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Dosimetric Evaluation of Static and Rotating Gamma Ray Systems for Intracranial SRS/SRT

Q Jiang 1*, A Eldib2, L Chen3, D wu4, B Wang5, S Li6, C Miyamoto7, J Li8, B Nguyen9, C Ma10, (1) The First Affiliated Hospital of Chongqing Medical University, Chongqing, China, (2) Fox Chase Cancer Center, Philadelphia, PA (3) Fox Chase Cancer Center, Philadelphia, PA (4) The People`s Hospital of Guangxi Zhuang Autonomous Region ,Guangxi, China (5) Temple University Hospital, Philadelphia, PA, (6) Temple University Hospital, Philadelphia, PA (7) Temple University, Philadelphia,(8) ,Huntingdon Valley, PA, (9) Prowess Inc., Concord, CA, (10) Fox Chase Cancer Center, Philadelphia, PA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Both static and rotating Gamma-ray delivery systems have been developed and used clinically for intracranial SRS/SRT. This work investigated the dosimetric parameters and treatment plan quality for both delivery systems.

Methods: The GammaKnife(GK) system uses 192 static cobalt-60 sources to deliver noncoplanar beams while the new rotating Gamma-ray system(RGS) uses 16 cobalt-60 sources to deliver non-coplanar arcs. The latter also allows the treatment head to swing 30° in the superior direction for flexible non-coplanar arc delivery and critical-structure avoidance. This work investigated 12 previous GammaKnife cases. The Prowess TPS was used to generate 3 RGS plans for each case including manual-forward(MF), manual-forward with swing angle(MS) and inverse-automated optimization(IAO). The dosimetry parameters for both delivery systems were evaluated including target coverage, conform index(CI), gradient index(GI) and beam-on time

Results: The lesion volume varied from 0.15cm3 to 15.46cm3. The mean target coverage was 99.8%±0.19, 99.2%±0.85, 99.13±0.84, 98.8±1.45 for MF, MS, IAO, GK, respectively (p>0.05). The median CI was 0.47, 0.51, 0.48, 0.42 for MF, MS, IAO, GK, respectively (p= 0.98). The difference between mean target dose, minimum and maximum dose was statistically insignificant for these plans. The median GI was 3.52, 3.29, 3.37, 2.73 for MF, MS, IAO, GK, respectively. The median number of shots to achieve an acceptable plan was 3, 6, 6, 5 and the mean beam-on time to deliver the plan was 25.5±12.8, 24.3±11.8, 22.2±9.2, 36.9±13.4 minutes for MF, MS, IAO, GK, respectively. Four cases had optical nerve and brain stem involvement but showed no significant dose difference in the critical structures.

Conclusion: Both delivery systems could provide clinically acceptable dose distributions for intracranial SRS/SRT with small differences in target coverage, CI, GI and treatment time. Prowess provided flexible planning options for the new RGS to achieve superior target dose coverage and critical structure sparing.


Stereotactic Radiosurgery, Dosimetry, Gamma Knife


TH- External Beam- Photons: intracranial stereotactic/SBRT

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