IMRT planning and delivery incorporating daily dose from mega‐voltage cone‐beam computed tomography imaging

Abstract

The technology of online mega-voltage cone-beam (CB) computed tomography (MV-CBCT) imaging is currently used in many institutions to generate a 3D anatomical dataset of a patient in treatment position. It utilizes an accelerator therapy beam, delivered with 200 degrees gantry rotation, and captured by an electronic portal imager to account for organ motion and setup variations. Although the patient dose exposure from a single volumetric MV-CBCT imaging procedure is comparable to that from standard double-exposure orthogonal portal images, daily image localization procedures can result in a significant dose increase to healthy tissue. A technique to incorporate the daily dose, from a MV-CBCT imaging procedure, in the IMRT treatment planning optimization process was developed. A composite IMRT plan incorporating the total dose from the CB was optimized with the objective of ensuring uniform target coverage while sparing the surrounding normal tissue. One head and neck cancer patient and four prostate cancer patients were planned and treated using this technique. Dosimetric results from the prostate IMRT plans optimized with or without CB showed similar target coverage and comparable sparing of bladder and rectum volumes. Average mean doses were higher by 1.6 +/- 1.0 Gy for the bladder and comparable for the rectum (-0.3 +/- 1.4 Gy). In addition, an average mean dose increase of 1.9 +/- 0.8 Gy in the femoral heads and 1.7 +/- 0.6 Gy in irradiated tissue was observed. However, the V65 and V70 values for bladder and rectum were lower by 2.3 +/- 1.5% and 2.4 +/- 2.1% indicating better volume sparing at high doses with the optimized plans incorporating CB. For the head and neck case, identical target coverage was achieved, while a comparable sparing of the brain stem, optic chiasm, and optic nerves was observed. The technique of optimized planning incorporating doses from daily online MV-CBCT procedures provides an alternative method for imaging IMRT patients. It allows for daily treatment modifications where other volumetric tomographic imaging techniques may not be feasible and/or available and where accurate patient localization with a high degree of precision is required.

Investigation into the radiobiological consequences of pre-treatment verification imaging with megavoltage X-rays in radiotherapy

“…Since the dose received from pre-treatment verification imaging can be considerable, 3,8 it has been suggested that this dose should be accounted for at the treatment planning stage. 3,29,30 Although this allows for the correct calculation of normal tissue and tumour dose, imaging dose incorporation has the potential to impact the treatment efficacy in an adverse manner. This is because in the time between pre-treatment imaging and delivery of the remaining treatment dose, sublethal damage repair may occur, 31 which may lead to a reduced amount of sublethal damage that can be subsequently compounded to lethal damage by the treatment dose.…”

Efficacy of Daily Cone-Beam Computed Tomography as Part of a Rescan Protocol for Large Offset to Reduce the Inter-Fractional Motion of the Prostate

“…For example, Ding et al reported the detailed information concerning the additional imaging doses to patients' radiosensitive organs from a KV CBCT scan; for an abdominal scan, the mean doses were 3 and 7 cGy to the prostate and 7 and 17 cGy to the femoral heads for a large adult patient and a 31-month-old pediatric patient, respectively [17]. Recently, a method to incorporate the daily megavoltage CBCT dose into the IMRT planning process was developed and implemented in the treatment of prostate cancer patients [18]. This technique has the potential to greatly improve the accuracy of treatment delivery, while maintaining target coverage and sparing the organs at risk.…”

Dosimetric integration of daily mega-voltage cone-beam CT for image-guided intensity-modulated radiotherapy

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Sophisticated radiotherapy techniques like fractionated stereotactic radiotherapy (FSRT) or intensity-modulated radiotherapy (IMRT) allow for high dose deposition to the target volume, while sparing adjacent normal tissue by steep dose gradients [5,11,12,15,16,19,21,22,23]. Depending on the chosen immobilization device, variations in daily treatment set-up regarding patient and organ movement have been reported [1,3,8].

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“…The purpose of our study was to establish a practical method to handle the additional patient dose of MV-CBCT for IGRT/IMRT. Only a few reports on patient dose considerations for routine short scan MV-CBCT imaging in the head and neck and pelvis regions can be found in the literature [11,13]. However, There are areas with lower doses and areas with higher doses.…”