PTCOG Gastrointestinal Subcommittee Lower Gastrointestinal Tract Malignancies Consensus Statement.

Purpose: Radiotherapy delivery in the definitive management of lower gastrointestinal (LGI) tract malignancies is associated with substantial risk of acute and late gastrointestinal (GI), genitourinary, dermatologic, and hematologic toxicities. Advanced radiation therapy techniques such as proton beam therapy (PBT) offer optimal dosimetric sparing of critical organs at risk, achieving a more favorable therapeutic ratio compared with photon therapy. Materials and Methods: The international Particle Therapy Cooperative Group GI Subcommittee conducted a systematic literature review, from which consensus recommendations were developed on the application of PBT for LGI malignancies. Results: Eleven recommendations on clinical indications for which PBT should be considered are presented with supporting literature, and each recommendation was assessed for level of evidence and strength of recommendation. Detailed technical guidelines pertaining to simulation, treatment planning and delivery, and image guidance are also provided. Conclusion: PBT may be of significant value in select patients with LGI malignancies. Additional clinical data are needed to further elucidate the potential benefits of PBT for patients with anal cancer and rectal cancer.

EFOMP policy statement 18: Medical physics education for the non-physics healthcare professions.

Although Medical Physics educators have historically contributed to the education of the non-physics healthcare professions, their role was not studied in a systematic manner. In 2009, EFOMP set up a group to research the issue. In their first paper, the group carried out an extensive literature review regarding physics teaching for the non-physics healthcare professions. Their second paper reported the results of a pan-European survey of physics curricula delivered to the healthcare professions and a Strengths-Weaknesses-Opportunities-Threats (SWOT) audit of the role. The group's third paper presented a strategic development model for the role, based on the SWOT data. A comprehensive curriculum development model was subsequently published, whilst plans were laid to develop the present policy statement. This policy statement presents mission and vision statements for Medical Physicists teaching non-physics users of medical devices and physical agents, best practices for teaching non-physics healthcare professionals, a stepwise process for curriculum development (content, method of delivery and assessment), and summary recommendations based on the aforementioned research studies.

Absolute dosimetry for FLASH proton pencil beam scanning radiotherapy.

A paradigm shift is occurring in clinical oncology exploiting the recent discovery that short pulses of ultra-high dose rate (UHDR) radiation-FLASH radiotherapy-can significantly spare healthy tissues whilst still being at least as effective in curing cancer as radiotherapy at conventional dose rates. These properties promise reduced post-treatment complications, whilst improving patient access to proton beam radiotherapy and reducing costs. However, accurate dosimetry at UHDR is extremely complicated. This work presents measurements performed with a primary-standard proton calorimeter and derivation of the required correction factors needed to determine absolute dose for FLASH proton beam radiotherapy with an uncertainty of 0.9% (1[Formula: see text]), in line with that of conventional treatments. The establishment of a primary standard for FLASH proton radiotherapy improves accuracy and consistency of the dose delivered and is crucial for the safe implementation of clinical trials, and beyond, for this new treatment modality.

Pre-treatment analysis of non-rigid variations can assist robust intensity-modulated proton therapy plan selection for head and neck patients.

PURPOSE: To incorporate small non-rigid variations of head and neck patients into the robust evaluation of intensity-modulated proton therapy (IMPT) for the selection of robust treatment plans. METHODS: A cohort of 20 nasopharynx cancer patients with weekly kilovoltage CT (kVCT) and 15 oropharynx cancer patients with weekly cone-beam CT (CBCT) were retrospectively included. Anatomical variations between week 0/week 1 of treatment were acquired using deformable image registration (DIR) for all 35 patients and then applied to the planning CT of four patients who have kVCT scanned each week to simulate potential small non-rigid variations (sNRVs). The robust evaluations were conducted on IMPT plans with: (1) different number of beam fields from 3-field to 5-field; (2) different beam angles. The robust evaluation before treatment, including the sNRVs and setup uncertainty, referred to as sNRV+R evaluation was compared with the conventional evaluation (without sNRVs) in terms of robustness consistency with the gold standard evaluation based on weekly CT. RESULTS: Among four patients (490 scenarios), we observed a maximum difference in the sNRV+R evaluation to the nominal dose of: 9.37% dose degradation on D95 of clinical target volumes (CTVs), increase in mean dose (D mean $_{\text{mean}}$ ) of parotid 11.87 Gy, increase in max dose (D max $_{\text{max}}$ ) of brainstem 20.82 Gy. In contrast, in conventional evaluation, we observed a maximum difference to the nominal dose of: 7.58% dose degradation on D95 of the CTVs, increase in parotid D mean $_{\text{mean}}$ by 4.88 Gy, increase in brainstem D max $_{\text{max}}$ by 13.5 Gy. In the measurement of the robustness ranking consistency with the gold standard evaluation, the sNRV+R evaluation was better or equal to the conventional evaluation in 77% of cases, particularly, better on spinal cord, parotid glands, and low-risk CTV. CONCLUSION: This study demonstrated the additional dose discrepancy that sNRVs can make. The inclusion of sNRVs can be beneficial to robust evaluation, providing information on clinical uncertainties additional to the conventional rigid isocenter shift.

Ultrahigh dose rate pencil beam scanning proton dosimetry using ion chambers and a calorimeter in support of first in-human FLASH clinical trial.

PURPOSE: To provide ultrahigh dose rate (UHDR) pencil beam scanning (PBS) proton dosimetry comparison of clinically used plane-parallel ion chambers, PTW (Physikalisch-Technische Werkstaetten) Advanced Markus and IBA (Ion Beam Application) PPC05, with a proton graphite calorimeter in a support of first in-human proton FLASH clinical trial. METHODS: Absolute dose measurement intercomparison of the plane-parallel plate ion chambers and the proton graphite calorimeter was performed at 5-cm water-equivalent depth using rectangular 250-MeV single-layer treatment plans designed for the first in-human FLASH clinical trial. The dose rate for each field was designed to remain above 60 Gy/s. The ion recombination effects of the plane-parallel plate ion chambers at various bias voltages were also investigated in the range of dose rates between 5 and 60 Gy/s. Two independent model-based extrapolation methods were used to calculate the ion recombination correction factors ks to compare with the two-voltage technique from most widely used clinical protocols. RESULTS: The mean measured dose to water with the proton graphite calorimeter across all the predefined fields is 7.702 ± 0.037 Gy. The average ratio over the predefined fields of the PTW Advanced Markus chamber dose to the calorimeter reference dose is 1.002 ± 0.007, whereas the IBA PPC05 chamber shows ∼3% higher reading of 1.033 ± 0.007. The relative differences in the ks values determined from between the linear and quadratic extrapolation methods and the two-voltage technique for the PTW Advanced Markus chamber are not statistically significant, and the trends of dose rate dependence are similar. The IBA PPC05 shows a flat response in terms of ion recombination effects based on the ks values calculated using the two-voltage technique. Differences in ks values for the PPC05 between the two-voltage technique and other model-based extrapolation methods are not statistically significant at FLASH dose rates. Some of the ks values for the PPC05 that were extrapolated from the three-voltage linear method and the semiempirical model were reported less than unity possibly due to the charge multiplication effect, which was negligible compared to the volume recombination effect in FLASH dose rates. CONCLUSIONS: The absolute dose measurements of both PTW Advanced Markus and IBA PPC05 chambers are in a good agreement with the National Physical Laboratory graphite calorimeter reference dose considering overall uncertainties. Both ion chambers also demonstrate good reproducibility as well as stability as reference dosimeters in UHDR PBS proton radiotherapy. The dose rate dependency of the ion recombination effects of both ion chambers in cyclotron generated PBS proton beams is acceptable and therefore, both chambers are suitable to use in clinical practice for the range of dose rates between 5 and 60 Gy/s.

Improving workflow for adaptive proton therapy with predictive anatomical modelling: A proof of concept.

PURPOSE: To demonstrate predictive anatomical modelling for improving the clinical workflow of adaptive intensity-modulated proton therapy (IMPT) for head and neck cancer. METHODS: 10 radiotherapy patients with nasopharyngeal cancer were included in this retrospective study. Each patient had a planning CT, weekly verification CTs during radiotherapy and predicted weekly CTs from our anatomical model. Predicted CTs were used to create predicted adaptive plans in advance with the aim of maintaining clinically acceptable dosimetry. Adaption was triggered when the increase in mean dose (Dmean) to the parotid glands exceeded 3 Gy(RBE). We compared the accumulated dose of two adaptive IMPT strategies: 1) Predicted plan adaption: One adaptive plan per patient was optimised on a predicted CT triggered by replan criteria. 2) Standard replan: One adaptive plan was created reactively in response to the triggering weekly CT. RESULTS: Statistical analysis demonstrates that the accumulated dose differences between two adaptive strategies are not significant (p > 0.05) for CTVs and OARs. We observed no meaningful differences in D95 between the accumulated dose and the planned dose for the CTVs, with mean differences to the high-risk CTV of -1.20 %, -1.23 % and -1.25 % for no adaption, standard and predicted plan adaption, respectively. The accumulated parotid Dmean using predicted plan adaption is within 3 Gy(RBE) of the planned dose and 0.31 Gy(RBE) lower than the standard replan approach on average. CONCLUSION: Prediction-based replanning could potentially enable adaptive therapy to be delivered without treatment gaps or sub-optimal fractions, as can occur during a standard replanning strategy, though the benefit of using predicted plan adaption over the standard replan was not shown to be statistically significant with respect to accumulated dose in this study. Nonetheless, a predictive replan approach can offer advantages in improving clinical workflow efficiency.

Proton Therapy for Breast Cancer: A Consensus Statement From the Particle Therapy Cooperative Group Breast Cancer Subcommittee.

Radiation therapy plays an important role in the multidisciplinary management of breast cancer. Recent years have seen improvements in breast cancer survival and a greater appreciation of potential long-term morbidity associated with the dose and volume of irradiated organs. Proton therapy reduces the dose to nontarget structures while optimizing target coverage. However, there remain additional financial costs associated with proton therapy, despite reductions over time, and studies have yet to demonstrate that protons improve upon the treatment outcomes achieved with photon radiation therapy. There remains considerable heterogeneity in proton patient selection and techniques, and the rapid technological advances in the field have the potential to affect evidence evaluation, given the long latency period for breast cancer radiation therapy recurrence and late effects. In this consensus statement, we assess the data available to the radiation oncology community of proton therapy for breast cancer, provide expert consensus recommendations on indications and technique, and highlight ongoing trials' cost-effectiveness analyses and key areas for future research.

Proton Accelerated Partial Breast Irradiation: Clinical Outcomes at a Planned Interim Analysis of a Prospective Phase 2 Trial.

PURPOSE: To perform a planned interim analysis of acute (within 12 months) and late (after 12 months) toxicities and cosmetic outcomes after proton accelerated partial breast irradiation (APBI). METHODS AND MATERIALS: A total of 100 patients with pTis or pT1-2 N0 (≤3cm) breast cancer status after segmental mastectomy were enrolled in a single-arm phase 2 study from 2010 to 2019. The clinically determined postlumpectomy target volume, including tumor bed surgical clips and operative-cavity soft-tissue changes seen on imaging plus a radial clinical expansion, was irradiated with passively scattered proton APBI (34 Gy in 10 fractions delivered twice daily with a minimum 6-hour interfraction interval). Patients were evaluated at protocol-specific time intervals for recurrence, physician reports of cosmetic outcomes and toxicities, and patient reports of cosmetic outcomes and satisfaction with the treatment or experience. RESULTS: Median follow-up was 24 months (interquartile range [IQR], 12-43 months). Local control and overall survival were 100% at 12 and 24 months. There were no acute or late toxicities of grade 3 or higher; no patients experienced fat necrosis, fibrosis, infection, or breast shrinkage. Excellent or good cosmesis at 12 months was reported by 91% of patients and 94% of physicians; at the most recent follow-up, these were 94% and 87%, respectively. The most commonly reported late cosmetic effect was telangiectasis (17%). The total patient satisfaction rate for treatment and results at 12 and 24 months was 96% and 100%, respectively. Patients' mean time away from work was 5 days (IQR, 2-5 days), and the median out-of-pocket cost was $700 (IQR, $100-$1600). The mean left-sided heart dose was 2 cGy (range, 0.2-75 cGy), and the mean ipsilateral lung dose was 19 cGy (range, 0.2-164 cGy). CONCLUSIONS: Proton APBI is a maturing treatment option with high local control, favorable intermediate-term cosmesis, high treatment satisfaction, low treatment burden, and exceptional heart and lung sparing.

Impact of varying planning parameters on proton pencil beam scanning dose distributions in four commercial treatment planning systems.

PURPOSE: In pencil beam scanning proton therapy, target coverage is achieved by scanning the pencil beam laterally in the x- and y-directions and delivering spots of dose to positions at a given radiological depth (layer). Dose is delivered to the spots on different layers by pencil beams of different energy until the entire volume has been irradiated. The aim of this study is to investigate the implementation of proton planning parameters (spot spacing, layer spacing and margins) in four commercial proton treatment planning systems (TPSs): Eclipse, Pinnacle3 , RayStation and XiO. MATERIALS AND METHODS: Using identical beam data in each TPS, plans were created on uniform material synthetic phantoms with cubic targets. The following parameters were systematically varied in each TPS to observe their different implementations: spot spacing, layer spacing and margin. Additionally, plans were created in Eclipse to investigate the impact of these parameters on plan delivery and optimal values are suggested. RESULTS: It was found that all systems except Eclipse use a variable layer spacing per beam, based on the Bragg peak width of each energy layer. It is recommended that if this cannot be used, then a constant value of 5 mm will ensure good dose homogeneity. Only RayStation varies the spot spacing according to the variable spot size with depth. If a constant spot spacing is to be used, a value of 5 mm is recommended as a good compromise between dose homogeneity, plan robustness and planning time. It was found that both Pinnacle3 and RayStation position spots outside of the defined volume (target plus margin). CONCLUSIONS: All four systems are capable of delivering uniform dose distributions to simple targets, but their implementation of the various planning parameters is different. In this paper comparisons are made between the four systems and recommendations are made as to the values that will provide the best compromise in dose homogeneity and planning time.

Radiation-Drug Combinations to Improve Clinical Outcomes and Reduce Normal Tissue Toxicities: Current Challenges and New Approaches: Report of the Symposium Held at the 63rd Annual Meeting of the Radiation Research Society, 15-18 October 2017; Cancun, Mexico.

The National Cancer Institute's (NCI) Radiation Research Program (RRP) is endeavoring to increase the relevance of preclinical research to improve outcomes of radiation therapy for cancer patients. These efforts include conducting symposia, workshops and educational sessions at annual meetings of professional societies, including the American Association of Physicists in Medicine, American Society of Radiation Oncology, Radiation Research Society (RRS), Radiosurgery Society, Society of Nuclear Medicine and Molecular Imaging, Society for Immunotherapy of Cancer and the American Association of Immunology. A symposium entitled "Radiation-Drug Combinations to Improve Clinical Outcomes and Reduce Normal Tissue Toxicities" was conducted by the NCI's RRP during the 63rd Annual Meeting of the RRS on October 16, 2017 in Cancun, Mexico. In this symposium, discussions were held to address the challenges in developing radiation-drug combinations, optimal approaches with scientific evidence to replace standard-of-care, approaches to reduce normal tissue toxicities and enhance post-treatment quality-of-life and recent advances in antibody-drug conjugates. The symposium included two broad overview talks followed by two talks illustrating examples of radiation-drug combinations under development. The overview talks identified the essential preclinical infrastructure necessary to accelerate progress in the development of evidence and important challenges in the translation of drug combinations to the clinic from the laboratory. Also addressed, in the example talks (in light of the suggested guidelines and identified challenges), were the development and translation of novel antibody drug conjugates as well as repurposing of drugs to improve efficacy and reduce normal tissue toxicities. Participation among a cross section of clinicians, scientists and scholars-in-training alike who work in this focused area highlighted the importance of continued discussions to identify and address complex challenges in this emerging area in radiation oncology.

Analysis of geometric variation of neck node levels during image-guided radiotherapy for nasopharyngeal carcinoma: recommended planning margins.

BACKGROUND: To quantify the geometrical changes of each neck nodal level (NNL) and estimate the geometric planning target volume (PTV) margin during image-guided radiotherapy (IGRT) for nasopharyngeal cancer (NPC). METHODS: Twenty patients with locally advanced NPC underwent one planning computed tomography (CTplan) and 6 weekly repeat CT (CTrep) scans during chemoradiotherapy. Each CTrep was rigidly registered to the CTplan. All the NNLs were manually delineated in each transverse CT section. When comparing the NNL in CTrep with CTplan, their volumes, displacement of the center of the mass, and the shortest perpendicular distance (SPD) were automatically calculated. This was followed by calculation of the systematic and random errors, overlapping index (OI), and dice similarity coefficient (DSC). With PTVs isotropically expanded from NNL by 1, 2, 3, 4, and 5 mm, they were compared with NNL itself; OI >0.95 was defined as the acceptable geometrical coverage. The Mann-Whitney test was used for statistical analysis. RESULTS: All volumes, OI, and DSC of the NNLs (not including level IA) showed a linear decrease over time throughout the treatment course. The volume of NNLs decreased by 1-6% in the first week and 10-21% in the sixth week. The mean SPD was 1.3-1.7 and 1.9-3.5 mm in the first and sixth week respectively. The DSCs for nodal level IB, II, III, and IV were >0.7 and that of level V was <0.7 throughout the treatment course. For level IA and VI, DSC was <0.7 after the 2nd week. To maintain the OI >0.95, 2-5 mm was needed to expand the different NNLs. CONCLUSIONS: The geometrical changes of each NNL are substantial and the necessary margin of 2-5 mm depended on individual NNL is needed to maintain geometrical coverage throughout the course of IGRT for NPC.

Characterizing proton-activated materials to develop PET-mediated proton range verification markers.

Conventional proton beam range verification using positron emission tomography (PET) relies on tissue activation alone and therefore requires particle therapy PET whose installation can represent a large financial burden for many centers. Previously, we showed the feasibility of developing patient implantable markers using high proton cross-section materials ((18)O, Cu, and (68)Zn) for in vivo proton range verification using conventional PET scanners. In this technical note, we characterize those materials to test their usability in more clinically relevant conditions. Two phantoms made of low-density balsa wood (~0.1 g cm(-3)) and beef (~1.0 g cm(-3)) were embedded with Cu or (68)Zn foils of several volumes (10-50 mm(3)). The metal foils were positioned at several depths in the dose fall-off region, which had been determined from our previous study. The phantoms were then irradiated with different proton doses (1-5 Gy). After irradiation, the phantoms with the embedded foils were moved to a diagnostic PET scanner and imaged. The acquired data were reconstructed with 20-40 min of scan time using various delay times (30-150 min) to determine the maximum contrast-to-noise ratio. The resultant PET/computed tomography (CT) fusion images of the activated foils were then examined and the foils' PET signal strength/visibility was scored on a 5 point scale by 13 radiologists experienced in nuclear medicine. For both phantoms, the visibility of activated foils increased in proportion to the foil volume, dose, and PET scan time. A linear model was constructed with visibility scores as the response variable and all other factors (marker material, phantom material, dose, and PET scan time) as covariates. Using the linear model, volumes of foils that provided adequate visibility (score 3) were determined for each dose and PET scan time. The foil volumes that were determined will be used as a guideline in developing practical implantable markers.

Proton partial breast irradiation in the supine position: Treatment description and reproducibility of a multibeam technique.

PURPOSE: Proton-accelerated partial breast irradiation (APBI) is early in its developmental phase without standardized treatment parameters. We report an approach to multibeam proton APBI using a universally available supine setup and deliberate beam arrangement strategy to limit the total area of skin receiving a full dose while being robust for interfraction variation. METHODS AND MATERIALS: Thirty-three American Society for Radiation Oncology consensus-suitable/cautionary APBI candidates were treated using a passively scattered proton beam between 2010 and 2014 to 34 Gy relative biological effectiveness in 10 fractions twice daily. All patients were immobilized in a Vac-Lok cradle, typically with the arm down, and adducted to mound the breast and facilitate multiple, optimal en face beams. Radiopaque wires were placed on the surgical scar and 3 markers separate from the scar were placed elsewhere on the breast. All markers were used for each setup and removed before treatment. Marker displacement, wire rotation, and wire displacement were recorded from 10 random patients (100 orthogonal films). A 15-mm expansion was made to the tumor bed to obtain a clinical target volume, and followed by a 5-mm skin contraction and exclusion of the chest wall. A radial planning target volume margin of 5 mm was used. RESULTS: Across 100 pretreatment images, median displacement of 3 distinct skin set-up markers was 3, 4, and 3 mm. Displacement of the scar wire in the X and Y direction was 0 and 1 mm, respectively. Among 28 verification scans performed, only 1 resulted in adaptive planning because of the initial presence of an air pocket in the lumpectomy cavity that resolved spontaneously during treatment. CONCLUSIONS: APBI proton treatment using a supine approach was largely reproducible. Inter-fraction variation demonstrates 5-mm radial planning margins were adequate; however, outliers do occur and films should be reviewed critically and in real time. This technique is straightforward and could be used at any proton facility without the need for specialized equipment.

Quality of life and toxicity from passively scattered and spot-scanning proton beam therapy for localized prostate cancer.

PURPOSE: To report quality of life (QOL)/toxicity in men treated with proton beam therapy for localized prostate cancer and to compare outcomes between passively scattered proton therapy (PSPT) and spot-scanning proton therapy (SSPT). METHODS AND MATERIALS: Men with localized prostate cancer enrolled on a prospective QOL protocol with a minimum of 2 years' follow-up were reviewed. Comparative groups were defined by technique (PSPT vs SSPT). Patients completed Expanded Prostate Cancer Index Composite questionnaires at baseline and every 3-6 months after proton beam therapy. Clinically meaningful differences in QOL were defined as ≥0.5 × baseline standard deviation. The cumulative incidence of modified Radiation Therapy Oncology Group grade ≥2 gastrointestinal (GI) or genitourinary (GU) toxicity and argon plasma coagulation were determined by the Kaplan-Meier method. RESULTS: A total of 226 men received PSPT, and 65 received SSPT. Both PSPT and SSPT resulted in statistically significant changes in sexual, urinary, and bowel Expanded Prostate Cancer Index Composite summary scores. Only bowel summary, function, and bother resulted in clinically meaningful decrements beyond treatment completion. The decrement in bowel QOL persisted through 24-month follow-up. Cumulative grade ≥2 GU and GI toxicity at 24 months were 13.4% and 9.6%, respectively. There was 1 grade 3 GI toxicity (PSPT group) and no other grade ≥3 GI or GU toxicity. Argon plasma coagulation application was infrequent (PSPT 4.4% vs SSPT 1.5%; P=.21). No statistically significant differences were appreciated between PSPT and SSPT regarding toxicity or QOL. CONCLUSION: Both PSPT and SSPT confer low rates of grade ≥2 GI or GU toxicity, with preservation of meaningful sexual and urinary QOL at 24 months. A modest, yet clinically meaningful, decrement in bowel QOL was seen throughout follow-up. No toxicity or QOL differences between PSPT and SSPT were identified. Long-term comparative results in a larger patient cohort are warranted.

Multifield optimization intensity-modulated proton therapy (MFO-IMPT) for prostate cancer: Robustness analysis through simulation of rotational and translational alignment errors.

To evaluate the dosimetric consequences of rotational and translational alignment errors in patients receiving intensity-modulated proton therapy with multifield optimization (MFO-IMPT) for prostate cancer. Ten control patients with localized prostate cancer underwent treatment planning for MFO-IMPT. Rotational and translation errors were simulated along each of 3 axes: anterior-posterior (A-P), superior-inferior (S-I), and left-right. Clinical target-volume (CTV) coverage remained high with all alignment errors simulated. Rotational errors did not result in significant rectum or bladder dose perturbations. Translational errors resulted in larger dose perturbations to the bladder and rectum. Perturbations in rectum and bladder doses were minimal for rotational errors and larger for translational errors. Rectum V45 and V70 increased most with A-P misalignment, whereas bladder V45 and V70 changed most with S-I misalignment. The bladder and rectum V45 and V70 remained acceptable even with extreme alignment errors. Even with S-I and A-P translational errors of up to 5mm, the dosimetric profile of MFO-IMPT remained favorable. MFO-IMPT for localized prostate cancer results in robust coverage of the CTV without clinically meaningful dose perturbations to normal tissue despite extreme rotational and translational alignment errors.

Standardized treatment planning methodology for passively scattered proton craniospinal irradiation.

BACKGROUND: As 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). METHODS: We 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. RESULTS: The 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. CONCLUSIONS: This 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.