Comprehensive Dosimetric Evaluation of a Biology-Guided Radiotherapy Machine in Treatment Plans for Brain, Lung, Head and Neck, Esophagus, and Prostate Malignancies

Abstract

A new biology-guided radiotherapy (BgRT) delivery machine is currently under development. It combines a compact 6 MV linear accelerator and a binary multileaf collimator with PET, kVCT, and MV imaging systems on the same ring gantry that rotates continuously at 60 rotations per minute while the patient is translated through the bore with small increments. We aimed to perform inter-comparison of treatment plans for typical clinical disease sites between the new BgRT machine and existing IMRT delivery techniques. To ensure objective comparison, biology guidance was not assumed in planning for the new system and the same planning margins were used for each case with all the delivery techniques. We retrospectively retrieved one clinical external-beam radiotherapy treatment plan for each of the five disease sites: intracranial lesion for stereotactic radiosurgery (SRS), early-stage lung lesion for stereotactic body radiotherapy (SBRT), head and neck, esophagus, and prostate with seminal vesicle and pelvic lymph node treatments. Both a helical tomotherapy (HT) plan (using a 1-cm or 2-cm jaw size) and a volumetric modulated arc therapy (VMAT) plan (using 0.5-cm MLC or 0.25-cm MLC leaves) were generated for each clinical case. A treatment plan (the prototype plan) for the new system was generated for each case using either a 1-cm jaw size for the intracranial SRS and lung SBRT plans, and a 2-cm jaw size for the other sites. Dosimetric constraints in national radiotherapy treatment protocols (RTOG-0813, NRG-HN001, RTOG-1010, and RTOG-0534) were used to facilitate dosimetric comparison of treatments plans. The prototype plans met all the dosimetric constraints in all disease sites. The relative strengths with each delivery technique differ with respect to the disease site. With the head & neck case, while the VMAT and HT plans shows similar normal organ dose, the prototype plan achieved comparable PTV dose coverage and lower dose to most critical organs including a 40% reduction in parotid mean dose compared to the HT and the VMAT plans. With the intracranial SRS case, the VMAT plan achieved slightly better dose conformity and faster dose drop-off compared to the HT and prototype plans, while all the plans achieved comparable dose to the normal brain and other organs-at-risk. With the lung SBRT case, both the VMAT and the prototype plans achieve similar dose to the normal lung volume and other organs. In both the prostate and esophagus cases, mixed results were observed with one technique achieving better sparing to certain organs. While all the delivery technique met given dosimetric constraints in most disease sites, the prototype system was shown to achieve better normal organ sparing with the head & neck site, while the VMAT technique with smaller MLC leaves was more suitable for intracranial SRS. Actual dosimetric measurements will follow to verify dose delivery accuracy with the new BgRT machine.