Dosimetric Impact of Inter-Fraction Variation in Interstitial HDR Brachytherapy

Abstract

Background: Patient setup errors in External Beam Radiotherapy (EBRT) are minimized to a great extent, due to recent technological developments, but in contrary brachytherapy received less attention in inter-fraction catheter movement and its impact in dose delivery. This article deals with inter-fraction interstitial catheter movement and its impact in dose delivery to the target. An attempt is made to study the dosimetric impact of this variation. Objectives: The objective of the study is to evaluate the inter-fraction variation in the position of implanted interstitial applicators and to assess the dosimetric impact in interstitial High Dose Rate (HDR) brachytherapy. Materials and Methods: 55 patients treated for carcinoma tongue, breast, buccal mucosa, cervix, floor of the mouth and soft tissue sarcoma over a period of 2 years (December 2011-May 2013) were considered. All the patients underwent CT scan the next day of the implanting and 3D planning was done either by Eclipse or Oncentra Master Plan Treatment Planning System (TPS). Patients were treated by HDR brachytherapy remote after-loading units, either by Gamma Med iX plus or Microselectron. At the end of the last fraction, CT scan was repeated and re-planning done. The variation in the position of the implanted applicators/catheters and its impact on dosimetric parameters was evaluated and analyzed. Results: The range of positional displacement of the interstitial catheters ranges from 4.5 mm to 6.8 mm. The maximum variation in prescribed dose to D90 of Clinical Target Volume was 10.88%. Conclusions: If the total duration of the interstitial implant of HDR brachytherapy extends for more than a week from the day of imaging, it is recommended to do CT imaging and re-plan again. It is mandatory to suture the buttons of the implanting to the skin. Edema and movement of organs (e.g., tongue) are the main cause for the positional variation of the catheters.

An <i>In-Vivo</i> Study during Combined Intracavitary and Interstitial Brachytherapy of Gynaecological Malignancies Using microMOSFET

“…Kandasamy et al [14] con-cluded that repeat-CT on the fifth day from the application is sufficient. CT/MRI imaging before each fraction can be an effective way to find the tumor shrinkage, edema and applicator displacement.…”

Inter-Fraction and Intra-Fraction Variation in the Absorbed-Dose Delivery during Interstitial High Dose Rate Brachytherapy—A Study Using MicroMOSFET <i>In-Vivo</i> Dosimeter

“…In our study for flexible catheter based interstitial Brachytherapy, the planning CT scan was done 1 or 2 days after the implant. This had the beneficial effect of reduced tissue edema and hence a reduction in the effect of Kandasamy et al [14] observed inter-fraction errors frequently in the interstitial implants and recommended imaging before each fraction and re-planning based on that. In-vivo dosimetry with microMOSFET can be alternative for pre-treatment CT method with the added advantage of instant verification, convenient to patient, save the quality time of man power and no additional exposure unlike the multiple CT.…”

“…This method drastically cut down the D90 of CTV within ±5% in contrast with their earlier study of 35% to 40%. Kandasamy et al [14] suggested piece of micropore paper pasted on each applicator can minimize the displacement significantly. We also used the same method to arrest the applicator movement at certain extent.…”