Dosimetric Comparison of Isodose Surface Volume and Total Reference Air Kerma (TRAK) based Volume in Cervical Cancer Brachytherapy.

OBJECTIVE: We aim to compare TRAK & TPS based isodose volumes in cervical cancer brachytherapy and assess the feasibility, accuracy and potential future implications of TRAK in this regard and as a newer emerging tool to assess treatment intensity in cervical cancer brachytherapy. METHODS: one hundred patients with histologically proven squamous cell carcinoma of cervix uteri were assessed for brachytherapy (after completion of external radiation) and prospectively enrolled for the study. 60 Gy, 75 Gy, and 85 Gy isodose volumes were obtained from the TPS (VTPS) for 50, 25 & 25 patients with Manchester, Fletcher & interstitial implant respectively, receiving various fractionation schedules by Ir192 HDR remote after-loading system. Using the formula Vpred=4965(TRAK/dref)3/2+170(TRAK/dref)-1.5 the TRAK based isodose surface volumes (Vpred) were derived. Reference doses (dref) were calculated based on accumulated EBRT and brachytherapy doses. The two sets of volume were compared with respect to applicator type, standard, and optimised plan. Surrogate point A dose was also correlated. RESULT: VTPS - Vpred were 5.24 ± 2.7%, all volumes being predicted within 10%. Correlation of TRAK vs VTPS60/ VTPS75/ VTPS85 showed R2 of 0.994, 0.987 and 0.971 respectively. There was no significant difference in predicted volumes with respect to applicator type. The surrogate point A showed mean volume and standard deviation of 7.44 ± 13.4%, 17.63 ± 16.38 and 3.5 ± 0.95 for Manchester optimised, Fletcher optimised and standard plans respectively. TRAK with point A (R2=0.5632), bladder (R2=0.2015) and rectal doses (R2=0.121) yielded no correlation. CONCLUSION: Volumes calculated by TRAK correlate with TPS obtained volumes significantly and the formula predicting isodose surface volumes within 10% accuracy for ICBT applications and not for pure interstitial implants. However, TRAK fails to correlate with surrogate point A, bladder and rectal doses hence has questionable utility as a marker for biological response & treatment intensity.

Estimation of dose-volume parameters of female urethra as organ-at-risk during interstitial brachytherapy in gynecological malignancies.

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.

Evaluation of dosimetric impact of inter-application and intra-application variations in fractionated high-dose-rate intra-cavitary brachytherapy of cervical cancer.

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.

Abscopal effect in a patient with chronic lymphocytic leukemia during radiation therapy: a case report.

Radiotherapy has a significant impact on the local tumor environment and its distant component. Abscopal effect is the bystander effect of radiotherapy observed at a site distant to that irradiated within the same subject. Abscopal effect even though described, is not a common clinical event. We report a documented observation of abscopal effect in a patient of Chronic Lymphocytic Leukemia during radiation therapy.