TITLE:
Inter-Fraction and Intra-Fraction Variation in the Absorbed-Dose Delivery during Interstitial High Dose Rate Brachytherapy—A Study Using MicroMOSFET In-Vivo Dosimeter
AUTHORS:
Seenisamy Ramapandian, Vivekanandan Nagarajan, Ashutosh Mukherji, Parthasarathy Vedasoundaram, K. S. Reddy, Vivekanandam Singhavajala, Vijayaprabhu Neelakandan
KEYWORDS:
MicroMOSFET, Interstitial Brachytherapy, MicroMOSFET in Brachytherapy, In-Vivo Dosimetry in Brachytherapy, Dose Verification in Brachytherapy
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.6 No.4,
November
29,
2017
ABSTRACT: Background: The
delivered dose has to be checked and verified with planned dose since precise
and accurate dose delivery is essential in Brachytherapy. Sources of
uncertainty during Brachytherapy are intra-fraction, inter-fraction and
inter-application variations. In-vivo dosimetry is the direct method to monitor
the radiation dose delivered to a patient during radiotherapy. In this study, assessment
of the inter-fraction and intra-fraction variations in the interstitial
Brachytherapy was done with microMOSFET. Aim: To analyze the inter-fraction
variations in dose delivery during interstitial HDR Brachytherapy and to
compare the measured point dose with the TPS-calculated point dose, intra-fraction variation, using the
microMOSFET in-vivo dosimeter. Materials and
Methods: From May 2014 to
February 2016, 22 patients with Head and
Neck cancers and 8 patients with Soft-Tissue Sarcomas (STS) were selected
for this study. All these patients underwent CT imaging more than 24 hours
after the application. Brachyvision 3DTPS and GammaMed Plus iX HDR unit were used for treatments. MicroMOSFET in-vivo dosimeter after calibration was used for the
measurements of dose inside the treated volume. Intra & Inter-fraction
variations were analyzed and reported. Results: The SD of inter-fraction
variation among 22 Head & Neck patients ranges from 2.14% to 14.26%.
Minimum & maximum dose variation with first fraction dose of patients
ranged from -22.33% to +26.71% and the mean
doses were -6.42% to +19.76%. Differences of TPS dose and microMOSFET measured first fraction dose, intra-fraction
variation, ranged from -12.36%
to +5.05%. The SD of inter-fraction variation
for 8 STS patients was from 2.81% to 14.43%. Minimum and maximum doses vary from -38.72% to +25.74% and mean dose
varies from -21.5% to +12.53%. Differences of point doses of TPS and measured, intra-fraction variation, were from -5.86% to 4.88%. Conclusions: MicroMOSFET has the potential to minimize the gross errors during
multi-fractionated Interstitial Brachytherapy. Edema, applicator displacements and placement of
microMOSFET are the main influencing factors for inter-fraction
uncertainty in dose delivery. Re-planning with re-simulated images should be considered whenever the microMOSFET readings vary more than ±10% of the planned dose inside the CTV measured in two
successive fractions.