Study of positional dependence of dose to bladder, pelvic wall and rectal points in High-Dose-Rate Brachytherapy in cervical cancer patients

Dose to pelvic lymph nodes during brachytherapy of locally advanced cervical cancer with 60Co HDR source

PURPOSE

This study investigated the correlation between the prescription dose and dose to the Manchester and International Commission on Radiation Units and Measurements-report 38 (ICRU-38) lymphatic trapezoid points during high-dose-rate (HDR) brachytherapy of locally advanced cervical cancer with (Cobalt-60) 60Co .

METHODS AND MATERIALS

A retrospective study was designed for; patients with locally advanced cervical cancer, treated by external beam radiotherapy and concurrent weekly Cisplatin-based chemotherapy, had no extended parametrial invasion and was treated by tandem-ovoid set, from 2017 to 2020. Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) based target's volume, ICRU-89 revised version of Manchester points A and B, and ICRU-38 lymph node surrogate points were determined, and their dose was recorded. Paired sample t-test, linear regression analysis, and Pearson correlation analyses were done considering a statistical significance level of 0.05 and using IBM SPSS statistics (Version 23, IBM Crop.).

RESULTS

Seventy-four brachytherapy cases were included. A positive and strong correlation was observed between D₉₀ of clinical target volume (CTV_HR) and points A and B dose for CTV_HR〈 15 cc and 〉 35 cc. Strong and significant (p < 0.05) correlations were achieved between pelvic wall points dose and D₉₀ and D₁₀₀ of the obturator and between D₅₀ and hot points of internal iliac lymph nodes. A strong correlation was obtained between D₅₀ and D₉₀ of external iliac lymph nodes and their ICRU points.

CONCLUSIONS

Strong correlations were obtained between dose to the pelvic lymphatic chains and their historical ICRU-38 surrogate points during HDR brachytherapy of locally advanced cervical cancer patients with 60Co tandem-ovoid applicator sets. The correlation strength between point A and prescription dose highly depends on the CTV_HR volume.

Interfraction Variation and Dosimetric Changes in Patients With Cervical Cancer Treated With Intracavitary Brachytherapy

PURPOSE

Intracavitary brachytherapy is integral in the treatment of cervical cancer. Because of interfraction variation, the current standard is replanning with every fraction. This study aimed to determine whether there was a difference in relative dosimetry if the source position and dwell time of the first fraction were applied to subsequent fractions.

MATERIALS AND METHODS

The authors performed a retrospective review of charts and films from 2007 to 2012. Eligible cases were patients with cervical cancer treated with brachytherapy with the same dose prescription to point A. Replanning was done on the first set of orthogonal plates. Source position and dwell time were subsequently applied to the remaining fractions using actual films.

RESULTS

Twenty-nine patients were included in this study. The results showed that cervical, rectal, and bladder dose between the actual plan and the hypothetical plan were not statistically different. In the hypothetical plan, the source activity and dwell time of the first plan were applied to the orthogonal films of the subsequent fractions and showed no significant difference in all dose points.

CONCLUSION

The results of this study showed proof of concept of the safety of using the source position and dwell time of the first plan for subsequent fractions. Until further studies are performed (also using three-dimensional planning software), the concept should be considered investigational because of the small sample size of the study. Until such research is performed, it is still strongly recommended that replanning be performed with every fraction whenever it is feasible.

Three-dimensional treatment planning for vaginal cuff brachytherapy: dosimetric effects on organs at risk according to patients position

PURPOSE

Aim of this study was to evaluate dose distribution within organs at risk (OARs) and planning target volume (PTV) based on three-dimensional treatment planning according to two different setup positions in endometrial carcinoma patients submitted to postoperative brachy-radiotherapy on vaginal vault.

METHODS AND MATERIALS

Patients with endometrial cancer necessitating of adjuvant brachytherapy on vaginal vault were enrolled. Pelvic computed tomography studies were prospectively obtained in two different setup positions: extend legs (A position) and gynecological (B position). Contoured OARs were bladder, rectum, and small bowel. The PTV was identified as applicator's surface with an isotropic 5-mm margin expansion. Radiation dose delivered in 1 cc (D1cc) and 2 cc (D2cc) of OAR were calculated.

RESULTS

Coverage of PTV and values of D1cc and D2cc obtained for bladder and small bowel were similar in the two positions. For rectum, both D1cc and D2cc had statistically significant lower values in A with respect to B position.

CONCLUSIONS

Both in A and B positions, radiation doses delivered do not exceed the dose constraints. However, A setup seems to significantly reduce doses to rectum while obtaining the same PTV coverage. The findings from our study provide evidence supporting the use of A position setup for delivering vaginal vault brachytherapy.