A newly designed radiation port for medulloblastoma to prevent metastasis to the cribriform plate region

Novel hybrid treatment planning approach for irradiation a pediatric craniospinal axis

This study presents a new treatment planning approach merging 3D-CRT and VMAT fields into a hybrid treatment plan (HybTP), in order to achieve an optimum dose coverage of the planning target volume (PTV) and protection of OAR. Craniospinal axis irradiation (CSI) treated with 3D conformal radiotherapy (3D-CRT) is associated with high doses to the heart and eye lenses but provides better sparing of lungs and kidneys compared to volumetric modulated arc therapy (VMAT). VMAT treatment spares eye lenses and the heart, but lungs and kidneys are not as effective as 3D-CRT. Thus, a combination of both techniques (HybTP) may be optimal in sparing all these organs at risk (OAR). The results of HybTP are compared with helical tomotherapy (HT), intensity modulated radio therapy (IMRT), VMAT, and 3D-CRT plans. Hybrid, HT, VMAT, IMRT, and 3D-CRT treatment plans for a male child (age 6 years) with medulloblastoma were created and compared. A total dose of 35.2 Gy (PTV) with a dose per fraction of 1.6 Gy was prescribed. The following dose acceptance criteria were defined: The plans were compared regarding dose homogeneity index (HI) and conformity index (CI), PTV coverage, (particularly at cribriform plate) and doses at OARs. Best conformity was achieved with HT (CI = 0.98) followed by VMAT (CI = 0.96), IMRT (CI = 0.91), HybTP (CI = 0.86), and 3D-CRT (CI = 0.83). The homogeneity index varied marginally. For both HT and IMRT the HI was 0.07, and for 3D-CRT, VMAT and HybTP the HI was between 0.13 and 0.15. The cribriform plate was sufficiently covered by HybTP, VMAT, and 3D-CRT. The dose acceptance criteria for OARs were met by HT and HybTP. VMAT did not meet the criteria for lung (Dmean = right 10.4 Gy/left 10.2 Gy), 3D-CRT did not meet the criteria for eye lenses (Dmax = right 32.3 Gy/left 33.1), and heart (V25≈44%) and IMRT did not meet the criteria for lung (Dmean = right 11.1 Gy/left 11.2 Gy) and eye lenses (Dmax = right 12.2 Gy/left 13.1). HybTP meets all defined acceptance criteria and has proved to be a reasonable alternative for CSI. With HybTP that combines VMAT at the brain and heart with 3D-CRT posterior spinal fields (to spare lungs and kidneys), both appropriate coverage of the PTV and sparing of OAR can be achieved.

Variation in Proton Craniospinal Irradiation Practice Patterns in the United States: A Pediatric Proton Consortium Registry (PPCR) Study

PURPOSE

Craniospinal irradiation (CSI) is commonly used for pediatric brain tumors with a propensity for spread in craniospinal fluid, principally medulloblastoma. Evolving technology has led to the use of highly conformal radiation therapy (RT) techniques for CSI, including proton therapy. Target delineation and plan coverage are critical for CSI, but there is ongoing controversy and variability in these realms, with little available data on practice patterns. We sought to characterize proton CSI practice patterns in the United States by examining CSI plans in the Pediatric Proton/Photon Consortium Registry (PPCR).

MATERIALS AND METHODS

PPCR was queried for data on proton CSI patients from 2015 to early 2020. Each plan was manually reviewed, determining patient position; prescription dose; and coverage of optic nerves, vertebral bodies, spinal nerve roots, sacral nerves, and cranial foramina, among other variables. Two radiation oncologists blinded to clinical data and treating institution assessed coverage at the 95% prescription isodose line and per published European Society for Paediatric Oncology guidelines. Variability in coverage was assessed with nonparametric tests and univariate and multivariate logistic regression.

RESULTS

PPCR supplied data for 450 patients, 384 of whom had an evaluable portion of a CSI plan. Most patients (90.3%) were supine. Optic nerves were fully covered in 48.2%; sacral nerves in 87.7%; cranial foramina in 69.3%; and spinal nerves in 95.6%. Vertebral body (VB) sparing was used in 18.6% of skeletally immature cases, increasing over time (P < .001). Coverage in all categories was significantly different among treating institutions, on univariate and multivariate analyses. Cribriform plate deficits were rare, with marginal misses of the foramen ovale (17.4%) and frontal lobe (12%) most common.

CONCLUSION

We found consistent variation based on treating institution in proton CSI practices including optic nerve, VB, sacral nerve, cranial, and spinal nerve coverage. These data may serve as a baseline quantification of current proton CSI practices in the United States as they continue to evolve.

Medulloblastoma in childhood: Impact of radiation technique upon the outcome of treatment

BACKGROUND

Medulloblastoma is an infratentorial primitive neuroectodermal tumour, diagnosed in paediatric population. The radiotherapy is an essential method of treatment for these tumours. The impact of technical quality of radiation therapy on survival was recently considered. In this study treatment-related variables are analysed with a special focus on radiotherapy technical factors.

PROCEDURE

The population of 158 children with a diagnosis of medulloblastoma had been undergoing postoperative radiotherapy at MCMCC in Warsaw in the period 1983-1997. The medical data of these patients were analysed. Simulation films of the whole-brain irradiation fields were retrospectively reviewed at 112 patients. The distance from the field margin to the cribriform plate and to the floor of the temporal fossa was assessed and correlated with supratentorial relapse.

RESULTS

Five-year overall survival (OS) and 5-year disease free survival (DFS) were 46% and 40%, respectively. In multivariate analysis gender (P = 0.008), neurological status before radiotherapy (P = 0.029), M-stage (P < 0.001) and sequence of craniospinal irradiation (P = 0.019) were significant prognostic factors for OS. For DFS significant factors were M-stage (P < 0.001) and neurological status (P < 0.001). The cranial fields were not fully correctly covered at 43% patients. The field incorrectness was correlated with isolated supratentorial failure (P = 0.049).

CONCLUSIONS

Our results are similar to those published in literature. M0-stage was the most powerful favourable prognostic factor. Male gender and neurological status before radiation treatment were associated with poor survival. Also protracted radiotherapy and quality of radiation technique may have an impact on the outcome.

Comparison of manual and computer-generated customized blocks for whole brain fields used in the treatment of medulloblastoma

BACKGROUND

By using CT simulation and three-dimensional planning, we have developed a simple but accurate method of producing customized blocks for the cranial fields in the treatment of medulloblastoma. We compare here the margins and the volume of normal tissues included in the treatment volume with those obtained using blocks generated manually.

PROCEDURE

Customized blocks for the whole brain field are generated using CT planning and autoblock function. The clinical target volume (CTV) is defined as the whole cerebrospinal fluid pathway, and the whole brain and spinal cord are contoured. A margin of 1.1 cm is generated using the autoblock function to account for set-up errors (3-5 mm) and penumbra (approximately 7 mm). A separate set of blocks was generated manually without the knowledge of the ones generated by the CT-simulator. These 2 sets of blocks were compared for a cohort of 7 consecutive patients.

RESULTS

Overall, the manual blocks and the computer-generated blocks were quite similar. Those generated manually had more variations; they were always tighter (median of 6 mm tighter; range: 3-7 mm) at the level of the cribriform plate and in 5/7 patients were more generous (median of 6 mm more generous, range: 0-6 mm) at the temporal lobes. Dosimetric analysis showed that both methods provide adequate coverage of the CTV, with 100% of the CTV receiving > 95% of the prescribed dose for both.

CONCLUSIONS

The customized block method for whole brain fields is simple to use and ensures adequate coverage of the target volume.

The role of CT simulation in whole-brain irradiation

PURPOSE

Evidence is growing that incorrect field-shaping is a major cause of treatment failure in whole-brain irradiation (WBI). To evaluate the potential benefits of CT simulation in WBI we compared field-shaping based on 3D CT simulation to conventional 2D simulation.

METHODS

CT head scans were obtained from 20 patients. Conventional 2D planning was imitated by drawing the block contours on digitally reconstructed radiographs (DRR) by four radiotherapists. Critical parts of the target and the eye lenses were subsequently marked and planning was repeated using 3D information ("3D planning"). The results of both methods were compared by evaluation of the minimal distance from the field edge according to each site.

RESULTS

In conventional planning using DRR, major geographic mismatches (< -3 mm) occurred in the subfrontal region and both eye lenses with 1% each location. Minor mismatches (-3 to 0 mm) predominantly occurred in the contralateral lens (21%), ipsilateral lens (10%), and subfrontal region (9%). Close margins (0-5 mm) were most frequently noted at the contralateral lens (49%), ipsilateral lens (35 %), and the subfrontal region (28%). When 3D planning was used, mismatches were not found. However, close margins were inevitable at the ipsilateral lens (5%), subfrontal region (30%), and contralateral lens (70%).

CONCLUSIONS

CT simulation in WBI is significantly superior to conventional simulation with respect to complete coverage of the target volume and protection of the eye lenses. The narrow passage between the ocular lenses and lamina cribrosa represents a serious limitation. These patients are safely identified with CT simulation and can be referred for modified irradiation techniques.

Impact of targeting deviations on outcome in medulloblastoma: study of the French Society of Pediatric Oncology (SFOP)

PURPOSE

To correlate targeting deviation in external beam radiation therapy with site of relapse in a prospective study of 174 patients treated for medulloblastoma.

METHODS AND MATERIALS

Between February 1992 and February 1998 the radiotherapy treatment records were reviewed by a panel of radiation oncologists for 174 children treated with radiation therapy for medulloblastoma. The review was done without knowledge of patient outcome. Patterns of relapse were correlated with the results of the quality control review.

RESULTS

Among the 174 patients five relapsed before the start of radiotherapy. One hundred sixty-nine patients were evaluable for correlation between targeting deviation and site of relapse. Number of major deviations in radiation therapy treatment is strongly correlated with the risk of tumor relapse (67% [95% CI: 28-91] of 3-year relapse rate in patient group with 2 major deviations and 78% [95% CI: 35-96] with 3 major deviations). This is particularly correlated with relapse in the frontal region of the brain: 5 relapses occurred in the frontal region in patients with major deviation in this area. An erroneous choice of electron beam energy is also linked with craniospinal fluid (CSF) relapse (3-year relapse rate of 68% [95% CI: 42-86]). Minor deviations in therapy technique are slightly associated with an increased risk of relapse in the same range as the group with only one major deviation.

CONCLUSION

The quality of medulloblastoma radiation therapy technique is strongly correlated with outcome. Pretreatment central quality assurance review or standardized computer-designed blocks would improve survival to an extent equivalent to that attributed to adjuvant chemotherapy.

Impact of radiation technique upon the outcome of treatment for medulloblastoma

Craniospinal irradiation (CSI) is an essential component of the therapy of medulloblastoma. Because medulloblastoma disseminates via the cerebrospinal fluid (CSF), CSI technique involves the irradiation of all CSF-bearing areas which are at risk for tumor seeding. Underdosing with radiation because of inadequacies in CSI technique will produce dose "cold spots" which have the potential of serving as a nidus for tumor recurrence. A simple mathematic model of subclinical disease in medulloblastoma based on the available data concerning the radiosensitivity of medulloblastoma cell lines as well as the known clinical dose-response relationships support the hypothesis that for most cases of medulloblastoma, the radiotherapist is working in a range of doses arrayed on the steep portion of the tumor control probability curve. Underdosing of CSF-bearing areas because of technical problems at the junction of the cranial and spinal fields of irradiation, placement of shielding blocks in the cribiform plate-subfrontal region, and/or anatomic errors in the design of the caudal end of the CSI fields may lead to significant risks of tumor relapse. One may debate the necessity of a posterior fossa boost encompassing the entire anatomic posterior fossa rather than the primary tumor volume with a margin. This review critically evaluates the potential impact of CSI technique upon the outcome of treatment for medulloblastoma, and suggests future areas of inquiry.

The radiation treatment of medulloblastoma

Following the introduction of CS-RT the survival rate for this malignant tumour rose from zero to approximately 50%. It appears that the major advances over the last twenty years associated with the introduction of CT/MRI, adequate staging, total resection, adjuvant therapy and improved radiation technique has only added 10-20% to the survival rate making it extremely difficult to evaluate the impact of these advances. While radiation treatment is currently omitted or delayed under the age of 36 months, due to enhanced neurocognitive toxicity, and replaced by maintained systemic therapy, the early encouraging results must stand the test of time in order to become standard practice. The treatment of a child with medulloblastoma with radiation treatment remains the corner stone of treatment while additional novel therapies are being developed.

Secondary manifestation of medulloblastoma: metastases and local recurrences in 66 patients

Although primary treatment of medulloblastoma is now successful in a high percentage of patients, its secondary manifestations still bear a poor prognosis. Thorough studies of secondary manifestations are therefore pivotal to plan therapeutic approaches for the long-term management of medulloblastoma. Here we describe the incidence of secondary tumour manifestations in 66 patients of a single centre who underwent surgery for medulloblastoma between 1975 and 1990. No patient was excluded due to a poor postoperative course. Thirty-five patients showed evidence of secondary tumour growth. Of these, 17 suffered from local recurrence, and 27 developed metastastatic disease. The median latencies for secondary manifestations were 25 months for local recurrence (n = 17), 11 months for spinal metastases (n = 10), 15 months for supratentorial metastases (n = 8), 8 months for subleptomeningeal dissemination (n = 6), and 23 months for systemic metastases (n = 8). Two patients developed primary metastatic spread to the posterior fossa. Of 8 patients with supratentorial metastases, 6 developed fronto-basal lesions. In our patients, 89% of secondary lesions occurred within less than 3 years after primary diagnosis. 85% of patients with extra-axial tumour spread had been treated with a permanent shunt. Radical tumour resection and radiotherapy with 30 Gy to the neuraxis and 20 Gy boost to the posterior fossa was an important prognostic factor in this series. Patients with additional chemotherapy did not benefit significantly from this treatment. We conclude that optimal management of the primary lesions should aim at (i) total resection, (ii) avoid permanent shunting, and (iii) completion of the radiotherapy with inclusion of the medial frontobasal cisterns in the radiotherapeutic regimen. Our analysis suggests that adequate postoperative screening programmes should consist of 3-monthly scans of the neuraxis in the first three postoperative years and 6-monthly scans thereafter.