RESUMO
PURPOSE: Respiratory-induced tumor motion is a major challenge in lung cancer (LC) radiotherapy. Four-dimensional computed tomography (4D-CT) using a maximum intensity projection (MIP) dataset is a commonly used and time-efficient method to generate internal target volume (ITV). This study compared ITV delineation using MIP or tumor delineation on all phases of the respiratory cycle. MATERIALS AND METHODS: Thirty consecutive patients of LC who underwent 4D-CT from January 2014 to March 2017 were included. ITV delineation was done using MIP (ITVMIP) and all ten phases of the respiratory cycle (ITV10Phases). Both volumes were analyzed using matching index (MI). It is the ratio of the intersection of two volumes to the union of two volumes. A paired sample t-test was used for statistical analysis, and P < 0.05 was considered statistically significant. RESULTS: The mean ± standard deviation volume of ITV10Phases was significantly larger compared to ITVMIP (134 cc ± 39.1 vs. 113 cc ± 124.2, P = 0.000). The mean MI was 0.75 (range 0.57-0.88). The mean volume of ITV10Phases not covered by ITVMIP was 26.33 cc (23.5%) and vice versa was 5.51 cc (6.1%). The mean MI was 0.73 for tumors close to the mediastinum, chest wall, and diaphragm. MI was not different between tumors ≤5 cm and >5 cm. The average time required for delineation was 9 and 96 min, respectively. The center of mass of two ITVs differed by 0.01 cm. CONCLUSION: ITV using MIP is significantly smaller and may miss a tumor compared to ITV delineation in 10 phases of 4D-CT. However, the time required is significantly less with MIP. Caution should be exercised in tumors proximity to the mediastinum, chest wall, and diaphragm.
RESUMO
PURPOSE: A prospective phase 2 study was conducted to evaluate the feasibility and safety of single-application multifractionated (SA-MF), high-dose-rate (HDR), image guided adaptive brachytherapy (IGABT) for cervical cancer. METHODS AND MATERIALS: Patients (N = 41) with International Federation of Gynaecology and Obstetrics 2009 stage IIB-IVA disease recruited between 2017 and 2019 underwent SA-MF. After completion of external beam radiation therapy of 50 Gy in 25 fractions, patients received magnetic resonance IGABT. The IGABT protocol consisted of a single brachytherapy (BT) application and treatment with 3 fractions of HDR (9 Gy on day 1; 2 fractions of 7 Gy with a minimum 6-hour gap on day 2) after achieving planning aims of the high-risk clinical target volume (HRCTV) receiving >84 Gy EQD2 and 2 cm3 of the bladder and rectum/sigmoid receiving ≤85 Gy and <71 Gy, respectively. Interfraction variation was addressed by performing computed tomography planning and coregistration using a mutual information-based coordinate system on day 2 before the second fraction. Organ at risk contouring was done on computed tomography, and doses were re-evaluated and reoptimized if required. RESULTS: Thirty-eight patients were treated as per the protocol. All patients underwent Intracavitary + Interstitial BT with needles (median, 4; range, 3-11). The mean ± standard deviation HRCTV volume was 41 ± 21 cm3 and HRCTV D90 dose was 87.2 ± 3.6Gy. The 0.1 cm3 and 2 cm3 to bladder, rectum, and sigmoid were -103.2 ± 10.6 Gy and -84.6 ± 6.8 Gy, 82.2 ± 9.5 Gy and -68.3 ± 5.7 Gy, and 83.5 ± 9.8 Gy and -69.5 ± 5.9 Gy, respectively. Six patients required reoptimization before the second fraction to meet planning aims. Mean overall treatment time was 47 ± 6 days. With a median follow up of 22 months (range, 2-37), 2-year local control and disease-free and overall survival were 90.1%, 85%, and 94.5%, respectively. So far 1 patient with grade II and 2 patients with grade III rectal toxicities have been reported. CONCLUSION: Magnetic resonance IGABT with SA-MF BT was feasible in 95% of patients. The dosimetric parameters and clinical results achieved so far look promising.
