Moderate hypofractionation and simultaneous integrated boost with volumetric modulated arc therapy (RapidArc) for prostate cancer

Purpose

In the present study, the acute toxicity profiles for prostate patients treated with simultaneous integrated boost (SIB) with volumetric modulated arcs in a hypofractionated regime are reported.

Patients and methods

A total of 70?patients treated with RapidArc between May 2010 and September 2011 were retrospectively evaluated. Patients were stratified into low (36%), intermediate (49%), and high-risk (16%) groups. Target volumes (expanded to define the planning volumes (PTV)) were clinical target volume (CTV) 1: prostate; CTV2: CTV1 + seminal vesicles; CTV3: CTV2 + pelvic nodes. Low-risk patients received 71.4?Gy to PTV1; intermediate-risk 74.2?Gy to PTV1 and 61.6 or 65.5?Gy to PTV2; high-risk 74.2?Gy to PTV1, 61.6 or 65.5?Gy to PTV2, and 51.8?Gy to PTV3. All treatments were in 28?fractions. The median follow-up was 11?months (range 3.5–23?months). The acute rectal, gastrointestinal (GI) and genitourinary (GU) toxicities were scored according to EORTC/RTOG scales.

Results

Acute toxicities were recorded for the GU G0?=?31/70 (44%), G1?=?22/70 (31%); G2?=?16/70 (23%); G3?=?1/70 (1%)], the rectum G0?=?46/70 (66%); G1?=?12/70 (17%); G2?=?12/70 (17%); no G3], and the GI G0?=?54/69 (77%); G1?=?11/69 (16%); G2?=?4/69 (6%); no G3]. Median time to rectal, GU, and GI toxicities were 27, 30, and 33 days, respectively. Only the GI toxicity correlated with stage and pelvic irradiation. Univariate analysis presented significant correlations between GI toxicity and intestinal irradiation (V_50?Gy and V_60?Gy). In the multivariate analysis, the only significant dosimetric variable was V_50?Gy for the intestinal cavity.

Conclusion

Moderate hypofractionation with SIB and RapidArc was shown to be safe, with acceptable acute toxicity. Longer follow-up is needed to assess late toxicity and clinical outcome.