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Inter-fraction dosimetric variation in Point A, Bladder, rectum during high dose rate brachytherapy treatment of the carcinoma of uterine cervix Dr. Sounik Das, Dr. Annesha Lahiri, Dr. Bikramjit Chakraborty, Dr. Santanu Pal IPGMER & SSKM Hospital, Kolkata Purpose - Quantification of inter-fraction percentage dose variations to point A, bladder and rectal points using Fletcher suite applicator Background - In India, every year, 122, 844 women are diagnosed with cervical cancer and 67, 477 die from the disease. Ranking as the second most common cancer among women aged 15-44 years, it becomes imperative to identify patients at an early stage, and offer the best treatment modality. Beyond FIGO stage IIA, chemoradiation followed by brachytherapy is a potentially curable treatment modality. India has developed by leaps and bounds in every discipline. Yet, huge deficit exists where radiation therapy is concerned, being mostly confined to the big cities. Further, centres offering brachytherapy to the poor are even fewer and far between. Brachytherapy is usually administered in fractionated doses over 2-4 weeks. Planning prior to each fraction takes into account the inter-fraction changes in tumour volume, anatomy, applicator placement geometry etc. Considering the huge burden of the disease, we have attempted to evaluated the validity of the plan done during first fraction when applied to subsequent fractions of brachytherapy. Materials and methods - A total of 225 patients of carcinoma cervix attended the Out Patient Department of Radiotherapy, SSKM hospital from November 2016 to July 2017. Out of these, patients receiving External Beam Radiotherapy followed by 3 fractions of HDR-Intra-cavitary Brachytherapy (Nucletron - Ir192) with Fletcher Suite applicator, to achieve a final EQD2 of 80- 90Gy to Point A were analysed and 18 patients were selected. For each patient the applicator, tandem angle, placement of OS guard, ovoids and vaginal gauze packing was kept constant throughout fractions. A pelvic CT scan was performed after each insertion, catheter reconstruction, placement of ICRU reference points, dose prescription to Point A and optimization was performed by the same team of physicist and radiation oncologist. Plans were examined retrospectively and patients undergoing improper insertion during first fraction were excluded. Of the selected patients first fraction prescription dose, dwell position and weightage was noted and applied on 2nd and 3rd fraction planning CT, thus creating a hypothetical plan which can be compared to 2nd and 3rd fraction optimized plans. Since prescribed dose was not always the same in all fractions we calculated the percentage of prescribed dose to Point A, percentage of point A dose to bladder and rectum. Hypothetical vs optimized plans' means were compared using Paired-t test with SPSS version 23. Result - 17 out of 18 patients completed 3 fraction of HDR ICBT, 1 patient after completing 2nd fraction, dropped out of 3rd fraction. Absolute mean dose of optimized plans • Point A - 689.89 cGy • Bladder Point - 495.42 cGy • Rectal Point - 468.81 cGy Absolute mean dose of hypothetical plans • Point A - 682.84 cGy • Bladder Point - 573.04 cGy • Rectal Point - 518.6 cGy The difference in mean percentage of prescribed dose to Point A • 1st & 2nd fraction - (-)6.76 % (n=18, p= 0.348) • 1st & 3rd fraction - 1.44 % (n= 17, p= 0.826) The difference in mean percentage of Point A to: Bladder • 1st & 2nd fraction - 12.17 % (n=18, p= 0.00024) • 1st & 3rd fraction - 11.36 % (n= 17, p= 0.026) Rectum • 1st & 2nd fraction - 11.78 % (n= 18, p= 0.018) • 1st & 3rd fraction - 9.12 % (n= 17, p= 0.025) Conclusions - There is no significant inter-fraction difference as far as the dose to point A is concerned. Even after recreating similar situations every time and applying the first plan to subsequent fractions, dose to point A were more or less constant and close to our prescribed dose but bladder and rectum doses were increased & statistically significant. According to EMBRACE 2015 study (ICRU report 89), rectal point estimates 20% higher dose than corresponding D2cc rectum. On the other hand, the bladder point estimates 20% lower than its D2cc dose. In a busy institute with a huge patient load where bladder and rectal points are being used instead of D2cc, time could rather be utilized in treating more number of patients per day. Thus it might be prudent to use the same plan for subsequent fractions, as statistically significant difference of dose to tumour does not exist. This will make it logistically possible to provide a potentially curable treatment to many more patients, reducing the prevalence of the disease, at least, until centers for brachytherapy are increased manifold. [ABSTRACT FROM AUTHOR]

Purpose - Quantification of inter-fraction dose variations to point A, bladder and rectal points using Fletcher suite applicator. Background - It is a well established fact that planning prior to each ICBT fraction is an accurate method of dose delivery keeping in mind the change in applicator position, tumour volume shrinkage and change in anatomy. But in a busy institute with a huge patient load, how feasible is application of data from the plan of first fraction to subsequent fractions. Methods - A total of 46 patients of locally advanced carcinoma cervix from November 2016 to June 2017 received External Beam Radiotherapy (Bhabatron II Co60) followed by 3# of HDR-Intra-cavitary Brachytherapy (Nucletron - Ir192) with Fletcher Suite applicator, final EQD2 of 80-90Gy . For each of 3 ICBT applications same applicator and similar vaginal gauze packing was done, a pelvic CT scan was performed and dose at point A, bladder and rectal points were defined according to ICRU 38, by same physicist. Planning was done on Oncentra Brachy Treatment Planning. Variation of dose at Point A, bladder and rectal points for 1st fraction ICBT was compared with 2nd and 3rd fractions, using paired-t test. Data was analysed using SPSS Version 24. Results- 42 patients completed 3 fraction of HDR ICBT, 4 patients after completing 2nd fraction, dropped out of 3rd fraction. Difference between 1st vs 2nd fraction mean doses of: • Point A 7.13 cGY (n=46, p=0.632) • Bladder point 28.06 cGY (n=46, p=0.188) • Rectal Point 21.06 cGY (n=46, p=0.176) Difference between 1st vs 3rd fraction mean doses of: • Point A 6.22 cGy (n=42, p=0.625) • Bladder point 0.81 cGy (n42, p=0.976) • Rectal Point 21.18 cGy (n42, p=0.211) Conclusions - First fraction TPS planning and its use for subsequent fractions is justified as the inter-fraction differences of dose to Point A, Bladder and rectal points are statistically not significant, ensuring correct instrument placement and similar vaginal gauze packing. We also found out that the major variation was in the Bladder point dose, with minimum difference of 0.5cGy(1st vs 2nd ) maximum difference of 314.80(1st vs 3rd). Variations in Rectal dose was much lesser, minimum difference of 6.82cGY(1st vs 2nd ) and maximum difference of 199.50 cGY (1st vs 3rd) We conclude that a single plan created at the time of first fraction can be used for a single patient for three fractions, without significant variation of dose to cervix, bladder and rectum. Thus saving valuable brachytherapy OT time which can be utilised to treat other patients, specially in a country like India where Brachytherapy machines are scarce and patient load is mammoth. [ABSTRACT FROM AUTHOR]