Early Investigation of High Precision Radiotherapy Prior to Commencing Standard Radiotherapy for Prostate Cancer
Condition: Prostate Cancer
MeSH terms: Prostatic Neoplasms
Study type: Interventional

Summary: 
      Current standard treatment for prostate cancer involves giving patients approximately 40
      doses of radiotherapy, one dose per day over an 8 week period. The purpose of this study is
      to assess the effects of giving two separate high doses of a special type of precision
      radiotherapy to the prostate and then 5 weeks (instead of 8 weeks) of standard radiotherapy.

      Hypothesis: It is safe to give patients an extra two doses of high-precision radiotherapy
      prior to commencing a shorter period of standard radiotherapy for prostate cancer.
    

Detailed description: 
      Prostate cancer accounts for one third of all new cancer diagnoses in men and approximately
      30% of men will have External Beam Radiotherapy (EBRT) as primary local therapy. Local
      persistence of prostate cancer treated with radiotherapy is under-appreciated. Prostate
      cancer has a long natural history and the consequences of local persistence may not be
      realized for many years.

      Prostate cancer has a slow growth with a potential doubling time ranging from weeks to months
      (median 42 days) which has led to the hypothesis that prostate cancer will behave more like a
      late reacting tissue(1). Brenner et al. (2) used data from prostate Low Dose Rate (LDR)
      permanent seed implants and EBRT series to derive an alpha/beta of approximately 1.5. Many
      groups have also calculated the alpha/beta ratio to be in the < 3.0 range(3).

      If the alpha/beta ratio for prostate cancer is lower than the surrounding normal tissues
      (Brenner et al. have estimated the alpha/beta for the rectum to be over 5.0), doses greater
      than 2 Gy (hypofractionation) will afford an advantage as there will be a greater sensitivity
      of prostate cancer to radiation, as compared to the bladder or rectum. This benefit has been
      exploited for many years with High Dose Rate (HDR) brachytherapy using Iridium -192. Typical
      doses for HDR are 19Gy in two fractions in addition to 46Gy in 23 fractions of EBRT (4). With
      reference to our own institutional data from HDR brachytherapy we calculated the dose
      distribution in recently treated patients. Due to the nature of the iridium dose
      distribution, there are considerable areas of much higher dose delivered; 200% of the dose
      (38Gy) to 12.7% of the target volume, 150% (13.75Gy) to 32.6% of the target volume and 125%
      (11.9Gy) to 60.1% of the target. Despite the high doses to the periphery of the prostate it
      is possible to limit the dose to the rectum and bladder to 1cc < 75% (14.25Gy) and the 1cc
      urethra to <125% (23.75Gy) (4). HDR brachytherapy series have reported durable long term
      Biochemical Failure Free Survival (BFFS), which are as good or better than comparable
      external beam or surgical series(5). However despite the low toxicity and excellent
      biochemical outcomes, HDR brachytherapy utilization in Australia is low, with under 300 cases
      in total per year. This is due to the logistical difficulty of HDR brachytherapy, anaesthetic
      requirements, nursing care and patient discomfort.

      There have been five published studies investigating stereotactic boost in addition to
      standard fractionation EBRT without using brachytherapy, four reports with the Cyberknife
      platform (6-9) and one with Intensity Modulated Radiotherapy (IMRT) (10). All of these series
      have early follow up (FU) with reported BFFS between 77% and 100%. The largest experience is
      from Katz et al. (8) who reported 73 patients with both intermediate (n= 41) and high risk
      (n=32) disease. They treated patients with the Cyberknife platform to deliver between 18 and
      21 Gy in three fractions in addition to 45 Gy in 25 fractions EBRT. With a median follow up
      of 33 months, BFFS was 89.5% and 77.7% for the intermediate and high risk patients
      respectively. A 5 mm expansion from the prostate to the Planned Treatment Volume (PTV) was
      used except posteriorly, where the margin was 3mm. There was 7% Grade 2 acute genitourinary
      (GU) and gastrointestinal (GI) toxicity, with late Grade 2 estimates at three years of 5.5%
      (GU) and 8.2% (GI). Three other series using Cyberknife to mimic HDR were reported between
      2008 and 2012 (6, 7, 9). These studies used margins of 0-2 mm posteriorly and 3-5 mm in other
      directions and reported low rates of Grade 2 and Grade 3 toxicity. Two of these reports
      specifically attempted to reproduce the heterogeneity of HDR with large areas of the PTV
      receiving >125% (40% to 45%) and >150% (5% to 10%) of the prescribed dose. Miralbell et al.
      (10) reported a Linac based IMRT boost in 50 patients in 2010. This series used an endorectal
      balloon but no image guidance, which may be the cause of their unacceptably high five year
      estimates of late GI Grade 2 toxicity of 26%.

      Primary objective:

      The primary study goal is to assess the acute toxicity of Stereotactic Body Radiotherapy
      (SBRT) boost with three increasing dose levels.

      Secondary objectives:

        -  Nadir PSA at three months and over duration of follow-up

        -  Three year and five year Freedom From Biochemical Failure (FFBF) (Nadir + 2.0)

        -  Planning feasibility (Minor and Major planning violations)

        -  Late Gastrointestinal and Genitourinary Toxicity (modified Radiation Therapy Oncology
           Group (RTOG) scale)

        -  Patient reported QOL (EPIC-SF-12)

      Hypothesis: It is safe to dose escalate prostate cancer treatment with a stereotactic boost
      of up to 30Gy in two fractions to the dominant nodule combined with external beam
      radiotherapy of 46Gy in 23 fractions with < 15% Grade 2 acute morbidity and < 5% Grade 3
      acute morbidity.
    

Intervention name(s): Dose escalation using stereotactic boost
Intervention type(s): Radiation
Intervention description(s): This is a dose escalation study. Participants will be allocated to the current dose level, or if the current dose level has been filled and acceptable toxicity has been established, they will be enrolled into the next dose level.
The first dose level will be 20Gy in 2 fractions to PTV and 25Gy to Gross Target Volume (GTV) if identified. The second dose level will be 22Gy in 2 fractions to PTV and 27.5Gy to GTV if identified. The dose level will be 24 Gy in 2 fractions to PTV and 30Gy to GTV if identified.
Following stereotactic boost, all participants will receive 46Gy in 23 fractions radiotherapy to the prostate / seminal vesicles +/- lymph nodes.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Prostate Cancer; Dose escalation; Stereotactic; SBRT; Hypofractionation