Dose to craniofacial region through portal imaging of pediatric brain tumors

Abstract

The purpose of this study was to determine dose to the planning target volume (PTV) and organs at risk (OARs) from portal imaging (PI) of the craniofacial region in pediatric brain tumor patients treated with intensity‐modulated radiation therapy (IMRT). Twenty pediatric brain tumor patients were retrospectively studied. Each received portal imaging of treatment fields and orthogonal setup fields in the craniofacial region. The number of PI and monitor units used for PI were documented for each patient. Dose distributions and dose‐volume histograms were generated to quantify the maximum, minimum, and mean dose to the PTV, and the mean dose to OARs through PI acquisition. The doses resulting from PI are reported as percentage of prescribed dose. The average maximum, minimum, and mean doses to PTV from PI were 2.9±0.7%, 2.2±1.0%, and 2.5±0.7%, respectively. The mean dose to the OARs from PI were brainstem 2.8±1.1%, optic nerves/chiasm 2.6±0.9%, cochlea 2.6±0.9%, hypothalamus/pituitary 2.4±0.6%, temporal lobes 2.3±0.6%, thyroid 1.6±0.8%, and eyes 2.6±0.9%. The mean number of portal images and the mean number of PI monitor units per patient were 58.8 and 173.3, respectively. The dose from PI while treating pediatric brain tumors using IMRT is significant (2%–3% of the prescribed dose). This may result in exceeding the tolerance limit of many critical structures and lead to unwanted late complications and secondary malignancies. Dose contributions from PI should be considered in the final documented dose. Attempts must be made in PI practices to lower the imaging dose when feasible.PACS numbers: 87.55ne, 87.55Qr

The Advantages of Two Dimensional Techniques (2D) in Pituitary Adenoma Treatment

“…Therefore, the target volume should be covered by the 95% isodose; wherever, required and achievable, the minimum doses to critical organs without compromising the PTV coverage of at least 95% dose to 95% of PTV volume (8) .…”

The Advantages of Three Dimensional Techniques (3D) in Pituitary Adenoma Treatment

“…The size of sample population is about 300 patients of pituitary adenoma, because the planning target volume (PTV) to organs at risk (OAR) limits the ability of three-dimensional 3D application to deliver a prescribed dose to PTV while sparing OAR (7) . The target volume is covered by the 95% isodose; to obtain possible minimum doses to critical organs without compromising the PTV coverage of at least 95% dose to 95% of PTV volume (8) .The Conventional CRT is used to give the total dose of 45 to 50 Gy at 1.8 Gy per fractionation (9) . The irradiation of treatment area control remains a significant problem in management of pituitary tumour, but the dose distribution of 3D technique in pituitary tumour will eventually provide an answer to the problem in management of pituitary tumour with the ability to deliver a conformed radiation to the target volume.…”

Reducing excess radiation from portal imaging of pediatric brain tumors

“…Radiation therapy is an important treatment modality for pediatric brain tumors. However, concerns over long‐term side effects from pediatric cranial irradiation include secondary malignancies, deficits in neurocognitive and endocrine functioning, and psychosocial sequaelae (2–5) . Highly conformal radiation treatment plans distribute dose to the planning target volumes (PTVs) while sparing nearby organs at risk (OARs).…”