Is Hypofractionated Elective Nodal Irradiation Safe in High-Risk Prostate Cancer? A Single-Institution Prospective Study

Abstract

<h3>Purpose/Objective(s)</h3> Hypofractionated EBRT is beneficial in localized prostate cancer in view of the low alpha by beta ratio of prostate cancer cells, however, the role of elective nodal irradiation with the hypofractionated regimen is not well established, as concern regarding toxicity with hypofractionated nodal irradiation remains. <h3>Materials/Methods</h3> Patients with Carcinoma prostate were prospectively selected for treatment with hypofractionated EBRT. Patients with high-risk prostate cancer (T3a-T3b, GS>/= 8, PSA>20ng/ml) with an estimated risk of nodal involvement > 30% were radically treated with 60Gy and 44 Gy in 20 fractions to the primary and elective nodal area, respectively. Similarly, postoperative patients with high-risk features (pT3a-T3b, GS>/=8, estimated risk of nodal involvement >30%) were treated with early salvage EBRT, upon two consecutive rises of serum PSA above 0.1ng/ml. The dose prescribed was 52.5Gy and 44Gy in 20 fractions to primary bed and elective nodal area, respectively. Contouring for radical and salvage EBRT was done as per CHHiP and RADICALS RT protocol, respectively. Nodal volume was contoured as per the RTOG contouring guideline. Acute toxicities were recorded during and 6 months after treatment, as per RTOG grading criteria. All patients were treated with IMRT or VMAT plan. All patients received concurrent & adjuvant hormonal therapy. <h3>Results</h3> Between 1^st January 2020 to 30^th June 2021, 26 patients were treated with the hypofractionated regimen and elective nodal irradiation, of which 14 patients (54%) received radical EBRT and 12 patients (46%) received early salvage EBRT. The median age of patients was 66 years. Patients were prospectively followed up with a median follow-up period of 12 months. For patients treated with radical EBRT, D95% to primary PTV was 60.06 Gy (Median, IQ range 59.8-60.2Gy) and D95% to nodal PTV was 44.1 Gy (Median, IQ range 43.7-44.3Gy). V48Gy of Bladder was 23.2% (Median, IQ range 21.5-26.6%). V40Gy for bowel bag was 112cc (Median, IQ range 90-145cc). Similarly in patients receiving early salvage EBRT, D95% to primary bed was 51.5Gy (Median, IQ range 51.2-51.7 Gy), D95% to the nodal area was 43.9Gy (Median, IQ range 43.1-44.5 Gy). V48Gy of bladder was 38% (Median, IQ range 28-47.6%) and V40Gy for bowel bag was 210cc (Median, IQ range 123-253cc). Overall, 5 patients (19%) had grade 2 genitourinary toxicities and 6 patients (23%) had grade 2 bowel toxicity. No patients experienced grade 3 or 4 bowel and bladder toxicity. Historical data for grade 2 or more acute bowel and bladder toxicities were 38% and 49% respectively in the CHHiP trial, which used IMRT plan for only 30% of patients. No patient in our study had a biochemical recurrence in the short follow-up period. <h3>Conclusion</h3> Hypofractionated elective nodal irradiation can be safely delivered in high-risk prostate cancer patients without any undue increase in acute bowel and bladder toxicities.