5 percent who were high risk based only on presence of Gleason 8 disease
  • Among those who did not receive adjuvant ADT, the median PSA nadir and time to nadir were:
    • Low risk: 0.3 ng/ml and 4.2 years
    • Intermediate risk: 0.2 ng/ml and 3.6 years
    • High risk: 0.3 ng/ml and 2.2 years

Of the 94 patients who had biochemical failure:

  • 42 had biochemical failure only
  • 6 had local (biopsy-proven) failure only
  • 10 had pelvic lymph node failure only
  • 24 had distant metastases only
  • 12 had failure in a combination of sites

Survival and freedom from metastases were 95+ percent in all risk groups.

Toxicity

  • Acute genitourinary (GU) toxicity ≥ Grade 3: 1 percent (12 patients)
  • Late GU toxicity ≥ Grade 3: 5 percent (61 patients)
  • Interventions for Grade 3 GU toxicity included catheterization, hyperbaric oxygen therapy, blood transfusion, TURP, and cauterization for symptoms including urinary obstruction, bladder irritation, hematuria, irritative symptoms, incontinence, and pain.
  • Larger prostates, ADT use, pre-treatment urinary therapy, diabetes, and higher doses to the bladder were associated with greater GU toxicity.
  • Late gastrointestinal (GI) toxicity ≥ grade 3: 1 percent (9 patients)
  • Interventions for Grade 3 GI toxicity included transfusion and colostomy for diarrhea, rectal bleeding, and ulceration.
  • Long-term patient-reported urinary and bowel status were unchanged from baseline.
  • Sexual quality of life scores declined by 22 points (29 percent) by 4 years post-treatment (excluding those who used ADT).

Comparison to other radiation therapies

The following table shows some oncological and toxicity outcomes at 5 years for various radiation therapies as practiced at single institutions in the last several years. While differences in patient selection confound our ability to rigorously compare the therapies, they do show a general range of best-expected outcomes. Until we see the results of large-scale prospective randomized comparative trials, this is about as good as we can do in comparing them.

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*For high-risk HDR-BT patients, please click here.
References: PBRT: Bryant et al. (78 GyE median dose, 15% received ADT). IMRT: Liauw et al. (76 Gy median dose, 50% received ADT, 4-year data). SBRT: Katz et al. (35 Gy/5fx, 18% received ADT). LDR-BT (low-dose-rate brachytherapy as monotherapy): Kittel et al. (18% received ADT). HDR-BT (high-dose-rate brachytherapy as monotherapy): Hauswald et al. (43.5 Gy/6fx, 9% received ADT, 10-year data).

Proton therapy afforded rates of cancer control comparable to the other monotherapies. Urinary and rectal toxicity were similar as well. Sexual quality of life deterioration was also similar to what we have seen for IMRT and LDR-BT (see this link). HDR-BT and SBRT seem to be superior in preserving erectile function.

If they can bring down the cost of proton therapy, it can be competitive with IMRT. As with IMRT, hypofractionation (fewer treatments) of proton therapy may deliver equivalent results at lower cost. Pencil-beam proton therapy may be able to improve toxicity still further.

Editorial note: This commentary was written for The “New” Prostate Cancer InfoLink by Allen Edel.

4 Responses

  1. Thanks for this excellent report!

    Very impressive results for proton beam at Jacksonville!

  2. I remain a pessimist about proton therapy. It appears to deliver comparable results; however, the hype was for better outcomes with lower toxicity. There has yet to be clear evidence this expensive therapy is worth the added cost. The payers should be asking for proof of added benefit before paying a premium price.

  3. Gerry:

    I think most of the major payers are already refusing to pay any more for PBRT than they pay for IMRT … with the threat that it’s the same cost or no PBRT.

  4. As a former skeptic about PBRT, I am impressed with the results reported above, as mentioned previously. However, I see the overall and key question of worth the same way you do Dr. Chodak and Sitemaster.

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