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HyperArc Planning for Fractionated Stereotactic Radiotherapy of Pituitary Tumors

A Ballesio1*, R Pino2, H Wang3, B Teh4, (1) Houston Methodist Hospital, Houston, TX, (2) Methodist Hospital, Houston, TX, (3) Methodist Hospital, Houston, TX, (4) Houston Methodist Hospital, Houston,

Presentations

PO-BPC-Virtual-16 (Saturday, 4/17/2021)   [Eastern Time (GMT-4)]

Purpose: 30-fraction fractionated stereotactic radiotherapy is the standard of care in our clinic for pituitary tumors due to normal tissue repair as well as for the safer management of treatment setup errors compared with single-fraction stereotactic radiosurgery (SRS). However, the conformal dose provided by SRS can prove helpful in avoiding the several organs at risk near the pituitary. Planning these cases with HyperArc (HA) also provides short delivery times and avoids potential collision issues. Our goal is to combine these benefits by planning pituitary cases with HyperArc while still delivering multiple fractions.

Methods: Five pituitary patients treated with 30-fraction VMAT were replanned using HyperArc on Eclipse v15.6. The optimization objectives were unchanged, but the SRS NTO optimization objective was used. Conformity index, Paddick conformity index, gradient index, and heterogeneity index are evaluated and compared.

Results: The average conformity index (CI) is 0.984±0.019 for HA and 1.044±0.029 for VMAT. Average Paddick conformity index (PCI) is 0.871±0.011 for HA and 0.838±0.029 for VMAT. Average gradient index (GI) is 2.824±0.216 for HA and 3.739±0.326 for VMAT. Average heterogeneity index (HI) is 1.285±0.103 for HA and 1.216±0.078 for VMAT. Two-tail t-test shows that the differences in the averages are statistically significant (a=0.05) for CI and GI, but not for PCI and HI.

Conclusion: On average, PCIs and HIs are comparable between VMAT and HA plans. CI and GI improvements indicate potential superior sparing of organs at risk. HI is somewhat larger for HA than VMAT plans, however the maximum doses are still reasonable. IMRT QA using portal dosimetry confirmed there are no significant delivery issues with the HyperArc plans.

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