Purpose/Objective(s):
To report toxicity of pelvic VMAT with hypofractionated simultaneous integrated boost (SIB) to the prostate for patients with high-risk or very high risk prostate cancer.
Materials/Methods:
Forty-three consecutive patients, diagnosed with high risk or locally advanced prostate cancer, and minimum follow-up of 24 months were included . Androgen suppression was given for all of them . On the planning-CT CTV1(prostate), CTV2 (CTV1 plus seminal vesicles) and CTV3 (CTV2 plus pelvic nodes) were delineated. CTVs were expanded to generate the planning target volumes (PTV) The VMAT plans were designed to deliver 67,5 Gy in 27 fractions (2.5 Gy/fr) to the prostate, 59,4 Gy (2,2Gy/fr) while delivering simultaneously 48.6 Gy in 27 fractions(1.8 Gy/fr) to the pelvic lymph nodes. In patients with N1, dose was increased to 59,4 Gy at 2.2 Gy given simultaneously, and HDR brachytherapy 9 Gy/1 fr was done in unfavourable dosimetry for integrated boost to the prostate. Toxicity was scored by CTCAEv4.0. Univariate and multivariate analysis were performed looking for correlations among patient characteristics, dose values and toxicity.
Results:
Median age of patients was 69,8 years old. Gleason score was 8 or higher in 74,4% of patients. The median follow-up period was 53 months (from 25 to 75 months). All patients received the prescribed external radiation dose in 27 fractions. Thirty-four patients received 67.5 Gy to the CTV1 plus margin at 2,5 Gy per fraction. Brachytherapy boost was performed in nine patients delivering 9 Gy in one fraction over 59.4 Gy at 2,2 to the CTV2 plus margin. Six patients died during the follow-up period. One of them because a second tumour and another for prostate cancer progression. Acute urinary toxicity was scored as 2 in 25.6% of patients. Rectal acute toxicity grade 2 with mucosal discharge was present in 27.9% of patients. No late toxicity exceeding Grade 3 was observed. Rectal toxicity grade 2 or less was 11,7% and one patient showed grade 3 toxicity. Urinary toxicity grade 2 or less was 16,3%. Grade 2 acute or late bowel toxicity were seen in 11.8% and 7% respectively. Grade 2 acute or late bowel toxicity was not associated with bowel volume receiving V30, V40, V50, or V60Gy. Acute or late bladder and rectal toxicity did not correlate with any of the dosimetric parameters examined.
Conclusions:
Pelvic VMAT with SIB or sequential HDR brachytherapy to the prostate were well tolerated in this series, with acceptable rates of acute and subacute toxicity. SIB-VMAT combines pelvic radiotherapy and hypofractionation to the primary site and offers an accelerated approach to treating high-risk disease. Additional follow-up is necessary to fully define the long-term toxicity after hypofractionated, whole pelvic treatment combined with androgen suppression.
