Hypofractionated Prostate Radiotherapy with or without Conventionally Fractionated Nodal Irradiation: Clinical Toxicity Observations and Retrospective Daily Dosimetry

Purpose. To evaluate toxicity associated with the addition of elective nodal irradiation (ENI) to a hypofractionated regimen for the treatment of prostate cancer. Methods and Materials. Fifty-seven patients received pelvic image-guided IMRT to 50.4？Gy in 28 fractions with a hypofractionated simultaneous boost to the prostate to 70？Gy. Thirty-one patients received prostate-only treatment to 70？Gy in 28 fractions. Results. Median followup was 41.1 months. Early grade ≥2 urinary toxicity rates were 49% (28 of 57) for patients receiving ENI and 58% (18 of 31) for those not ( ). Early grade ≥2 rectal toxicity rates were 40% (23 of 57) and 23% (7 of 31), respectively ( ). The addition of ENI resulted in a 21% actuarial rate of late grade ≥2 rectal toxicity at 4 years, compared to 0% for patients treated to the prostate only ( ). Retrospective daily dosimetry of patients experiencing late rectal toxicity revealed an average increase of 2.67% of the rectal volume receiving 70？Gy compared to the original plan. Conclusions. The addition of ENI resulted in an increased risk of late rectal toxicity. Grade ≥2 late rectal toxicity was associated with worse daily rectal dosimetry compared to the treatment plan. 1. Introduction Hypofractionated treatment regimens for clinically localized prostate cancer remain a topic of debate as large prospective trials such as RTOG 0415 continue to mature. The large retrospective series from Cleveland Clinic as well as recently published phase III data by Arcangeli et al. indicate that hypofractionated RT is well-tolerated and offers high rates of biochemical control [1, 2]. However, most published series focus primarily on patients with a relatively low risk of lymph node involvement and have, therefore, restricted treatment to the prostate and seminal vesicles only. Traditionally, patients with high-risk prostate cancer receive whole-pelvic radiotherapy (WPRT), and such regimens have formed the backbone of large-scale clinical trials such as RTOG 8531, RTOG 9202, and EORTC 22863 [3–6]. Though conventionally fractionated WPRT has been safely delivered on a number of clinical trials, little data exists concerning treatment of the pelvic lymph nodes as part of a hypofractionated regimen. To date, there has only been one phase III trial which utilized hypofractionated WPRT for patients with high-risk disease [7]. While the short-term toxicity results of this study are promising, a detailed report of the long-term toxicities is pending. Advances in radiation delivery such as intensity-modulated radiotherapy (IMRT) and image-guided