Dosimetric and Radiobiological Evaluation of Hybrid Inverse Planning and Optimization for Cervical Cancer Brachytherapy.
OBJECTIVE
To compare manual graphical optimization (GrO) with hybrid inverse planning optimization (HIPO) of cervical cancer brachytherapy treatment plans using physical and radiobiological tools.


METHODS
Ten patients suffering from cervical cancer, treated with pulsed brachytherapy using GrO plans, were included in the study. For each patient, four different HIPO class solutions with different dose objectives to the target and constraints to the organs at risk (OAR) produced four optimized plans, that were each compared to the corresponding GrO plan. Class solution in HIPO is a set of parameters consisting of dose constraints and penalty weights, which are used for optimization. The comparison was based on the following dosimetric parameters: conformity index (COIN), minimum dose received by 98% and 90% of the high-risk clinical target volume (represented by D98 and D90, respectively), and the minimum dose imparted to 2 cm(3) (D2cm(3)) of the most exposed OAR i.e. bladder, sigmoid colon or rectum. The HIPO class solution which produced plans with overall better dosimetric parameters was selected and its plans were compared with manual GrO plans from a radiobiological viewpoint based on the calculated complication-free tumour control probability, P+.


RESULTS
The average COIN for the GrO and the selected HIPO plans were 0.22 and 0.30, respectively. The median COIN of the GrO and the HIPO plans were not statistically different (p>0.05, Wilcoxon test). The relative percentage difference of the averaged P(+) values between the HIPO and GrO plans evaluated together with the external beam radiation therapy plans was 0.01%, 0.37% and 0.98% for the bladder, sigmoid colon and rectum, respectively. The lowest P+ value for all the plans was 98.44% for sigmoid colon.


CONCLUSIONS
HIPO presented comparable results in relation to manual planning with respect to dosimetric and radiobiological parameters.
Medical Radiation Physics, Department of Physics, Stockholm University, Stockholm, Sweden Department of Physics, Eduardo Mondlane University, Maputo, Mozambique Lucilio.Matias@ki.se.
Lucílio Dos S
Ldos S
Matias
Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden.
Tomas
T
Palmqvist
Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden.
Jeanette
J
Wolke
Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden.
Josef
J
Nilsson
Department of Gynecologic Oncology, Karolinska University Hospital, Stockholm, Sweden.
Catharina
C
Beskow
Department of Physics, Eduardo Mondlane University, Maputo, Mozambique.
Alexandre M
AM
Maphossa
Medical Radiation Physics, Department of Physics, Stockholm University, Stockholm, Sweden.
Iuliana
I
Toma-Dasu
D000465:Algorithms; D001918:Brachytherapy / Q000592:standards*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D058958:Organs at Risk; D011379:Prognosis; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000592:standards*; D002583:Uterine Cervical Neoplasms / Q000188:drug therapy* / Q000473:pathology
HIPO; Pulsed brachytherapy; optimization; radiobiology; treatment planning