Late rectal toxicity after image-based high-dose-rate interstitial brachytherapy for postoperative recurrent and/or residual cervical cancers: EQD2 predictors for Grade ≥II toxicity
Introduction
Interstitial brachytherapy (ISBT) for gynecologic cancers is used wherein standard intracavitary brachytherapy (ICBT) or intravaginal brachytherapy is expected to result in inferior local control due to suboptimal dose distribution within the lateral parametrial tissues for bulky cervical cancers. Boost ISBT has also been used in patients with primary vaginal or postoperative residual and/or recurrent cervical and endometrial cancers for tumors extending beyond the medial parametrium or upper one-third of anterior or posterior vaginal wall. However, the use of high-dose-rate (HDR) or low-dose-rate ISBT is associated with 4–24% incidence of severe rectal toxicity [1], [2], [3], [4], [5], [6], [7], [8], [9], [10].
In comparison with ICBT, the larger clinical target volume (CTV) implanted during ISBT, proximity of the implanted needles to the rectum, and use of single or multiple daily fractionation regimen may predispose patients to higher incidence of rectal toxicity. Although the rectal dose–volume thresholds for moderate-to-severe late rectal toxicity have been investigated and defined for patients undergoing image-guided ICBT for cervical cancer [11], [12], [13], they have not been validated in patients undergoing ISBT.
The present study was designed to investigate if rectal dose–volume thresholds recommended for ICBT were accurate predictors for moderate-to-severe late rectal morbidity in patients undergoing pelvic ISBT.
Section snippets
Methods
From October 2009 to November 2012, patients undergoing external beam radiation therapy (EBRT), concurrent chemotherapy, and ISBT within the context of ongoing trials were included [14], [15]. Patients with postoperative residual and/or recurrent cervical cancer were included. Patients with disease extension toward lateral pelvic wall or paracolpos at baseline were considered eligible for boost ISBT.
Results
Fifty consecutive patients were included. The median age was 49 years (35–70). All patients had postsurgical residual and/or recurrent cervical cancer and received chemoradiation followed by ISBT (Table 1). None of the patients had received prior pelvic radiation. Overall, 43 patients received IMRT and 7 received 3DCRT. All patients received >4 cycles of concurrent weekly cisplatin. All patients completed the planned EBRT dose without any break. All patients underwent interstitial implantation
Discussion
In this study, we investigated the correlation of rectal dose volume metrics with late rectal toxicity among patients undergoing HDR ISBT for locally recurrent or residual cervical cancer. We observed 22% incidence of Grade II or higher late rectal toxicity and 4% incidence of Grade III toxicity. We identified RM doses to have higher predictive value for late rectal toxicity. Although RM was delineated after placing intrarectal flatus tube, we appreciate that delineating RM may not be
Conclusions
Correlating dose volume metrics with toxicity data demonstrates that the hazard of developing Grade ≥II rectal toxicity after ISBT is at a lower dose threshold than that described in ICBT literature. The rectal and/or RM dose–volume thresholds proposed within the study could be used to predict and/or minimize rectal toxicity after ISBT.
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2021, International Journal of Radiation Oncology Biology PhysicsCitation Excerpt :However, this study with long-term follow-up lacks dose–volume parameters and therefore does not provide accurate information to guide treatment optimization. In adult patients with locally advanced cervical cancer treated with image-guided brachytherapy, strong correlations have been shown between dose–volume parameters and the probability of rectal complications.21,31,32 To our knowledge, our study is the first to show such a correlation in children.
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2020, BrachytherapyA Phase II Trial of Stereotactic Ablative Radiation Therapy as a Boost for Locally Advanced Cervical Cancer
2020, International Journal of Radiation Oncology Biology PhysicsCitation Excerpt :Studies from heavy ion therapy revealed a cumulative rectal dose, not corrected for fraction size, of 60 GyE to be associated with high-grade toxicity.25 For interstitial implants, a retrospective single institution analysis from Tata Memorial hospital revealed a correlation between rectal mucosa D2cc > 62.3 Gy and the incidence of grade ≥ 2 rectal toxicity.29 In our study, patients did receive large doses to the rectum, with a median rectal EQD2 2cc dose of 90.63 Gy and a median rectal boost 2cc dose of 25.57 Gy.
Financial disclosure: The Department of Science and Technology, Tata Memorial Centre (DST SR/FT/LS:111/2012) provided funding for part of this study.
The authors report no conflicts of interest.