Dosimetric Analysis of 3DCRT or IMRT with Vaginal-cuff Brachytherapy (VCB) for Gynaecological Cancer

Transcription

1 Dosimetric Analysis of 3DCRT or IMRT with Vaginal-cuff Brachytherapy (VCB) for Gynaecological Cancer Tan Chek Wee National University Cancer Institute, Singapore Clinical Care Education Research

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3 Singapore Located at the southern tip of Peninsular Malaysia Population of 5.4 millions Total land area of 704 square km (278 square miles) Temperature ranges from 28C to 32C ( F)

4 Multi-racial and culture country Consisting of 4 main ethic groups Celebrated 50 years of independence last year

5 Public General Hospitals and National Specialist Centres

6 National University Cancer Institute, Singapore 19-storey building Radiotherapy Department located on the 8 th Floor 6 bunkers 3 Synergy Elekta Linear Accelarator, Mosaiq, 5 Monaco and 4 Xio TPS Shaping Medicine for the Future

7 The research aims to analyse the dosimetric impact of combined brachytherapy with intensity modulated radiation therapy (IMRT) or 3 dimensional conformal radiotherapy (3DCRT) in terms of planned target volume (PTV) coverage especially the vaginal vault PTV region and dose to surrounding organs at risk (OARs).

8 Content Introduction Material and Methods Result Discussion Conclusion

9 2. Introduction Divider Introducing new topic

10 Introduction Radiotherapy for gynaecological cancers is often delivered by a combination of brachytherapy and external beam irradiation. Brachytherapy is used to deliver high doses of radiation to the primary tumour region where as external beam irradiation covers the whole pelvic region.

11 Rectovaginal fistula Complications! Thickening of small bowel wall

12 IMRT Use of intensity modulated radiation therapy (IMRT) has been shown to have advantages in improving target coverage and sparing of organs at risks (OARs) when compared with conventional radiotherapy. Allow for better conformity of the high dose region to irregular target volumes as the steep dose gradient created can better spare surrounding OARs Multiple dose level delivery at one time

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14 Concerns on the use of IMRT for gynaecological cancers Hot spot in adjacent normal tissue Internal Organ Motion and volume changes during treatment Concerns on the use of IMRT for Gynaecological Cancer Tumour Regression Target volume delineation

15 Improvement in Imaging and Treatment Technology Availability of MRI scan for RT planning, cone beam computed tomography (CBCT) an other online monitoring and dose tracking system

16 IMRT for Gynaecological Cancer Consensus Guidelines for Delineation of Clinical Target Volume for IMRT Pelvic Radiotherapy for the Definitive Treatment of Cervix Cancer. Results from RTOG 0418 which is a Phase II study designed to determine the transportability of pelvic IMRT to a multi-institutional setting RTOG Randomized Phase III Study Of Standard Vs. IMRT Pelvic Radiation For Post-Operative Treatment Of Endometrial And Cervical Cancer Group European de Curie-European Society for Therapeutic Radiology and Oncology (GEC-ESTRO) guidelines for target volumes delineation and OARS delineation

17 4. 2. Divider Material and Method Introducing new topic

18 Material and Methods 21 post operative patients who were previously treated with 3DCRT and brachytherapy were retrospectively planned using IMRT Patients underwent CT simulation with full bladder on a Philips Big Bore CT scanner in the supine position acquired with 5mm CT slices External beam dose given was 50.4Gy in 28 fractions followed by single channel brachytherapy of 10Gy at 5mm depth in 2 fractions. Plans were reviewed together with imaged-based 3D brachytherapy plans to assess combined dose distribution

19 Treatment Planning Patients were retrospectively planned using IMRT to a total dose of 50.4Gy in 28 fraction based on RTOG 1203 planning guidelines IMRT was planned using 7 coplanar beams using either 6MV or 10 MV dynamic modulated radiotherapy (DMLC) technique on Monaco treatment planning system version DCRT planning was performed using Xio Treatment Planning System version 4.2 with either 6MV or 10MV photon to generate a four-field box technique to cover the whole pelvis.

20 Constraints used for IMRT planning PTV coverage Rectum Bladder Small Bowel Pelvic Bone 97% of PTV received 100% of the dose 0.03cc of any volume within PTV should not receive more than 110% no volume within the PTV that is 0.03cc or larger should receive < 93% of the prescribed dose D100%< 40Gy D70% < 45GY D70% < 40Gy D90%< 25GY D60%<40Gy **planning objectives used were based on the radiation therapy oncology group (RTOG) 1203 protocol

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22 Contouring Accuracy and consistency in the contouring of planning target volume (PTV) and organs at risk (OARs) are important in ensuring reliability and generalizability of the planning data Delineation of the PTV and OARs for IMRT planning were based on the Radiation Therapy Oncology Group (RTOG) 1203 Protocol and GYN GEC ESTRO guidelines for 3D brachytherapy Study only had one consultant radiation oncologist (RO) to delineate the PTV and OARs and another consultant RO to verify to avoid introducing inter-observable variabilities in the study

23 Evaluation Quantitative evaluation of the plans was performed by the use of standard dose-volume histogram (DVH). Analysis for IMRT vs 3DCRT includes D97% (dose received by the 97% of the volume), maximum dose at 0.03cc, conformity index (CI) and the dose for bladder, rectum, small bowel and pelvic bones. Analysis of IMRT + Brachytherapy vs 3DCRT + Brachytherapy includes D100 and D90 for PTV coverage and maximum dose expressed as D2cc and D1cc for OARs such as bladder, rectum and sigmoid.

24 Table 1 Comparison between IMRT vs 3DCRT IMRT 3DCRT PTV Nodes Max Dose PTV vault Bladder Rectum Small Bowel PTV node Max Dose PTV Vault Bladder Rectum Small Bowel 97% coverage in % 97% coverage 45Gy< 70% 45Gy<100% 40Gy<70% 97% coverage in % 97% coverage 45<70% 45Gy<100% 40Gy<70% T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T Mean Mean SD SD

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26 Brachytherapy Brachytherapy was done using iridium-192 (high-dose-rate) source with standard single channel vaginal applicator 3D treatment planning was done on the Oncentra Masterplan planning system version 4.3.

27 Brachytherapy Planning Treatment is prescribed at 5mm depth from the applicator surface, to a dose of 5Gy per fraction for 2 fractions Cover 1/3 to1/2 of the vaginal length from top Reporting for 3D gynaecological brachytherapy includes the D100 and D90 for the vaginal vault PTV, D1cc and D2cc dose for rectum, bladder and sigmoid 5mm

28 Combining external beam with brachytherapy Due to the different treatment fraction size and dose rate, need to take into account the EQD2- Equivalent dose in 2Gy/Fraction EQD2= BED/ (1+2/ α/β), where BED is the biological effective dose and the α/β proposed for target is = 10 and 3 for the OARs EQD2 dose from external beam radiotherapy and brachytherapy is summed up to serve as an estimation of the worst case scenario assuming that the points of interest and volumes received the full dose

29 Statistical Analysis Null hypothesis: There is no difference between IMRT and 3DCRT when combined with brachytherapy in terms of target coverage and dose to OARs and the alternative hypothesis is that there is a difference between IMRT and 3DCRT. Variation in volumetric data and DVH parameter were assessed using Wilcoxon signed rank test where p<0.5 was considered significant

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31 Table 2 Total EQD2 IMRT + BT Vs Total 3DCRT + BT Total EQD2 IMRT + BT Total EQD2 3DCRT + BT PTV, Gy, α/β =10 Bladder, Gy, α/β =3 Rectum, Gy, α/β =3 Sigmoid, Gy, α/β =3 PTV, Gy, α/β =10 Bladder, Gy, α/β =3 Rectum, Gy, α/β =3 Sigmoid, Gy, α/β =3 D100 D90 D2cc D1cc D2cc D1cc D2cc D1cc D100 D90 D2cc D1cc D2cc D1cc D2cc D1cc 1 T T T T T T T T T T T T T T T T T T T T T Averag e SD

32 Result When combined with brachytherapy, IMRT resulted in significantly better PTV coverage where the p value < 0.05 for both D100 and D90 Use of IMRT also resulted in significantly increase in dose to bladder, rectal and sigmoid D1cc and D2cc dose as the p value is less than 0.05 for above organs As the p value is less than 0.05, the null hypotheses is rejected as there is significance difference between the IMRT combined doses compared to 3DCRT.

33 3. Discussion Divider Introducing new topic

34 Bladder Rectum

35 Table 3 IMRT Rectum 40Gy< 80% or 80%< 45Gy<100% 3DCRT Rectum 45Gy<100% T T T T T T T T T T T T T T T T T T T T T Mean SD

36 Table 4 Mea EQD2 IMRT EQD2 3DCRT EQD2 IMRT + BT EDQ2 3DCRT +BT Case study Rectum, Gy, α/β =3 Rectum, Gy, α/β =3 Rectum, Gy, α/β =3 Rectum, Gy, α/β =3 D2cc D1cc D2cc D1cc D2cc D1cc D2cc D1cc T T T T T T T T T VS T T T T T T T T T T T T Mean

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38 Limitation Current TPS doesn t allow for summation or deformable registration of multiple brachytherapy plans or combined external beam treatment plan with brachytherapy plan. The evaluation of dose is based on the summation of the DVH value. Assessment of IMRT plans is based on the dosimetry and DVH of the planning CT scan taken before the start of treatment, hence does not necessarily represent the actual dose delivered to the tumour and OARs if intrafraction and interfraction organ motion, tumour regression and set-up reproducibility

39 Conclusions Use of IMRT in gynaecological cancer can help to improve target coverage to the vaginal cuff and reduce bladder, rectum and small bowel dose when compared with 3DCRT. Combined mean EQD2 dose of D1cc and D2cc of bladder, rectum and small bowel is however significantly higher in IMRT compared to 3DCRT. Hence, during IMRT planning may need to evaluate the D1cc and D2cc dose of the OARs to limit these dose to avoid exceeding tolerance dose when combine with brachytherapy

40 References Heron DE, Gerszten K, Selvaraj RN. et al. Conventional 3D conformal versus intensity- modulated radiotherapy for the adjuvant treatment of gynecologic malignancies: a comparative dosimetric study of dose-volume histograms. Gynecol Oncol 2003:91: Lim K, Kelly V, Stewart J. et al Pelvic Radiotherapy for cancer of the cervix: Is what you plan actually what you deliver? Int J of Radiat Oncol, Biol, Phys 2009; 74: Macdonald DM, Lin LL, Biehl K, Mutic S, Nantz R, Grigsby W. Combined intensity modulated radiation therapy and brachytherapy in the treatment of cervical cancer. Int J of Radiat Oncol, Biol, Phys 2008;71: Mundt AJ et al. (2002)-Intensity-modulated whole pelvic radiotherapy in women with gynecologic malignancies. International Journal of Radiation Oncology Biology Physics. 52(5), Potter R, Haie-Meder, C, Limbergen EV, et al. Recommendations from gynaecological (GYN) GEC ESTRO working group (II): Concepts and terms in 3D image-based treatment planning in cervix cancer brachytherapy- 3D dose volume parameters and aspects of 3D image-based anatomy, radiation physics, radiobiology. Radiother and Oncol 2006;78:67-77

41 Thank you for your attention Research Clinical Care Education