Standardized treatment planning methodology for passively scattered proton craniospinal irradiation

Abstract

BackgroundAs the number of proton therapy centers increases, so does the need for studies which compare proton treatments between institutions and with photon therapy. However, results of such studies are highly dependent on target volume definition and treatment planning techniques. Thus, standardized methods of treatment planning are needed, particularly for proton treatment planning, in which special consideration is paid to the depth and sharp distal fall-off of the proton distribution. This study presents and evaluates a standardized method of proton treatment planning for craniospinal irradiation (CSI).MethodsWe applied our institution’s planning methodology for proton CSI, at the time of the study, to an anatomically diverse population of 18 pediatric patients. We evaluated our dosimetric results for the population as a whole and for the two subgroups having two different age-specific target volumes using the minimum, maximum, and mean dose values in 10 organs (i.e., the spinal cord, brain, eyes, lenses, esophagus, lungs, kidneys, thyroid, heart, and liver). We also report isodose distributions and dose-volume histograms (DVH) for 2 representative patients. Additionally we report population-averaged DVHs for various organs.ResultsThe planning methodology here describes various techniques used to achieve normal tissue sparing. In particular, we found pronounced dose reductions in three radiosensitive organs (i.e., eyes, esophagus, and thyroid) which were identified for optimization. Mean doses to the thyroid, eyes, and esophagus were 0.2%, 69% and 0.2%, respectively, of the prescribed dose. In four organs not specifically identified for optimization (i.e., lungs, liver, kidneys, and heart) we found that organs lateral to the treatment field (lungs and kidneys) received relatively low mean doses (less than 8% of the prescribed dose), whereas the heart and liver, organs distal to the treatment field, received less than 1% of the prescribed dose.ConclusionsThis study described and evaluated a standardized method for proton treatment planning for CSI. Overall, the standardized planning methodology yielded consistently high quality treatment plans and perhaps most importantly, it did so for an anatomically diverse patient population.

A comparative study on the risks of radiogenic second cancers and cardiac mortality in a set of pediatric medulloblastoma patients treated with photon or proton craniospinal irradiation

“…This volume included the brain, the spinal canal, and the entire vertebral body for patients younger than 15 years (to prevent bone growth deformity due to non-uniform dose distribution in the vertebral body), and only the brain and spinal canal for patients 15 years old or older (with a 2–3 mm margin anteriorly). Typical target volumes for representative patients were shown in previous reports [16,17]. The proton treatment plans included right and left posterior oblique cranial fields and 1–3 posterior-anterior spinal fields, depending on the length of the patient's spinal axis.…”

“…The treatment plans were designed to deliver 23.4 Gy (relative biological effectiveness [RBE]) (proton beam RBE of 1.1 was used here [18]) for proton CSI or 23.4 Gy for photon CSI to the age specific target volume at 1.8 Gy/fraction. Additional details about the proton and photon radiation therapy plans and typical isodose distributions for representative patients can be found in previous reports [16,17]. …”

Outcomes and Acute Toxicities of Proton Therapy for Pediatric Atypical Teratoid/Rhabdoid Tumor of the Central Nervous System

“…For craniospinal irradiation (CSI), the brain was treated with opposed oblique fields and the spine was treated with two posterior-anterior spinal fields [23]. Junctions between fields were 1 cm apart and were shifted every 4 – 5 fractions.…”

“…Clinical tumor volume (CTV) was a 1 cm anatomically-constrained volumetric expansion of the GTV. To ensure coverage of the CTV, fields were designed to encompass the CTV plus uncertainty margins [23]. Distal and proximal margins included factors to account for uncertainties in the CT number and stopping power as well as a range uncertainty of 0.3 cm.…”

Comparison of risk of radiogenic second cancer following photon and proton craniospinal irradiation for a pediatric medulloblastoma patient

“…Both photon and proton treatment planning were carried out according to the standard of care at our institution. Details treatment plans are briefly described in the following paragraphs and a more thorough description can be found in the literature (Giebeler et al , 2012; Howell et al , 2012). The final plans for this patient were approved by one of us (A Mahajan), a board certified radiation oncologist who specializes in pediatric radiation oncology.…”