PMID- 24007135
OWN - NLM
STAT- MEDLINE
DCOM- 20140321
LR  - 20211021
IS  - 2473-4209 (Electronic)
IS  - 0094-2405 (Print)
IS  - 0094-2405 (Linking)
VI  - 40
IP  - 9
DP  - 2013 Sep
TI  - Simultaneous optimization of dose distributions and fractionation schemes in 
      particle radiotherapy.
PG  - 091702
LID - 10.1118/1.4816658 [doi]
LID - 091702
AB  - PURPOSE: The paper considers the fractionation problem in intensity modulated 
      proton therapy (IMPT). Conventionally, IMPT fields are optimized independently of 
      the fractionation scheme. In this work, we discuss the simultaneous optimization 
      of fractionation scheme and pencil beam intensities. METHODS: This is performed 
      by allowing for distinct pencil beam intensities in each fraction, which are 
      optimized using objective and constraint functions based on biologically 
      equivalent dose (BED). The paper presents a model that mimics an IMPT treatment 
      with a single incident beam direction for which the optimal fractionation scheme 
      can be determined despite the nonconvexity of the BED-based treatment planning 
      problem. RESULTS: For this model, it is shown that a small alpha∕beta ratio in the tumor 
      gives rise to a hypofractionated treatment, whereas a large alpha∕beta ratio gives rise 
      to hyperfractionation. It is further demonstrated that, for intermediate alpha∕beta 
      ratios in the tumor, a nonuniform fractionation scheme emerges, in which it is 
      optimal to deliver different dose distributions in subsequent fractions. The 
      intuitive explanation for this phenomenon is as follows: By varying the dose 
      distribution in the tumor between fractions, the same total BED can be achieved 
      with a lower physical dose. If it is possible to achieve this dose variation in 
      the tumor without varying the dose in the normal tissue (which would have an 
      adverse effect), the reduction in physical dose may lead to a net reduction of 
      the normal tissue BED. For proton therapy, this is indeed possible to some degree 
      because the entrance dose is mostly independent of the range of the proton pencil 
      beam. CONCLUSIONS: The paper provides conceptual insight into the interdependence 
      of optimal fractionation schemes and the spatial optimization of dose 
      distributions. It demonstrates the emergence of nonuniform fractionation schemes 
      that arise from the standard BED model when IMPT fields and fractionation scheme 
      are optimized simultaneously. Although the projected benefits are likely to be 
      small, the approach may give rise to an improved therapeutic ratio for tumors 
      treated with stereotactic techniques to high doses per fraction.
FAU - Unkelbach, Jan
AU  - Unkelbach J
AD  - Department of Radiation Oncology, Massachusetts General Hospital and Harvard 
      Medical School, Boston, Massachusetts 02114, USA. junkelbach@partners.org
FAU - Zeng, Chuan
AU  - Zeng C
FAU - Engelsman, Martijn
AU  - Engelsman M
LA  - eng
GR  - C06 CA059267/CA/NCI NIH HHS/United States
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
PL  - United States
TA  - Med Phys
JT  - Medical physics
JID - 0425746
SB  - IM
MH  - *Dose Fractionation, Radiation
MH  - Humans
MH  - Neoplasms/radiotherapy
MH  - Proton Therapy/*methods
MH  - Radiotherapy Planning, Computer-Assisted
MH  - Radiotherapy, Intensity-Modulated/*methods
MH  - Time Factors
PMC - PMC3751965
EDAT- 2013/09/07 06:00
MHDA- 2014/03/22 06:00
PMCR- 2014/09/01
CRDT- 2013/09/07 06:00
PHST- 2013/09/07 06:00 [entrez]
PHST- 2013/09/07 06:00 [pubmed]
PHST- 2014/03/22 06:00 [medline]
PHST- 2014/09/01 00:00 [pmc-release]
AID - 008309MPH [pii]
AID - 10.1118/1.4816658 [doi]
PST - ppublish
SO  - Med Phys. 2013 Sep;40(9):091702. doi: 10.1118/1.4816658.