Differential hepatic avoidance radiation therapy: Proof of concept in hepatocellular carcinoma patients.
OBJECTIVE
To evaluate the feasibility of a novel planning concept that differentially redistributes RT dose away from functional liver regions as defined by (99m)Tc-sulphur colloid (SC) uptake on patient SPECT/CT images.


METHODS
Ten HCC patients with different Child-Turcotte-Pugh scores (A5-B9) underwent SC SPECT/CT scans in treatment position prior to RT that were registered to planning CT scans. Proton pencil beam scanning (PBS) therapy plans were optimized to deliver 37.5-60.0Gy (RBE) over 5-15 fractions using single field uniform dose technique robust to range and setup uncertainty. Photon volumetrically modulated arc therapy (VMAT) plans were optimized to the same prescribed dose and minimum target coverage. For both treatment modalities, differential hepatic avoidance RT (DHART) plans were generated to decrease dose to functional liver volumes (FLV) defined by a range of thresholds relative to maximum SC uptake (43-90%) in the tumor-subtracted liver. Radiation dose was redistributed away from regions of increased SC uptake in each FLV by linearly scaling mean dose objectives during PBS or VMAT optimization. DHART planning feasibility was assessed by a significantly negative Spearman's rank correlation (RS) between dose difference and SC uptake. Patient, tumor, and treatment planning characteristics were tested for association to DHART planning feasibility using non-parametric Kruskal-Wallis ANOVA.


RESULTS
Compared to conventional plans, DHART plans achieved a 3% FLV dose reduction for every 10% SC uptake increase. DHART planning was feasible in the majority of patients with 60% of patients having RS<-0.5 (p<0.01, range -1.0 to 0.2) and was particularly effective in 30% of patients (RS<-0.9). Mean dose to FLV was reduced by up to 20% in these patients. Only fractionation regimen was associated with DHART planning feasibility: 15 fraction courses were more feasible than 5-6 fraction courses (RS<-0.93 vs. RS>-0.60, p<0.02).


CONCLUSIONS
Differential avoidance of functional liver regions defined on sulphur colloid SPECT/CT is achievable with either photon VMAT or proton PBS therapy. Further investigation with phantom studies and in a larger cohort of patients may validate the utility of DHART planning for HCC radiotherapy.
University of Washington School of Medicine, Department of Radiation Oncology, Seattle, USA; University of Washington School of Medicine, Department of Radiology, Seattle, USA. Electronic address: srbowen@uw.edu.
Stephen R
SR
Bowen
Seattle Cancer Care Alliance Proton Therapy Center, USA.
Jatinder
J
Saini
University of Washington School of Medicine, Department of Radiation Oncology, Seattle, USA.
Tobias R
TR
Chapman
University of Washington School of Medicine, Department of Radiology, Seattle, USA.
Robert S
RS
Miyaoka
University of Washington School of Medicine, Department of Radiology, Seattle, USA.
Paul E
PE
Kinahan
University of Washington School of Medicine, Department of Radiation Oncology, Seattle, USA.
George A
GA
Sandison
Seattle Cancer Care Alliance Proton Therapy Center, USA.
Tony
T
Wong
University of Washington School of Medicine, Department of Radiology, Seattle, USA.
Hubert J
HJ
Vesselle
University of Washington School of Medicine, Department of Radiation Oncology, Seattle, USA.
Matthew J
MJ
Nyflot
University of Washington School of Medicine, Department of Radiation Oncology, Seattle, USA.
Smith
S
Apisarnthanarax
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006528:Carcinoma, Hepatocellular / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D017785:Photons / Q000627:therapeutic use; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods; D014057:Tomography, X-Ray Computed
Dose painting; Functional avoidance; HCC; PBS; SPECT; Sulphur colloid