SAMPLE SIZE CALCULATION:
CRR with chemoradiotherapy based on a meta-analysis in 2017 is about 80%; with advanced RT techniques, based on a multi-center, prospective study, local control rate \>90% could be achieved.
Based on retrospective studies, CRR with HF-RT without concurrent chemotherapy (ChT) followed by BRT, using 2D techniques, is about 70%. This is comparable to CRR for conventionally fractionated RT without concurrent ChT in the above meta-analysis. Given the retrospective nature of HF-RT data, a low CRR of 64% could be projected (p0). Given that in the current study, the investigators propose to do dose-adapted radiation by using more advanced RT and BRT, a high CRR of 84% could be projected (p1).
In the first stage, 28 patients will be accrued, including the 3 or 6 patients enrolled in the MTD level from phase 1. If there are ≤18 responses in these 28 patients, the study will be stopped. Otherwise, 22 additional patients will be accrued in the second stage, for a total of 50.
The null hypothesis will be rejected if \>38 responses are observed in 50 patients. This design yields a type I error rate of 5% and power of 95% when the true response rate is ≥84%.
Accounting for 10% attrition, a sample size of 55 will be targeted.
INDICATION:
Patients must meet all the inclusion criteria and none of the exclusion criteria to be eligible for this trial. Contraindication to ChT may be due to a medical contraindication or patient refusal to receive chemotherapy, and will be documented by the referring/attending gynecologic oncologist in the referral letter.
To effectively manage any conflict of interest, the attending/referring gynecologic oncologist shall not participate in the recruitment process. Any eligible patient will be referred to the Radiation Oncology Department, where the recruitment process will be initiated by the Primary Investigator or a delegated radiation oncology consultant.
TREATMENT REGIMEN:
The regimen consists of whole pelvic photon RT, using IMRT, followed by high dose rate (HDR) BRT. Inguinal fields shall be included in case of lower vaginal or inguinal nodal involvement. The prescription dose is 40 Gy in 15 fractions at 2.67 Gy/fraction.
The nSIB in the phase 2 will be given according to the MTD level in phase 1. The nSIB is indicated for any adenopathy detected by either positron emission tomography (PET)-positivity, by computed tomography (CT)/ magnetic resonance imaging (MRI) criteria such as a short axis diameter \>10mm (15mm, for inguinal nodes), or histologically positive on surgical sampling. The gross nodal planning target volume (PTV) boost will receive 45-48 Gy in 3.0-3.2 Gy/fraction, depending on the projected contribution of BRT and location of the lymph node. Assuming both nodal boost dose levels are found to be associated with acceptable toxicity: common iliac or inguinal nodes will be boosted to 48 Gy; and external or internal iliac nodes, to 45 Gy given the BRT contribution to the total nodal dose.
The RT will be given once daily from Monday to Friday, 5 fractions per week.
BRT will be given after completion of pelvic RT, ideally within two weeks from completion. Two insertions per week may be done. If multiple fractions will be given using the same implant, these will be given twice daily, 6 hours apart.
