Spot scanning proton therapy minimizes neutron dose in the setting of radiation therapy administered during pregnancy.
This is a real case study to minimize the neutron dose equivalent (H) to a fetus using spot scanning proton beams with favorable beam energies and angles. Minimum neutron dose exposure to the fetus was achieved with iterative planning under the guidance of neutron H measurement. Two highly conformal treatment plans, each with three spot scanning beams, were planned to treat a 25-year-old pregnant female with aggressive recurrent chordoma of the base of skull who elected not to proceed with termination. Each plan was scheduled for delivery every other day for robust target coverage. Neutron H to the fetus was measured using a REM500 neutron survey meter placed at the fetus position of a patient simulating phantom. 4.1 and 44.1 μSv/fraction were measured for the two initial plans. A vertex beam with higher energy and the fetal position closer to its central axis was the cause for the plan that produced an order higher neutron H. Replacing the vertex beam with a lateral beam reduced neutron H to be comparable with the other plan. For a prescription of 70 Gy in 35 fractions, the total neutron H to the fetus was estimated to be 0.35 mSv based on final measurement in single fraction. In comparison, the passive scattering proton plan and photon plan had an estimation of 26 and 70 mSv, respectively, for this case. While radiation therapy in pregnant patients should be avoided if at all possible, our work demonstrated spot scanning beam limited the total neutron H to the fetus an order lower than the suggested 5 mSv regulation threshold. It is far superior than passive scattering beam and careful beam selection with lower energy and keeping fetus further away from beam axis are essential in minimizing the fetus neutron exposure.
The University of MD Anderson Cancer Center. xawang@mdanderson.org.
Xin
X
Wang
Falk
F
Poenisch
Narayan
N
Sahoo
Ronald X
RX
Zhu
MingFwu
M
Lii
Michael T
MT
Gillin
Jing
J
Li
David
D
Grosshans
D000328:Adult; D005260:Female; D005333:Fetus / Q000528:radiation effects*; D006801:Humans; D009381:Neoplasms, Radiation-Induced / Q000209:etiology / Q000517:prevention & control*; D009502:Neutrons / Q000009:adverse effects*; D058958:Organs at Risk / Q000528:radiation effects*; D011247:Pregnancy; D061766:Proton Therapy; D011835:Radiation Protection; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000009:adverse effects*; D012542:Scattering, Radiation; D012888:Skull Neoplasms / Q000532:radiotherapy*; D011522:Protons
D011522:Protons
Radiother Oncol. 1998 Sep;48(3):293-305
9925249
Acta Paediatr. 1999 Jul;88(7):693-702
10447122
Med Phys. 2006 Jul;33(7):2479-90
16898451
Int J Radiat Oncol Biol Phys. 2010 Apr;76(5):1563-70
20097484
Med Phys. 2009 Sep;36(9):4068-83
19810479
Med Phys. 2012 Jun;39(6):3484-92
22755728
Phys Med Biol. 2016 Jan 21;61(2):683-95
26716718
Phys Med Biol. 2008 Feb 7;53(3):693-717
18199910
Phys Med Biol. 2009 Aug 21;54(16):4907-26
19641238
Rep Pract Oncol Radiother. 2014 May 01;19(6):376-84
25337410
Med Phys. 2007 Sep;34(9):3449-56
17926946
Phys Med Biol. 2007 Aug 7;52(15):4481-96
17634645
Phys Med Biol. 2005 Sep 21;50(18):4337-53
16148397
Med Phys. 2010 Jun;37(6):2910-7
20632602
Clin Obstet Gynecol. 2011 Dec;54(4):591-601
22031249
Phys Med Biol. 2013 Nov 21;58(22):8235-51
24201018
Int J Radiat Oncol Biol Phys. 2002 May 1;53(1):244-51
12007965
Int J Radiat Oncol Biol Phys. 1983 Aug;9(8):1177-83
6409854
Int J Radiat Oncol Biol Phys. 2006 May 1;65(1):1-7
16618572
Med Phys. 2008 Jan;35(1):128-44
18293570
Phys Med Biol. 2008 Jan 7;53(1):187-201
18182696
Med Phys. 1995 Jan;22(1):63-82
7715571
J Appl Clin Med Phys. 2013 Mar 04;14(2):4139
23470942