Clinical implementation of IMRT step and shoot with simultaneous integrated boost for breast cancer: A dosimetric comparison of planning techniques
Purpose: Radiotherapy post-lumpectomy with two coplanar tangent beams is the standard treatment for women with early stage breast cancer. Despite the use of wedges as tissue compensators, the resultant plans often contains a significant dose gradient and 'hot spots' in excess of 15% or more of prescribed dose. In recent years a field-in-field (FIF) dose-compensation technique, which use two standard tangent fields and one or two (rarely three) small beams within these, was developed. It allows to obtain a more uniform dose throughout the target volume in the majority of cases but not in all. This study presents our experience to develop optimal intensity modulated radiation therapy (IMRT) techniques to be applied clinically in those cases where the traditional technique with two tangent fields or its variant field in field (FIF) are unable to achieve a satisfactory planning target volumes (PTVs) coverage and dose objectives to the organs at risk (OARs).
Methods: We investigated two pure IMRT plans (named 3F-IMRT and 4F-IMRT) and a hybrid one (H-IMRT). Treatment plans were performed for 7 left-sided and 4 right-sided breasts using simultaneously integrated boost (SIB) planned technique with inverse optimization. Results were compared with those obtained with FIF technique. Dose prescribed was 45 Gy/20 fractions to the breast and 50 Gy /20 fractions to the lumpectomy cavity delivered in 5 fr/week. Dose–volume histograms were generated and parameters as target dose coverage, conformity and homogeneity as well as OARs dose distribution were analyzed. Finally the secondary cancer risk to contralateral breast due to radiation was evaluated as a further parameter for the choice of the optimal plan.
Results: Compared to the FIF, the three IMRT plans provided the same target coverage and a better dose conformation, but a worst dose homogeneity of the boost target. The volume of the OARs, receiving higher doses than 15 Gy was reduced but was increased the volume receiving low doses. This causes the increase of the risk of radiation induced cancer, especially for the contralateral breast. For this organ, the highest value of the excess absolute risk (EAR) was associated to the 4F-IMRT, while the lower, to the FIF.
Conclusion: The intensity-modulated radiation therapy techniques 5F-IMRT and 4F-IMRT were the best to be applied clinically in those cases, where the traditional technique of irradiation of the breast is unable to achieve the PTVs coverage and dose objectives to the OARs. However, all the IMRT techniques showed an increased volume of healthy tissues receiving low doses, so they should not be used in extensive manner and in particular should be avoided in the cases of young women due to the excess of risk to develop a secondary cancer.
AIRTUM Working Group. I Tumori in Italia: rapporto. La prevalenza dei tumori in Italia: persone che convivono con un tumore, lungo sopravviventi e guariti. Epidemiologia Prevenzione. 2010;34(5-6) suppl 2.
Ferlay J, Shin HR, Parkin DM, et al. Estimates of worldwide burden of cancer in 2008: GLOBOCAN 2008. Int J Cancer. 2010;127(12):2893–917.
Clarke M, Collins R, Darby R, et al. Effects of radiotherapy and of differences in the extent of surgery for early breast cancer on local recurrence and 15-year survival: an overview of the randomised trials. Lancet. 2005; 366(9503):2087–106.
Ragaz J, Olivotto IA, Spinelli JJ, et al. Locoregional radiation therapy in patients with high-risk breast cancer receiving adjuvant chemotherapy: 20-year results of the British Columbia randomized trial. J Nat Cancer Inst. 2005;97(2):116–26.
Poortmans PM, Collette L, Bartelink H, et al. The addition of a boost dose on the primary tumour bed after lumpectomy in breast conserving treatment for breast cancer. A summary of the results of EORTC 22881-10882 “boost versus no boost” trial. Cancer Radiother. 2008;12:565–70.
Bartelink H, Horiot JC, Poortmans P, et al. Recurrence rates after treatment of breast cancer with standard radiotherapy with or without additional radiation. N Engl J Med. 2001;345:1378–87.
Prescribing, Recording and Reporting Photon Beam Therapy (Supplement to ICRU Report 50). International Commission on Radiological Units and Measurement (ICRU). 1999;62:1-48.
Prescribing, Recording and Reporting Photon Beam Intensity Modulated Radiation Therapy. International Commission on Radiological Units and Measurement (ICRU). 2010;83:1-106.
Michalski A, Atyeo J, Cox J, et al. A dosimetric comparison of 3D-CRT, IMRT, and static tomotherapy with an SIB for large and small breast volumes. Med Dosim. 2014;39:163–8.
Mayo CS, Urie MM and Fitzgerald TJ. Hybrid IMRT plans-Concurrently treating conventional and IMRT beams for improved breast irradiation and reduced planning time. Int J Rad Onc Biol Phys. 2005;61(3):932-92.
Rudra S, Al-Hallaq HA, Feng C, et al. Effect of RTOG breast/chest wall guidelines on dose-volume histogram parameters. J Appl Clin Med Phys. 2014;15(2):127-37.
Lomax NJ and Scheib SG. Quantifying the degree of conformity in radiosurgery treatment planning. Int J Radiat Oncol Biol Phys. 2003; 55(5):1409-19.
Van't Riet A, Mak AC, Moerland MA, et al. A conformation number to quantify the degree of conformality in brachytherapy and external beam irradiation: application to the prostate. Int J Radiat Oncol. 1997;37:731-6.
Feuvret L, Noël G, Mazeron JJ, et al. Conformity index: a review. Int J Radiat Oncol Biol Phys. 2006;64(2): 333-42.
International Commission on Radiological Protection (ICRP), The Recommendations of the International Commission on Radiological Protection” Publication. Annals of the ICRP. 2007;103:37(2-4).
BEIR (Biological Effects of Ionizind Radiation) VII Phase 2 models, Health risks from exposure to low levels of ionizing radiation. National research council of the national academies, The National Academic press, Washington DC. 2006.
Schneider U. Modeling the Risk of Secondary Malignancies after Radiotherapy. Genes (Basel). 2011;1049–933.
Abo-Madyan Y, Aziz MH, Aly MM et al. Second cancer risk after 3D-CRT, IMRT and VMAT for breast cancer. Radiother Oncol. 2014;110: 471–6.
Preston DL, Ron E, Tokuoka S, et al. Solid Cancer Incidence in atomic bomb survivors: 1958–1998. Radiat Res. 2007;168:1–64.
This work is licensed under a Creative Commons Attribution 3.0 License.
International Journal of Cancer Therapy and Oncology (ISSN 2330-4049)
© International Journal of Cancer Therapy and Oncology (IJCTO)
To make sure that you can receive messages from us, please add the 'ijcto.org' domain to your e-mail 'safe list'. If you do not receive e-mail in your 'inbox', check your 'bulk mail' or 'junk mail' folders.