Dose Escalated Liver Stereotactic Body Radiation Therapy at the Mean Respiratory Position

Abstract

Purpose The dosimetric impact of dose-probability based PTV margins for liver cancer patients receiving SBRT was compared to standard PTV based on the internal target volume (ITV). Plan robustness was evaluated by accumulating the treatment dose to ensure delivery of the intended plan. Methods and Materials Twenty patients planned on exhale CT for 27–50 Gy in 6 fractions using an ITV-based PTV and treated free-breathing were retrospectively evaluated. Iso-toxic, dose-escalated plans were created on mid-position CT, representing the mean breathing position, using a dose-probability PTV. The delivered doses were accumulated using biomechanical deformable registration of the daily cone-beam CT based on liver targeting at the exhale or mean breathing position, for the exhale and mid-position CT plans respectively. Results The dose-probability PTVs were on average 38% smaller than the ITV-based PTV enabling an average±standard deviation increase in the planned dose to 95% of the PTV of 4.0±2.8 Gy (9±5%) on the mid-position CT (p<0.01). For both plans, the delivered minimum GTV doses were greater than the planned nominal prescribed dose in all 20 patients and greater than the planned dose to 95% of the PTV in 18 (90%) patients. Nine patients (45%) had one or more GTVs with a delivered minimum dose more than 5 Gy higher with the mid-position CT plan using dose-probability PTV, compared to the delivered dose with the exhale CT plan using ITV-based PTV. Conclusions For iso-toxic liver SBRT planned and delivered at the mean respiratory, reduced dose-probability PTV enables a mean escalation of 4 Gy (9%) in 6 fractions over ITV-based PTV. This may potentially improve local control without increasing the risk of tumor under-dosing.

Dosimetric Advantages of Midventilation Compared With Internal Target Volume for Radiation Therapy of Pancreatic Cancer

“…These results of sufficient target coverage and a significant reduction of the PTV are in agreement with the use of a midV approach for the liver (15).…”

“…However, the penumbra in the abdominal region is known to be narrower (13,14), which could partly depreciate the added value of using the midV concept instead of an ITV. It has been shown that for liver tumors, the midV approach ensured sufficient target coverage, and a mean PTV reduction of 38% was reported (15). However, no information on dose to the surrounding OARs was provided.…”

Individualized 4-Dimensional Computed Tomography Proton Treatment for Pancreatic Tumors

“…Our results show that for patients with less than 8 mm of anterior abdominal motion, the T0, T50, or average phases of the 4D CT produced acceptable target coverage over the 10 phases of the 4D CT (2,11). This data provides initial evidence that using planning techniques for bolus design, smearing parameters, blocks, and modulation wheel selection as described by Moyers et al (10) are sufficient to accommodate for WPL changes due to respiration for tumors of the pancreas.…”

Individualized 4-dimensional computed tomography proton treatment for pancreatic tumors

“…Our results show that for patients with less than 8 mm of anterior abdominal motion, the T0, T50, or average phases of the 4D CT produced acceptable target coverage over the 10 phases of the 4D CT (2,11). This data provides initial evidence that using planning techniques for bolus design, smearing parameters, blocks, and modulation wheel selection as described by Moyers et al (10) are sufficient to accommodate for WPL changes due to respiration for tumors of the pancreas.…”