Reporting of inter fraction dose variations of organs at risk in computed tomography-guided high dose rate intracavitary brachytherapy in carcinoma cervix :[PAUTHORS], Journal of Medical Physics

TECHNICAL NOTE
Year : 2022 | Volume : 47 | Issue : 4 | Page : 394--397

Reporting of inter fraction dose variations of organs at risk in computed tomography-guided high dose rate intracavitary brachytherapy in carcinoma cervix

Moujhuri Nandi, Neelima Pokala, Vaishnavi Perumareddy, Sujata Sarkar, Sudeep Chanda
Department of Radiation Oncology, Meherbai Tata Memorial Hospital, Jamshedpur, Jharkhand, India

Correspondence Address:
Dr. Moujhuri Nandi
Meherbai Tata Memorial Hospital, Northern Town, Stocking Road, Bistupur, Purbi Singbhum, Jamshedpur - 831 001, Jharkhand
India

Abstract

Assess the interfraction dose variations of the organs at risk (OARs) in carcinoma cervix high dose rate (HDR) computed tomography (CT)-guided intra cavitary brachytherapy (ICBT). 120 CT scans of 40 patients who had undergone three fractions of ICBT (7 Gy/fr) were analyzed. Dose to Point A and the minimum doses to the volumes of 2, 1, and 0.1cc of bladder, rectum and sigmoid colon were recorded. Revised plans were generated in 20 patients. Paired t-test was used to compare the difference in the means. Point “A” mean dose difference was statistically significant between the treated and revised plans. For bladder, the difference in means of dosage to all volumes, whilst for the rectum and sigmoid colon, the low volume dosage (0.1cc) was statistically significant. Absence of individualized planning would have resulted in underdosage of tumor and increased dosage of up to 30% to OARs. CT-guided ICBT should be implemented for each HDR fraction treatment.

How to cite this article:
Nandi M, Pokala N, Perumareddy V, Sarkar S, Chanda S. Reporting of inter fraction dose variations of organs at risk in computed tomography-guided high dose rate intracavitary brachytherapy in carcinoma cervix.J Med Phys 2022;47:394-397

How to cite this URL:
Nandi M, Pokala N, Perumareddy V, Sarkar S, Chanda S. Reporting of inter fraction dose variations of organs at risk in computed tomography-guided high dose rate intracavitary brachytherapy in carcinoma cervix. J Med Phys [serial online] 2022 [cited 2023 Mar 31 ];47:394-397
Available from: https://www.jmp.org.in/text.asp?2022/47/4/394/367432

Full Text

Introduction

Cancer cervix is the second most common cancer in India and more than 60% of cases present in advanced stages.[1] The standard of care for advanced stages involves external beam radiotherapy to the pelvis concurrently with cisplatin followed by or interdigitated with intra cavitary brachytherapy (ICBT).[2],[3],[4] ICBT helps to deliver high dose to the tumor while sparing the critical organs at risk (OARs), thus improving local control rates and overall survival.[5],[6],[7]

Traditionally, low dose rate ICBT was the standard form of treatment when remote after loading facilities were unavailable and it involved exposure of radiation personnel.[8] With the advent of newer technology of remote after loading techniques and artificial radionuclide (Ir192), high dose rate (HDR) ICBT has been the standard of care for the last 30 years or so. The radiobiological disadvantage of HDR ICBT is overcome by delivering smaller doses over shorter period of time. The advantages of HDR ICBT include ease of applicability, outpatient procedure, shorter treatment times, individualized treatment planning and dose optimization, and complete radiation protection for health-care workers.[9],[10]

The international Commission on Radiation Units and Measurements (ICRU) recommends three-dimensional (3D) image-based brachytherapy planning for each fraction.[11] It is important to note the doses to OAR and tumor for each and every fraction, as there may be differences in the geometrical application and organ motion between two insertions, which can lead to important clinical ramifications.

Materials and Methods

One hundred and twenty (40 × 3) computed tomography (CT) image dataset-based plans of 40 consecutive carcinoma cervix patients were retrospectively evaluated. The stage of presentation ranged from IB2-IVA as per International Federation of Gynecology and Obstetric 2018 staging system.[12] Post external beam RT dose of 46–50 Gy in 23–25 fractions over 4.5–5 weeks (with concurrent cisplatin) by 3D conformal technique, patients received ICBT to a total dose of 21 Gy in 3 fractions (7 Gy/fraction) a week apart (Varian Gamma Med Plus).

Patients were kept nil per mouth overnight and prescribed laxatives (Tab bisacodyl 5 mg–2 tablets at night time). Every woman was explained about the procedure and informed consent obtained. The application was performed under general anesthesia. Foley's catheter was inserted into urinary bladder, balloon was inflated with 7 cc of radio opaque solution (1:6 dilution), and the catheter remained unclamped. Usually 15/30° tandem of lengths 6, 5 or 4 cm was used with ovoids of varying sizes as per vaginal room. Postplacement of applicator, adequate vaginal packing was done to avoid their displacement, and to move bladder and rectum away from the field of treatment.

3D images of pelvis to include the applicator were acquired on positron emission tomography-CT simulator (Siemens Biograph Horizon) with 3mm slice thickness. Acquired images were imported into 3D computerized brachytherapy planning system (Brachy vision v. 13.6.32). Applicator reconstruction and contouring of OARs were done following the ABS/GEC-ESTRO[13],[14],[15] guidelines. Dose was prescribed to point A and planning optimization was done to keep critical organs dosage to the prescribed constraints of 90 Gy and 75 Gy to 2cc volume of bladder, and rectum and sigmoid colon, respectively while trying to achieve a Equieffective dose at 2 Gy of 76–80 Gy to the tumor.

Revised plans were generated in 20 cases to compare with the treatment plans of 2nd and 3rd fraction of ICBT (Plan 2R, Plan 3R) using the dwell times and source position corresponding to the first fraction of treatment. The mean point A doses and the minimum doses to the volumes of 2cc, 1cc, and 0.1 cc of OARs in the treated and revised plans were noted, and the difference in their means were compared. Paired t-test was used to compare the difference in means between any two fractions at a time. All tests were two tailed and P < 0.05 was taken as significant.

Results

The mean dose to point “A” in the three treated fractions and the revised plans (Plan 2R, Plan 3R) have been tabulated. The difference in means was statistically significant between the first and third treated plans and also between the delivered and revised plans [Table 1].{Table 1}

The difference in volumes of the OARs in the three different fractions was statistically insignificant. Comparatively, higher minimum doses to the volumes of 2cc, 1cc and 0.1cc of bladder were delivered in the 2nd fraction, whilst for rectum it was lowest in the 2nd fraction. Sigmoid colon received higher doses in the last treated fraction [Table 2].{Table 2}

The difference in mean values of the minimum doses to 2cc, 1cc and 0.1cc of bladder volumes was statistically significant between the treated and revised plans. In absence of re-planning, the different volumes of bladder would have received up to 20% increased dosage. Statistically significant difference between the delivered and revised plans was found in the low volume (0.1cc) dosage for rectum and sigmoid colon. Consistently higher doses were delivered to all volumes of OARs in the revised plans [Table 2] and [Table 3].{Table 3}

Discussion

This study evaluated the difference in the mean doses to the point A and to the volumes of OARs amongst the three treated fractions and the revised plans. Significant difference was revealed in the means of the minimum doses to all volumes of bladder, and to 0.1 cc volumes of rectum and sigmoid colon in comparison with the revised plans though the difference in total volumes of OARs remained insignificant among the treated fractions.

Chakraborty et al.,[16] in their study of 44 patients treated with CT-based ICRT (9Gy x 2) showed that absence of individualized planning resulted in higher doses to the OARs in the second fraction. Dose constraints to OARs would have been exceeded in 16% of patients if imaging was avoided in the 2nd fraction treatment. They concluded that organ deformations were the offenders for the variation in OAR doses.

Jones et al.[17] in their study found an increase of 5%, 6% and 11% in the dose to the rectum, bladder, and vaginal surface respectively, on the usage of the initial treatment plan for successive insertion. They concluded that at-risk structures were at increased risk of exceeding dose constraints if customized treatment planning was not performed.

Davidson et al.[18] in their study found that there was a significant increase in doses to ICRU bladder and rectal points and to their 2 cc volumes when a single plan was used for the treatment of both fractions. Usage of a single plan for an entire course of ICBT resulted in discernible increase in doses to critical organs, especially for sigmoid and small bowel.

Sharma et al.[19] noted no variations in doses when each fraction was planned and treated individually, but usage of the same plan to treat subsequent fractions resulted in an increase of OAR doses by about 30%. Applicator geometry, disease response and organ deformation were considered as the attributing factors of above variation.

Limitation of this study was the fewer patient number and the use of point-based dose prescription. Higher number of patients would have yielded more conclusive results. Volume based prescription would have helped us to achieve better tumor coverage whilst limiting the doses to the OARs.

Conclusion

In conclusion, absence of re-planning would lead to underdosing of tumor, and an increased dosage to the OARs (up to 30%) exceeding tolerance dose limit in 60% cases. Thus, individualized treatment planning is recommended for each fraction treatment in HDR ICBT.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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