Out-of-field organ doses from therapeutic irradiation during childhood: is there an excess risk for second cancer induction?

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1 Out-of-field organ doses from therapeutic irradiation during childhood: is there an excess risk for second cancer induction? Poster No.: C-0096 Congress: ECR 2012 Type: Scientific Paper Authors: M. Mazonakis, K. Kourinou, F. Lyraraki, J. Damilakis; Iraklion/GR Keywords: Radiation physics, Radioprotection / Radiation dose, Oncology, Dosimetry, Radiation effects, Radiation therapy / Oncology, Biological effects DOI: /ecr2012/C-0096 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 17

2 Purpose The advances in childhood cancer diagnosis and treatment over the last thirty years have resulted in an improved 5-year survival rate of 81 % compared to 58 % during the 1970s [1]. The respective 10-year survival in many European countries and USA is about 75 % [2]. Radiotherapy of pediatric patients with megavoltage photon beams may be employed for the tumor management [3]. However, this type of treatment exposes the organs at risk to ionizing radiation even if they are located outside the collimated beam [4,5]. The present study was conducted to measure the radiation dose to out-of-field organs and to estimate the associated risk for second cancer induction from radiotherapy of common pediatric malignancies. Page 2 of 17

3 Methods and Materials Radiotherapy techniques Two humanoid phantoms (Atom Ltd, Norfolk, Virginia, USA) constructed from tissue equivalent material were employed to simulate 5- and 10-year-old patients (Fig. 1 on page 5). The treatment planning procedure on these pediatric phantoms was performed by an experienced radiotherapist using a computerized planning system (XiO, CMS, St Louis, MO, USA) and an X-ray simulator (Simview NT, Siemens, Erlangen, Germany). Anteroposterior (AP) and posteronaterior (PA) field irradiations were used for treatment of Hodgkin's disease in the abdomen, neuroblastoma in the chest region and Wilms' tumor. Radiotherapy of brain tumors and leukemia in head region was performed with right lateral (RLAT) and left lateral (LLAT) portals. Spinal irradiation for leukemia was simulated with a PA field. The prescribed tumor doses for radiotherapy of brain malignancies, Hodgkin's disease, neuroblastoma and Wilms' tumor were 55 Gy, 24 Gy, 30 Gy and 20 Gy, respectively. The tumor dose for treatment of leukemia with cranial and spinal fields was 18 Gy and 12 Gy, respectively. For each phantom, the field dimensions were similar with those used for an average pediatric patient. Phantoms' exposures were made on an MLC linear accelerator (Primus, Siemens, Germany) producing 6 MV X-rays. Dose/risk estimation Lithium fluoride thermoluminescence dosemeters (TLD-100, Harshaw, OH, USA) were used for organ dose measurements. The calibration of the dosemeters was performed against a 0.3 cc thimble ionization chamber (M31003, PTW, Freiburg, Germany) using a 6 MV photon beam. The crystals were read using a Harshaw 3500 reader (Harshaw, Solon, OH, USA). The standard deviation of the sensitivity factors was below 4.0 % for each batch of TLDs. Scattered dose measurements were carried out for the following organs/tissues: thyroid, breast, lung, stomach, liver, prostate, bladder, ovary, colon and uterus. For each of the above organs, the BEIR-VII report has provided sex- and age-specific coefficients for estimating the lifetime attributable risk (LAR) of radiation induced cancer [6]. The organ locations within the pediatric phantoms were determined in the simulator of our department with the aid of a radiation oncologist. Two TLD crystals were placed at a position corresponding to the center of each organ-at-risk. The average reading of the two crystals was considered as the organ dose. Measurements were not performed when an organ was entirely or partly included within the applied treatment field. Organ dose reduction Page 3 of 17

4 The possibility of reducing the scattered dose to organs located at shallow depths, such as thyroid gland and breast, was investigated using the phantom simulating a 10-year-old patient. Two different 10-mm-thick lead shields were directly placed over the aforementioned organs during treatment of Hodgkin's disease, neuroblastoma and Wilms' tumor with AP fields. The above shielding thickness had a tolerable weight and it could be easily adapted to match with the anatomic region of interest. Organ protection from lateral exposures used for head radiotherapy was achieved with a 6-cm-thick cerrobend blocks placed over the treatment couch [7]. These couch blocks were placed 2 cm in front of the neck and thoracic region to shield the thyroid and breast, respectively. Page 4 of 17

5 Images for this section: Fig. 1: Humanoid phantoms simulating 5- and 10-year old patients. Atom Ltd, Norfolk, Va, USA Page 5 of 17

6 Results Simulated measurements on two pediatric phantoms (Fig. 1 on page 7) revealed that the scattered dose to organs is dependent upon the primary irradiation site and beam orientation. For a 5-year-old patient, organ dose varied from 0.02 % to 4.75 % (Fig. 2 on page 7). The corresponding dose variation at the age of 10 years was % (Fig. 3 on page 8). The use of a 10-mm-thick lead shield during AP field irradiations reduced the thyroid dose from 29.3 % to 35.1 %. The respective breast dose reduction was %. The appropriate positioning of a couch block in lateral field exposures reduced the thyroid and breast doses up to 41.4 % and 51.0 %, respectively. The total out-of-field organ doses resulting from the entire radiotherapy courses at the age of 5 years were mgy (Fig. 4 on page 8). The corresponding doses at the advanced patient age were mgy (Fig. 5 on page 9). For a 5-year-old male patient, the LAR varied from % to 1.3 % (Fig. 6 on page 10), whereas the risk for female patients increased to % (Fig. 7 on page 11). The LAR range for 10-year-old male and female patients was % (Fig. 8 on page 12) and % (Fig. 9 on page 13), respectively. Breast cancer was the most probable detrimental effect for female patients following irradiation of Hodgkin's disease in the abdominal region during childhood. The corresponding effect for male pediatric patients was bladder cancer after radiotherapy of Wilms' tumor. Page 6 of 17

7 Images for this section: Fig. 1: Humanoid phantoms simulating 5- and 10-year old patients. Atom Ltd, Norfolk, Va, USA Page 7 of 17

8 Fig. 2: Out-of-field organ doses, expressed as a % of the given tumor dose, for a 5-yearold patient undergoing radiotherapy. M. Mazonakis; Department of Medical Physics, University of Crete, Greece Fig. 3: Out-of-field organ doses, expressed as a % of the given tumor dose, for a 10year-old patient undergoing radiotherapy. M.Mazonakis; Department of Medical Physics, University of Crete, Greece Page 8 of 17

9 Fig. 4: Total out-of-field organ doses for a 5-year-old patient undergoing radiotherapy. M. Mazonakis; Department of Medical Physics, University of Crete, Greece Page 9 of 17

10 Fig. 5: Total out-of-field organ doses for a 10-year-old patient undergoing radiotherapy. M.Mazonakis; Department of Medical Physics, University of Crete, Greece Page 10 of 17

11 Fig. 6: LAR values for a 5-year-old male patient undergoing radiotherapy. M.Mazonakis; Department of Medical Physics, University of Crete, Greece Page 11 of 17

12 Fig. 7: LAR values for a 5-year-old female patient undergoing radiotherapy. M. Mazonakis; Department of Medical Physics, University of Crete, Greece Page 12 of 17

13 Fig. 8: LAR values for a 10-year-old male patient undergoing radiotherapy. M. Mazonakis; Department of Medical Physics, University of Crete, Greece Page 13 of 17

14 Fig. 9: LAR values for a 10-year-old female patient undergoing radiotherapy. M.Mazonakis; Department of Medical Physics, University of Crete, Greece Page 14 of 17

15 Conclusion The organ exposure to scattered radiation attributable to radiotherapy of pediatric malignant diseases may be strongly associated with the development of subsequent neoplasms. The magnitude of the second cancer risk varies considerably by the organ predilection to cancer as expressed by the risk coefficients introduced by the BEIR-VII report [6], the scattered dose received by the organ of interest and the patient's age at the time of treatment. The current study provides analytical tabular and graphical data sets that enable the direct estimations of the out-of-field organ doses resulting from radiotherapy during childhood. The above dose estimations are required to quantify the risk for developing new malignancies. Accurate risk knowledge may be of value for radiotherapists and clinicians to determine the appropriate follow-up procedures for childhood cancer survivors. Page 15 of 17

16 References Jemal A (2010) Cancer statistics, CA Cancer J Clin 60: Brenner H, Steliarova-Foucher E, Arndt V (2007) Up-to-date monitoring of childhood cancer long term survival in Europe: methodology and application to all forms of cancer combined. Ann Oncol 18: Barrett A, Dobbs J, Morris S, Rocques T (2009) Practical radiotherapy th planning, 4 edition. Hodder Arnold, London Mazonakis M, Zacharopoulou F, Varveris H, Damilakis J (2008) Peripheral dose measurements for 6 and 18 MV photon beams on a linear accelerator with multileaf collimator. Med Phys 35: Chofor N, Harder D, Ruhmann A, Wilborn KC, Wiezorek T, Poppe B (2010) Experimental study on photon-beam peripheral doses, their components and some possibilities for their reduction. Phys Med Biol 21: BEIR-VII report (2006) Health risks from exposure to low level of ionizing radiation. National Academy Press, Washington DC Mazonakis M, Tzedakis A, Damilakis J, Varveris H, Kachris S, Gourtsoyiannis N (2006) Scattered dose to thyroid from prophylactic cranial irradiation during childhood: A Monte Carlo study. Phys Med Biol 51:N Page 16 of 17

17 Personal Information Michalis Mazonakis Assistant Professor of Medical Physics Department of Medical Physics Faculty of Medicine University of Crete Iraklion Crete Greece Page 17 of 17