ABSTRACT
PURPOSE: Interstitial brachytherapy (ISBT) is often used as post-external beam radiotherapy (EBRT) to treat locally advanced gynecological malignancies. Female urethra is in close proximity to the target during ISBT. However, it has not been evaluated as an organ-at-risk (OAR). Overlapping symptoms caused by radiation-induced bladder toxicity vs. urethral toxicity make it difficult to identify and report urethral toxicities separately. This was a retrospective study to estimate dose-volume parameters of female urethra during high-dose-rate ISBT. MATERIAL AND METHODS: Data of 24 patients with gynecological malignancies treated by ISBT were selected. Urethra and periurethral regions were retrospectively contoured. Mean volume, Dmax, Dmean, D2cc, D1cc, D0.5cc, D0.2cc, and D0.1cc were documented. Unpaired t-test was used for comparison of means. RESULTS: 20/24 Ca. cervix, 1/24 Ca. vagina, and 3/24 Ca. vaginal vault received 6-6.5 Gy in 4 ISBT fractions. Mean urethral length was 3.54 ±0.55 cm. Mean doses received by urethra per BT fraction were Dmax = 4.23 ±1.32 Gy, Dmean = 2.71 ±1.01 Gy, D0.2cc = 3.31 ±1.07, and D0.1cc = 3.54 ±1.09 Gy. Comparison of total BT 2 Gy equivalent dose (EQD2) with 4 fractions for urethra between patients with (9/24) and without anterior vaginal wall (15/24) involvement included Dmean = 18.79 ±7.49 Gy vs. 11.14 ±6.15 Gy*, D1cc = 10.90 ±10.03 Gy vs. 4.54 ±3.93 Gy*, D0.5cc = 19.50 ±8.69 Gy vs. 11.97 ±6.54 Gy*, D0.2cc = 23.78 ±8.94 Gy vs. 15.51 ±7.39 Gy*, and D0.1cc = 25.88 ±9.37 Gy vs. 17.39 ±8.03 Gy*, respectively (*p < 0.05). CONCLUSIONS: Female urethra receives significant doses during ISBT for gynecological malignancies, especially when the anterior vaginal wall is within the target volume. Reporting doses to urethra would enable to develop clinical correlation and dose-volume constraints for urethra as organ-at-risk in future.
ABSTRACT
PURPOSE: To evaluate feasibility and safety of execution of optimized intra-cavitary brachytherapy (ICBT) plan of first fraction in subsequent fractions in high-volume, low-resource centers. MATERIAL AND METHODS: This non-randomized prospective study included 30 cervical cancer patients, who underwent 4 fractions of high-dose-rate (HDR)-ICBT in 2 applications, one week apart, 2 fractions per application delivered on two consecutive days. Computed tomography (CT) simulation was done before each fraction, organs at risk (OARs) were contoured on all sets of CT images. Optimized plans were generated for each set of CT images and executed for the treatment. Test treatment plans were retrospectively generated by applying first treatment fraction's dwell times adjusted for decay, and dwell positions of the applicator for subsequent treatment fractions paired t-test was performed to analyze D2cc dose variations of OARs among the paired sets of plans. RESULTS: Comparison between the plans showed daily plans provided lower D2cc to OARs than test plans. In intra-application plan comparison, there was a significant dose reduction to 2 cc sigmoid (p = 0.021) and bladder (p = 0.007) in daily plan. Mean D2cc of optimized and unoptimized plans were 361.35 ±114.01 and 411.70 ±152.73 for sigmoid, and 511.23 ±85.47 cGy and 553.57 ±111.23 cGy for bladder, respectively. In inter-application, D2cc rectum and sigmoid demonstrated a statistically significant dose variation (p = 0.002) and (p = 0.007), with mean D2cc rectum of optimized and unoptimized plans being 401.06 ±83.53 cGy and 452.46 ±123.97 cGy, and of 2 cc sigmoid 340.84 ±117.90 cGy and 387.79 ±141.36 cGy, respectively. CONCLUSIONS: Fractionated HDR brachytherapy amounts to significant variation in OAR doses if re-simulation and re-plan is not performed for every fraction and ICBT application. Therefore, plan of the day with optimization of the doses to target and OARs must be followed for each fraction.
ABSTRACT
PURPOSE: A feasibility study of 3D volume-based interstitial brachytherapy using thermoplastic polyether ether ketone (PEEK) catheters in advanced cervical cancer MR-based brachytherapy, when MR-compatible applicators are not available. MATERIAL AND METHODS: Five cervical cancer patients received EBRT dose of 50 Gy in 25 fractions to whole pelvis using 3D conformal radiotherapy after standard pre-treatment evaluation. In our institute, interstitial brachytherapy (ISBT) is planned in BrachyVision TPS and routinely performed using stainless steel needles with Syed-Neblett template. Standard MR-compatible ISBT applicators were not available; therefore, the implant was carried out using PEEK catheters and Syed-Neblett template. The T1 and T2 MR and CT images of patients were acquired for treatment planning. Gross tumor volume (GTV), high-risk clinical target volume (HR-CTV), intermediate-risk clinical target volume (IR-CTV), and organs at risk (OARs) were delineated with the use of MR T2 weighted images, following GEC-ESTRO guidelines. Volumetric optimization was used for planning, and the treatment plan was executed with high-dose-rate (HDR) 192Ir Gammamed Plus device. RESULTS: The dose prescribed to HR-CTV was 30 Gy low-dose-rate (LDR) equivalent (5 Gy × 4 fractions). Doses to target volume and OARs were analyzed using dose volume histogram (DVH). Dose values were biologically normalized to equivalent doses of 2 Gy fractions (EQD2). The average tumor volume was 67 cc and the average D90 of HR-CTV was 29 Gy (5.7 Gy/fraction) EQD2. D100 of HR-CTV volume was 18 Gy (3.8 Gy/fraction) EQD2. The total doses of 2 cc of rectum and bladder were 70 Gy and 76 Gy EQD2 (3.71 Gy and 4.04 Gy dose/fraction), respectively. CONCLUSIONS: When the facilities for MR-compatible applicators are not available, MR-based ISBT is feasible with PEEK catheters using available resources for advanced cervical cancer. Doses to HR-CTV and IR-CTV were achieved, restricting doses to OARs as per GEC-ESTRO guidelines.
