gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Estimation of secondary cancer risk induced by itensity modulated radiotherapy and passive proton beam therapy

Meeting Abstract

  • S. H. Ahn - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • J. Kim - Samsung Medical Center, Seoul, Korea, Republic of Korea
  • M. Cheong - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • D. Shin - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • S. Y. Park - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • S. Lee - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • M. Yoon - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • K. H. Shin - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • K. H. Cho - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog001

DOI: 10.3205/09ptcog001, URN: urn:nbn:de:0183-09ptcog0017

Published: September 24, 2009

© 2009 Ahn et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.


Outline

Text

Background: Protons are used in radiation therapy due to their advantageous physical properties which includes a near-zero exit or distal dose just beyond the target volume, resulting in reduced proton doses to normal tissue. In general, tumors in cancer patients undergoing radiation treatment are exposed to high prescription doses, whereas the surrounding normal tissues are exposed to intermediate doses and the rest of the body is exposed to low doses. In contrast, while proton therapy may result in reduced exposure of adjacent normal tissue to intermediate doses, it may lead to an increase in low doses to the rest of the body, due to the number of neutrons produced by the scattering components of passively scattered proton beams, which may exceed that produced by conventional photon treatment. Thus, proton therapy may have a higher risk of radiation-induced secondary cancers than photon therapy, diminishing the superiority of proton therapy. In this study, Secondary cancer risk induced by intensity-modulated radiotherapy and passive proton beam therapy was estimated and compared for prostate and head & neck patients.

Method and materials: The concept of an organ equivalent dose (OED) for radiation-induced cancer was applied to dose distributions of patients to estimate organ specific radiation-induced cancer risk. 3D Conformal Radiotherapy, IMRT with 6 MV photons and proton beam therapy were planned for 5 prostate patients, and IMRT and proton therapy were planed for 5 head & neck cancer patients. The treatment beams were delivered to humanoid phantom and secondary doses during irradiation were measured at various points from 20 cm to 60 cm apart from the beam isocenter on humanoid phantom using ion chamber and CR-39 detectors for X-ray radiation therapy and passive proton beam therapy, respectively.

Results: The average secondary doses for prostate cancer patients in passive proton beam therapy, which is neutron dose equivalent to the proton absorbed dose (H(10)/D) measured from 20 to 60 cm from the isocenter, ranged from 0.4 mSv/Gy to 0.1 mSv/Gy. The average secondary doses in IMRT for prostate patients, ranged between 3 mSv/Gy and 1 mSv/Gy whose values are approximately order of magnitude higher than the proton therapy. Although the average secondary doses for head & neck cancer patients in proton therapy were less than the average secondary doses in IMRT, the difference was not significant as the prostate cases.

Conclusion: By a comparison between passive proton beam therapy and IMRT for diseases of prostate and head & neck, it was shown that the estimated secondary cancer risk using scattering mode in proton beam therapy is either significantly lower than the cases in IMRT treatment or, at least, does not exceed the risk induced by conventional IMRT treatment.