Proton Therapy (PT) is a high-quality radiation therapy and initially used to treat  human patients in Lawrence Berkeley Laboratory. For about 50 years of its use in treating cancer, it has been reported to have an excellent clinical result especially in prostate cancer (Smith, 2006). The precise dose deposition to the tumor volume prescribed in a cancer patient (Kim, 2006) improved local control and a disease-free survival (Smith, 2006).

What other scientists say

Weber et al (2004) concluded that spot-scanning PT is an effective treatment for patient with untreated, recurrent or incompletely resected intracranial meningiomas. Since it offers highly conformal irradiation for complex-shaped intracranial meningiomas,

spot-scanning PT dose to normal tissues are minimal.

Though, there is an observed dose-related ophthalmologic toxicity in the study.  Another spot-scanning PT is done for chordoma and chondrosarcoma in children and adolescents by Bolsi et al (2008). They evaluated postoperative spot-scanning PT with these patients and found out that

the initial result is “perfectly” satisfactory in this group.

Subsequent study in children evaluated the outcome and tolerance of high-dose photon and proton therapy for the management of skull base and cervical canal primary bony malignancies by Habrand et al (2008). In this study, PT is well tolerated in children and

allowed excellent local control with minimal long-term toxicity.

Recent study about Conformal PT (CPT) to treat craniopharyngioma in children is done by Winkfield (2009). This benign slow growing tumor is reported to cause symptoms, even with gross total resection, and can be reformed. To avoid marginal failure, they recommended a routine imaging every fortnight, but possibly every week for craniopharyngiomas with large cystic growth.

No comment about the advantage of PT.

Comparative study to investigate the improvement in paranasal sinus when nominal dose constraints are applied using intensity modulated X-ray therapy (IMXT) and intensity modulated proton therapy (IMPT) plans is done by Lomax et al (2002). Result showed that

 only the intensity modulated protons spared the critical structures at all dose levels.

Dose homogeneity within the target volume is found to be acceptable in IMPT, though both modalities provide comparable target volume conformation and sparing of critical structures. Another comparison of different modalities is done by Trofimov et al (2007). They compared intensity modulated radiotherapy (IMRT) with 3-D CPT for early-stage prostate cancer, and explore the potential utility of IMPT.  It is concluded that IMRT, at the range higher than 60 Gy/CGE, achieve a better sparing of the bladder and showed similar result in rectal sparing with 3D-CPT. However, the

dose to healthy tissues is found to be lower with proton therapy in the range lower than 50% of the target prescription.

Another study of PT in prostate cancer

yielded disease-free survival rates comparable with other forms of local therapy, and with minimal morbidity (Slater, 2004).

Hence, dose escalation technique is implemented at the time in Loma Linda University to improve long-term results. Hillbrand et al (2008) made an effort to evaluate the dosimetric benefits of advanced radiotherapy techniques for the treatment of abdominal lesions during early childhood. In this study,

PT improved all dosimetric parameters for Nueroblastoma and Wilms Tumor patients in comparison to standard and advanced photon therapy.

IMXT showed limited improvement due to parameters related to the steep high-dose gradient.
Studies about the dosimetric comparison became the focus of study for few scientists. Moon et al (2008) compared 4 different external beam accelerated partial breast irradiation (EB-APBI) plans in 4 different modalities [3D-CRT, IMRT, PT, and Helical Tomotherapy (TOMO)]. All plans showed acceptable coverage of the Patient Target Volume and

no distinct advantage of PT has been claimed.

Recently, another dosimetric comparison about the dose distribution to target and non target tissues in Hodgkin’s lymphoma patients are done by Chera et al (2009). They used conventional CRT, IMRT, and 3D-PT plans and found out that

3D PT reduced the dose to the breast, lung, and total body

for Hodgkin’s lymphoma patients without disease in or below the hila. They deduced that by reducing the risk of late radiation effects related to low-to-moderate doses in non target tissues, clinical outcomes of Hodgkin’s lymphoma patients might improve using 3D-PT. Some other studies in different sites are done for olfactory neuroblastoma (ONB), invasive bladder cancer (IBC), and hepatocellular carcinoma (HCC). Result of PT in ONB achieved

excellent local control and survival rates without serious adverse effects (Nishimura et al, 2007).

Hence, it is concluded that PT is safe and effective modality but needs further study. For IBC study of hata el al (2006), the outcome is

effective, but they are unsure if local control is improved.

For HCC study of Fukumitsu et al (2009),

hypofractionated PT is safe and well-tolerated but undecided if it is an effective alternative to other modalities.

In summary, 1 out of 13 papers is unsure of local tumor control; 1, no
comment; 1, did not observe any advantage over the other modalities;
and 1, undecided if it is an effective alternative to other modalities. 

In 2007, Olsena et al done a systematic review of clinical effectiveness of PT and stated that

 "The evidence on clinical efficacy of proton therapy relies to a large extent on non-controlled studies, and thus is associated with low level of evidence according to standard heath technology assessment and evidence based medicine criteria."

The common denominator for all the papers is that PROTON THERAPY has good benefits for cancer patients.  Some postulate that this is the future of radiation oncology, though it doesn't show that it is always better than the other existing treatment modalities.

To know more about Proton Therapy, click here

References

1. Smith A. Proton Therapy. Phys. Med. Biol. 51 (2006) R491-R504






2. Moyers M, Pouliot J, Orton C. POINT/COUNTERPOINT: Proton therapy is the best radiation treatment modality for prostate cancer. Med. Phys. 34(2), February 2007, doi:10.1118/1.2405703.






3. Kim CM, Youn MY, Kim JW. Prompt gamma measurements for locating the dose falloff region in the proton therapy. Applied Physics Letters 89, 183517 (2006).






4. Weber D, Lomax A, Rutz HP, et al. Spot-scanning proton radiation therapy for recurrent, residual or untreated intracranial meningiomas. Radiotherapy and Oncology 71 (2004) 251-258.






5. Bolsi A, Lomax A, Pedroni E, et al. Postoperative spot-scanning proton radiation therapy for chordoma and chondrosarcoma in childer and adolescents: Initial experience at Paul Scherrer Institute. Int. J. Radiation Oncology Biol. Phys., Vol. 71, No. 1, pp. 220–225, 2008.






6. Habrand J-L, Schneider R, Alapetite C, et al. Proton therapy in pediatric skull base and cervical canal low-grade bone malignancies. Int. J. Radiation Oncology Biol. Phys., Vol. 71, No. 3, pp. 672–675, 2008.






7. Winkfield K, Linsenmeier C, Yock T, et al. Surveillance of craniopharyngioma cyst growth in children treated with proton radiotherapy. Int. J. Radiation Oncology Biol. Phys., Vol. 73, No. 3, pp. 716–721, 2009.






8. Lomax A, Goitein M, Adams J. Intensity modulation in radiotherapy:photons versus protons in the paranasal sinus. Radiotherapy and Oncology 66 (2003) 11–18.






9. Trofimov A, Nguyen P, Coen J, et al. Radiotherapy treatment of early-stage prostate cancer with IMRT and Protons: A treatment planning comparison. Int. J. Radiation Oncology Biol. Phys., Vol. 69, No. 2, pp. 444–453, 2007.






10. Slater J, Rossi C, Yonemoto L, et al. Proton Therapy for prostate cancer: The initial Loma Linda University experience. Int. J. Radiation Oncology Biol. Phys., Vol. 59, No. 2, pp. 348–352, 2004.






11. Hillbrand M, Georg D, Gadner H, et al. Abdominal cancer during early childhood: A dosimetricn comparison of proton beams to standard and advanced photon radiotherapy. Radiotherapy and Oncology 89 (2008) 141–149.






12. Moona SH, Shin KH, Kim TH, et al. Dosimetric comparison of four different external beam partial breast irradiation techniques: Three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, helical tomotherapy, and proton beam therapy. Radiotherapy and Oncology 90 (2009) 66–73.






13. Chera B, Rodriguez C, Morris C, et al. Dosimetric comparison of three different involved nodalirradiation techniques for stage II hodgkin’s lymphoma patients: conventional radiotherapy, intensity-modulated, and three-dimensional proton radiotherapy. Int. J. Radiation Oncology Biol. Phys., pp1–8, 2009.






14. Nishimura H, Ogino T, Kawashima M, et al. Proton-Beam therapy for olfactory neuroblastoma. Int. J. Radiation Oncology Biol. Phys., Vol. 68, No. 3, pp. 758–762, 2007.






15. Hata M, Miyanaga N, Tokuuye K, et al. Proton beam therapy for invasive bladder cancer: A prospective study of bladder-preservering therapy with combined radiotherapy and intra-arterial chemotherapy. Int. J. Radiation Oncology Biol. Phys., Vol. 64, No. 5, pp. 1371–1379, 2006.






16. Fukumitsu N, Sugahara S, Nakayama H, et al. A prospective study of hypofractionated proton beam therapy for patients with hepatocellular carcinoma. Int. J. Radiation Oncology Biol. Phys., Vol. 74, No. 3, pp. 831–836, 2009.






17. Olsena D, Brulanda O, Frykholmc G, et al. Proton therapy - A systematic review of clinical effectiveness. Radiotherapy and Oncology 83 (2007) 123–132.